LM3554 LM3554 Synchronous Boost Converter with 1.2A Dual High Side LED Drivers and I 2 C-Compatible Interface Literature Number: SNVS549A LM3554 Synchronous Boost Converter with 1.2A Dual High Side LED Drivers and I2C-Compatible Interface General Description Features The LM3554 is a 2MHz fixed frequency, current mode synchronous boost converter. The device is designed to operate as a dual 600mA (1.2A total) constant-current driver for highcurrent white LEDs, or as a regulated 4.5V or 5V voltage source. The dual high-side current sources allow for grounded cathode LED operation. An adaptive regulation method ensures the current source for each LED remains in regulation and maximizes efficiency. The main features include: an I2C-compatible interface for controlling the LED current or the desired output voltage, a hardware Flash enable input for direct triggering of the Flash pulse, and dual TX inputs which force the Flash pulse into a low-current Torch mode allowing for synchronization to RF power amplifier events or other high-current conditions. Additionally, an active high hardware enable (HWEN) input provides a hardware shutdown during system software failures. Five protection features are available within the LM3554 including a software selectable input voltage monitor, an internal comparator for interfacing with an external temperature sensor, four selectable current limits to ensure the battery current is kept below a predetermined peak level, an overvoltage protection feature to limit the output voltage during LED open circuits, and an output short circuit protection which limits the output current during shorts to GND. Additionally, the device provides various fault indicators including: a thermal fault flag indicating the LED temperature has tripped the thermal threshold, a flag indicating a TX event has occurred, a flag indicating the flash timeout counter has expired, a flag indicating the devices die temperature has reached the thermal shutdown threshold, and a flag indicating an open or short LED. Dual High Side Current Sources Grounded Cathode Allowing for Better Heat Sinking and LED Routing >90% Efficiency Ultra-Small Solution Size: < 23mm2 Four Operating Modes: Torch, Flash, LED Indicator and Voltage Output Accurate and Programmable LED Current from 37.5mA to 1.2A Programmable 4.5V or 5.0V Constant Output Voltage Hardware Flash and Torch Enable LED Thermal Sensing and Current Scaleback Software Selectable Input Voltage Monitor Programmable Flash Timeout Dual Synchronization Inputs for RF Power Amplifier Pulse Events Open and Short LED Detection Active High Hardware Enable for Protection Against System Faults 400kHz I2C-Compatible Interface 16-Bump (1.7mm x 1.7mm x 0.6mm) micro SMD Applications Camera Phone LED Flash Controller Class D Audio Amplifier Power LED Current Source Biasing Typical Application Circuits 30042001 30042002 Example Layout (c) 2011 National Semiconductor Corporation 300420 www.national.com Synchronous Boost Converter with 1.2A Dual High Side LED Driver and I2C-Compatible Interface April 12, 2011 LM3554 Application Circuit Component List Component Manufacturer Value Part Number Size (mm) Rating L TOKO 2.2H FDSE0312-2R2M 3x3x1.2 2.3A(0.2) COUT Murata 4.7F/10F GRM188R60J475M, or GRM188R60J106M 1.6x0.8x0.8 (0603) 6.3V CIN Murata 4.7F GRM185R60J475M 1.6x0.8x0.8 (0603) 6.3V LEDs Lumiled LXCL-PWF4 1.5A Connection Diagram 30042003 Pin Descriptions Pin Name Function A1 LED1 High-Side Current Source Output for Flash LED. A2, B2 OUT Step-Up DC/DC Converter Output. A3, B3 SW Drain Connection for Internal NMOS and Synchronous PMOS Switches. A4, B4 GND Ground LED2 High-Side Current Source Output for Flash LED. B1 LEDI/NTC Configurable as a High-Side Current Source Output for Indicator LED or Threshold Detector for LED Temperature Sensing. C2 TX1/TORCH/ GPIO1 Configurable as a RF Power Amplifier Synchronization Control Input (TX1), a Hardware Torch Enable (TORCH), or a programmable general-purpose logic Input/Output (GPIO1). C3 STROBE C4 IN Input Voltage Connection. Connect IN to the input supply, and bypass to GND with a minimum 4.7F ceramic capacitor. D1 ENVM/TX2/ GPIO2/INT Configurable as an Active High Voltage Mode Enable (ENVM), Dual Polarity Power Amplifier Synchronization Input (TX2), or Programmable General Purpose Logic Input/Output (GPIO2). D2 SDA Serial Data Input/Output. D3 SCL Serial Clock Input. D4 HWEN C1 Active High Hardware Flash Enable. Drive STROBE high to turn on Flash pulse. Active Low Hardware Reset. Ordering Information Order Number Package Package Marking Supplied As No-Lead LM3554TME TMD16CCA SF 250 units, Tape-and-Reel YES (NOPB) LM3554TMX TMD16CCA SF 3000 units, Tape-and-Reel YES (NOPB) www.national.com 2 VIN Junction Temperature (TJ) Ambient Temperature (TA) (Note 5) 2) If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications. VIN, VSW, VOUT VSCL, VSDA, VHWEN, VSTROBE, VTX1/ TORCH, VENVM/TX2, VLED1, VLED2, VLEDI/ NTC Continuous Power Dissipation(Note 3) Junction Temperature (TJ-MAX) Storage Temperature Range Maximum Lead Temperature (Soldering) (Note 1, Note 2) -0.3V to 6V 2.5V to 5.5V -30C to +125C -30C to +85C Thermal Properties -0.3V to to (VIN +0.3V) w/ 6.0V max Internally Limited +150C -65C to +150C Junction-to-Ambient Thermal Resistance (JA), TMD16 Package(Note 6) 60C/W (Note 4) ESD Caution Notice National Semiconductor recommends that all integrated circuits be handled with appropriate ESD precautions. Failure to observe proper ESD handling techniques can result in damage to the device. Electrical Characteristics Limits in standard typeface are for TA = +25C. Limits in boldface type apply over the full operating ambient temperature range (-30C TA +85C). Unless otherwise specified, VIN = 3.6V, VHWEN = VIN. (Note 2, Note 7) Symbol Parameter Conditions Min Typ Max 1128 1200 1284 541 600 657 Units Current Source Specifications ILED VHR IMATCH Current Source Accuracy 600mA Flash ILED1+ILED2 LED Setting, ILED1 or ILED2 VOUT = VIN mA 17mA Torch Current I +I Setting, VHR = LED1 LED2 500mV 30.4 33.8 37.2 Current Source Regulation Voltage (VOUT VLED) 600mA setting, VOUT = 3.75V 300 mV LED Current Matching 600mA setting, VLED = 3.2V 0.35 % Step-Up DC/DC Converter Specifications VREG Output Voltage Accuracy 2.7V VIN 4.2V, IOUT = 0mA, VENVM = VIN, OV bit = 0 4.8 5 5.2 On Threshold, 2.7V VIN 5.5V 5.4 5.6 5.7 VOVP Output OverVoltage Protection Trip Point(Note 8) RPMOS RNMOS V V Off Threshold 5.3 PMOS Switch On-Resistance IPMOS = 1A 150 m NMOS Switch On-Resistance INMOS = 1A 150 m ICL Switch Current Limit(Note 9) IOUT_SC Output Short Circuit Current Limit CL bits = 00 0.711 1.05 CL bits = 01 1.295 1.51 1.8 CL bits = 10 1.783 1.99 2.263 CL bits = 11 2.243 2.45 2.828 VOUT < 2.3V 550 3 1.373 A mA www.national.com LM3554 Operating Ratings Absolute Maximum Ratings (Note 1, Note LM3554 Symbol Parameter Conditions Min IND1, IND0 bits = 00 ILED/NTC Typ Max Units 2.3 IND1, IND0 bits = LEDI/NTC bit 01 Indicator Current =0 IND1, IND0 bits = 10 4.6 mA 6.9 IND1, IND0 bits = 11 8.2 Comparator Trip LEDI/NTC bit = 1, 2.7V VIN Threshold 5.5V 0.947 1.052 1.157 V fSW Switching Frequency 2.7V VIN 5.5V 1.75 2 2.23 MHz IQ Quiescent Supply Current Device Not Switching 630 ISHDN Shutdown Supply Current 2.7V VIN 5.5V 3.5 tTX Flash-to-Torch LED Current Settling Time TX_ Low to High, ILED1 + ILED2 = 1.2A to 180mA 20 VTRIP VIN_TH VIN Monitor Trip VIN Falling, VIN Monitor Register = Threshold 0x01 (Enabled with VIN_TH = 3.1V) 6.6 A s 3.23 V 0 0.4 V 1.2 VIN V 400 mV 2.95 3.09 A TX1/TORCH/GPIO1, STROBE, HWEN, ENVM/TX2/GPIO2 Voltage Specifications 2.7V VIN 5.5V VIL Input Logic Low VIH Input Logic High 2.7V VIN 5.5V VOL Output Logic Low RTX1/TORCH RSTROBE ILOAD = 3mA, 2.7V VIN 5.5V Internal Pulldown Resistance at TX1/TORCH 300 k Internal PullDown Resistance at STROBE 300 k I2C-Compatible Voltage Specifications (SCL, SDA) 2.7V VIN 5.5V VIL Input Logic Low VIH Input Logic High 2.7V VIN 5.5V VOL Output Logic Low (SCL) 0 0.4 V 1.22 VIN V 400 mV ILOAD = 3mA, 2.7V VIN 5.5V I2C-Compatible Timing Specifications (SCL, SDA) -- See Figure 1 1/t1 SCL Clock Frequency t2 Data In Setup Time to SCL High t3 400 kHz 100 ns Data Out Stable After SCL Low 0 ns t4 SDA Low Setup Time to SCL Low (Start) 160 ns t5 SDA High Hold Time After SCL High (Stop) 160 ns www.national.com 4 Note 2: All voltages are with respect to the potential at the GND pin. Note 3: Internal thermal shutdown circuitry protects the device from permanent damage. Thermal shutdown engages at TJ=150C (typ.) and disengages at TJ=135C (typ.). Note 4: For detailed soldering specifications and information, please refer to National Semiconductor Application Note 1112: Micro SMD Wafer Level chip Scale Package (AN-1112) Note 5: In applications where high power dissipation and/or poor package thermal resistance is present, the maximum ambient temperature may have to be derated. Maximum ambient temperature (TA-MAX) is dependent on the maximum operating junction temperature (TJ-MAX-OP = +125C), the maximum power dissipation of the device in the application (PD-MAX), and the junction-to-ambient thermal resistance of the part/package in the application (JA), as given by the following equation: TA-MAX = TJ-MAX-OP - (JA x PD-MAX). Note 6: Junction-to-ambient thermal resistance (JA) is taken from a thermal modeling result, performed under the conditions and guidelines set forth in the JEDEC standard JESD51-7. The test board is a 4-layer FR-4 board measuring 102mm x 76mm x 1.6mm with a 2x1 array of thermal via's. The ground plane on the board is 50mm x 50mm. Thickness of copper layers are 36m/18m/18m/36m (1.5oz/1oz/1oz/1.5oz). Ambient temperature in simulation is 22C, still air. Power dissipation is 1W. Note 7: Min and Max limits are guaranteed by design, test, or statistical analysis. Typical (Typ) numbers are not guaranteed, but do represent the most likely norm. Unless otherwise specified, conditions for typical specifications are: VIN = 3.6V and TA = +25C. Note 8: The typical curve for Over-Voltage Protection (OVP) is measured in closed loop using the typical application circuit . The OVP value is found by forcing an open circuit in the LED1 and LED2 path and recording the peak value of VOUT. The value given in the Electrical Table is found in an open loop configuration by ramping the voltage at OUT until the OVP comparator trips. The closed loop data can appear higher due to the stored energy in the inductor being dumped into the output capacitor after the OVP comparator trips. At worst case is an open circuit condition where the output voltage can continue to rise after the OVP comparator trips by approximately IINxsqrt(L/COUT). Note 9: The typical curve for Current Limit is measured in closed loop using the typical application circuit by increasing IOUT until the peak inductor current stops increasing. The value given in the Electrical Table is measured open loop and is found by forcing current into SW until the current limit comparator threshold is reached. Closed loop data appears higher due to the delay between the comparator trip point and the NFET turning off. This delay allows the closed loop inductor current to ramp higher after the trip point by approximately 20ns x VIN/L Note 10: Current Matching = Absolute Value((ILED1 - ILED2)/(ILED1 + ILED2)) x 100 Note 11: Current Accuracy = Absolute Value(ITARGET - (ILED1 + ILED2)) x 100 30042004 FIGURE 1. I2C Timing 5 www.national.com LM3554 Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the device may occur. Operating Ratings are conditions under which operation of the device is guaranteed. Operating Ratings do not imply guaranteed performance limits. For guaranteed performance limits and associated test conditions, see the Electrical Characteristics table. LM3554 Typical Performance Characteristics VIN = 3.6V, LEDs are Lumiled PWF-4, COUT = 10F, CIN = 4.7F, L = FDSE0312-2R2 (2.2H, RL = 0.15), TA = +25C unless otherwise specified. LED Efficiency vs VIN (Single LED, L = TOKO FDSE0312-2R2) LED Efficiency vs VIN (Dual LEDs, L = TOKO FDSE0312-2R2) 30042048 30042049 Input Current vs VIN (Single LED, L = TOKO FDSE0312-2R2) LED Efficiency vs VIN (Single LED, L = Coilcraft LPS4018-222) 30042051 30042050 LED Efficiency vs VIN (Dual LED's, L = Coilcraft LPS4018-222) Input Current vs VIN (Single LED, L = Coilcraft LPS4018-222) 30042053 30042052 www.national.com 6 LM3554 Efficiency vs IOUT (Voltage Output Mode, VOUT = 5V) Efficiency vs VIN (Voltage Output Mode, VOUT = 5V) 30042055 30042056 VOUT vs IOUT (Voltage Output Mode, VOUT = 5V) VOUT vs VIN (Voltage Output Mode, VOUT = 5V) 30042057 30042058 Torch Current Matching vs Code (VIN= 3.6V, VLED1, VLED2 = 3.2V, TA = -40C to +85C, (Note 10) ) Torch Current vs VIN (VLED1, VLED2 = 3.2V, TA = +25C, 75mA setting) 30042096 30042094 7 www.national.com LM3554 Torch Current vs VIN (VLED1, VLED2 = 3.2V, TA = +85C, 75mA setting) Torch Current vs VIN (VLED1, VLED2 = 3.2V, TA = -40C, 75mA setting) 300420102 300420104 Flash Current Matching vs Code (VIN= 3.6V, VLED1, VLED2 = 3.2V, TA = -40C to +85C, (Note 10) Flash Current vs VIN (VLED1, VLED2 = 3.2V, TA = +25C, 600mA setting) 30042097 30042095 Flash Current vs VIN (VLED1, VLED2 = 3.2V, TA = +85C, 600mA setting) Flash Current vs VIN (VLED1, VLED2 = 3.2V, TA = -40C, 600mA setting) 300420103 www.national.com 300420105 8 LM3554 Switching Frequency vs VIN Shutdown Current vs VIN (VHWEN = 0V) 30042089 300420101 Active (Non-Switching) Supply Current vs VIN (VLED = 1.5V) Active (Switching) Supply Current vs VIN (VOUT = 5V, IOUT = 400mA) 30042074 30042075 Closed Loop Current Limit vs VIN (Flash Duration Register bits [6:5] = 00, (Note 8)) Closed Loop Current Limit vs VIN (Flash Duration Register bits [6:5] = 01, (Note 8) ) 30042085 30042086 9 www.national.com LM3554 Closed Loop Current Limit vs VIN (Flash Duration Register bits [6:5] = 10, (Note 8)) Closed Loop Current Limit vs VIN (Flash Duration Register bits [6:5] = 11, (Note 8)) 30042087 30042088 VIN Monitor Thresholds vs Temperature OVP Thresholds vs VIN (Note 9) 30042078 30042079 Short Circuit Current Limit vs VIN Indicator Current vs VIN, VLEDI = 2V (Torch Brightness Register bits[7:6] = 00) 30042080 30042090 www.national.com 10 Indicator Current vs VIN, VLEDI = 2V (Torch Brightness Register bits[7:6] = 10) 30042091 30042092 Indicator Current vs VIN, VLEDI = 2V (Torch Brightness Register bits[7:6] = 11) NTC Comparator Trip Threshold vs VIN 30042098 30042093 Startup into Flash Mode Single LED IFLASH = 1.2A Startup into Torch Mode Single LED, Hardware Torch Mode, 90mA Torch Setting ITORCH = 180mA 30042060 Channel 1: VOUT (2V/div) Channel 4: ILED (500mA/div) Channel 2: IL (500mA/div) Channel 3: STROBE (5V/div) Time Base: (100s/div) 30042061 Channel 1: VOUT (2V/div) Channel 4: ILED (100mA/div) Channel 2: IL (500mA/div) Channel 3: TX1 (5V/div) Time Base: (100s/div) 11 www.national.com LM3554 Indicator Current vs VIN, VLEDI = 2V (Torch Brightness Register bits[7:6] = 01) LM3554 Torch Mode to Flash Mode Transition Single LED ITORCH = 295mA, IFLASH = 1.2A TX1 Interrupt Operation, TX1 Rising Single LED IFLASH = 1.2A, ITORCH = 180mA 30042062 Channel 1: VOUT (5V/div) Channel 4: ILED (500mA/div) Channel 2: IL (1A/div) Channel 3: STROBE (5V/div) Time Base: (100s/div) 30042063 Channel 1: VOUT (2V/div) Channel 4: ILED (500mA/div) Channel 2: IL (1A/div) Channel 3: TX1 (5V/div) Time Base: (20s/div) TX1 Interrupt Operation, TX1 Falling Single LED IFLASH = 1.2A, ITORCH = 180mA Line Transient (LED Mode, Single LED, IFLASH = 1.2A) 30042065 30042064 Channel 1: VOUT (2V/div) Channel 4: ILED (500mA/div) Channel 2: IL (1A/div) Channel 3: TX1 (5V/div) Time Base: (20s/div) www.national.com Channel 3: VIN (1V/div) Channel 4: ILED (500mA/div) Channel 2: IL (1A/div) Time Base: (400s/div) 12 Line Transient IOUT = 500mA (Voltage Output Mode, VOUT = 5V) 30042066 Channel 1: VOUT (500mV/div, AC Coupled) Channel 4: IOUT (200mA/div) Channel 2: IL (500mA/div) Time Base: (40s/div) 30042067 Channel 3 (Top Trace): VIN (1V/div) Channel 1: VOUT (100mV/div, AC Coupled) Channel 2: IL + IIN (500mA/div) Time Base: (200s/div) Flash Pulse to HWEN Low Single LED, ILED = 1.2A Flash Pulse to Flash Pulse + VOUT Mode Single LED, ILED = 1.2A, VOUT = 5V 30042068 Channel 1: VOUT (2V/div) Channel 4: ILED (500mA/div) Channel 2: IL (1A/div) Channel 3: HWEN (5V/div) Time Base: (20s/div) LM3554 Load Transient VIN = 3.6V (Voltage Output Mode, VOUT = 5V) 30042072 Channel 1: VOUT (2V/div) Channel 4: ILED (500mA/div) Channel 2: IL (1A/div) Channel 3: ENVM (5V/div) Time Base: (100s/div) 13 www.national.com LM3554 Flash Pulse + VOUT to Flash Pulse Single LED, ILED = 1.2A, VOUT = 5V NTC Mode Response Single LED, ILED = 1.2A Circuit of Figure 25 (R(T) = 100k (@+25C), R3 = 9k) 30042073 30042076 Channel 1: VOUT (2V/div) Channel 4: ILED (500mA/div) Channel 2: IL (1A/div) Channel 3: ENVM (5V/div) Time Base: (100s/div) Channel 3: NTC Pin Voltage (500mV/div) Channel 4: ILED (500mA/div) Time Base: (200ms/div) VIN Monitor Response Single LED, ILED = 1.2A 3.1V UVLO Setting 30042077 Channel 3: VIN (1V/div) Channel 4: ILED (500mA/div) Time Base: (100ms/div) www.national.com 14 LM3554 Block Diagram 30042005 In Voltage Output mode the LM3554 operates as a voltage output boost converter with selectable output voltages of 4.5V and 5V. In this mode the LM3554 is able to deliver up to typically 5W of output power. At light loads and in Voltage Output mode the PWM switching converter changes over to a pulsed frequency regulation mode and only switches as necessary to ensure proper LED current or output voltage regulation. This allows for improved light load efficiency compared to converters that operate in fixed-frequency PWM mode at all load currents. Additional features of the LM3554 include 4 logic inputs, an internal comparator for LED thermal sensing, and a low-power indicator LED current source. The STROBE input provides a hardware Flash mode enable. The ENVM/TX2/GPIO2 input is configurable as a hardware Voltage Output mode enable (ENVM), an active high Flash interrupt that forces the device from FLASH mode to a low-power TORCH mode (TX2), or as a programmable logic input/output (GPIO2). The TX1 input is configurable as an active high Flash interrupt that forces the device from FLASH mode to a low-power TORCH mode (TX1), as a hardware Torch mode enable (TORCH), or as a programmable logic input/output (GPIO1) . The HWEN input provides for an active low hardware shutdown of the device. Finally, the LEDI/NTC pin is configurable as a low-power indicator LED driver (LEDI), or as a threshold detector for thermal sensing (NTC). In NTC mode when the threshold (VTRIP) at the LEDI/NTC pin is crossed (VLEDI/NTC falling), the Overview The LM3554 is a high-power white LED flash driver capable of delivering up to 1.2A of LED current into a single LED, or up to 600mA into two parallel LEDs. The device incorporates a 2MHz constant frequency, synchronous, current mode PWM boost converter, and two high-side current sources to regulate the LED current over the 2.5V to 5.5V input voltage range. The LM3554 operates in two modes: LED mode or constant Voltage Output mode. In LED mode when the output voltage is greater than VIN - 150mV, the PWM converter switches and maintains at least 300mV (VHR) across both current sources (LED1 and LED2). This minimum headroom voltage ensures that the current sinks remain in regulation. When the input voltage is above VLED + VHR, the device operates in Pass mode with the device not switching and the PFET on continuously. In Pass mode the difference between (VIN ILEDxRON_P) and VLED is dropped across the current sources. If the device is operating in Pass mode, and VIN drops to a point that forces the device into switching, the LM3554 will make a one-time decision to jump into switching mode. The LM3554 remains in switching mode until the device is shutdown and re-enabled. This is true even if VIN were to rise back above VLED + 300mV during the current Flash or Torch cycle. This prevents the LED current from oscillating when VIN is operating close to VOUT. 15 www.national.com LM3554 Flash pulse is forced to the Torch current setting, or into shutdown depending on the NTC Shutdown bit setting . Control of the LM3554 is done via an I2C-compatible interface. This includes switch-over from LED to Voltage Output mode, adjustment of the LED current in TORCH mode, adjustment of the LED current in FLASH mode, adjustment of the indicator LED currents, changing the flash LED current duration, changing the switch current limit. Additionally, there are 5 flag bits that can be read back indicating flash current timeout, over-temperature condition, LED failure (open or short), LED thermal failure, and an input voltage fault. load comparator is disabled the LM3554 will operate at a constant frequency down to ILOAD = 0. Disabling light load can be useful when a more predictable switching frequency across the entire load current range is desired. VOLTAGE OUTPUT MODE Bit 2 (VM) of the Torch Brightness Register, bit 2 (VM) of the Flash Brightness Register, or the ENVM input enables or disables the Voltage Output mode. In Voltage Output mode the device operates as a simple boost converter with two selectable voltage levels (4.5V and 5V). Write a (1) to bit 1 (OV) of Configuration Register 1 to set VOUT to 5V. Write a (0) to this bit to set VOUT to 4.5V. In Voltage Output mode the LED current sources can continue to operate; however, the difference between VOUT and VLED will be dropped across the current sources. (See MAXIMUM OUTPUT POWER section.) In Voltage Output mode when VIN is greater than VOUT the LM3554 operates in Pass Mode (see PASS MODE section). At light loads the LM3554 switches over to a pulsed frequency mode operation (light load comparator enabled). In this mode the device will only switch as necessary to maintain VOUT within regulation. This mode provides a better efficiency due to the reduction in switching losses which become a larger portion of the total power loss at light loads. STARTUP Turn on of the LM3554 is done through bits [2:0] of the Torch Brightness Register (0xA0), bits [2:0] of the Flash Brightness Register (0xB0), the ENVM input, or the STROBE input. Bits [1:0] of the Torch Brightness Register or Flash Brightness Register enables/disables the current sources (LED1, LED2, and LEDI). Bit [2] enables/disables the voltage output mode. A logic high at STROBE enables Flash mode. A logic high on the ENVM input forces the LM3554 into Voltage Output mode. On startup, when VOUT is less than VIN the internal synchronous PFET turns on as a current source and delivers typically 350mA to the output capacitor. During this time all current sources (LED1, LED2, and LEDI) are off. When the voltage across the output capacitor reaches 2.2V, the current sources can turn on. At turn-on the current sources step through each FLASH or TORCH level until the target LED current is reached (16 s/step). This gives the device a controlled turn-on and limits inrush current from the VIN supply. OVER-VOLTAGE PROTECTION The output voltage is limited to typically 5.6V (5.7V max). In situations such as the current source open, the LM3554 will raise the output voltage in order to try and keep the LED current at its target value. When VOUT reaches 5.6V the overvoltage comparator will trip and turn off both the internal NFET and PFET. When VOUT falls below 5.4V (typical), the LM3554 will begin switching again. PASS MODE Once the Output voltage charges up to VIN - 150mV the LM3554 will decide if the part operates in Pass Mode or Boost mode. If the voltage difference between VOUT and VLED is less than 300mV, the device will transition in Boost Mode. If the difference between VOUT and VLED is greater than 300mV, the device will operate in Pass Mode. In Pass Mode the boost converter stops switching, and the synchronous PFET turns fully on bringing VOUT up to VIN - IINxRPMOS (RPMOS = 150m). In Pass Mode the inductor current is not limited by the peak current limit. In this situation the output current must be limited to 2.5A. CURRENT LIMIT The LM3554 features 4 selectable current limits: 1A, 1.5A, 2A, and 2.5A. These are selectable through the I2C-compatible interface via bits 5 (CL0) and 6 (CL1) of the Flash Duration Register. When the current limit is reached, the LM3554 stops switching for the remainder of the switching cycle. Since the current limit is sensed in the NMOS switch there is no mechanism to limit the current when the device operates in Pass Mode. In situations where there could potentially be large load currents at OUT, and the LM3554 is operating in Pass mode, the load current must be limited to 2.5A. In Boost mode or Pass mode if VOUT falls below approximately 2.3V, the part stops switching, and the PFET operates as a current source limiting the current to typically 350mA. This prevents damage to the LM3554 and excessive current draw from the battery during output short circuit conditions. LIGHT LOAD DISABLE Configuration Register 1 bit [0] = 1 disables the light load comparator. With this bit set to 0 (default) the light load comparator is enabled. Light Load mode only applies when the LM3554 is active in Voltage Output mode. In LED mode the Light Load Comparator is always disabled. When the light www.national.com 16 LM3554 MAXIMUM LOAD CURRENT (VOLTAGE MODE) Assuming the power dissipation in the LM3554 and the ambient temperature are such that the device will not hit thermal shutdown, the maximum load current as a function of IPEAK is: Figure 2 shows the theoretical maximum Output current vs theoretical Efficiency at different input and output voltages using the previous two equations for IL and ILOAD with a peak current of 2.5A. This plot represents the theoretical maximum output current (for the LM3554 in Voltage Output mode) that the device can deliver just before hitting current limit. Where is efficiency and is found in the efficiency curves in the Typical Performance Characteristics and 30042008 FIGURE 2. LM3554 Maximum Output Current therefore increase the die temperature. This can be additionally compounded if the LED current sources are operating while the device is in Voltage Output mode since the difference between VOUT and VLED is dropped across the current sources. Any circuit configuration must ensure that the die temperature remains below +125C taking into account the ambient temperature derating. MAXIMUM OUTPUT POWER Output power is limited by three things: the peak current limit, the ambient temperature, and the maximum power dissipation in the package. If the LM3554's die temperature is below the absolute maximum rating of +125C, the maximum output power can be over 6W. However, any appreciable output current will cause the internal power dissipation to increase and Maximum Output Power (Voltage Output Mode) In Voltage Output mode the total power dissipated in the LM3554 can be approximated as: PN is the power lost in the NFET, PP is the PFET power loss, PLED1, PLED2, and PIND are the losses across the current sinks. An approximate calculation of these losses gives: 30042010 The above formulas consider the average current through the NFET and PFET. The actual power losses will be higher due to the RMS currents and the quiescent power into IN. These, however, can give a decent approximation. 17 www.national.com LM3554 Maximum Output Power (Led Boost Mode) In LED mode with VOUT > VIN the LM3554's boost converter will switch and make VOUT = VLED + 0.3V. In this situation the total power dissipated in the LM3554 is approximated as: 30042011 Equation 1 and the PFET is fully on. The difference between VIN - ILOADxRPMOS and VLED will be dropped across the current sources. In this situation the total power dissipated in the LM3554 is approximated as: Maximum Output Power (Led Pass Mode) In LED mode with VIN - ILOAD x RPFET > VLED + 0.3V, the LM3554 operates in Pass Mode. In this case. the NFET is off, 30042012 Equation 2 Once the total power dissipated in the LM3554 is calculated the ambient temperature and the thermal resistance of the 16bump micro SMD (TMD16) are used to calculate the total die temperature (or junction temperature TJ). As an example, assume the LM3554 is operating at VIN = 3.6V and configured for Voltage Output mode with VOUT = 5V and IOUT = 0.7A. The LED currents are then programmed in Torch mode with 150mA each at VLED = 3.6V. Additionally, the indicator LED has 10mA at VIND = 3.6V. Using Equations 1 and 2 above, the approximate total power dissipated in the device is: be above the absolute maximum ratings, and the load current would need to be scaled back. This example demonstrates the steps required to estimate the amount of current derating based upon operating mode, circuit parameters, and the device's junction-toambient thermal resistance. In this example a thermal resistance of 60C/W was used (JESD51-7 standard). Since thermal resistance from junction-to-ambient is largely PCB layout dependent, the actual number used will likely be different and must be taken into account when performing these calculations. FLASH MODE In Flash mode the LED current sources (LED1 and LED2) each provide 16 different current levels from typically 34mA to approximately 600mA. The Flash currents are set by writing to bits [6:3] of the Flash Brightness Resister. Flash mode is activated by either writing a (1, 1) to bits [1:0] of the Torch Brightness Register, writing a (1,1) to bit [1:0] of the Flash Brightness Register, or by pulling the STROBE pin high. Once the Flash sequence is activated, both current sinks (LED1 and LED2) will ramp up to the programmed Flash current by stepping through all Flash levels (16s/step) until the programmed current is reached. The die temperature approximation will be: In this case the device can operate at these conditions. If then the ambient temperature is increased to +85C, the die temperature would be +140.8C; thus, the die temperature would www.national.com 18 ENVM/TX2/GPIO2 The ENVM/TX2/GPIO2/INT pin has four functions. In ENVM mode (Configuration Register 1 bit [5] = 0), the ENVM/TX2/ GPIO2/INT pin is an active high logic input that forces the LM3554 into Voltage Output Mode. In TX2 mode (Configuration Register 1 bit [5] = 1), the ENVM/TX2/GPIO2/INT pin is a Power Amplifier Synchronization input that forces the LM3554 from Flash mode into Torch mode. In GPIO2 mode (GPIO Register Bit [3] = 1) the ENVM/TX2/GPIO2/INT pin is configured as a general purpose logic input/output and controlled via bits[3:5] of the GPIO Register. In INT mode the ENVM/TX2/GPIO2/INT pin is a hardware interrupt output which pulls low when the LM3554 is in NTC mode, and the voltage at LEDI/NTC falls below VTRIP. In TX2 mode, when Configuration Register 1 bit [6] = 0 the ENVM/TX2/GPIO2 pin is an active low transmit interrupt input. Under this condition, when the LM3554 is engaged in a Flash event, and ENVM/TX2/GPIO2 is pulled low, both LED1 and LED2 are forced into either Torch mode or LED shutdown depending on the logic state of Configuration Register 2 bit [0]. In TX2 mode with Configuration Register 1 bit [6] = 1, the ENVM/TX2/GPIO2 pin is an active high transmit interrupt. Under this condition when the LM3554 is engaged in a Flash event, and the TX2 pin is driven high, both LED1 and LED2 are forced into Torch mode or LED shutdown, depending on the logic state of Configuration Register 2 bit [0]. After a TX2 event, if the ENVM/TX2/GPIO2 pin is disengaged, and the TX2 Shutdown bit is set to force Torch mode, the LED current will ramp back to the previous Flash current level. If the TX2 shutdown bit is programmed to force LED shutdown upon a TX2 event the Flags Register must be read to resume normal LED operation. Table 2, Figure 8 and Figure 9 detail the functionality of the ENVM/TX2 input. FLASH TERMINATION (I2C-INITIATED FLASH) For I2C initated flash pulses, the flash LED current can be terminated by either waiting for the timeout duration to expire or by writing a (0, 0) to bits [1:0] of the Torch Brightness Register, or Flash Brightness Register. If the timeout duration is allowed to elapse, the flash enable bits of the Torch Brightness and Flash Brightness Registers are automatically reset to 0. FLASH TIMEOUT The Flash Timeout period sets the duration of the flash current pulse. Bits [4:0] of the Flash Duration Register programs the 32 different Flash Timeout levels in steps of 32ms giving a Flash Timeout range of 32ms to 1024ms (see Table 7). TORCH MODE In Torch mode the current sources LED1 and LED2 each provide 8 different current levels (see Table 2). The Torch currents are adjusted by writing to bits [5:3] of the Torch Brightness Register. Torch mode is activated by setting Torch Brightness Register bits [1:0] to (1, 0) or Flash Brightness bits [1:0] to (1, 0). Once the Torch mode is enabled the current sources will ramp up to the programmed Torch current level by stepping through all of the Torch currents at 16s/step until the programmed Torch current level is reached. ENVM/TX2/GPIO2/INT as an Interrupt Output In GPIO2 mode the ENVM/TX2/GPIO2 pin can be made to reflect the inverse of the LED Thermal Fault flag (bit[5] in the Flags Register). Configure the LM3554 for this feature by: set GPIO Register Bit [6] = 1 (NTC External Flag) set GPIO Register Bit [3] = 1 (GPIO2 mode) set GPIO Register Bit [4] = 1 (GPIO2 is an output) set Configuration Register 1 Bit [3] = 1 (NTC mode) When the voltage at the LEDI/NTC pin falls below VTRIP (1.05V typical), the LED Thermal Fault Flag (bit [5] in the Flags Register) is set, and the ENVM/TX2/GPIO2/INT pin is forced low. In this mode the interrupt can only be reset to the opendrain state by reading back the Flags register. TX1/TORCH The TX1/TORCH/GPIO1 input has a triple function. With Configuration Register 1 Bit [7] = 0 (default), TX1/TORCH/GPIO1 is a Power Amplifier Synchronization input (TX1 mode). This is designed to reduce the current pulled from the battery during an RF power amplifier transmit event. When the LM3554 is engaged in a Flash event, and the TX1 pin is pulled high, both LED1 and LED2 are forced into Torch mode at the programmed Torch current setting. If the TX1 pin is then pulled low before the Flash pulse terminates the LED current will ramp back to the previous Flash current level. At the end of the Flash timeout whether the TX1 pin is high or low, the LED current will turn off. With the Configuration Register Bit [7] = 1, TX1/TORCH/ GPIO1 is configured as a hardware Torch mode enable (TORCH). In this mode a high at TORCH turns on the LED current sources in Torch mode. STROBE (or I2- initiated flash) will take precedence over the TORCH mode input. Figure 12 details the functionality of the hardware TORCH mode. Additionally, when a flash pulse is initiated during hardware TORCH mode, the hardware torch mode bit is reset at the end INDICATOR LED/THERMISTOR (LEDI/NTC) The LEDI/NTC pin serves a dual function, either as an LED indicator driver or as a threshold detector for a negative temperature coefficient (NTC) thermistor. Led Indicator Mode (LEDI) LEDI/NTC is configured as an LED indicator driver by setting Configuration Register 1 bit [3] = (0) and Torch Brightness Register bits [1:0] = (0, 1), or Flash Brightness Register bits [1:0] = (0, 1). In Indicator mode there are 4 different current levels available (2.3mA, 4.6mA, 6.9mA, 8.2mA). Bits [7:6] of 19 www.national.com LM3554 of the flash pulse. In order to re-enter hardware Torch mode, bit [7] of Configuration Register 1 would have to be re-written with a 1. The TX1/TORCH/GPIO1 input can also be configured as a GPIO input/output. for details on this, refer to the GPIO REGISTER ection of the datasheet. FLASH TERMINATION (STROBE-INITIATED FLASH) Bit [7] of the Flash Brightness Register (STR bit) determines how the Flash pulse terminates with STROBE-initated flash pulses. With the STR bit = 1 the Flash current pulse will only terminate by reaching the end of the Flash Timeout period. With STR = 0, Flash mode can be terminated by pulling STROBE low, or by allowing the Flash Timeout period to elapse. If STR = 0 and STROBE is toggled before the end of the Flash Timeout period, the Timeout period resets on the rising edge of STROBE. See LM3554 TIMING DIAGRAMS regarding the Flash pulse termination for the different STR bit settings. After the Flash pulse terminates, either by a flash timeout, or pulling STROBE low, LED1 and LED2 turn completely off. This happens even when Torch is enabled via the I2C-compatible interface, and the Flash pulse is turned on by toggling STROBE. After a Flash event ends the EN1, EN0 bits (bits [1:0] of the Torch Brightness Register, or Flash Brightness Register) are automatically re-written with (0, 0). LM3554 the Torch Brightness Register set the 4 different indicator current levels. The LEDI current source has a 1V typical headroom voltage. Torch mode only for the duration of the timeout counter. At the end of the timeout counter the LEDs will turn off. With Configuration Register 2 bit [2] set to (1) the operation of TX1/TORCH becomes dependent on its occurrence relative to STROBE. In this mode if TX1/TORCH goes high first, then STROBE goes high, the LEDs are forced into Torch mode with no timeout. In this mode if TX1/TORCH goes high after STROBE has gone high then the TX1/TORCH pin operates as a normal TX interrupt, and the LEDs will turn off at the end of the timeout duration. (See LM3554 TIMING DIAGRAMS, Figure 10, and Figure 11.) Thermal Comparator Mode (NTC) Writing a (1) to Configuration Register 1 bit [3] disables the indicator current source and configures the LEDI/NTC pin as a detector for an NTC thermistor. In this mode LEDI/NTC becomes the negative input of an internal comparator with the positive input internally connected to a reference (VTRIP = 1.05V typical). Additionally, Configuration Register 2 bit [1] determines the action the device takes if the voltage at LEDI/ NTC falls below VTRIP (while the device is in NTC mode). With Configuration register 2 bit [1] = 0, the LM3554 will be forced into Torch mode when the voltage at LEDI/NTC falls below VTRIP. With Configuration Register 2 bit [1] = 1 the device will shut down the current sources when VLEDI/NTC falls below VTRIP. When the LM3554 is forced from Flash into Torch (by VLEDI/NTC falling below VTRIP), normal LED operation (during the same Flash pulse) can only be re-started by reading from the Flags Register (0xD0) and ensuring the voltage at V LEDI/ NTC is above VTRIP. When VLEDI/NTC falls below VTRIP, and the Flags register is cleared, the LM3554 will go through a 250s deglitch time before the flash current falls to either torch mode or goes into shutdown. INPUT VOLTAGE MONITOR The LM3554 has an internal comparator that monitors the voltage at IN and can force the LED current into Torch mode or into shutdown if VIN falls below the programmable VIN Monitor Threshold. Bit 0 in the VIN Monitor register (0x80) enables or disables this feature. When enabled, Bits 1and 2 program the 4 adjustable thresholds of 3.1V, 3.2V, 3.3V, and 3.4V. Bit 3 in Configuration Register 2 (0xF0) selects whether an under-voltage event forces Torch mode or forces the LEDs off. See Figure 21/Table 7 and Figure 23/Table 9 for additional information. There is a set 100mV hysteresis for the input voltage monitor. When the input voltage monitor is active, and VIN falls below the programmed VIN Monitor Threshold, the LEDs will either turn off or their current will get reduced to the programmed Torch current setting. To reset the LED current to its previous level, two things must occur. First, VIN must go at least 100mV above the UVLO threshold and secondly, the Flags register must be read back. ALTERNATIVE EXTERNAL TORCH (AET MODE) Configuration Register 2 bit [2] programs the LM3554 for Alternative External Torch mode. With this bit set to (0) (default) TX1/TORCH is a transmit interrupt that forces Torch mode only during a Flash event. For example, if TX1/TORCH goes high during a Flash event then the LEDs will be forced into www.national.com 20 LM3554 LM3554 TIMING DIAGRAMS 30042037 FIGURE 3. Normal Torch to Flash Operation (Default, Power On or RESET state of LM3554) 30042038 FIGURE 4. TX1 Event During a Flash Event (Default State,TX1/TORCH is an Active High TX Input) 30042039 FIGURE 5. TX1 Event Before and After Flash Event (Default State, TX1/TORCH is an Active High TX Input) 21 www.national.com LM3554 30042040 FIGURE 6. STROBE Input is Level Sensitive (Default State, STR bit = 0) 30042041 FIGURE 7. STROBE Input is Edge Sensitive (STR bit = 1) www.national.com 22 LM3554 30042042 FIGURE 8. ENVM/TX2 Pin is Configured as an Active High TX Input 30042043 FIGURE 9. ENVM/TX2 Pin is Configured as an Active Low TX Input 23 www.national.com LM3554 30042044 FIGURE 10. Alternative External Torch Mode (TX1/TORCH Turns on Before STROBE) 30042045 FIGURE 11. Alternative External Torch Mode (STROBE Goes High Before TX1/TORCH, Same as Default with SEM = 0) 30042046 FIGURE 12. TX1/TORCH Configured as a Hardware Torch input www.national.com 24 Flash Timeout The TO flag (bit [0] of the Flags Register) reads back a (1) if the LM3554 is active in Flash mode and the Timeout period expires before the Flash pulse is terminated. The flash pulse can be terminated before the Timeout period expires by pulling the STROBE pin low (with STR bit '0'), or by writing a `0' to bit 0 or 1 of the Torch Brightness Register or the Flash Brightness Register. The TO flag is reset to (0) by pulling HWEN low, removing power to the LM3554, reading the Flags Register, or when the next Flash pulse is triggered. LED Thermal Fault The NTC flag (bit [5] of the Flags Register) reads back a (1) if the LM3554 is active in Flash or Torch mode, the device is in NTC mode, and the voltage at LEDI/NTC has fallen below VTRIP (1.05V typical). When this has happened and the LM3554 has been forced into Torch or LED shutdown (depending on the state of Configuration Register 2 bit [1], the Flags Register must be read in order to place the device back in normal operation. (See Thermal Comparator Mode (NTC) section for more details.) Thermal Shutdown When the LM3554's die temperature reaches +150C the boost converter shuts down, and the NFET and PFET turn off. Additionally, all three current sources (LED1, LED2, and LEDI) turn off. When the thermal shutdown threshold is tripped a (1) gets written to bit [1] of the Flag Register (Thermal Shutdown bit). The LM3554 will start up again when the die temperature falls to below +135C. During heavy load conditions when the internal power dissipation in the device causes thermal shutdown, the part will turn off and start up again after the die temperature cools. This will result in a pulsed on/off operation. The OVT bit however will only get written once. To reset the OVT bit pull HWEN low, power down the LM3554, or read the Flags Register. Input Voltage Monitor Fault The VIN Monitor Flag (bit [6] of the Flag Register) reads back a '1' when the Input Voltage Monitor is enabled and VIN falls below the programmed VIN Monitor threshold. This flag must be read back in order to resume normal operation after the LED current has been forced to Torch mode or turned off due to a VIN Monitor event. LED Fault The LED Fault flag (bit 2 of the Flags Register) reads back a (1) if the part is active in Flash or Torch mode and either LED1 or LED2 experience an open or short condition. An LED open condition is signaled if the OVP threshold is crossed at OUT while the device is in Flash or Torch mode. An LED short condition is signaled if the voltage at LED1 or LED2 goes below 500mV while the device is in Torch or Flash mode. There is a delay of 250s before the LEDF flag is valid on a LED short. This is the time from when VLED falls below the LED short threshold of 500mV (typical) to when the fault flag is valid. There is a delay of 2s from when the LEDF flag is valid on an LED open. This delay is the time between when the OVP threshold is triggered and when the fault flag is valid. The LEDF flag can only be reset to (0) by pulling HWEN low, removing power to the LM3554, or reading the Flags Register. TX1 and TX2 Interrupt Flags The TX1 and TX2 interrupt flags (bits [3] and [4]) indicate a TX event on the TX1/TORCH and ENVM/TX2 pins. Bit 3 will read back a (1) if TX1/TORCH is in TX1 mode and the pin has changed from low to high since the last read of the Flags Register. Bit 4 will read back a (1) if ENVM/TX2 is in TX2 mode and the pin has had a TX event since the last read of the Flags Register. A read of the Flags Register automatically resets these bits. The ENVM/TX2/GPIO2 pin, when configured in TX2 mode, has a TX event that can be either a high-to-low transition or a low-to-high transition depending on the setting of the TX2 polarity bit (see Configuration Register 1 Bit [6]). 25 www.national.com LM3554 FLAGS REGISTER AND FAULT INDICATORS The Flags Register (0xD0) contains the Interrupt and Fault indicators. Five fault flags are available in the LM3554. These include a Thermal Shutdown, an LED Failure Flag (LEDF) , a Timeout indicator Flag (TO), a LED Thermal Flag (NTC), and a VIN Monitor Flag. Additionally, two interrupt flag bits TX interrupt and TX2 interrupt indicate a change of state of the TX1/ TORCH pin (TX1 mode) and ENVM/TX2 pin (TX2 mode). Reading back a "1" indicates the TX lines have changed state since the last read of the Flags Register. A read of the Flags Register resets these bits. LM3554 I2C-Compatible Interface transitioning from HIGH to LOW while SCL is HIGH. A STOP condition is defined as SDA transitioning from LOW to HIGH while SCL is HIGH. The I2C master always generates the START and STOP conditions. START AND STOP CONDITIONS The LM3554 is controlled via an I2C-compatible interface. START and STOP conditions classify the beginning and end of the I2C session. A START condition is defined as SDA 30042018 FIGURE 13. Start and Stop Sequences The I2C bus is considered busy after a START condition and free after a STOP condition. During data transmission the I2C master can generate repeated START conditions. A START and a repeated START condition are equivalent function-wise. The data on SDA must be stable during the HIGH period of the clock signal (SCL). In other words, the state of SDA can only be changed when SCL is LOW. Figure 1 and Figure 14 show the SDA and SCL signal timing for the I2CCompatible Bus. See the Electrical Characteristics Table for timing values. 30042019 FIGURE 14. I2C-Compatible Timing a WRITE and R/W = 1 indicates a READ. The second byte following the device address selects the register address to which the data will be written. The third byte contains the data for the selected register. I2C-COMPATIBLE CHIP ADDRESS The device address for the LM3554 is 1010011 (53). After the START condition, the I2C master sends the 7-bit address followed by an eighth bit, read or write (R/W). R/W = 0 indicates 30042020 FIGURE 15. Device Address www.national.com 26 27 www.national.com LM3554 master. The master releases SDA (HIGH) during the 9th clock pulse (write mode). The LM3554 pulls down SDA during the 9th clock pulse, signifying an acknowledge. An acknowledge is generated after each byte has been received. TRANSFERRING DATA Every byte on the SDA line must be eight bits long, with the most significant bit (MSB) transferred first. Each byte of data must be followed by an acknowledge bit (ACK). The acknowledge related clock pulse (9th clock pulse) is generated by the LM3554 Register Descriptions TABLE 1. LM3554 Internal Registers Register Name Internal Hex Address Power On or Reset Value Torch Brightness 0xA0 0x50 Flash Brightness 0xB0 0x68 Flash Duration 0xC0 0x4F Flag Register 0xD0 0x40 Configuration Register 1 0xE0 0x42 Configuration Register 2 0xF0 0xF0 GPIO Register 0x20 0x80 VIN Monitor Register 0x80 0xF0 TORCH BRIGHTNESS REGISTER Bits [2:0] of the Torch Brightness Register, or bits [2:0] of the Flash Brightness Register place the device in shutdown or control the on/off state of Torch, Flash, the Indicator LED and the Voltage output mode (see Table 2). Writing to Torch Brightness Register bits [2:0] automatically updates the Flash Brightness Register bits [2:0]; writing to bits [2:0] of the Flash Brightness Register automatically updates bits [2:0] of the Torch Brightness Register. Bits [5:3] set the current level in Torch mode (see Table 2). Bits [7:6] set the LED Indicator current level (see Table 2). 30042021 FIGURE 16. Torch Brightness Register Description TABLE 2. Torch Brightness Register Bit Settings Bit 7 (IND1) Bit 6 (IND0) Indicator Current Select Bits 00 = 2.3mA 01 = 4.6mA (default state) 10 = 6.9mA 11 = 8.2mA www.national.com Bit 5 (TC2) Bit 4 (TC1) Bit 3 (TC0) Torch Current Select Bits 000 = 17mA (34mA total) 001 = 35.5mA (71mA total) 010 = 54mA (108mA total) default state 011 = 73mA (146mA total) 100 = 90mA (180mA total) 101 = 109mA (218mA total) 110 = 128mA (256mA total) 111 = 147.5mA (295mA total) 28 Bit 2 (VM) Bit 1 (EN1) Bit 0 (EN0) Enable Bits 000 = Shutdown (default) 001 = Indicator Mode 010 = Torch Mode 011 = Flash Mode (bits reset at timeout) 100 = Voltage Output Mode 101 = Voltage Output + Indicator Mode 110 = Voltage Output + Torch Mode 111 = Voltage Output + Flash Mode (bits [1:0] are reset at end of timeout) Register bits [2:0] automatically updates the Torch Brightness Register bits [2:0]. Bits [6:3] set the current level in Flash mode (see Table 3). Bit [7] sets the STROBE Termination select bit (STR) (see Table 3). 30042022 FIGURE 17. Flash Brightness Register Description TABLE 3. Flash Brightness Register Bit Settings Bit 7 (STR) STROBE Edge or Level Select 0 = (Level Sensitive) When STROBE goes high, Flash current will turn on and remain on for the duration the STROBE pin is held high or when Flash Timeout occurs, whichever comes first.(default) 1 = (Edge Triggered) When STROBE goes high , Flash current will turn on and remain on for the duration of the Flash Timeout. Bit 6 (FC3) Bit 5 (FC2) Bit 4 (FC1) Bit 3 (FC0) Flash Current Select Bits 0000 = 35.5mA (71mA total) 0001 = 73mA (146mA total) 0010 = 109mA (218mA total) 0011 = 147.5mA (295mA total) 0100 = 182.5mA (365mA total) 0101 = 220.5mA (441mA total) 0110 = 259mA (518mA total) 111 = 298mA (596mA total) 1000 =326mA (652mA total) 1001 = 364.5mA (729mA total) 1010 = 402.5mA (805mA total) 1011 = 440.5mA (881mA total) 1100 = 480mA (960mA total) 1101 = 518.5mA (1037mA total) Default 1110 = 556.5mA (1113mA total) 1111 = 595.5mA (1191mA total) 29 Bit 2 (VM) Bit 1 (EN1) Bit 0 (EN0) Enable Bits 000 = Shutdown (default) 001 = Indicator Mode 010 = Torch Mode 011 = Flash Mode (bits reset at timeout) 100 = Voltage Output Mode 101 = Voltage Output + Indicator Mode 110 = Voltage Output + Torch Mode 111 = Voltage Output + Flash Mode (bits [1:0] are reset at end of timeout) www.national.com LM3554 FLASH BRIGHTNESS REGISTER Bits [2:0] of the Torch Brightness Register, or bits [2:0] of the Flash Brightness Register place the device in shutdown or control the on/off state of Torch, Flash, the Indicator LED and the Voltage output mode. Writing to the Flash Brightness LM3554 FLASH DURATION REGISTER Bits [4:0] of the Flash Duration Register set the Flash Timeout duration. Bits [6:5] set the switch current limit. Bit [7] defaults as a '1' and is not used (see Table 4). 30042023 FIGURE 18. Flash Duration Register Description TABLE 4. Flash Duration Register Bit Settings Bit 7 (Not used) Bit 6 (CL1) Bit 5 (CL0) Reads Back '0' Current Limit Select Bits 00 = 1A Peak Current Limit 01 = 1.5A Peak Current Limit t10 = 2A Peak Current Limi (default) 11 = 2.5A Peak Current Limit www.national.com Bit 4 (T4) Bit 3 (T3) Flash Timeout Select Bits 00000 = 32ms timeout 00001 = 64ms timeout 00010 = 96ms timeout 00011 = 128ms timeout 00100 = 160ms timeout 00101 = 192ms timeout 00110 = 224ms timeout 00111 = 256ms timeout 01000 = 288ms timeout 01001 = 320ms timeout 01010 = 352ms timeout 01011 = 384ms timeout 01100 = 416ms timeout 01101 = 448ms timeout 01110 = 480ms timeout 01111 = 512ms timeout (default) 10000 = 544ms timeout 10001 = 576ms timeout 10010 = 608ms timeout 10011 = 640ms timeout 10100 = 672ms timeout 10101 = 704ms timeout 10110 = 736ms timeout 10111 = 768ms time-out 11000 = 800ms timeout 11001 = 832ms timeout 11010 = 864ms timeout 11011 = 896ms timeout 11100 = 928ms timeout 11101 = 960ms timeout 11110 = 992ms timeout 11111 = 1024ms timeout 30 Bit 2 (T2) Bit 1 (T1) Bit 0 (T0) VIN Monitor Fault, LED over temperature (NTC), and a TX interrupt. (See Figure 18 and Table 4.) 30042024 FIGURE 19. Flags Register Description TABLE 5. Flags Register Bit Settings Bit 7 (VIN Monitor Fault Fault) 0=No Fault at VIN (default) 1=Input Voltage Monitor is enabled and VIN has fallen below the programmed threshold Bit 6 (Unused) Bit 5 (LED Thermal Fault) Bit 4 (TX2 Interrupt) Bit 3 (TX1 Interrupt ) Not Used 0=LEDI/NTC 0=ENVM/TX2 0=TX1/TORCH (Reads Back pin is above has not has not changed '1') VTRIP (default) changed state state (default) (default) 1=LEDI/NTC has fallen below VTRIP (NTC mode only) Bit 2 (Led Fault) Bit 1 (Thermal Shutdown) Bit 0 (Flash Timeout) 0 = Proper LED Operation (default) 0 = Die Temperature below Thermal Shutdown Limit (default) 0 = Flash TimeOut did not expire (default) 1 = Die Temperature has crossed the Thermal Shutdown Threshold 1 = Flash TimeOut Expired 1=ENVM/TX2 1=TX1/TORCH 1 = LED has changed pin has changed Failed (Open state (TX2 state (TX1 mode or Short mode only) only) 31 www.national.com LM3554 FLAGS REGISTER The Flags Register holds the status of the flag bits indicating LED Failure, Over-Temperature, the Flash Timeout expiring, LM3554 CONFIGURATION REGISTER 1 Configuration Register 1 holds the light load disable bit, the voltage mode select bit (OV), the external flash inhibit bit, the control bit for the LEDI/NTC pin, the control bit for ENVM to TX2 mode, the polarity selection bit for the TX2 input, and the control bit for the TX1/TORCH bit (see Figure 20 and Table 6). 30042025 FIGURE 20. Configuration Register1 Description TABLE 6. Configuration Register 1 Bit Settings Bit 7 (Hardware Torch Mode Enable) Bit 6 (TX2 Polarity) Bit 5 (ENVM/ TX2) Bit 4 (N/A) Bit 3 (LEDI/ NTC) Bit 2 (External Flash Inhibit) Bit 1 (OV, Output Voltage Select) Bit 0 (Disable Light Load ) 0 = TX1/ 0 = ENVM/TX2 0 = ENVM Reads Back '0' 0 = LEDI/NTC 0 = STROBE 0 = Voltage TORCH is a pin is an active Mode The pin in Indicator Input Enabled Mode output TX1 flash low Flash ENVM/TX2 pin mode (default) voltage is 4.5V interrupt input inhibit is a logic input (default) (default) to enable Voltage Mode. A high on ENVM/TX2 will force Voltage Output Mode (default) 0 = Light load comparator is enabled. The LM3554 will go into PFM mode at light load (default). 1 = TX1/ 1 = ENVM/TX2 1 = TX2 Mode TORCH pin is pin is an active The ENVM/ a hardware high Flash TX2 is a Power TORCH inhibit Amplifier enable (default) Synchronizati on input. A high on ENVM/TX2 will force the LM3554 from Flash to Torch mode. 1 = Light load comparator is disabled. The LM3554 will not go into PFM mode at light load. www.national.com 1 = LEDI/NTC 1 = STROBE pin in Thermal Input Disabled Comparator Mode. Indicator current is disabled. 32 1 = Voltage Mode output voltage is 5V (default) LEDs into shutdown. Additionally, bit [2] (AET bit) selects the Alternate External Torch mode (see Figure 21 and Table 7). 30042036 FIGURE 21. Configuration Register 2 Description TABLE 7. Configuration Register 2 Bit Settings Bit 7 (Not used) Bit 6 (Not used) Bit 5 (Not used) Bit 4 (Not used) Bit 3 (VIN Monitor Shutdown) Bit 2 (AET mode) Bit 1 (NTC Shutdown) Bit 0 (TX2 Shutdown) Reads Back '1' Reads Back '1' Reads Back '1' Reads Back '1' 0 = If IN drops 0 = Normal 0 = LEDI/NTC 0 = TX2 event below the operation for pin going forces the programmed TX1/TORCH below VTRIP LEDs into threshold and high before Torch mode forces the the VIN STROBE (TX1 (TX2 mode LEDs into Monitor mode only) only) default Torch mode feature is default (NTC mode enabled, the only) default LED's are forced into Torch mode (default) 1 = If IN drops 1 = Alternative 1 = LEDI/NTC 1 = TX2 event below the External Torch pin going forces the programmed operation. below VTRIP LEDs into threshold and TX1/TORCH shutdown forces the the VIN high before (TX2 mode LEDs into Monitor STROBE only) shutdown feature is forces Torch (NTC mode enabled, the mode with no only) LED's turn off timeout (TX1 mode only) GPIO REGISTER The GPIO register contains the control bits which change the state of the TX1/TORCH/GPIO1 pin and the ENVM/TX2/ GPIO2 pin to general purpose I/O's (GPIO's). Additionally, bit [6] of this register configures the ENVM/TX2/GPIO2 as a hardware interrupt output reflecting the NTC flag bit in the Flags Register. Figure 22 and Table 8 describe the bit description and functionality of the GPIO register. 30042026 FIGURE 22. GPIO Register Description 33 www.national.com LM3554 CONFIGURATION REGISTER 2 Configuration Register 2 contains the bits to select if TX2, NTC, and the VIN monitor force Torch mode or force the Flash LM3554 TABLE 8. GPIO Register Bit Settings Bit 7 (Not Used) Reads Back '1' Bit 6 (NTC Bit 5 (ENVM/ External Flag) TX2/GPIO2 data) 0 = NTC External Flag mode is disabled (default) This bit is the read or write data for the ENVM/TX2/ GPIO2 pin in GPIO mode (default is 0) 1 = When ENVM/TX2/ GPIO2 is configured as a GPIO output the ENVM/ TX2/GPIO2 pin will pull low when the LED Thermal Fault Flag is set Bit 4 (ENVM/ TX2/GPIO2 data direction) Bit 3 (ENVM/ TX2/GPIO2 Control) Bit 2 (TX1/ TORCH/ GPIO1 data) Bit 1 (TX1/ TORCH/ GPIO1 data direction) Bit 0 (TX1/ TORCH/ GPIO1 Control) 0 = ENVM/ 0 = ENVM/ TX2/GPIO2 is TX2/GPIO2 is a GPIO Input configured (default) according to the Configuration Register bit 5 (default) This bit is the read or write data for the TX1/TORCH/ GPIO1 pin in GPIO mode (default is 0) 0 = TX1/ TORCH/ GPIO1 is a GPIO input (default) 0 = TX1/ TORCH/ GPIO1 pin is configured as an active low reset input (default) 1 = TX!/ TORCH/ GPIO1 is an output 1 = TX1/ TORCH/ GPIO1 pin is configured as a GPIO 1 = ENVM/ 1 = ENVM/ TX2/GPIO2 is TX2/GPIO2 is a GPIO Output configured as a GPIO VIN MONITOR REGISTER The VIN Monitor Register controls the on/off state of the VIN Monitor comparator as well as selects the 4 programmable thresholds. Figure 23 and Table 9 describe the bit settings of the VIN Monitor feature. 30042047 FIGURE 23. VIN Monitor Register Description TABLE 9. VIN Monitor Register Bit Settings Bit 7 (Not used) Bit 6 (Not used) Bit 5 (Not used) Bit 4 (Not used) Bit 3 (Not used) Reads Back '1' Reads Back '1' Reads Back '1' Reads Back '1' Reads Back '0' www.national.com 34 Bit 2 (VIN Threshold) Bit 1 (VIN Threshold) Bit 0 (VIN Monitor Enable) 00 = 3.1V threshold (VIN 0 = VIN falling) Default Monitoring 01=3.2V threshold (VIN falling) Comparator is disabled 10 = 3.3V threshold (VIN (default) falling) 11 = 3.4V threshold (VIN 1 = VIN falling) Monitoring Comparator is enabled. OUTPUT CAPACITOR SELECTION The LM3554 is designed to operate with a at least a 4.7F ceramic output capacitor in LED mode and a 10F output capacitor in Voltage Output Mode. When the boost converter is running the output capacitor supplies the load current during the boost converters on-time. When the NMOS switch turns off the inductor energy is discharged through the internal PMOS switch supplying power to the load and restoring charge to the output capacitor. This causes a sag in the output voltage during the on-time and a rise in the output voltage during the off-time. The output capacitor is therefore chosen to limit the output ripple to an acceptable level depending on load current and input/output voltage differentials and also to ensure the converter remains stable. For proper LED operation the output capacitor must be at least a 4.7F ceramic (10F in Voltage Output Mode). Larger capacitors such as 10F or 22F can be used if lower output voltage ripple is desired. To estimate the output voltage ripple considering the ripple due to capacitor discharge (VQ) and the ripple due to the capacitors ESR (VESR) use the following equations: For continuous conduction mode, the output voltage ripple due to the capacitor discharge is: In ceramic capacitors the ESR is very low so assume that 80% of the output voltage ripple is due to capacitor discharge and 20% from ESR. Table 10 lists different manufacturers for various output capacitors and their case sizes suitable for use with the LM3554. INPUT CAPACITOR SELECTION Choosing the correct size and type of input capacitor helps minimize the voltage ripple caused by the switching of the LM3554's boost converter and reduces noise on the devices input terminal that can feed through and disrupt internal analog signals. In the Typical Application Circuit a 4.7F ceramic input capacitor works well. It is important to place the input capacitor as close as possible to the LM3554's input (IN) terminals. This reduces the series resistance and inductance that can inject noise into the device due to the input switching currents. Table 10 lists various input capacitors that or recommended for use with the LM3554. TABLE 10. Recommended Input/Output Capacitors (X5R Dielectric) Manufacturer Part Number Value Case Size Voltage Rating TDK Corporation C1608JB0J475K 4.7F 0603(1.6mmx0.8mmx0.8mm) 6.3V TDK Corporation C1608JB0J106M 10F 0603(1.6mmx0.8mmx0.8mm) 6.3V TDK Corporation C2012JB1C475K 4.7F 0805(2mmx1.25mmx1.25mm) 16V TDK Corporation C2012JB1A106M 10F 0805(2mmx1.25mmx1.25mm) 10V TDK Corporation C2012JB0J226M 22F 0805(2mmx1.25mmx1.25mm) 6.3V Murata GRM188R60J475KE19 4.7F 0603(1.6mmx0.8mmx0.8mm) 6.3V Murata GRM21BR61C475KA88 4.7F 0805(2mmx1.25mmx1.25mm) 16V Murata GRM21BR61A106KE19 10F 0805(2mmx1.25mmx1.25mm) 10V Murata GRM21BR60J226ME39L 22F 0805(2mmx1.25mmx1.25mm) 6.3V circuit performance ensure that the inductor saturation and the peak current limit setting of the LM3554 is greater than IPEAK can be calculated by: INDUCTOR SELECTION The LM3554 is designed to use a 2.2H inductor. Table 11 lists various inductors and their manufacturers that can work well with the LM3554. When the device is boosting (VOUT > VIN) the inductor will typically be the biggest area of efficiency loss in the circuit. Therefore, choosing an inductor with the lowest possible series resistance is important. Additionally, the saturation rating of the inductor should be greater than the maximum operating peak current of the LM3554. This prevents excess efficiency loss that can occur with inductors that operate in saturation and prevents over heating of the inductor and possible damage. For proper inductor operation and SW = 2MHz; can be found in the Typical Performance Characteristics plots. TABLE 11. Recommended Inductors Manufacturer L Part Number TOKO 2.2H FDSE0312-2R2M 3mmx3mmx1.2mm 2A TDK 2.2H VLS252012T-2R2M1R3 2mmx2.5mmx1.2mm 1.5A Coilcraft 2.2H LPS4018-222ML 3.9mmx3.9mmx1.7mm 2.3A 35 Dimensions (LxWxH) ISAT www.national.com LM3554 The output voltage ripple due to the output capacitors ESR is found by: Applications Information LM3554 NTC THERMISTOR SELECTION NTC thermistors have a temperature to resistance relationship of: Choosing R3 here gives a more linear response around the temperature trip voltage. For example, with VBIAS = 2.5V, a thermistor whose nominal value at +25C is 100k and a = 4500K, the trip point is chosen to be +93C. The value of R (T) at 93C is: where is given in the thermistor datasheet and R25C is the thermistors value at +25C. R3 in Figure 25 is chosen so that it is equal to: Figure 24 shows the linearity of the thermistor resistive divider of the previous example. where R(T)TRIP is the thermistors value at the temperature trip point, VBIAS is shown in Figure 25, and VTRIP = 1.05V (typical). 30042034 FIGURE 24. Thermistor Resistive Divider Response vs Temperature Another useful equation for the thermistor resistive divider is developed by combining the equations for R3, and R(T) and solving for temperature. This gives the following relationship. VBIAS in order to help better choose the thermal components for practical values of thermistors, series resistors (R3), or reference voltages VBIAS. Programming bit [3] of the Configuration register with a (1) selects Thermal Comparator mode making the LEDI/NTC pin a comparator input for flash LED thermal sensing. Figure 25 shows the internal block diagram of the thermal sensing circuit which is OR'd with both the TX1 and ENVM/TX2 (TX2 mode) to force the LM3554 from Flash to Torch mode. This is intended to prevent LED overheating during flash pulses. Using a spreadsheet such as Excel, different curves for the temperature trip point T(C) can be created vs R3, Beta, or www.national.com 36 LM3554 30042030 FIGURE 25. Thermistor Voltage Divider and Sensing Circuit the thermistor sensing input. To filter out this noise it is necessary to place a 0.1F or larger ceramic capacitor close to the LEDI/NTC pin. The filter capacitor's return must also connect with a low-impedance trace, as close as possible to the PGND pin of the LM3554. NTC THERMISTOR PLACEMENT The termination of the thermistor must be done directly to the cathode of the Flash LED in order to adequately couple the heat from the LED into the thermistor. Consequentally, the noisy environment generated from the switching of the LM3554's boost converter can introduce noise from GND into 37 www.national.com LM3554 4. Layout Recommendations The high frequency and large switching currents of the LM3554 make the choice of layout important. The following steps should be used as a reference to ensure the device is stable and maintains proper voltage and current regulation across its intended operating voltage and current range. 1. Place CIN on the top layer (same layer as the LM3554) and as close to the device as possible. The input capacitor conducts the driver currents during the lowside MOSFET turn-on and turn-off and can see current spikes over 1A in amplitude. Connecting the input capacitor through short wide traces on both the IN and GND terminals will reduce the inductive voltage spikes that occur during switching and which can corrupt the VIN line. 2. Place COUT on the top layer (same layer as the LM3554) and as close as possible to the OUT and GND terminal. The returns for both CIN and COUT should come together at one point, and as close to the GND pin as possible. Connecting COUT through short wide traces will reduce the series inductance on the OUT and GND terminals that can corrupt the VOUT and GND line and cause excessive noise in the device and surrounding circuitry. 3. Connect the inductor on the top layer close to the SW pin. There should be a low impedance connection from the inductor to SW due to the large DC inductor current, and at the same time the area occupied by the SW node should be small so as to reduce the capacitive coupling of the high dV/dt present at SW that can couple into nearby traces. www.national.com 5. 6. 38 Avoid routing logic traces near the SW node so as to avoid any capacitively coupled voltages from SW onto any high-impedance logic lines such as TX1/TORCH/ GPIO1, ENVM/TX2/GPIO2, HWEN, LEDI/NTC (NTC mode), SDA, and SCL. A good approach is to insert an inner layer GND plane underneath the SW node and between any nearby routed traces. This creates a shield from the electric field generated at SW. Terminate the Flash LED cathodes directly to the GND pin of the LM3554. If possible, route the LED returns with a dedicated path so as to keep the high amplitude LED currents out the GND plane. For Flash LEDs that are routed relatively far away from the LM3554, a good approach is to sandwich the forward and return current paths over the top of each other on two layers. This will help in reducing the inductance of the LED current paths. The NTC Thermistor is intended to have its return path connected to the LED's cathode. This allows the thermistor resistive divider voltage (VNTC) to trip the comparators threshold as VNTC is falling. Additionally, the thermistor-to-LED cathode junction can have low thermal resistivity since both the LED and the thermistor are electrically connected at GND. The drawback is that the thermistor's return will see the switching currents from the LM3554's boost converter. Because of this, it is necessary to have a filter capacitor at the NTC pin which terminates close to the GND of the LM3554 and which can conduct the switched currents to GND. LM3554 Physical Dimensions inches (millimeters) unless otherwise noted 16 Bump SMD (0.4mm pitch) For Ordering, Refer to Ordering Information Table NS Package Number TMD16CCA X1 = 1.695mm (0.03mm), X2 = 1.695mm (0.03mm), X3 = 0.6mm(0.075mm) 39 www.national.com Synchronous Boost Converter with 1.2A Dual High Side LED Driver and I2C-Compatible Interface Notes For more National Semiconductor product information and proven design tools, visit the following Web sites at: www.national.com Products Design Support Amplifiers www.national.com/amplifiers WEBENCH(R) Tools www.national.com/webench Audio www.national.com/audio App Notes www.national.com/appnotes Clock and Timing www.national.com/timing Reference Designs www.national.com/refdesigns Data Converters www.national.com/adc Samples www.national.com/samples Interface www.national.com/interface Eval Boards www.national.com/evalboards LVDS www.national.com/lvds Packaging www.national.com/packaging Power Management www.national.com/power Green Compliance www.national.com/quality/green Switching Regulators www.national.com/switchers Distributors www.national.com/contacts LDOs www.national.com/ldo Quality and Reliability www.national.com/quality LED Lighting www.national.com/led Feedback/Support www.national.com/feedback Voltage References www.national.com/vref Design Made Easy www.national.com/easy www.national.com/powerwise Applications & Markets www.national.com/solutions Mil/Aero www.national.com/milaero PowerWise(R) Solutions Serial Digital Interface (SDI) www.national.com/sdi Temperature Sensors www.national.com/tempsensors SolarMagicTM www.national.com/solarmagic PLL/VCO www.national.com/wireless www.national.com/training PowerWise(R) Design University THE CONTENTS OF THIS DOCUMENT ARE PROVIDED IN CONNECTION WITH NATIONAL SEMICONDUCTOR CORPORATION ("NATIONAL") PRODUCTS. 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