LinearTechnologyChronicle A Showcase of Linear Technology's Focus Products October 1998 100 Product of the Month VIN = 10V Vol. 7 No. 10 VOUT = 5V LTC1625: No RSENSE DC/DC Controller Achieves 97% Efficiency region, the RDS(ON) of the device can be used as a sense resistance. This is tricky to implement because inductor current information is only available when the MOSFET is turned on (see Linear Technology magazine, August 1998). Because the new LTC1625 fully recovers the inductor current information, it behaves identically to traditional current mode controllers that use a sense resistor. Thus the circuit delivers the benefits of current mode control without the penalties of a sense resistor. The LTC(R)1625 is a synchronous stepdown controller that drives external N-channel MOSFETs using few external components. Current mode control with MOSFET VDS sensing eliminates the need for a sense resistor and improves control and efficiency (Figure 1). Additional Features The LTC1625 is designed to drive two N-channel power MOSFETs in synchronous applications. The controller runs at a nominal 150kHz frequency that also may be set at 225kHz and can be locked to an external clock. Soft start capability has been built into the circuit to provide limited inrush current and a controlled delay for supply sequencing. Providing gate charge to the power switches is a major source of efficiency loss. No Sense Resistor Many switching regulators require a sense resistor in order to limit output current under fault conditions. This resistor reduces the efficiency of the converter while adding both cost and complexity to the design. The LTC1625 enlists "sense resistors" already in the system. The power MOSFET switches do double duty as current sense elements. By measuring the drain-to-source voltage of a MOSFET operating in the triode SYNC CSS 0.1F VIN RUN/SS + TK M1 Si4410DY TG LTC1625 ITH RC 10k CC 2.2nF SW CB 0.22F BOOST VPROG INTVCC SGND L1 10H DB CMDSH-3 CVCC 4.7F + BG D1 MBRS140T3 CIN 10F 30V x2 + VIN 5V TO 28V VOUT 3.3V COUT 4.5A 100F 10V x3 M2 Si4410DY VOSENSE PGND 1625 F01 Figure 1. High Efficiency Step-Down Converter EFFICIENCY (%) 90 TM VOUT = 3.3V 80 70 60 0.01 0.1 1 LOAD CURRENT (A) 10 1625 TA01 Figure 2. Efficiency vs Load Current The LTC1625 reduces that loss. At low load current, the MOSFETs are turned off for a few cycles while the output capacitors support the load. This Burst ModeTM operation saves gate charge at the expense of fixed frequency operation. (Burst Mode operation may be overridden.) Also, the gate charge may be drawn from a more efficient second voltage source, if available, for further power savings. The LTC1625 can be configured for a wide variety of output voltages. 3.3V and 5V outputs may be selected without an external resistive divider. With a divider, the LTC1625 is capable of regulating anywhere between the input voltage and the 1.19V internal reference. This is a significant improvement over prior current mode controllers that were constrained by the common mode range of the sense amplifier. The input voltage range is very wide, 3.7V to 36V, making the LTC1625 an extremely versatile circuit for efficiency- and controlsensitive products such as cellular phones, wireless modems and distributed power systems. Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www.linear-tech.com. Inside This Issue: LT (R)1610: Micropower Boost Converter Offers Smallest Footprint .......................................... 2 LT1614: Tiny, Low Noise DC/DC Inverter Works to 1V Input .................................................. 2 LT1021-5: Ultralow Noise Power Supply ................................................................................. 3 LTC1706-19: Adds Digital Voltage Control to an Entire Family of LTC Regulators ................ 3 LT1636: Rugged Micropower Op Amp--Rail-to-Rail, Over-The-TopTM , 44V Breakdown ....... 4 LT1671: Fast and Low Power Comparator ............................................................................. 4 Linear Technology Chronicle * October 1998 , LTC and LT are registered trademarks of Linear Technology Corporation. Over-The-Top, Burst Mode and No RSENSE are trademarks of Linear Technology Corporation. 1 LT1610: Micropower Boost Converter Offers Smallest Footprint The new LT (R)1610 is a versatile, micropower DC/DC converter that provides the smallest solution for generating a regulated output voltage from a battery input as low as 1V. The LT1610 addresses board space limitations in several ways. First, the switching frequency is 1.7MHz, allowing the use of tiny, inexpensive, minimum height inductors and capacitors. Second, the frequency compensation components have been integrated into the IC, eliminating an external RC in most cases. Finally, the device comes in LTC's 8-lead MSOP package, one-half the size of the 8-lead SO package. The LT1610's input voltage range is from 1V up to 8V. Combined with its 30V, 300mA onboard switch, the circuit is useful for many regulator configurations, including boost, SEPIC and flyback. Output voltage can be up to 28V in the boost design. The device can generate 3V at 30mA from a single (1V) cell or 5V at 100mA from two cells (2V). As a Li-Ion cell to 3.3V SEPIC converter, the LT1610 can deliver 100mA. The circuit can also convert 3.3V to 5V at an output current of 200mA. Operating quiescent current is only 50A unloaded. The circuit includes a shut- down function that reduces the supply current to 0.5A. The LT1610 features Burst Mode operation at light loads to provide high efficiency over a broad range of load current (Figure 2). LT1614: Tiny, Low Noise DC/DC Inverter Works to 1V Input simple, the best charge pump solutions have output impedances in the 5 to 10 range which result in significant regulation problems when the load increases beyond a few tens of milliamperes. The LT1614 inductorbased inverting DC/DC converter uses closed-loop regulation to obtain an output impedance of 0.1, eliminating output voltage droop under load. The LT1614 utilizes a low noise topology and a fixed 600kHz operating frequency to ensure an output voltage free from low frequency switching harmonics, making it ideal for supplying low noise bias voltages for MR heads. The LT1614 can generate up to a 28V differential between input and out- 85 6 + VIN C1 33F 100k 5 SW VIN 3 + C1 22F FB SHDN 8 COMP GND VC R2 681k + C2 22F VIN = 1.25V 70 VIN = 1V 65 55 50 0.1 C1, C2: AVX TAJA226M010R D1: MOTOROLA MBR0520 L1: MURATA LQH3C4R7M24 1610 TA01 L2 22H VOUT - 5V 200mA SW SHDN LT1614 VC NFB GND 69.8k D1 24.9k C2 33F 1nF Figure 1. 5V to - 5V Converter 1 10 LOAD CURRENT (mA) 100 1610 TA02 Figure 1. Single Cell to 3V Converter Delivers 30mA C3 1F VIN = 1.5V 75 60 PGND 4 1 1614 TA01 2 R1 1M 7 80 VOUT 3V 30mA 2 LT1610 1 CELL VOUT = 3V D1 EFFICIENCY (%) L1 4.7H L1 22H VIN 5V C1, C2: AVX TAJB336M010 C3: AVX 1206CY106 D1: MBR0520 L1, L2: MURATA LQH3C220 Single Cell to 3V Converter Example A 1V to 3V boost converter is shown in Figure 1. The components take up very little space. The inductor measures 2.5mm by 3.2mm and is only 2mm tall. The tantalum capacitors measure 1.6mm by 3.2mm and are 1.6mm tall. Circuit efficiency, which reaches 77%, is detailed in Figure 2. + The LT1614 is a fixed frequency, inverting mode switching regulator that provides a low noise negative output to -24V from as low as a 1V supply. It is designed for low power, noise-sensitive, space-limited portable products. The inverting DC/DC converter function is traditionally realized with a capacitor-based charge pump. Although By simply changing the feedback resistor values (to 1M and 322k), the circuit can generate 5V from 2 cells or from a 3.3V input. The efficiency of that circuit reaches 83%. The LT1610's 1.7MHz operating frequency, internal compensation and tiny MSOP package result in a low cost and minimal board space overall solution. For a data sheet and evaluation samples, contact your local Linear Technology sales office. Visit our web site at www.linear-tech.com for more information. Figure 2. Single Cell to 3V Converter Efficiency Reaches 77% put from a 1V to 5V input. The LT1614's tiny 8-lead MSOP package and small, minimal external components allow it to fit in tight places. The circuit contains a low-battery detector with a 200mV reference and shuts down to less than 10A current drain. No load quiescent current is 1mA and the internal 0.6 NPN power switch handles a 500mA current with only a voltage drop of 295mV. Figure 1 shows the 5V to - 5V application. The LT1614 operates by driving its NFB pin to a voltage of -1.24V, allowing direct regulation of the negative output. This converter topology, which consists of inductors in series with both input and output, results in low output noise and also in low reflected noise on the input supply. Output ripple is 40mV due to the ESR of the tantalum output capacitor C2. It may be substantially reduced further by use of a ceramic capacitor. Efficiency of the circuit is above 70% from 10mA to 200mA. For a data sheet and evaluation samples, contact your local Linear Technology sales office. Fore more information, visit our web site at www.linear-tech.com. Linear Technology Chronicle * October 1998 Application of the Month INPUT 9V TO 12V Ultralow Noise Power Supply Low noise synthesizers need quiet power supplies for their VCOs and other critical circuitry. 3-terminal linear voltage regulators exhibit far too much noise for this application, calling instead for a regulator constructed from a voltage reference. A practical example is shown in Figure 1. Current through the LT1021-5 reference is used to drive the base of a PNP pass device, resulting in an available output current of at least 1A. In this example, the current is intentionally limited to 200mA by the addition of emitter degeneration and LTC1706-19 Adds Digital Voltage Control to an Entire Family of LTC Regulators The relentless push of microprocessor development for higher speed and lower power dissipation, especially in laptop computers, is driving supply voltages to new low levels. Supply voltage has become so critical that different processors demand different yet precise levels to perform optimally. The LTC1706-19 takes a 4-bit digital word from a VID (Voltage Identification) microprocessor system and precisely controls the output voltage of a high performance DC/DC converter like the LTC1435A. The output of the regulator can be adjusted from 1.3V to 2V in 50mV increments. The LTC1706-19 is available right now and works with an entire family of LTC regulators (listed in Table 1) that have internal 1.19V references. Also, the LTC1706-19 is fully compliant with the Intel Mobile VID specification. High Accuracy, Versatile, Small Package The digitally programmed resistive divider in the LTC1706-19 is better than 0.25% accurate across the 1.3V to 2V range and is unaffected by temperature. This results in an overall accuracy of 1.25% when coupled with the LTC1435A in the Intel Mobile Pentium(R) II processor VID power converter shown in Figure 1. The Linear Technology Chronicle * October 1998 base clamping. The low noise of the reference is preserved, giving a 100-fold improvement over the noise of an equivalent 5V, 3-terminal regulator, plus improved initial accuracy and long-term stability. Typical output noise is 7VP-P over a 10kHz bandwidth. The LT1236-5 may also be used in this circuit. Other output voltages may be obtained with the wide selection of references available from Linear Technology. For more information, see data sheets and Application Note 42. four, 40k, pull-up resistors on the VID digital inputs are built in, and the LTC1706-19 is housed in a space efficient SO-8 package. The LTC1706-19 can also be used to program the output voltages of regulators with different onboard references. Used Table 1. Compatible LTC Processor Power Supply Products LTC Switcher LTC1433/LTC1434 LTC1435A LTC1436A LTC1436A-PLL LTC1437A LTC1438/LTC1439 LTC1538/LTC1539 LTC1624 LTC1625 VIN 4.5V TO 22V CSS 0.1F 1 COSC 43pF 2 Potential Application Low Power Supplies for DSPs or Palm Computer CPUs Mobile Pentium II CPU Power Cellular Telephones and NoiseSensitive Equipment Multiple Voltage Systems High Performance DSP Power Industrial and Single Board Computer CPU Power VIN COSC TG RUN/SS SW 3 ITH 51pF INTVCC RC 10k 5 6 BOOST SGND BG VOSENSE PGND SENSE - 7 SENSE+ 8 1000pF 4.7 220 CF 0.1F 16 ZBD949* IN 10 1/2W LT1021-5 OUTPUT 5V/200mA OUT GND 2 + *ZETEX INC (516) 864-7630 **GLOWS IN CURRENT LIMIT. DO NOT OMIT 100F TANT Figure 1. Ultralow Noise 5V, 200mA Supply Output Noise Is 7VRMS over a 10Hz to 10kHz Bandwidth. Reference Noise Is Guaranteed to Less Than 11VRMS. Standard 3-Terminal Regulators Have One Hundred Times the Noise and No Guarantees with the LT1575, an UltraFastTM transient response, low dropout linear regulator controller with a 1.21V reference, the output will range from 1.27V to 2.03V in steps of 50.8mV. Using only one N-channel power MOSFET, the two circuits make an extremely flexible, efficient, compact power supply. The LTC1706-19 is the ideal companion chip to provide precise, programmable low voltage outputs for DC/DC converters. Its compact size, compatibility and high accuracy are just the right features for today's portable equipment. Contact your local Linear Technology sales office for a data sheet and evaluation samples. For more information, visit our web site at www. linear-tech.com. UltraFast is a trademark of Linear Technology Corporation. Pentium is a registered trademark of Intel Corporation. + M1 Si4410DY 14 L1 3.3H 12 CIN 10F 30V x2 VOUT 1.3V TO 2V 7A RSENSE 0.015 SENSE VCC DB 0.22F 15 + 11 47F RF, 4.7 13 LTC1435A CC 1000pF CC2 220pF + RED LED** 4.7F M2 Si4410DY LTC1706-19 D1 FB 10 DB: CMDSH-3 D1: MBRS140T3 + COUT 820F 4V x2 VID 0 1 2 3 GND FROM P Figure 1. Intel Mobile Pentium II Processor Power Converter 3 Rugged LT1636 Micropower Op Amp: Rail-to-Rail, Over-The-Top, 44V Breakdown The LT1636 is a 55A rail-to-rail input/output op amp capable of handling supply voltages from 2.7V to 44V. It features a high level of fault protection and an output shutdown function. The LT1636 is a single op amp in a tiny MSOP-8 package (SO-8 and DIP also available). Tough Op Amp An Over-The-Top amplifier, the LT1636's unique input stage can handle up to 44V common mode voltage while operating on a supply as low as 2.7V. It offers protection against reverse supply voltages up to 27V and includes built-in resistors that protect inputs for fault voltages as great as 22V below the negative supply. This broad voltage range capability eliminates the need for protection circuitry, allowing designers to increase circuit versatility and to reduce the size and expense of products. the wall adapter or the charge source is removed. Unlike most micropower op amps the LT1636 can drive heavy loads; its railto-rail output drives 18mA and is unity-gain stable. The maximum supply current of 55A is reduced to 4A in shutdown mode. The circuit is specified on 3V, 5V and 15V supplies. The LT1636 is a precision amplifier with less than 225V input offset voltage and less than 8nA of input bias current (see Table 1). The LT1636's combination of features makes it useful in a wide range of Over-The-Top Current Sense 0.1V TO 44V LT1636 VOUT (0V TO 4.3V) - ILOAD LOAD ILOAD = R2 2k VOUT (RS)(R2/R1) 140 VS = 5V VSTEP = 100mV TA = 25C RL = 1M 120 80 FALLING EDGE (tPDHL) 60 20 RISING EDGE (tPDLH) 0 10 2.7V to 44V Supply Current (Max) 55A Shutdown Current (Max) 12A Offset Voltage (Max) 225V Input Offset Voltage Drift (Max) Input Bias Current (Max) 10V/C 8nA Gain Bandwidth (Typ) 220kHz CMRR (Typ) 110dB products including battery charging and current monitoring, high side current sensing and charge control in portables and high speed modems, bias voltage tracking in passive LCD displays and battery buffering in high voltage industrial control systems and electric vehicles. Dual and quad op amps with similar features and specifications are the LT1490/ LT1491 and the faster LT1638/LT1639. For a data sheet and evaluation samples, contact your local Linear Technology sales office. For more information, visit our web site at www.linear-tech.com. 20 30 OVERDRIVE (mV) 40 5V 2k 1MHz CRYSTAL (AT-CUT) + 2k LT1671 OUTPUT - 2k 0.068F 1671 TA01 Figure 2. 1MHz Crystal Oscillator Linear Technology Products Are Distributed By: 100 40 Supply Voltage Range 1636 TA08 high. The complementary outputs allow for differential signaling and improved noise performance. These features combine to make the LT1671 well-suited for applications such as high performance micropower crystal oscillators (Figure 2), single supply voltageto-frequency converters and high speed, high accuracy level detectors. The LT1671 is offered in SO-8 and is pin compatible with the industry-standard LT1016 and LT1116 comparators. Contact your local Linear Technology sale office for a data sheet and evaluation samples.Visit our web site at www.linear-tech.com for more information. TIME (ns) The LT1671 is a low power (450A), fast (60ns) comparator designed to operate on either single 5V or 5V supplies. It has maximum offset voltage of 2.5mV, complementary TTL compatible outputs and output latch capability. The wide input voltage range extends from the bottom supply rail to within 1.5V of the top rail. The LT1671 is made with Linear Technology's new 6GHz complementary bipolar technology, which results in a dramatically improved speed/ power product compared to industrystandard comparators developed in slower NPN-only technologies. Propagation delay (Figure 1) is less than 80ns (maximum) with 20mV overdrive (100ns maximum, with 5mV overdrive). These speeds are great for low power analog signal processing and data acquisition circuits. The LT1671's supply current is only 800A (maximum). The LT1671 includes a Latch Enable function that is useful for sampling signals. The latch allows the most recent output state to be retained as long as the latch pin is held + RS 0.2 Micropower and Precision The LT1636's inputs draw virtually no current in battery charging applications when LT1671 Fast and Low Power Comparator 5V R1 200 Table 1. LT1636 Overview 50 1671 TA02 Arrow Electronics Digi-Key Electrosonic Gerber Electronics Marshall Industries Phase 1 Figure 1. Propagation Delay vs Overdrive (c) 1998 Linear Technology Corporation/Printed in USA 4 Technology Corporation * 1630 McCarthy Blvd. * Milpitas, CA 95035-7417 * (408) 432-1900 * FAX: (408) 434-0507 Linear Linear * www.linear-tech.com Literature Only: 1-800-4-LINEAR Technology* For Chronicle * October 1998