General Description
The MAX17062 is a high-performance step-up DC-DC
converter that provides a regulated supply voltage for
active-matrix thin-film transistor (TFT) liquid-crystal dis-
plays (LCDs). The MAX17062 incorporates current-
mode, fixed-frequency, pulse-width modulation (PWM)
circuitry with a built-in n-channel power MOSFET to
achieve high efficiency and fast-transient response.
Users can select 640kHz or 1.2MHz operation using a
logic input pin (FREQ). The high switching frequencies
allow the use of ultra-small inductors and low-ESR
ceramic capacitors. The current-mode architecture pro-
vides fast transient response to pulsed loads. A com-
pensation pin (COMP) gives users flexibility in adjusting
loop dynamics. The 22V internal MOSFET can generate
output voltages up to 20V from an input voltage
between 2.6V and 5.5V. Soft-start slowly ramps the input
current and is programmed with an external capacitor.
The MAX17062 is available in a 10-pin TDFN package.
Applications
Notebook Computer Displays
LCD Monitor Panels
LCD TV Panels
Features
o90% Efficiency
oAdjustable Output from VIN to 20V
o2.6V to 5.5V Input Supply Range
oInput Supply Undervoltage Lockout
oPin-Programmable 640kHz/1.2MHz Switching
Frequency
oProgrammable Soft-Start
oImproved EMI
oFB Regulation Voltage Tolerance < 1%
oSmall 10-Pin TDFN Package
oThermal-Overload Protection
MAX17062
TFT-LCD Step-Up DC-DC Converter
________________________________________________________________
Maxim Integrated Products
1
Ordering Information
19-1042; Rev 0; 10/07
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
EVALUATION KIT
AVAILABLE
PART TEMP RANGE PIN-
PACKAGE
PKG
CODE
MAX17062ETB+T -40°C to +85°C10 TDFN-EP*
(3mm x 3mm) T1033-2
COMP
12345
10 9 8 7 6
FB
PGND
PGND
SHDN
SS
FREQ
LX
LX
IN
MAX17062
TOP VIEW
TDFN
(3mm x 3mm)
*EP = EXPOSED PAD.
*EP
Pin Configuration
LX LX
FB
PGND
PGND
AGND
FREQ
IN
COMP
SS
EP
1
4
5
2
3
9
8
67
10
VOUT
VIN
2.6V TO 5.5V
SHDN
MAX17062
Minimal Operating Circuit
+
Denotes a lead-free package.
*
EP = Exposed pad.
T = Tape and reel.
MAX17062
TFT-LCD Step-Up DC-DC Converter
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
ELECTRICAL CHARACTERISTICS
(VIN = VSHDN = 3V, FREQ = 3V, TA= 0°C to +85°C. Typical values are at TA= +25°C, unless otherwise noted.) (Note 1)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
LX to AGND ............................................................-0.3V to +22V
IN, SHDN, FREQ, FB to AGND..............................-0.3V to +7.5V
COMP, SS to AGND ....................................-0.3V to (VIN + 0.3V)
PGND to AGND .....................................................-0.3V to +0.3V
LX Switch Maximum Continuous RMS Current .....................3.2A
Continuous Power Dissipation (TA= +70°C)
10-Pin TDFN (derate 24.4mW/°C above +70°C) ..........1951mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature......................................................+150°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10s) .................................+300°C
PARAMETER CONDITIONS MIN TYP MAX UNITS
VOUT < 18V 2.6 5.5
Input Voltage Range 18V < VOUT < 20V 4.0 5.5 V
Output Voltage Range 20 V
IN Undervoltage-Lockout
Threshold VIN rising, typical hysteresis is 50mV 2.30 2.45 2.57 V
VFB = 1.3V, not switching 0.3 0.6
IN Quiescent Current VFB = 1.0V, switching 1.5 2.5 mA
SHDN = AGND, TA = +25°C 0.01 10.0
IN Shutdown Current SHDN = AGND, TA = +85°C 0.01 μA
Temperature rising 160
Thermal Shutdown Hysteresis 20 °C
ERROR AMPLIFIER
FB Regulation Voltage Level to produce VCOMP = 1.24V 1.23 1.24 1.25 V
FB Input Bias Current VFB = 1.24V 75 150 225 nA
FB Line Regulation Level to produce VCOMP = 1.24V, VIN = 2.6V to 5.5V 0.01 0.15 %/V
Transconductance 110 250 450 μS
Voltage Gain 2400 V/V
Shutdown FB Input Voltage SHDN = AGND 0.05 0.10 0.15 V
OSCILLATOR
FREQ = AGND 500 640 780
Frequency FREQ = IN 1000 1200 1400 kHz
Maximum Duty Cycle 88 91 94 %
n-CHANNEL MOSFET
Current Limit VFB = 1V, 75% duty cycle, IN = 5V 3.9 4.6 5.3 A
IN = 5V 100 170
On-Resistance IN = 3V 125 210 m
Leakage Current VLX = 20V 11 20 μA
Current-Sense Transresistance IN = 5V 0.09 0.15 0.25 V/A
SOFT-START
Reset Switch Resistance 100
Charge Current VSS = 1.2V 2 4 6 μA
MAX17062
TFT-LCD Step-Up DC-DC Converter
_______________________________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VSHDN = 3V, FREQ = 3V, TA= 0°C to +85°C. Typical values are at TA= +25°C, unless otherwise noted.) (Note 1)
PARAMETER CONDITIONS MIN TYP MAX UNITS
CONTROL INPUTS
SHDN, FREQ Input Low Voltage VIN = 2.6V to 5.5V 0.3
VIN V
SHDN, FREQ Input High Voltage VIN = 2.6V to 5.5V 0.7
VIN V
SHDN, FREQ Input Hysteresis VIN = 2.6V to 5.5V 0.1
VIN V
FREQ Pulldown Current 3 6 9 μA
SHDN = AGND, TA = +25°C -1 +1
SHDN Input Current SHDN = AGND, TA = +85°C 0 μA
ELECTRICAL CHARACTERISTICS
(VIN = VSHDN = 3V, FREQ = 3V, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)
PARAMETER CONDITIONS MIN TYP MAX UNITS
VOUT < 18V 2.6 5.5
Input Voltage Range 18V < VOUT < 20V 4.0 5.5 V
Output Voltage Range 20 V
IN Undervoltage-Lockout
Threshold VIN rising, typical hysteresis is 50mV 2.30 2.57 V
VFB = 1.3V, not switching 0.6
IN Quiescent Current VFB = 1.0V, switching 2.5 mA
ERROR AMPLIFIER
FB Regulation Voltage Level to produce VCOMP = 1.24V 1.227 1.253 V
FB Input Bias Current VFB = 1.24V 225 nA
FB Line Regulation Level to produce VCOMP = 1.24V, VIN = 2.6V to 5.5V 0.15 %/V
Transconductance 110 450 μS
Shutdown FB Input Voltage SHDN = AGND 0.05 0.15 V
OSCILLATOR
FREQ = AGND 450 830
Frequency FREQ = IN 950 1500 kHz
Maximum Duty Cycle 87 95 %
n-CHANNEL MOSFET
Current Limit VFB = 1V, 75% duty cycle, IN = 5V 3.9 5.3 A
IN = 5V 170
On-Resistance IN = 3V 210 m
Current-Sense Transresistance IN = 5V 0.09 0.25 V/A
SOFT-START
Reset Switch Resistance 100
Charge Current VSS = 1.2V 2 6 μA
MAX17062
TFT-LCD Step-Up DC-DC Converter
4 _______________________________________________________________________________________
Note 1: Limits are 100% tested at TA= +25°C. Maximum and minimum limits over temperature are guaranteed by design.
ELECTRICAL CHARACTERISTICS (continued)
(VIN = VSHDN = 3V, FREQ = 3V, TA= -40°C to +85°C, unless otherwise noted.) (Note 1)
PARAMETER CONDITIONS MIN TYP MAX UNITS
CONTROL INPUTS
SHDN, FREQ Input Low Voltage VIN = 2.6V to 5.5V 0.3
VIN V
SHDN, FREQ Input High Voltage VIN = 2.6V to 5.5V 0.7
VIN V
EFFICIENCY vs. LOAD CURRENT
(VIN = 5V, VOUT = 15V)
MAX17062 toc01
LOAD CURRENT (mA)
EFFICIENCY (%)
10010
60
70
80
90
100
50
1 1000
fOSC = 640kHz
L = 4.7μH
L = 2.7μH
fOSC = 1.2MHz
EFFICIENCY vs. LOAD CURRENT
(VIN = 3.3V, VOUT = 9V)
MAX17062 toc02
LOAD CURRENT (mA)
EFFICIENCY (%)
10010
60
70
80
90
100
50
1 1000
fOSC = 640kHz
L = 4.7μH
fOSC = 1.2MHz
L = 2.7μH
LOAD REGULATION
(VOUT = 15V)
MAX17062 toc03
LOAD CURRENT (mA)
LOAD REGULATION (%)
10010
-0.5
0
0.5
1.0
-1.0
1 1000
VIN = 5.0V
VIN = 3.3V
SWITCHING FREQUENCY
vs. INPUT VOLTAGE
MAX17062 toc04
INPUT VOLTAGE (V)
SWITCHING FREQUENCY (kHz)
5.04.54.03.53.0
600
700
800
900
1000
1100
1200
1300
1400
500
2.5 5.5
FREQ = IN
FREQ = GND
SUPPLY CURRENT
vs. SUPPLY VOLTAGE
MAX17062 toc05
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
5.04.54.03.53.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
0
2.5 5.5
SWITCHING
NONSWITCHING
Typical Operating Characteristics
(Circuit of Figure 1. VIN = 5V, VMAIN = 15V, TA= +25°C, unless otherwise noted.)
MAX17062
TFT-LCD Step-Up DC-DC Converter
_______________________________________________________________________________________
5
SOFT-START
(RLOAD = 30Ω)
MAX17062 toc06
2ms/div
OA
INDUCTOR
CURRENT
1A/div
OV
VOUT
5V/div
LOAD-TRANSIENT RESPONSE
(ILOAD = 50mA TO 550mA)
MAX17062 toc07
100μs/div
L = 2.7μH
RCOMP = 47kΩ
CCOMP1 = 560pF
0A
0V
INDUCTOR
CURRENT
2A/div
50mA
15V
VOUT
500mV/div
AC-COUPLED
IOUT
500mA/div
PULSED LOAD-TRANSIENT RESPONSE
(ILOAD = 100mA TO 1.1A)
MAX17062 toc08
10μs/div
0A
INDUCTOR
CURRENT
1A/div
0.1A
15V
VOUT
200mV/div
AC-COUPLED
IOUT
1A/div
L = 2.7μH
RCOMP = 47kΩ
CCOMP1 = 560pF
SWITCHING WAVEFORMS
(ILOAD = 600mA)
MAX17062 toc09
1μs/div
0A
INDUCTOR
CURRENT
1A/div
0V
LX
10V/div
Typical Operating Characteristics (continued)
(Circuit of Figure 1. VIN = 5V, VMAIN = 15V, TA= +25°C, unless otherwise noted.)
MAX17062
TFT-LCD Step-Up DC-DC Converter
6 _______________________________________________________________________________________
PIN NAME FUNCTION
1 COMP
Compensation Pin for Error Amplifier. Connect a series RC from COMP to ground. See the Loop
Compensation section for component selection guidelines.
2 FB
Feedback Pin. The FB regulation voltage is 1.24V nominal. Connect an external resistive voltage-divider
between the step-up regulator’s output (VOUT) and AGND, with the center tap connected to FB. Place the
divider close to the IC and minimize the trace area to reduce noise coupling. Set VOUT according to the
Output Voltage Selection section.
3SHDN Shutdown Control Input. Drive SHDN low to turn off the MAX17062.
4, 5 PGND Power Ground. Connect pins 4 and 5 directly together.
6, 7 LX Switch Pin. LX is the drain of the internal MOSFET. Connect the inductor/rectifier diode junction to LX and
minimize the trace area for lower EMI. Connect pins 6 and 7 together.
8 IN Supply Pin. Bypass IN with a minimum 1μF ceramic capacitor directly to AGND.
9 FREQ
Frequency-Select Input. When FREQ is low, the oscillator frequency is set to 640kHz. When FREQ is high,
the frequency is 1.2MHz. This input has a 6μA pulldown current.
10 SS
Soft-Start Control Pin. Connect a soft-start capacitor (CSS) to this pin. Leave open for no soft-start. The soft-
start capacitor is charged with a constant current of 4μA. Full current limit is reached when the voltage of
SS pin is charged to 1.5V, which is the current-limit time, t = 2.4 105 CSS. The soft-start capacitor is
discharged to ground when SHDN is low. When SHDN goes high, the soft-start capacitor is charged to 0.4V,
after which soft-start begins.
EP AGND Exposed Pad. Connect to AGND.
Pin Description
FB
PGND
PGND
AGND EP
FREQ
IN
COMP
SS
1
4
5
LX 7
LX 6
2
9
3
8
10
VOUT
+15V/600mA
VIN
4.5V TO 5.5V
SHDN
MAX17062
C2
4.7μF
10V
C1
4.7μF
10V
R1
10Ω
C3
1μF
C4
33nF
C5
560pF
C6
OPEN
L1
2.7μHD1
R2
47kΩ
R3
20kΩ
R4
221kΩ
C7
10μF
25V
C8
10μF
25V
Figure 1. Typical Operating Circuit
Detailed Description
The MAX17062 is a highly efficient power supply that
employs a current-mode, fixed-frequency, PWM archi-
tecture for fast-transient response and low-noise opera-
tion. The device regulates the output voltage through a
combination of an error amplifier, two comparators, and
several signal generators (Figure 2). The error amplifier
compares the signal at FB to 1.24V and varies the
COMP output. The voltage at COMP determines the
current trip point each time the internal MOSFET turns
on. As the load changes, the error amplifier sources or
sinks current to the COMP output to command the
inductor peak current necessary to service the load. To
maintain stability at high duty cycles, a slope-compen-
sation signal is summed with the current-sense signal.
At light loads, this architecture allows the MAX17062 to
“skip” cycles to prevent overcharging the output voltage.
In this region of operation, the inductor ramps up to a
peak value of approximately 50mA, discharges to the
output, and waits until another pulse is needed again.
Output Current Capability
The output current capability of the MAX17062 is a
function of current limit, input voltage, operating fre-
quency, and inductor value. Because of the slope com-
pensation used to stabilize the feedback loop, the
inductor current limit depends on the duty cycle. The
current limit is determined by the following equation:
ILIM = (1.26 - 0.35 x D) x ILIM_EC
where ILIM_EC is the current limit specified at 75% duty
cycle (see the
Electrical Characteristics
table) and D is
the duty cycle.
The output current capability depends on the current-
limit value and is governed by the following equation:
where ILIM is the current limit calculated above, ηis the
regulator efficiency (85% nominal), and D is the duty
cycle. The duty cycle when operating at the current
limit is:
where VDIODE is the rectifier diode forward voltage and
RON is the on-resistance of the internal MOSFET.
DVVV
VIRV
OUT IN DIODE
OUT LIM ON DIODE
=−+
−× +
II DV
fL
V
V
OUT MAX LIM IN
OSC
IN
OUT
()
.
=−
××
×
⎡
⎣
⎢
⎢
⎤
⎦
⎥
⎥××
05 η
MAX17062
TFT-LCD Step-Up DC-DC Converter
_______________________________________________________________________________________ 7
PGND
LX
IN
FREQ
FB
COMP
4μA
6μA
N
ERROR
COMPARATOR
ERROR
AMPLIFIER
SKIP
COMPARATOR
SS
CLOCK
SKIP
BIAS
SHDN
MAX17062
ΣCURRENT
SENSE
CONTROL
AND DRIVER
LOGIC
SOFT-
START
SLOPE
COMPEN-
SATION
OSCILLATOR
∞
1.24V
Figure 2. MAX17062 Functional Diagram
MAX17062
Soft-Start
The MAX17062 can be programmed for soft-start upon
power-up with an external capacitor. When the shutdown
pin is taken high, the soft-start capacitor (CSS) is immedi-
ately charged to 0.4V. Then the capacitor is charged at a
constant current of 4μA (typ). During this time, the SS
voltage directly controls the peak inductor current, allow-
ing 0A at VSS = 0.4V to the full current limit at VSS = 1.5V.
The maximum load current is available after the soft-start
is completed. When the SHDN pin is taken low, the soft-
start capacitor is discharged to ground.
Frequency Selection
The MAX17062’s frequency can be user selected to
operate at either 640kHz or 1.2MHz. Connect FREQ to
AGND for 640kHz operation. For a 1.2MHz switching
frequency, connect FREQ to IN. This allows the use of
small, minimum-height external components while
maintaining low output noise. FREQ has an internal
pulldown, allowing the user the option of leaving FREQ
unconnected for 640kHz operation.
Shutdown
The MAX17062 shuts down to reduce the supply cur-
rent to 0.01μA when SHDN is low. In this mode, the
internal reference, error amplifier, comparators, and
biasing circuitry turn off, and the n-channel MOSFET is
turned off. The step-up regulator’s output is connected
to IN by the external inductor and rectifier diode.
Thermal-Overload Protection
Thermal-overload protection prevents excessive power
dissipation from overheating the MAX17062. When the
junction temperature exceeds TJ= +160°C, a thermal
sensor immediately activates the fault protection, which
shuts down the MAX17062, allowing the device to cool
down. Once the device cools down by approximately
20°C, the MAX17062 starts up automatically.
Applications Information
Step-up regulators using the MAX17062 can be
designed by performing simple calculations for a first
iteration. All designs should be prototyped and tested
prior to production. Table 1 provides a list of power com-
ponents for the typical applications circuit (Figure 1).
Table 2 lists component suppliers.
External-component-value choice is primarily dictated
by the output voltage and the maximum load current,
as well as maximum and minimum input voltages.
Begin by selecting an inductor value. Once L is known,
choose the diode and capacitors.
Inductor Selection
The minimum inductance value, peak current rating, and
series resistance are factors to consider when selecting
the inductor. These factors influence the converter’s effi-
ciency, maximum output load capability, transient-
response time, and output-voltage ripple. Physical size
and cost are also important factors to be considered.
The maximum output current, input voltage, output volt-
age, and switching frequency determine the inductor
value. Very high inductance values minimize the cur-
rent ripple and therefore reduce the peak current,
which decreases core losses in the inductor and I2R
losses in the entire power path. However, large induc-
tor values also require more energy storage and more
turns of wire, which increase physical size and can
increase I2R losses in the inductor. Low inductance val-
ues decrease the physical size but increase the current
ripple and peak current. Finding the best inductor
involves choosing the best compromise between circuit
efficiency, inductor size, and cost.
The equations used here include a constant LIR, which
is the ratio of the inductor peak-to-peak ripple current
to the average DC inductor current at the full load cur-
rent. The best trade-off between inductor size and cir-
cuit efficiency for step-up regulators generally has an
LIR between 0.3 and 0.5. However, depending on the
TFT-LCD Step-Up DC-DC Converter
8 _______________________________________________________________________________________
DESIGNATION DESCRIPTION
C1, C2
4.7μF ±10%, 10V X5R ceramic capacitors
(0603)
TDK C1608X5RIA475K
C7, C8
10μF±10%, 25V X5R ceramic capacitors
(1210)
TDK C3225X5RIE106K
D1 3A, 30V Schottky diode (M-Flat)
Toshiba CMS03
L1 2.7μH ±20% power inductor
TOKO FDV0630-2R7M
Table 1. Component List
SUPPLIER PHONE FAX WEBSITE
TDK 847-803-6100 847-390-4405 www.component.tdk.com
TOKO 847-297-0070 847-699-7864 www.tokoam.com
Toshiba 949-455-2000 949-859-3963 www.toshiba.com/taec
Table 2. Component Suppliers
AC characteristics of the inductor core material and the
ratio of inductor resistance to other power-path resis-
tances, the best LIR can shift up or down. If the induc-
tor resistance is relatively high, more ripple can be
accepted to reduce the number of turns required and
increase the wire diameter. If the inductor resistance is
relatively low, increasing inductance to lower the peak
current can decrease losses throughout the power
path. If extremely thin high-resistance inductors are
used, as is common for LCD panel applications, the
best LIR can increase to between 0.5 and 1.0.
Once a physical inductor is chosen, higher and lower
values of the inductor should be evaluated for efficien-
cy improvements in typical operating regions.
Calculate the approximate inductor value using the typ-
ical input voltage (VIN), the maximum output current
(IMAIN(MAX)), the expected efficiency (ηTYP) taken from
an appropriate curve in the
Typical Operating
Characteristics
, and an estimate of LIR based on the
above discussion:
Choose an available inductor value from an appropriate
inductor family. Calculate the maximum DC input cur-
rent at the minimum input voltage VIN(MIN) using con-
servation of energy and the expected efficiency at that
operating point (ηMIN) taken from an appropriate curve
in the
Typical Operating Characteristics
:
Calculate the ripple current at that operating point and
the peak current required for the inductor:
The inductor’s saturation current rating and the
MAX17062’s LX current limit (ILIM) should exceed
IPEAK, and the inductor’s DC current rating should
exceed IIN(DC,MAX). For good efficiency, choose an
inductor with less than 0.1Ωseries resistance.
Considering the typical operating circuit (Figure 1), the
maximum load current (IMAIN(MAX)) is 600mA with a
15V output and a typical input voltage of 5V. Choosing
an LIR of 0.5 and estimating efficiency of 85% at this
operating point:
Using the circuit’s minimum input voltage (4.5V) and
estimating efficiency of 85% at that operating point:
The ripple current and the peak current are:
Output Capacitor Selection
The total output-voltage ripple has two components: the
capacitive ripple caused by the charging and discharg-
ing of the output capacitance, and the ohmic ripple due
to the capacitor’s equivalent series resistance (ESR):
and:
where IPEAK is the peak inductor current (see the
Inductor Selection
section). For ceramic capacitors,
the output-voltage ripple is typically dominated by
VRIPPLE(C). The voltage rating and temperature charac-
teristics of the output capacitor must also be considered.
VV V
V
RIPPLE RIPPLE C RIPPLE ESR
RIPPLE
() ( )
(
=+
CC MAIN
OUT
MAIN IN
MAIN OSC
I
C
VV
Vf
V
)≈−
⎛
⎝
⎜⎞
⎠
⎟
RRIPPLE ESR PEAK ESR COUT
IR
() ( )
≈
IVV V
H V MHz A
IA
AA
RIPPLE
PEAK
. ( .)
. . .
.
. .
=×−
μ× × ≈
=+ ≈
45 15 45
27 15 12 097
235 097
2284
IAV
V
A
IN DC MAX(, )
.
. .
.=×
×≈
06 15
45 085
235
LV
V
VV
AMHz..
=⎛
⎝
⎜⎞
⎠
⎟−
×
⎛
⎝
⎜⎞
⎠
⎟
5
15
15 5
06 12
2.
..
085
050 27
⎛
⎝
⎜⎞
⎠
⎟≈μH
II I
PEAK IN DC MAX RIPPLE
(, )
=+
2
IVVV
LV f
RIPPLE
IN MIN MAIN IN MIN
MAIN OSC
( )
() ()
=×−
××
IIV
V
IN DC MAX
MAIN MAX MAIN
IN MIN MIN
(, )
()
()
=×
×η
LV
V
VV
I f LIR
IN
MAIN
MAIN IN
MAIN MAX OSC
TYP
()
=⎛
⎝
⎜⎞
⎠
⎟−
×
⎛
⎝
⎜
⎜
⎞
⎠
⎟
⎟
⎛
⎝
⎜⎞
⎠
⎟
2η
MAX17062
TFT-LCD Step-Up DC-DC Converter
_______________________________________________________________________________________ 9
MAX17062
Input Capacitor Selection
The input capacitor (CIN) reduces the current peaks
drawn from the input supply and reduces noise injection
into the IC. Two 4.7μF ceramic capacitors are used in
the
Typical Operating Circuit
(Figure 1) because of the
high source impedance seen in typical lab setups.
Actual applications usually have much lower source
impedance since the step-up regulator often runs
directly from the output of another regulated supply.
Typically, CIN can be reduced below the values used in
the typical operating circuit. Ensure a low-noise supply
at IN by using adequate CIN. Alternatively, greater volt-
age variation can be tolerated on CIN if IN is decoupled
from CIN using an RC lowpass filter (see R1 and C3 in
Figure 1).
Rectifier Diode Selection
The MAX17062’s high switching frequency demands a
high-speed rectifier. Schottky diodes are recommend-
ed for most applications because of their fast recovery
time and low forward voltage. The diode should be
rated to handle the output voltage and the peak switch
current. Make sure that the diode’s peak current rating
is at least IPEAK calculated in the
Inductor Selection
section and that its breakdown voltage exceeds the
output voltage.
Output Voltage Selection
The MAX17062 operates with an adjustable output from
VIN to 20V. Connect a resistive voltage-divider from the
output (VMAIN) to AGND with the center tap connected
to FB (see Figure 1). Select R2 in the 10kΩto 50kΩ
range. Calculate R1 with the following equation:
where VFB, the step-up regulator’s feedback set point,
is 1.24V (typ). Place R1 and R2 close to the IC.
Loop Compensation
The voltage feedback loop needs proper compensation
to prevent excessive output ripple and poor efficiency
caused by instability. This is done by connecting a
resistor (RCOMP) and capacitor (CCOMP) in series from
COMP to AGND, and another capacitor (CCOMP2) from
COMP to AGND. RCOMP is chosen to set the high-
frequency integrator gain for fast transient response,
while CCOMP is chosen to set the integrator zero to
maintain loop stability. The second capacitor, CCOMP2,
is chosen to cancel the zero introduced by output-
capacitance ESR. For optimal performance, choose the
components using the following equations:
For the ceramic output capacitor, where ESR is small,
CCOMP2 is optional. The best gauge of correct loop
compensation is by inspecting the transient response
of the MAX17062. Adjust RCOMP and CCOMP as neces-
sary to obtain optimal transient performance.
Soft-Start Capacitor
The soft-start capacitor should be large enough that it
does not reach final value before the output has
reached regulation. Calculate CSS to be:
where COUT is the total output capacitance including
any bypass capacitor on the output bus, VOUT is the
maximum output voltage, IINRUSH is the peak inrush
current allowed, IOUT is the maximum output current
during power-up, and VIN is the minimum input voltage.
The load must wait for the soft-start cycle to finish
before drawing a significant amount of load current.
The duration after which the load can begin to draw
maximum load current is:
tMAX = 2.4 x 105x CSS
CC
VVV
VI I V
SS OUT
OUT IN OUT
IN INRUSH OUT OUT
>× × ×
−×
×−×
⎛
⎝
⎜
⎜
⎜
⎞
⎠
⎟
⎟
⎟
−
21 10 6
2
RVV C
LI
CVC
IR
CRLI
VV
COMP IN OUT OUT
MAIN MAX
COMP OUT OUT
MAIN MAX COMP
COMP
ESR MAIN MAX
IN OUT
.
()
()
()
≈×× ×
×
≈×
××
≈×××
×
315
10
0 0036
2
RR V
V
MAIN
FB
12 1 =× −
⎛
⎝
⎜⎞
⎠
⎟
TFT-LCD Step-Up DC-DC Converter
10 ______________________________________________________________________________________
Multiple-Output Power Supply for TFT-LCD
Figure 3 shows a power supply for active-matrix TFT-
LCD flat-panel displays. Output-voltage transient perfor-
mance is a function of the load characteristic. Add or
remove output capacitance (and recalculate compensa-
tion-network component values) as necessary to meet
the required transient performance. Regulation perfor-
mance for secondary outputs (VGON and VGOFF)
depends on the load characteristics of all three outputs.
PCB Layout and Grounding
Careful PCB layout is important for proper operation. Use
the following guidelines for good PCB layout:
1) Minimize the area of high-current loops by placing
the inductor, rectifier diode, and output capacitors
near the input capacitors and near the LX and
PGND pins. The high-current output loop goes from
the positive terminal of the input capacitor to the
inductor, to the IC’s LX pin, out of PGND, and to the
input capacitor’s negative terminal. The high-cur-
rent output loop is from LX switch node to the recti-
fier diode (D1) to the output capacitors, and
reconnecting negative terminals of output capaci-
tors to PGND of the IC. This loop has very high
di/dt, and it is critical to minimize the area of this
loop. Connect these loop components with short,
wide connections. Avoid using vias in the high-cur-
rent paths. If vias are unavoidable, use many vias in
parallel to reduce resistance and inductance.
2) Create a power ground island (PGND) consisting of
the input and output capacitor grounds and PGND
pins. Connect all these together with short, wide
traces or a small ground plane. Maximizing the
width of the power ground traces improves efficien-
cy and reduces output voltage ripple and noise
spikes. Create an analog ground plane (AGND)
consisting of the feedback-divider ground connec-
tion, the COMP and SS capacitor ground connec-
tions, and the device’s exposed backside pad.
Connect the AGND and PGND islands by connect-
ing the PGND pins directly to the exposed backside
pad. Make no other connections between these
separate ground planes.
MAX17062
TFT-LCD Step-Up DC-DC Converter
______________________________________________________________________________________ 11
FB
PGND
LX
PGND
FREQ
IN
COMP
SS
1
4
AGND EP
5
2
9
3
8
10
VIN
4.5V TO 5.5V
SHDN
MAX17062
U1
C2
4.7μF
10V
C1
4.7μF
10V
R1
100kΩ
R5
10Ω
C3
1μF
C4
33nF
C5
560pF
C6
OPEN
L1
2.7μHD1
6
LX 7
R2
47kΩ
R3
20kΩ
R4
221kΩ
C11
0.22μF
C15
0.22μF
D2 D3
1
33
2
2
1
C12
0.1μF
C14
0.1μF
VOUT
+15V/600mA
C7
10μF
25V
C8
10μF
25V
VGOFF
-15V
VGON
+29V
Figure 3. Multiple-Output TFT-LCD Power Supply
MAX17062
3) Place the feedback voltage-divider-resistors as
close to the FB pin as possible. The divider’s center
trace should be kept short. Placing the resistors far
away causes the FB trace to become an antenna
that can pick up switching noise. Avoid running the
feedback trace near LX.
4) Place the IN pin bypass capacitor as close to the
device as possible. The ground connection of the
IN bypass capacitor should be connected directly
to AGND pins with a wide trace.
5) Minimize the length and maximize the width of the
traces between the output capacitors and the load
for best transient responses.
6) Minimize the size of the LX node while keeping it
wide and short. Keep the LX node away from the
feedback node and analog ground. Use DC traces
as a shield if necessary.
Refer to the MAX17062 Evaluation Kit for an example of
proper board layout.
Chip Information
TRANSISTOR COUNT: 3612
PROCESS: BiCMOS
TFT-LCD Step-Up DC-DC Converter
12 ______________________________________________________________________________________
MAX17062
TFT-LCD Step-Up DC-DC Converter
______________________________________________________________________________________ 13
6, 8, &10L, DFN THIN.EPS
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
MAX17062
TFT-LCD Step-Up DC-DC Converter
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
14
____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600
© 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
COMMON DIMENSIONS
SYMBOL MIN. MAX.
A 0.70 0.80
D 2.90 3.10
E 2.90 3.10
A1 0.00 0.05
L 0.20 0.40
PKG. CODE N D2 E2 eJEDEC SPEC b[(N/2)-1] x e
PACKAGE VARIATIONS
0.25 MIN.k
A2 0.20 REF.
2.00 REF0.25±0.050.50 BSC2.30±0.1010T1033-1
2.40 REF0.20±0.05- - - - 0.40 BSC1.70±0.10 2.30±0.1014T1433-1
1.50±0.10 MO229 / WEED-3
0.40 BSC - - - - 0.20±0.05 2.40 REFT1433-2 14 2.30±0.101.70±0.10
T633-2 6 1.50±0.10 2.30±0.10 0.95 BSC MO229 / WEEA 0.40±0.05 1.90 REF
T833-2 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF
T833-3 8 1.50±0.10 2.30±0.10 0.65 BSC MO229 / WEEC 0.30±0.05 1.95 REF
2.30±0.10 MO229 / WEED-3 2.00 REF0.25±0.050.50 BSC1.50±0.1010T1033-2
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,
go to www.maxim-ic.com/packages.)
