19-1406; Rev 1; 1/99
KIT
ATION
EVALU
SHEET
A
T
A
WS D
FOLLO
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
The MAX1729 micropower step-up/step-down DC-DC
converter is ideally suited for electrically controlled birefringence (ECB) and liquid-crystal-display (LCD) biassupply generation. It provides step-up/step-down
voltage conversion and reduces output ripple by using
a step-up DC-DC converter followed by a linear regulator. This architecture permits a physically smaller inductor than those used in competing SEPIC and flyback
topologies. This device features low quiescent current
(67µA typical). A logic-controlled shutdown mode further reduces quiescent current to 0.4µA typical.
The MAX1729 features an input that dynamically
adjusts the output voltage to control display color or
contrast. It offers two feedback modes: internal and
external. Internal feedback mode allows output voltages between 2.5V and 16V, and is specifically
designed to hold temperature drift to ±11ppm/°C.
External feedback mode allows the MAX1729 output
voltage range to be tailored for various displays.
An on-chip temperature sensor with a positive temperature coefficient provides compensation for LCD/ECB
display temperature characteristics. In internal feedback mode, the buffered temperature sensor output is
read and used to adjust the output voltage via a digital
control signal. External feedback mode features an
additional compensation method in which the temperature output is summed directly into the feedback network to provide first-order negative temperature
compensation of the output voltage. The MAX1729 is
available in the space-saving 10-pin µMAX package.
Features
♦ High-Accuracy Reference Voltage (±1%)
♦ ±11ppm/°C Output Voltage Drift
♦ On-Chip Temperature Sensor Output
♦ Accurate Voltage and Temperature Provide:
Consistent ECB Colors
Consistent LCD Gray-Scale Contrast
♦ +2.7V to +5.5V Input Voltage Range
♦ Output Voltage Range
+2.5V to +16V in Internal Feedback Mode
Programmable in External Feedback Mode
♦ Dynamic Control of the Output Voltage
♦ 67µA Supply Current
♦ 0.4µA Shutdown Current
♦ 10-Pin µMAX Package (1.09mm max height)
♦ Evaluation Kit Available (MAX1729EVKIT)
Ordering Information
PART
MAX1729EUB
TEMP. RANGE
PIN-PACKAGE
-40°C to +85°C
10 µMAX
Typical Operating Circuit
Applications
ECB Display Bias & Color Adjustment
LCD Display Bias & Contrast Adjustment
VIN
2.7V to 5.5V
Cellular Phones
Personal Digital Assistants
IN
GND
Pin Configuration
REF
TOP VIEW
IN 1
10 GND
TC
2
9
LX
REF
3
8
PS
COMP
4
7
OUT
FB
5
6
CTLIN
MAX1729
LX
PS
DIGITAL
PWM
CONTROLLER
ADC
MAX1729
CTLIN
TC
OUT
VOUT
+2.5V to +16V
FB
COMP
µMAX
________________________________________________________________ Maxim Integrated Products
1
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.
MAX1729
General Description
MAX1729
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
ABSOLUTE MAXIMUM RATINGS
IN to GND .................................................................-0.3V to +6V
LX, PS, OUT to GND...............................................-0.3V to +20V
CTLIN, FB, REF, COMP, TC to GND ...........-0.3V to (VIN + 0.3V)
LX to PS ..................................................................-20V to +1.0V
LX, PS, OUT Current ...........................................................60mA
Continuous Power Dissipation (TA = +70°C)
10-pin µMAX (derate 5.6mW/°C above +70°C) ..........444mW
Operating Temperature Range ...........................-40°C to +85°C
Junction Temperature ......................................................+150°C
Storage Temperature Range .............................-65°C to +160°C
Lead Temperature (soldering, 10sec) .............................+300°C
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.
ELECTRICAL CHARACTERISTICS
(VIN = +3V, CTLIN = IN, FB = GND, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
MAX
UNITS
Operating Voltage Range
PARAMETER
VIN
2.7
5.5
V
Undervoltage Lockout
Threshold (Note 2)
VLO
2.0
2.6
V
37
50
µA
IN Supply Current
PS Supply Current
Shutdown Supply Current
SYMBOL
IPS
ISHDN
VREF
Minimum Output Voltage
VOUT
(MIN)
VOUT
(MAX)
Output Voltage
Temperature Coefficient
TCOUT
Maximum Output Current
IOUT
TC Output Voltage
VTC
TC Output Current
Feedback Set Voltage (FB)
FB Mode Threshold
FB Bias Current
CTLIN High Voltage
2
CTLIN = GND, ISHDN = IIN + IPS
IREF = 0
FB = GND, CTLIN =
0.1% duty cycle,
IOUT = 0 to 0.5mA
TCTC
VPS = +18V (Note 3)
VIH
TA = -40°C to +85°C
1.200
TA = 0°C to +85°C
2.35
TA = -40°C to +85°C
2.35
30
40
µA
0.4
2
µA
1.228
1.241
1.256
2.45
V
2.5
V
2.52
16
16.40
TA = 0°C to +85°C
13.90
13.95
TA = -40°C to +85°C
13.60
V
14.00
V/100%
14.20
TA = 0°C to +85°C
±11
±30
TA = -40°C to +85°C
±18
±65
0.5
2.5
1.178
1.228
1.278
TA = 0°C to +85°C
15.5
16.5
17.5
TA = -40°C to +85°C
14.5
16.5
18.5
TA = +25°C
1.215
1.228
1.241
TA = -40°C to +85°C
1.200
90
VFB = +1.25V
VIN = +5.5V
2
VIN = +2.7V
1.3
ppm/°C
mA
±50
VMODE
IFB
1.215
TYP
TA = +25°C
ITC
VFB
TA = +25°C
IOUT = 0 to 0.5mA
FB = GND, CTLIN =
0.1% to 100% duty
cycle, IOUT = 0
CTLIN to VOUT Gain
TC Output Temperature
Coefficient (Note 3)
MIN
IIN
Reference Output Voltage
Maximum Output Voltage
CONDITIONS
V
mV/°C
µA
1.256
V
122
150
mV
5
50
nA
_______________________________________________________________________________________
V
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
MAX1729
ELECTRICAL CHARACTERISTICS
(VIN = +3V, CTLIN = IN, FB = GND, TA = -40°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) (Note 1)
PARAMETER
SYMBOL
CONDITIONS
MIN
TYP
MAX
UNITS
CTLIN Low Voltage
VIL
VIN = +2.7V to +5.5V
0.4
V
CTLIN Bias Current
IIHL
VIN = +5.5V, CTLIN = GND or IN
±1
COMP Impedance
RCOMP
µA
kΩ
CTLIN Minimum Pulse Width
for Shutdown
tOFF
CTLIN Minimum Pulse Width
for VOUT Control
tCTLIN
VFB = 0, Internal Feedback Mode
33
VFB = +1.25V, External Feedback Mode
60
150
Ω
1250
2400
µs
(Note 4)
COMP Rise/Fall Time
tR/tF
VFB = +1.25V
Switch On-Resistance
RON
ILX = 30mA
Switch Off-Leakage Current
ILX(OFF)
VLX = 18V
LX to PS Diode Forward
Voltage
VLX-PS
IDIODE = 30mA
PFM On-Time Constant
K
PS to OUT Voltage (Note 5)
Note 1:
Note 2:
Note 3:
Note 4:
Note 5:
TA = +25°C
TA = -40°C to +85°C
700
25
ns
20
ns
VIN = +2.7V
2.5
VIN = +5.5V
1.5
6
5
0.4
5.0
Ω
0.1
1
µA
700
970
mV
8
10
0.6
11
1.0
V-µs
V
Specifications to -40°C are guaranteed by design, not production tested.
When VIN is below this level, the boost and LDO outputs are disabled.
Guaranteed by design.
Minimum time to hold CTLIN low to invoke shutdown. If CTLIN is held low for less than tOFF, device does not enter shutdown.
Switching regulator regulates this voltage to keep LDO from dropping out.
_______________________________________________________________________________________
3
Typical Operating Characteristics
(Circuit of Figure 2, TA = +25°C, unless otherwise noted.)
VIN = 5.5V
VIN = 5.5V
0.30
0.20
20
10
10
0.10
0
0.05
0.1
1
10
0.01
0.1
1
OUTPUT CURRENT (mA)
MAXIMUM OUTPUT CURRENT vs.
SUPPLY VOLTAGE
PS TO OUT (LDO)
POWER-SUPPLY REJECTION RATIO
-20
5
PSRR (dB)
VOUT = 9.4V
4
3
2
-40
-60
VOUT = 16.4V
-80
1
0
2.5
3.5
4.0
4.5
5.0
5.5
6.0
3.5
4.0
5.0
1.5
1.0
0
1
10
100
1k
10k
2.5
100k
3.0
3.5
4.0
4.5
5.0
OUTPUT VOLTAGE vs.
DUTY CYCLE
START-UP DELAY FROM SHUTDOWN
DELAY TO SHUTDOWN
MAX1729 toc 07
12
VCTLIN
5V/div
VCTLIN
5V/div
VREF
1V/div
VREF
1V/div
10
5.5
8
VTC
1V/div
VTC
1V/div
6
4
VOUT
10V/div
2
VIN = 5V
IO = 0.5mA
0
0
10 20 30 40 50 60 70 80 90 100
20ms/div
6.0
MAX1729 toc 09a
INPUT VOLTAGE (V)
14
6.0
2.0
FREQUENCY (Hz)
16
5.5
2.5
SUPPLY VOLTAGE (V)
18
VOUT
10V/div
VIN = 5V
IO = 0.5mA
500ms/div
DUTY CYCLE (%)
4
4.5
0.5
MAX1729 toc 08
3.0
3.0
3.0
-100
2.5
VOUT = 2.5V
SHUTDOWN SUPPLY CURRENT
MAX1729 toc 05
VOUT = +2.5V
6
VOUT = 9.4V
SUPPLY VOLTAGE (V)
0
MAX1729 toc 04
7
0.15
10
OUTPUT CURRENT (mA)
SHUTDOWN CURRENT (µA)
0.01
VOUT = 16.4V
0.25
20
0
MAXIMUM OUTPUT CURRENT (mA)
VIN = 2.7V
30
0.35
SUPPLY CURRENT (mA)
EFFICIENCY (%)
EFFICIENCY (%)
30
40
MAX1729 toc 03
50
VIN = 2.7V
40
0.40
MAX1729 toc 02
50
NO-LOAD SUPPLY CURRENT vs.
SUPPLY VOLTAGE
60
MAX1729 toc 01
60
EFFICIENCY vs. OUTPUT CURRENT
VOUT = 16.4 (CTLIN = IN)
MAX1729 toc 06
EFFICIENCY vs. OUTPUT CURRENT
VOUT = 9.4 (CTLIN AT 50% DUTY CYCLE)
OUTPUT VOLTAGE (V)
MAX1729
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
_______________________________________________________________________________________
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
IL
20mA/div
OUTPUT
RIPPLE
10mV/div
OUTPUT
RIPPLE
10mV/div
VTC
1V/div
VOUT
10V/div
VIN = 5V
IO = 0.5mA
IL
20mA/div
VLX
5V/div
VLX
5V/div
2µs/div
5ms/div
2µs/div
LOAD-TRANSIENT RESPONSE
MAX1729 toc 13
LINE-TRANSIENT RESPONSE
VOUT
20mV/div
CTLIN = IN
IOUT = 0.5mA
16.404
VOUT
20mV/div
MAX1729 toc 14
VREF
1V/div
MAX1729 toc 10
MAX1729 toc 09b
VCTLIN
5V/div
SWITCHING WAVEFORMS
MEDIUM LOAD
MAX1729 toc 11
SWITCHING WAVEFORMS
HEAVY LOAD
DELAY TO SHUTDOWN
16.400
500µA
5V
VIN
1V/div
4V
IOUT
250µA/div
20µA
1ms/div
2ms/div
_______________________________________________________________________________________
5
MAX1729
Typical Operating Characteristics (continued)
(Circuit of Figure 2, TA = +25°C, unless otherwise noted.)
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
MAX1729
Pin Description
PIN
NAME
FUNCTION
1
IN
Supply Input. Bypass with 0.1µF capacitor to ground. Connect to supply side of inductor (L1).
2
TC
Temperature-Sensor Output. Bypass to GND with a 1000pF capacitor.
3
REF
Reference Voltage Output. Bypass to GND with a 0.1µF capacitor.
4
COMP
5
FB
6
CTLIN
7
OUT
8
PS
Output of boost converter and input to LDO. Bypass to GND with a 0.068µF capacitor.
9
LX
Drain of the internal MOSFET Switch
10
GND
Compensation Pin. In internal feedback mode (Figure 2), bypass with a 1µF capacitor. In external feedback
mode, COMP is a buffered inverse version of CTLIN (Figure 3).
Feedback and Mode Control Input. Connect to GND for internal feedback mode operation.
Control Input. Drive low for more than 1.2ms to put the device into shutdown.
Bypass to GND with a 1.0µF capacitor.
Ground
Detailed Description
The MAX1729 is designed to provide bias voltage for
ECB or LCD displays. It is composed of a step-up
DC-DC converter followed by a linear regulator
(Figure 1), a combination that provides step-up/stepdown voltage conversion while minimizing output ripple. The device allows you to adjust a display’s color or
contrast by dynamically adjusting the MAX1729’s output voltage using a PWM control signal. In internal
feedback mode, the output voltage is adjustable
between +2.5V and +16V. In external feedback mode,
the output voltage is adjustable, and its range is set by
a resistor network that is programmed to match the output voltage range of LCD/ECB displays needing a maximum output up to +18V.
Boost Converter
The MAX1729’s DC-DC boost converter is implemented
with an on-chip N-channel MOSFET, a diode, and an
error comparator. The IC’s unique PFM control system
varies the on-time and off-time of the switch based on the
6
boost converter’s input and output voltage values, as follows:
t ON =
t OFF ≥
K
VIN
K
VPS − VIN
where K is typically 8V-µs. This timing maintains discontinuous conduction and sets the peak inductor current
(IPEAK) to:
K
IPEAK =
L
where L is the inductance of L1 (Figures 2, 3, and 4).
When the error comparator detects that the drop across
the linear regulator (VPS - VOUT) is less than approximately 0.6V, the internal switch is turned on (tON initiates) and
current through the inductor ramps to IPEAK. At the end of
tON, the switch is turned off for at least tOFF, allowing the
_______________________________________________________________________________________
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
TC
REF
TEMPERATURE
SENSOR
BOOST
CONVERTER
VOLTAGE
REFERENCE
LDO
LINEAR
REGULATOR
PS
Control Signal
OUT
MAX1729
FB
FEEDBACK
CONTROL
122mV
An externally generated PWM control signal on CTLIN
controls VOUT in internal feedback mode and influences VOUT in external feedback mode. In either mode,
if CTLIN is held low for longer than 1.24ms, the
MAX1729 enters shutdown mode, decreasing the supply current below 2µA. Shutdown mode limits the minimum duty cycle and frequency that may be used to
keep the device active. CTLIN frequencies between
2kHz and 12kHz are recommended.
Internal Feedback Mode
SHUTDOWN
CONTROL
VREF
CTLIN
GND
COMP
GND
NOTE: SWITCH STATES SHOWN FOR INTERNAL FEEDBACK MODE.
Figure 1. Internal Block Diagram
inductor current to ramp down and VPS to increase. If, at
the end of tOFF, VPS - VOUT is still too low, then another
tON is initiated immediately. Otherwise, the boost converter remains idle in a low-quiescent-current state until
VPS - VOUT drops again and the error comparator initiates another cycle.
Linear Regulator
The PNP low-dropout linear regulator of the MAX1729
regulates the boost-converter output to the desired output voltage. The boost converter’s regulation circuitry
holds the linear regulator’s input voltage (VPS) approximately 0.6V above the output voltage to keep the regulator out of dropout, thereby enhancing ripple rejection.
The linear regulator incorporates short-circuit protection, which limits the output current to approximately
6mA.
Temperature Sensor Output
The MAX1729 generates a temperature sensor voltage
(VTC) that varies at 16.5mV/°C (typ) and is nominally
In internal feedback mode, the signal at CTLIN is inversely buffered, level-shifted, and output at COMP through a
resistor. Internal resistance (33kΩ typical) and C6 then filter the signal before it is used by the internal feedback
network to set VOUT. If temperature compensation is
used, the temperature sensor output voltage is read by
an ADC and used to adjust the duty cycle of the PWM
control signal. See the Designing for Internal Feedback
Mode section for more information.
External Feedback Mode
In external feedback mode, the output voltage of the
MAX1729 is controlled by the duty cycle of the PWM
control signal and an external resistor network, as
shown in Figure 3. In this mode, the signal at CTLIN is
inverted, level-shifted, and presented directly to COMP.
R3, R4, and C6 filter the signal, before it is summed into
the feedback node.
Design Procedure
Designing for Internal Feedback Mode
For a 3kHz PWM control signal use a 1µF low-leakage
ceramic capacitor for C6. For applications requiring a
higher-frequency PWM control signal, reduce the value
of C6 to between 1µF and 0.22µF for frequencies
between 3kHz and 12kHz. Higher C6 values reduce
output ripple. In Figure 2, VOUT is governed by the following equation:
VOUT = VOUT(MIN) + Duty Cycle ⋅ Gain
where V OUT(MIN) is 2.45V and Gain is nominally
13.95V/100%, as listed in the Electrical Characteristics.
_______________________________________________________________________________________
7
MAX1729
LX
IN
equal to the reference voltage at room temperature. TC
is capable of sinking or sourcing 50µA. This output is
used to compensate for ECB color or LCD contrast
variations caused by changes in temperature. It may
be read with an ADC and used to modify an external
PWM control signal or, in external feedback mode,
summed directly into the feedback-resistor network.
MAX1729
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
To use a DC control signal to adjust the output voltage,
use the circuit shown in Figure 4. In this configuration,
VOUT is governed by the following equation:
VOUT ≈ 24.67VFB - 22.71VCOMP
The impedance looking into COMP is nominally 33kΩ.
A source output impedance of less than 500Ω is recommended. Also, ensure V OUT ≤ 18V by keeping
VCOMP above 0.6V.
External Component Value Formulas
1) Given the maximum output voltage needed (VMAX),
choose the maximum feedback current and solve for
R1 (10µA to 30µA is recommended for maximum feedback current) as follows:
V
- VFB
R1 = MAX
IFB
Designing for External Feedback Mode
L1
To solve for VOUT in external feedback mode, assume
the current into the FB pin is zero and the voltage at FB
is 1.228V. Then take the sum of the currents into FB
and solve for VOUT:
VIN
C1
0.1µF
1
1
1
1
VOUT = R1
+
+
+
V
R1 R2 R 3 + R4 R5 FB
C3
0.1µF
R1
R1
−
VCOMP −
V
R 3 + R4
R5 TC
PWM
GENERATOR
220µH
IN
LX
PS
GND
REF
MAX1729
C2
0.068µF
VOUT
OUT
C4
1µF
R1
CTLIN
FB
COMP
TC
R5
Using the following formulas, calculate the external
component values required for MAX1729 operation in
external feedback mode, as shown in Figure 3. An
example follows the formulas.
R4
R3
R2
C5
1000pF
C6
1µF
Figure 3. External Feedback Mode
L1
L1
VIN
C1
0.1µF
C3
0.1µF
DIGITAL
PWM
CONTROLLER
220µH
IN
LX
PS
GND
REF
MAX1729
CTLIN
ADC
TC
C5
1000pF
Figure 2. Internal Feedback Mode
8
VIN
OUT
C2
0.068µF
C4
1µF
VOUT
220µH
C1
0.1µF
C3
0.1µF
IN
LX
PS
GND
REF
MAX1729
CTLIN
FB
COMP
C6
1µF
C5
1000pF
TC
OUT
C2
0.068µF
C4
1µF
VOUT
FB
COMP
Figure 4. Using a DC Control Signal
_______________________________________________________________________________________
DC CONTROL
INPUT
VCOMP
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
R1
R3 = 1/2
VFB
VMAX – VMIN
R4 = R3
3) For first-order temperature compensation, calculate
R5 as shown below. (If temperature compensation is
not used, leave R5 open.)
R1
R5 =
16.5mV/ °C
Tempco
where Tempco is the negative temperature coefficient
needed to compensate the ECB or LCD display for
changes in temperature.
4) Solve for VCOMP. The duty cycle used here corresponds to the duty cycle that yields the maximum output voltage, not including first-order temperature
compensation.
R4
VCOMP =VFB 1 – Duty Cycle ⋅
R3 + R4
where a 90% duty cycle corresponds to Duty Cycle = 0.9.
5) Use the results from the above calculations to solve
for R2. (For applications not utilizing temperature compensation, use 1 / R5 = 0.)
1
1 VOUT VCOMP VFB
=
+
+
R2
VFB R1
R3
R5
1
1
1
−
+
+
R1 R3 R5
External Component Value Example
The example application requires the output voltage to
adjust between 5V and 10V, using the circuit shown in
Figure 3. The device in our example needs a temperature coefficient of 33mV/°C, which yields the following
results.
1) VMAX = 10V and IFB = 29.24µA is within the limits
and yields a reasonable resistor value, therefore:
R1 =
10V − 1.228V
= 300kΩ
29.24µA
2) VMAX = 10V and VMIN = 5V, therefore:
MAX1729
2) Given the maximum output voltage (VMAX) and minimum output voltage (VMIN), calculate values for R3 and
R4 as follows:
300kΩ
R3 = 1/2
1.228 = 36,840Ω
5V
with R3 = 36.7kΩ, then VMIN = 5.019V. Let R4 =
R3 = 36.7kΩ.
3) Tempco = 33mV/°C, therefore:
300kΩ
R5 =
16.5mV / °C = 150kΩ
33mV/ °C
4) If external circuitry limits the duty cycle to 90%, the
following equation is true:
0.9
VCOMP = 1.228 1 −
= 0.6754V
2
5) Solving for R2:
V
V 1
V
1
= OUT + COMP + FB
R2
R3
R5 V
R1
FB
1
1
1
1
−
+
+
=
R1 R3 R5
56560
With R2 = 56kΩ, a duty cycle of 87.4% generates a
VOUT of 10V.
Component Selection
Inductors
Use a 220µH inductor to maximize output current
(2.5mA typical). Use an inductor with DC resistance
less than 10Ω and a saturation current exceeding
35mA. For lower peak inductor current, use a 470µH
inductor with DC resistance less than 20Ω and a saturation current over 18mA. This limits output current to
typically less than 1mA. See Table 1 for a list of recommended inductors. The inductor should be connected
from the battery to the LX pin, as close to the IC as possible.
Capacitors
The equivalent series resistance (ESR) of output capacitor C2 directly affects output ripple. To minimize output
ripple, use a low-ESR capacitor. A physically smaller
capacitor, such as a common ceramic capacitor, minimizes board space and cost while creating an output
ripple that’s acceptable in most applications. Refer to
Table 2 for recommended capacitor values.
_______________________________________________________________________________________
9
MAX1729
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
Table 1. Recommended Inductors
SUPPLIER
PART
INDUCTANCE
(µH)
DC RESISTANCE
(Ω)
SATURATION
CURRENT (mA)
MAX HEIGHT
(mm)
Murata
LQH3C221K04M00
220
8.4
70
2.2
Panasonic
ELT3KN115B
470
19
40
1.6
Table 2. Recommended Capacitor Values
CAPACITOR
CAPACITANCE
(µF)
C1
0.1
C2
0.068
C3
0.1
C4
1
C5
1000pF
C6*
1
*Use a low-leakage capacitor.
Applications Information
PC Board Layout Considerations
Proper PC board layout minimizes output ripple and
increases efficiency. For best results, use a ground
plane, minimize the space between C1, C2, and GND
of the MAX1729, and place the inductor as close to LX
and IN as possible. For an example of proper PC board
layout, refer to the MAX1729 Evaluation Kit.
Chip Information
TRANSISTOR COUNT: 1154
10
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ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
10LUMAXB.EPS
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11
MAX1729
Package Information
MAX1729
ECB and LCD Display Bias Supply with Accurate
Output Voltage and Temperature Compensation
NOTES
12
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