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EVALUATION KIT

FOLLOWS DATA SHEET

ECB and LCD Display Bias Supply with Accurate

Output Voltage and Temperature Compensation

General Description

The MAX1729 micropower step-up/step-down DC-DC

converter is ideally suited for electrically controlled bire-

fringence (ECB) and liquid-crystal-display (LCD) bias-

supply 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 regula-

tor. This architecture permits a physically smaller induc-

tor than those used in competing SEPIC and flyback

topologies. This device features low quiescent current

(67µA typical). A logic-controlled shutdown mode fur-

ther 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 volt-

ages 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 tempera-

ture coefficient provides compensation for LCD/ECB

display temperature characteristics. In internal feed-

back 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 tempera-

ture output is summed directly into the feedback net-

work to provide first-order negative temperature

compensation of the output voltage. The MAX1729 is

available in the space-saving 10-pin µMAX package.

Applications

ECB Display Bias & Color Adjustment

LCD Display Bias & Contrast Adjustment

Cellular Phones

Personal Digital Assistants

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)

MAX1729

________________________________________________________________

Maxim Integrated Products

OUT

COMP

CTLIN

OUT

+2.5V to +16V

DIGITAL

PWM

CONTROLLER

GND

2.7V to 5.5V

MAX1729

REF

ADC

Typical Operating Circuit

19-1406; Rev 1; 1/99

PART

MAX1729EUB -40°C to +85°C

TEMP. RANGE PIN-PACKAGE

10 µMAX

Ordering Information

Pin Configuration

GND

OUTCOMP

REF

MAX1729

µMAX

TOP VIEW

CTLINFB

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.

Summary of content (12 pages)

PAGE 1
9-1406; 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.
PAGE 2
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 ...............................................
PAGE 3
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.
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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.
PAGE 5
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.
PAGE 6
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.
PAGE 7
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.
PAGE 8
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.
PAGE 9
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.
PAGE 10
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.
PAGE 11
ECB and LCD Display Bias Supply with Accurate Output Voltage and Temperature Compensation 10LUMAXB.
PAGE 12
MAX1729 ECB and LCD Display Bias Supply with Accurate Output Voltage and Temperature Compensation NOTES 12 ______________________________________________________________________________________