Datasheet

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General Description

The MAX1779 triple-output DC-DC converter provides

highly efficient regulated voltages required by small

active matrix, thin-film transistor (TFT) liquid-crystal dis-

plays (LCDs). One high-power DC-DC converter and

two low-power charge pumps convert the +2.7V to

+5.5V input supply voltage into three independent out-

put voltages.

The primary high-power DC-DC converter generates a

boosted output voltage (V

MAIN

) up to 13V that is regu-

lated within ±1%. The low-power BiCMOS control cir-

cuitry and the low on-resistance (1Ω) of the integrated

power MOSFET allows efficiency up to 91%. The

250kHz current-mode pulse-width modulation (PWM)

architecture provides fast transient response and

allows the use of ultra-small inductors and ceramic

capacitors.

The dual charge pumps independently regulate one

positive output (V

POS

) and one negative output (V

NEG

These low-power outputs use external diode and

capacitor stages (as many stages as required) to regu-

late output voltages up to +40V and down to -40V. A

proprietary regulation algorithm minimizes output rip-

ple, as well as capacitor sizes for both charge pumps.

The MAX1779 is available in the ultra-thin TSSOP pack-

age (1.1mm max height).

________________________Applications

TFT Active-Matrix LCD Displays

Passive-Matrix LCD Displays

PDAs

Digital-Still Cameras

Camcorders

Features

♦ Three Integrated DC-DC Converters

♦ 250kHz Current-Mode PWM Boost Regulator

Up to +13V Main High-Power Output

±1% Accuracy

High Efficiency (91%)

♦ Dual Charge-Pump Outputs

Up to +40V Positive Charge-Pump Output

Down to -40V Negative Charge-Pump Output

♦ Internal Supply Sequencing

♦ Internal Power MOSFETs

♦ +2.7V to +5.5V Input Supply

♦ 0.1µA Shutdown Current

♦ 0.5mA Quiescent Current

♦ Internal Soft-Start

♦ Power-Ready Output

♦ Ultra-Small External Components

♦ Thin TSSOP Package (1.1mm max)

MAX1779

Low-Power Triple-Output TFT LCD DC-DC

Converter

________________________________________________________________ Maxim Integrated Products 1

RDY TGND

PGND

SUPP

DRVP

SUPN

DRVN

SHDN

TOP VIEW

MAX1748

MAX8726

TSSOP

INTG

REF

GND

FBP

FBN

A "+" SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES.

Pin Configuration

19-1795; Rev 1; 9/05

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at

1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

Ordering Information

Typical Operating Circuit appears at end of data sheet.

16 TSSOP

PIN-PACKAGETEMP RANGE

-40°C to +85°CMAX1779EUE

PART

16 TSSOP-40°C to +85°CMAX1779EUE+

+ Denotes lead-free package.

Summary of content (18 pages)

PAGE 1
9-1795; Rev 1; 9/05 Low-Power Triple-Output TFT LCD DC-DC Converter The MAX1779 triple-output DC-DC converter provides highly efficient regulated voltages required by small active matrix, thin-film transistor (TFT) liquid-crystal displays (LCDs). One high-power DC-DC converter and two low-power charge pumps convert the +2.7V to +5.5V input supply voltage into three independent output voltages.
PAGE 2
MAX1779 Low-Power Triple-Output TFT LCD DC-DC Converter ABSOLUTE MAXIMUM RATINGS IN, SHDN, TGND to GND .........................................-0.3V to +6V DRVN to GND .........................................-0.3V to (VSUPN + 0.3V) DRVP to GND..........................................-0.3V to (VSUPP + 0.3V) PGND to GND.....................................................................±0.3V RDY to GND ...........................................................-0.3V to +14V LX, SUPP, SUPN to PGND .......
PAGE 3
Low-Power Triple-Output TFT LCD DC-DC Converter (VIN = +3.0V, SHDN = IN, VSUPP = VSUPN = +10V, TGND = PGND = GND, CREF = 0.22µF, CINTG = 2200pF, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER SYMBOL CONDITIONS MIN Operating Frequency FBP Regulation Voltage FBP Input Bias Current DRVP PCH On-Resistance TYP MAX 0.5 × fOSC VFBP IFBP VFBP = +1.5V 1.20 -50 VFBP = +1.200V DRVP NCH On-Resistance VFBP = +1.
PAGE 4
MAX1779 Low-Power Triple-Output TFT LCD DC-DC Converter ELECTRICAL CHARACTERISTICS (VIN = +3.0V, SHDN = IN, VSUPP = VSUPN = +10V, TGND = PGND = GND, CREF = 0.22µF, CINTG = 2200pF, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER Input Supply Range SYMBOL CONDITIONS VIN Input Undervoltage Threshold VUVLO IN Quiescent Supply Current IIN VIN rising, 40mV hysteresis (typ) MIN MAX UNITS 2.7 5.5 V 2.2 2.6 V 1 mA VFB = VFBP = +1.5V, VFBN = -0.
PAGE 5
Low-Power Triple-Output TFT LCD DC-DC Converter (VIN = +3.0V, SHDN = IN, VSUPP = VSUPN = +10V, TGND = PGND = GND, CREF = 0.22µF, CINTG = 2200pF, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN MAX UNITS 0.9 V 1 μA LOGIC SIGNALS SHDN Input Low Voltage 0.25V hysteresis (typ) SHDN Input High Voltage 2.1 SHDN Input Current V I SHDN RDY Output Low Voltage ISINK = 2mA 0.
PAGE 6
Typical Operating Characteristics (continued) (Circuit of Figure 5, VIN = +3.3V, TA = +25°C, unless otherwise noted.) EFFICIENCY vs. LOAD CURRENT (BOOST CONVERTER AND CHARGE PUMPS) -7.80 -7.88 -7.92 -7.96 VSUPN = +7V 60 50 100 150 200 40 -8.08 30 VNEG = -8V 0 250 5 10 POSITIVE CHARGE-PUMP OUTPUT VOLTAGE vs. LOAD CURRENT 15 20 INEG (mA) 10 INEG (mA) POSITIVE CHARGE-PUMP EFFICIENCY vs. LOAD CURRENT SWITCHING FREQUENCY vs. INPUT VOLTAGE IMAIN (mA) 0 90 12.12 VSUPP = +5V 12.
PAGE 7
Low-Power Triple-Output TFT LCD DC-DC Converter LOAD TRANSIENT WITHOUT INTEGRATOR (L = 10μH, 5μs PULSE) LOAD TRANSIENT WITHOUT INTEGRATOR (L = 10μH, 500μs PULSE) LOAD TRANSIENT (L = 33μH, 500μs PULSE) MAX1779-17 MAX1779-16 5.0V 5.0V A 5V A A 400mA 4.9V 200mA B 0 50mA B 4.9V 100mA 100mA B C 0 0 0 10μs/div A. VMAIN = 5V, 100mV/div B. IL, 200mA/div C. IMAIN = 10mA to 100mA, 100mA/div INTG = REF, FIGURE 6 100μs/div A. VMAIN = 5V, 50mV/div B.
PAGE 8
MAX1779 Low-Power Triple-Output TFT LCD DC-DC Converter Typical Operating Characteristics (continued) (Circuit of Figure 5, VIN = +3.3V, TA = +25°C, unless otherwise noted.) STARTUP WAVEFORM (L = 33μH) POWER-UP SEQUENCING MAX1779-23 MAX1779-22 2V A 2V 0 0 5V 5V A B B 3V 0 500mA -10V C 0 C 10V D 0 200μs/div A. VSHDN = 0 to 2V, 2V/div B. VMAIN = 5V, 1V/div C. IL, 500mA/div RMAIN = 50Ω 4ms/div A. VSHDN = 0 to 2V, 2V/div B. VMAIN = 5V, RMAIN = 50Ω, 2.5V/div C.
PAGE 9
Low-Power Triple-Output TFT LCD DC-DC Converter PIN NAME FUNCTION 10 DRVN Negative Charge-Pump Driver Output. Output high level is VSUPN, and low level is PGND. 11 SUPN Negative Charge-Pump Driver Supply Voltage. Bypass to PGND with a 0.1μF capacitor. 12 DRVP Positive Charge-Pump Driver Output. Output high level is VSUPP, and low level is PGND. 13 SUPP Positive Charge-Pump Driver Supply Voltage. Bypass to PGND with a 0.1μF capacitor. 14 PGND Power Ground. Connect to GND underneath the IC.
PAGE 10
MAX1779 Low-Power Triple-Output TFT LCD DC-DC Converter L1 VOUT = [1 + (R1 / R2)] x VREF VREF = 1.25V VIN = 2.7V TO 5.5V IN OSC LX S R VMAIN (UP TO 13V) D1 Q R1 + C1 ILIM + + - PGND Σ - SLOPE COMP + RCOMP FB + + Gm INTG CINTG REF + MAX1779 GND R2 C2 CCOMP 1.25V Figure 1. PWM Boost Converter Block Diagram (VC3 + VSUPP), charge flows from C3 to C4 until the diode (D3) turns off. Soft-Start The main boost regulator does not have soft-start.
PAGE 11
Low-Power Triple-Output TFT LCD DC-DC Converter MAX1779 VSUPN = 2.7V TO 13V SUPN OSC D4 C5 DRVN D5 R5 FBN + VNEG C6 + R6 VREF 1.25V REF MAX1779 CREF 0.22μF PGND GND ( ) VNEG = - R5 VREF R6 VREF = 1.25V Figure 2. Negative Charge-Pump Block Diagram VSUPP = 2.7V TO 13V SUPP OSC D2 C3 DRVP D3 R3 FBP + VPOS C4 + - R4 VREF 1.25V MAX1779 GND PGND ( )V VPOS = 1 + R3 R4 VREF = 1.25V REF Figure 3.
PAGE 12
MAX1779 Low-Power Triple-Output TFT LCD DC-DC Converter 1.125V), the active-low ready signal (RDY) is pulled low (see Power Ready section). Power Ready Power ready is an open-drain output. When the powerup sequence is properly completed, the MOSFET turns on and pulls RDY low with a typical 125Ω on-resistance. If a fault is detected, the internal open-drain MOSFET appears as a high impedance. Connect a 100kΩ pullup resistor between RDY and IN for a logiclevel output. output voltage.
PAGE 13
Low-Power Triple-Output TFT LCD DC-DC Converter Output Capacitor The output capacitor selection depends on circuit stability and output voltage ripple. In order to deliver the maximum output current capability of the MAX1779, the inductor must run in continuous-conduction mode (see Inductor Selection).
PAGE 14
MAX1779 Low-Power Triple-Output TFT LCD DC-DC Converter nated by the internal switch resistance and the diode impedance. Start with 0.1µF ceramic capacitors. Smaller values may be used for low-current applications. Charge-Pump Output Capacitor Increasing the output capacitance or decreasing the ESR reduces the output ripple voltage and the peak-topeak transient voltage.
PAGE 15
______________________________________________________________________________________ VNEG = -8V, 1mA 1.0μF (2) 4.7μF CINTG 3300pF 100k R5 320k CREF 0.22μF R6 49.9k 0.1μF 0.1μF GND TGND INTG REF FBN DRVN RDY SHDN IN MAX1779 10μH PGND FBP DRVP SUPP SUPN FB LX 0.47μF RCOMP 10k R4 49.9k 0.1μF R2 50k R1 150k R3 549k CCOMP 220pF COUT (2) 4.7μF VMAIN = +5V 1.0μF 1.0μF VPOS = +15V, 1mA MAX1779 VIN = +3.0V Low-Power Triple-Output TFT LCD DC-DC Converter Figure 4.
PAGE 16
VNEG -8V, 5mA C6 0.47μF C10 2.2μF CIN 10μF VIN = +3.3V CREF 0.22μF R5 320k R6 49.9k C9 0.22μF CINTG 2200pF C11 0.1μF C5 0.1μF RRDY 100k PGND REF FBN DRVN INTG RDY SHDN IN MAX1779 33μH GND TGND FBP DRVP SUPP SUPN FB LX C7 0.22μF C3 0.1μF R2 50k R1 150k CCOMP 470pF RCOMP 24k R4 49.9k C8 430k C3 0.47μF C8 2.2μF VPOS +12V, 5mA COUT 22μF VMAIN = +5.0V MAX1779 Low-Power Triple-Output TFT LCD DC-DC Converter Figure 5.
PAGE 17
______________________________________________________________________________________ VNEG -8V, 5mA C6 0.47μF CIN (2) 4.7μF CREF 0.22μF C10 2.2μF R5 320k R6 49.9k C9 0.22μF CINTG 2200pF C11 0.1μF C5 0.1μF RRDY 100k PGND REF FBN DRVN INTG RDY SHDN IN MAX1779 10μH GND TGND FBP DRVP SUPP SUPN FB LX C7 0.22μF C3 0.1μF R2 50k R1 150k CCOMP 220pF RCOMP 10k R4 49.9k R3 430k C4 0.47μF C8 2.2μF VPOS +12V, 5mA COUT (2) 4.7μF VMAIN = +5.0V MAX1779 VIN = +3.
PAGE 18
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.) TSSOP4.40mm.EPS MAX1779 Low-Power Triple-Output TFT LCD DC-DC Converter PACKAGE OUTLINE, TSSOP 4.40mm BODY 21-0066 G 1 1 Note: The MAX1779 16-pin TSSOP package does not have an exposed pad. Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product.