MAX1997 datasheet(15/31 Pages) MAXIM

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Quintuple/Triple-Output TFT LCD Power Supplies

with Fault Protection and VCOM Buffer

______________________________________________________________________________________

Standard Application Circuit

The standard application circuit (Figure 1) of the

MAX1997 is a complete power-supply system for TFT

liquid-crystal displays. The circuit generates 9V for source

drivers, +20V and -7V for gate drivers, a 2.5V logic supply

for the timing controller, a 8.6V gamma reference voltage,

and a VCOM buffer. The input voltage range is from 2.7V

to 5.5V. Table 1 lists the selected component options and

Table 2 lists the component suppliers.

Detailed Description

The MAX1997 and MAX1998 contain a high-perfor-

mance step-up switching regulator, two low-cost linear-

regulator controllers, and multiple levels of protection

circuitry. The MAX1997 also includes two additional lin-

ear-regulator controllers and a high-current VCOM

buffer. Figure 2 shows the MAX1997/MAX1998 system

functional diagram. The output voltage of the main

step-up regulator (VMAIN) can be set from VIN to 13V

with an external resistive voltage-divider. High switch-

ing frequency (375kHz/750kHz/1.5MHz) and current-

mode control provide fast transient response and allow

the use of low-profile inductors and ceramic capacitors.

The low RDS(ON) internal power MOSFET minimizes the

external component count and achieves high efficiency

using a lossless current-sense architecture.

Two charge pumps take energy from the main step-up

regulator’s switching node (LX) to generate positive and

negative supplies. Additional capacitor and diode stages

can be used to generate supply voltages greater than

+35V and less than -15V. The positive and negative

linear-regulator controllers postregulate the charge-pump

supply voltages and allow users to program the power-up

sequence as well.

The high-current VCOM buffer of the MAX1997 is ideal for

driving the backplane of a TFT LCD panel. It requires only

a 0.47µF ceramic output capacitor for stability. The

MAX1997’s two additional linear-regulator controllers can

be used to build the gamma reference and logic supply.

The unique input switch control of the MAX1997/

MAX1998 senses the current drawn from the input

power supply by monitoring the voltage drop across

the input P-channel MOSFET. The protection MOSFET

and all regulator outputs latch off if an overcurrent

condition lasts for more than the fault timer period.

Table 1. Selected Component List

DESIGNATION

DESCRIPTION

C2, C13

10µF, 6.3V X5R ceramic capacitors (1206), TDK C3216X5R0J106M

C4, C5, C6

4.7µF, 10V X7R ceramic capacitors (1210), Taiyo Yuden LMK352BJ475MF

1.0A, 30V Schottky diode (S-flat), Toshiba CRS02

D2, D3, D4

200mA, 25V dual-series Schottky diodes (SOT23), Fairchild BAT54S

D5, D6

200mA, 75V diode (SOT23), Fairchild MMBD4148

3.0µH, 1.3A inductor, Sumida CLS5D11HP-3R0NC

1.9A, 30V N-channel MOSFET (SuperSOT™-3), Fairchild FDN357P

2.4A, 20V P-channel MOSFET (SuperSOT-3), Fairchild FDN304P

3A, 25V PNP bipolar transistor (SuperSOT-3), Fairchild FSB749

Q2, Q3

200mA, 40V PNP bipolar transistors (SOT23), Fairchild MMBT3906

200mA, 40V NPN bipolar transistor (SOT23), Fairchild MMBT3904

SUPPLIER

PHONE

FAX

WEBSITE

Fairchild

408-822-2000

408-822-2102

www.fairchildsemi.com

Sumida

847-545-6700

847-545-6720

www.sumida.com

Taiyo Yuden

800-348-2496

847-925-0899

www.t-yuden.com

TDK

847-803-6100

847-390-4405

www.component.tdk.com

Toshiba

949-455-2000

949-859-3963

www.toshiba.com

Table 2. Component Suppliers

SuperSOT is a trademark of Fairchild Semiconductor.

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