MAX188 datasheet(13/32 Pages) MAXIM

13 / 32 page

Triple-Output TFT LCD Power Supply

with Fault Protection

______________________________________________________________________________________

Standard Application Circuit

The standard application circuit (Figure 1) of the

MAX1889 generates +9V, +20V, and -7V outputs for

TFT LCD displays. The input voltage is from 2.7V to

5.5V. Table 1 lists the recommended component

options and Table 2 lists the component suppliers.

Detailed Description

The MAX1889 contains a high-performance, step-up

switching regulator, two low-cost linear-regulator con-

trollers, and multiple levels of protection circuitry. Figure

2 shows the system functional diagram of the device.

The output voltage of the main step-up converter (VMAIN)

can be set from VIN to 13V with an external resistive volt-

age-divider. The high switching frequency (500kH/1MHz)

of the main step-up converter and current-mode control

provide fast transient response and allow the use of low-

profile inductors and ceramic capacitors. The internal

power MOSFET minimizes the external component count

while achieving high efficiency by incorporating a loss-

less current-sensing technology.

The switching node (LX) can generate both positive

and negative voltage supplies by driving charge-pump

stages of capacitors and diodes. The user can use as

many charge-pump stages as needed to generate sup-

ply voltages of more than +30V and -15V. The positive

and negative linear-regulator controllers postregulate

the charge-pump supply voltages and allow users to

program power-up sequencing as well.

The unique input switch control of the MAX1889 senses

the current drawn from the input power supply by moni-

toring the voltage drop across the input P-channel

MOSFET and latches off if an overcurrent condition

lasts for more than the fault timer period. In addition, all

three outputs are monitored for fault conditions that last

longer than the fault latch timer. If the junction tempera-

ture of the IC exceeds +160°C, the device goes into a

latched shutdown state.

Main Step-Up Regulator

The main step-up regulator switches at 1MHz (or 500kHz)

and employs a current-mode control architecture to

maximize loop bandwidth to provide fast-transient

response to pulsed loads found in source drivers for TFT

LCD panels. Also, the high switching frequency allows

the use of low-profile inductors and capacitors to

minimize the thickness of LCD panel designs. The

integrated high-efficiency MOSFET and the IC’s built-in

soft-start function reduce the number of external com-

ponents required while controlling inrush current.

DESIGNATION

DESCRIPTION

C2, C3

3.3µF, 6.3V X5R ceramic capacitors (0805)

Taiyo Yuden JMK212BJ335MG

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

250mA, 75V switching diode (SOT23)

Central Semiconductor CMPD914

6.8µH, 1.3A inductor

Coilcraft LPO2506IB-682

2.4A, 20V P-channel MOSFET

(3-pin SuperSOT)

Fairchild FDN304P

200mA, 40V NPN bipolar transistor (SOT23)

Fairchild MMBT3904

200mA, 40V PNP bipolar transistor (SOT23)

Fairchild MMBT3906

Table 1. Component List

SUPPLIER

PHONE

FAX

WEBSITE

Coilcraft

847-639-6400

847-639-1469

www.coilcraft.com

Fairchild

408-822-2000

408-822-2102

www.fairchildsemi.com

Taiyo Yuden

800-348-2496

847-925-0899

www.t-yuden.com

Toshiba

949-455-2000

949-859-3963

www.toshiba.com

Table 2. Component Suppliers

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