Datasheet

MAX1997/MAX1998
Quintuple/Triple-Output TFT LCD Power Supplies
with Fault Protection and VCOM Buffer
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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 (V
MAIN
) can be set from V
IN
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 R
DS(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
D1 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
L1 3.0µH, 1.3A inductor, Sumida CLS5D11HP-3R0NC
N1 1.9A, 30V N-channel MOSFET (SuperSOT™-3), Fairchild FDN357P
P1 2.4A, 20V P-channel MOSFET (SuperSOT-3), Fairchild FDN304P
Q1 3A, 25V PNP bipolar transistor (SuperSOT-3), Fairchild FSB749
Q2, Q3 200mA, 40V PNP bipolar transistors (SOT23), Fairchild MMBT3906
Q4 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.