MAX1512
EEPROM-Programmable TFT VCOM Calibrator
6 _______________________________________________________________________________________
Detailed Description
The MAX1512 is a solid-state alternative to mechanical
potentiometers used for adjusting the LCD backplane
voltage (VCOM) in TFT LCD displays. The MAX1512
attaches to an external resistive voltage-divider and
sinks a programmable current (I
OUT
), which sets the
VCOM level (Figure 1). An internal 7-bit DAC controls
the sink current and allows the user to increase or
decrease the VCOM level (Figure 2). The DAC is ratio-
metric relative to AVDD and is monotonic over all oper-
ating conditions. The user can store the DAC setting in
an internal EEPROM. On power-up, the EEPROM pre-
sets the DAC to the last stored setting. The single-wire
interface between the LCD panel and the programming
circuit adjusts the DAC, programs the EEPROM, and
provides programming power.
The resistive voltage-divider and the AVDD supply set
the maximum value of VCOM. The MAX1512 sinks cur-
rent from the voltage-divider to reduce the VCOM level.
The external resistor R
SET
sets the full-scale sink cur-
rent and the minimum value of VCOM.
Pin Description
PIN NAME FUNCTION
1 OUT
Adjustable Sink-Current Output. OUT connects to the resistive voltage-divider between AVDD and GND that
sets the VCOM voltage. I
OUT
lowers the divider voltage by an adjustable amount. See the SET pin
description.
2 AVDD High-Voltage Analog Supply. Connects to the panel source-driver supply rail.
3 N.C. No Connect. Not internally connected.
4 GND Ground
5V
DD
Supply Input. +2.6V to +3.6V input range.
6 CTL
VCOM Adjustment and EEPROM Programming Control. CTL sets the internal DAC code and programs the
EEPROM. A pulse-control method is used to adjust the VCOM level. See the VCOM Adjustment (CTL)
section. To program the DAC setting into the EEPROM as the power-on default, drive CTL to the EEPROM
programming voltage using the correct timing and voltage ramp rates. See the EEPROM Programming
(CTL) section.
7CE
Control Interface Enable. Connect CE to V
DD
to enable the CTL input. Connect CE to GND to disable the
CTL input and reduce the supply current.
8 SET
Full-Scale Sink-Current Adjustment Input. Connect a resistor, R
SET
, from SET to GND to set the full-scale
adjustable sink current. The full-scale adjustable sink current is equal to:
I
OUT
is equal to the current through R
SET
.
CE
CTL
AVDD
R
SET
25kΩ
OUT
R2
245kΩ
R1
200kΩ
VCOM
5V
SET
GND
V
DD
V
DD
3V
AVDD
10V
MAX1512
Figure 1. Standard Application Circuit
V
R
AVDD
SET
20 ×
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