ADD8754ACPZ-REEL Просмотр технического описания (PDF) - Analog Devices

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ADD8754ACPZ-REEL

LCD Panel Power, VCOM, and Gate Modulation

Analog Devices 

ADD8754

ADD8754

VCOM

4.0V

ADJUSTABLE FROM 3V TO 5V WITH

15mV PER STEP ADJUSTMENT

C10

2.2pF

VOUT

14V

R4

RB

315kΩ

6kΩ

VDD

RA

1kΩ

R3

10kΩ

AD5259BRMZ10

A

VLOGIC

W

SCL

B

SDA

GND AD0 AD1

C9

0.1μF

R10 R11

2.2kΩ 2.2kΩ

SIGNAL FROM FACTORY PC,

SOFTWARE PROVIDED BY ADI

Figure 27. ADD8754 with Programmable VCOM

The VCOM calibration for flicker reduction is one of the essential

steps in the panel manufacturing process. In a typical panel

production environment, such a process can take additional

time to complete and, therefore, impacts production throughput.

One additional concern is that a potentiometer typically used

only for calibration offers limited resolution. The resistance can

drift over time and can be noticeable after a few years of operation.

The production throughput, image quality, and panel reliability

concerns can all be solved by using a digital potentiometer. As

shown in Figure 27, AD5259, a low cost 256-step digital poten-

tiometer with nonvolatile memory, can calibrate the ADD8754

VCOM voltage precisely, reliably, and time efficiently.

In the worst case, where the temperature, aging effect, and

resistance tolerance of the AD5259 are all accounted for, the

circuit in Figure 27 makes the VCOM voltage adjustable from

3.0 V to 5.0 V with 15 mV per step adjustment. A micro-

controller or I2C programmer can be used to provide the

control signal for the AD5259, but ADI provides programming

software that simplifies the calibration process. The software

can be installed in the factory computer, and two tester probes

can be connected to the computer’s parallel port to implement the

VCOM programming.

The VCOM voltage can be calculated as

VCOM

=

D

256

× R AB

+

R3

R4 + RAB + R3

× 7 × VOUT

where:

D is the decimal code of the AD5259 programmable resistance

between the W-to-B terminals.

RAB is the AD5259 nominal resistance.

Rev. 0 | Page 24 of 28

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