AD8385 datasheet(17/24 Pages) AD

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AD8385

Rev. 0 | Page 17 of 24

Table 15. Truth Table @ TSTM = High. Thermal Switch

Enabled. Grounded Output Disabled.

SEN

Action

Load VAO2. No change to VAO1.

Load VAO1. No change to VAO2.

No change to VAO1 and VAO2 data.

Start a serial interface loading cycle.

No change to outputs.

X = Don’t Care.

OUTPUT OPERATING MODE

In normal operating mode, the voltage of the video outputs and

VAO1 is determined by the inputs.

In grounded output mode, the video outputs and VAO1 are

forced to (AGND + 0.1 V) typ.

OVERLOAD PROTECTION

The overload protection employs current limiters and a thermal

switch to protect the video output pins against accidental shorts

between any video output pin and AVCC or AGND.

The junction temperature trip point of the thermal switch is

165°C. Production test guarantees a minimum junction

temperature trip point of 125°C. Consequently, the operating

junction temperature should not be allowed to rise above 125°C

with the thermal switch enabled.

For systems that operate at high internal ambient temperatures

and require large capacitive loads to be driven by the AD8385 at

high frequencies, junction temperatures above 125°C may be

required. In such systems, the thermal switch should either be

disabled or a minimum airflow of 200 lfm be maintained.

SERIAL DACS

Both serial DACs are loaded via the serial interface. The output

voltage is determined by the following equation:

VAO1, VAO2 = SVRL + SD(0:7) × (SVRH – SVRL)/256

Output VAO1 is designed to drive very large capacitive loads,

above 0.047 µF. Lower capacitive loads may result in excessive

overshoot at VAO1.

Level Shifters

The characteristics of the level shifters are optimized based on

their intended use.

Seven level shifters—DX, CLX, CLXN, and ENBX[1:4]—are

optimized for the X direction and three—DY, CLY and CLYN—

are optimized for the Y direction control signals.

One level shifter—NRG—is designed to drive a large capacitive

load and is optimized for an X direction control signal. Two

level shifters—DIRX and DIRY—are optimized for very low

frequency control signals.

One level shifting edge detector—MONITI, MONITO—is

optimized to condition a synchronizing feedback reference

signal from the LCD.

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