PS081 datasheet(64/155 Pages) AMSCO

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4-7

PSØ81

lcd_r_const[1:0] 1

Defines the cross resistance of the LCD voltage

divider

0 = 30 k

1 = 50 k

2 = 200 k

3 = 800 k

lcd_charge[1:0] 0

Selects how many LCD clock cycles it is waited

before recharging

0 = each cycle

1 = second cycle

2 = fourth cycle

Zero is mandatory in stretched modes, not relevant in

direct drive mode

lcd_r_fastld

Configures the number of fast-load periods(10ms)

with low-resistance voltage divider

4.2.2.5

Crosstalk LCD Charge Pump - Measurement

The LCD charge pump might have a negative impact on the measurement quality due to crosstalk

from the charge pump. Typically, this becomes obvious by periodic oscillations of the measurement

result.

PSØ81 offers several configuration options to overcome this. In the following we show some measu-

res. There is not a unique solution but a need to select the right one for the application. In any case

of uncertainty please contact acam for support.

In Direct Drive Mode the LCD does not affect the measurement.

Selecting the right LCD frequency in many cases solves the problem. In general, the higher the

frequency the lower the distortion. Testing the different lcd_freq values will show the best choice.

The current consumption might be a little bit higher. In battery driven system this will not be a

problem. In solar applications we recommend direct drive, anyway.

LCD voltage divider resistors should be selected as high as possible. This might be in conflict to

measure 2, and segments to be off can be seen. The right choice has to be proven by experi-

ment.

The blocking capacitor at VCC_LCD can be increased. As a standard we recommend 4.7 µF. In

case of problems an increase up to 22 µF shows obvious improvements.

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PS081 Datasheet(PDF) 64 Page - ams AG