AN2686

Using the STVM100 to adjust the VCOM

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Using the STVM100 to adjust the VCOM

The digital VCOM calibrator STVM100 (refer to the datasheet) provided by

STMicroelectronics can completely replace the mechanical potentiometer and it is more

accurate, more robust and enables automation.

The STVM100 provides a digital I2C interface to control the sink current output (IOUT). This

output drives an external resistive voltage divider, which can then be applied to an external

VCOM buffer. Three external resistors R1, R2, and RSET determine the highest and lowest

value of the VCOM. An increase in the output sink current lowers the voltage on the external

divider so that the VCOM can be adjusted by 128 steps within this range. Once the desired

VCOM setting is achieved, it can be stored in the internal EEPROM that is automatically

recalled during each power-up. Figure 5 shows the basic connection of the STVM100 to

VCOM. With I2C interface to a flicker auto adjustment system, the VCOM can be adjusted in

a fully automated manner.

Figure 5.

STVM100 connected to VCOM

In order to allow the STVM100 to adjust LCD flicker in a fully automated manner,

STMicroelectronics has developed an LCD flicker auto adjustment system.

The STVM100 LCD flicker auto adjusting system includes the following major features:

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Available for dot, line, column and frame inversion

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1 gray scale accuracy out of a range of 128

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Fast adjusting: average time < 3.2 seconds

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VGA (Variable Gain Adjusting) technology to suit full size LCD panels

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Multichannel: support 1 - 5 input channel(s)

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Two input modes: buttons on board and PS/2 compatible keyboard

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Support serial port and USB links to PC

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Automated logging function via corresponding PC software tool

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Energy saving mode saves power consuming up to 85%