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VCOM adjustment for TFT LCDs

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article image Simplifies the VCOM-adjustment process and replaces mechanical potentiometers.

MAXIM Integrated Products, represented in Australia by Arrow Electronics , has released the MAX8738 I(2)C-programmable VCOM-adjustment solution for thin-film transistor (TFT) liquid-crystal displays (LCDs). It simplifies the VCOM-adjustment process and replaces mechanical potentiometers, reducing labour costs, increasing reliability and enabling automation.

The calibrator attaches to an external resistive voltage-divider and sinks a programmable current to set the VCOM voltage level. An internal seven-bit digital-to-analogue converter (DAC) controls the sink current. The DAC is ratiometric relative to AVDD and is guaranteed to be monotonic over all operating conditions.

The VCOM calibrator device includes an EEPROM to store the desired VCOM voltage level. The EEPROM can be programmed repeatedly, giving TFT LCD manufacturers the flexibility to calibrate the display panel as many times as the manufacturing process requires.

The MAX8738 has a two-wire I(2)C interface for DAC adjustment commands and EEPROM programming. Because the I(2)C interface uses the existing I(2)C bus on the LCD panel connector no additional panel connector pins are required.

The calibrator is available in an eight-pin microMAX package. To reduce design time, a pre-assembled MAX8738 evaluation kit is available with recommended external components.

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