The MAX9694 provides four static voltage references and 14 programmable voltage references for gamma correction in TFT LCDs. The MAX9694 also features a 7-bit digital variable resistor (DVR) for VCOM calibration in TFT LCDs. Gamma and DVR values are programmed into the registers through an I²C interface.
The 14 programmable reference voltages are divided evenly into seven upper and seven lower voltages for the upper and lower gamma curves of LCD column drivers. Each channel has a static 8-bit digital-to-analog
converter (DAC) and an isolation buffer to ensure stable reference voltages. This architecture reduces the effects of power-supply noise and kickback current from the source driver chips. Each buffer provides a high peak current to reduce the recovery time of the output voltages when critical levels and patterns are displayed.
The MAX9694 has two features to protect the column drivers during startup. First, the gamma outputs remain in a high-impedance state until the registers are loaded. Second, the four reference buffers ramp up proportionally with the analog supply, which ensures that OUT_REFL_H is always at a lower voltage than OUT_REFU_L.
