The MAX8739 evaluation kit (EV kit) is a fully assembled and tested surface-mount circuit board that provides the voltages and features required for active-matrix, thin-film transistor (TFT), liquid-crystal displays (LCDs). The EV kit contains a step-up switching regulator, a positive two-stage charge-pump for the TFT gate-on supply, and a negative single-stage charge pump for the TFT gate-off supply. Also included are two operational amplifiers that can be used to drive the LCD backplane (VCOM) or the gamma-correction divider string, and a logic-controlled, high-voltage switch with adjustable delay.
The EV kit operates from a DC supply voltage of +1.8V to +5.5V. The step-up switching regulator is configured for a +8V output providing at least 250mA from a 2.2V input. The positive charge pump is configured for a +22V output providing at least 20mA. The negative charge pump is configured for a -7V output providing at least 20mA. The two operational amplifiers are both configured for +4V, each capable of providing up to ±150mA peak. The high-voltage switch can be used to delay the output of the positive charge pump's startup. The delay time is set with an external capacitor, C6.
The MAX8739 EV kit demonstrates low quiescent current and high efficiency (85%) for maximum battery life. Operation at 1.2MHz allows the use of tiny surface-mount components. The MAX8739 TQFN package (0.8mm maximum height) with low-profile external components allows this circuit to be less than 1.25mm high.
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