The MAX8784 evaluation kit (EV kit) is a fully assembled
and tested surface-mount PCB that provides the voltages
and features required for active-matrix, thin-film
transistor (TFT) liquid-crystal display (LCD) panels in
LCD monitors and LCD TVs. The EV kit contains a step-up
switching regulator, a two-stage positive charge
pump for the TFT gate-on supply, a single-stage negative
charge pump for the TFT gate-off supply, and three
high-current op amps. Two capacitor-control delays are
available: one to control the initial startup of the step-up,
and the other to control the delay between the negative
and positive charge pumps. Also included is a
logic-controlled, high-voltage switch for the positive
gate-driver supply. A high-voltage stress (HVS) mode is
provided to increase the step-up and the positive
charge-pump output voltages for stress testing the display
panel during production. A capacitive dummy load
is provided at the high-voltage switch output for ease of
testing without a panel attached.
The EV kit operates from a DC supply voltage of +4.5V
to +5.5V, as configured. The step-up switching regulator
is configured for a +14V output providing at least
700mA. The positive charge pump is configured for a
+28V output providing at least 50mA. The negative
charge pump is configured for a -9V output providing at
least 50mA. The three high-current op amps are each
configured for a +7V output that can source or sink
180mA. The high-voltage switch can be controlled by
external logic. The EV kit's input voltage range can be
lowered to +4V at slightly lower load currents.
The MAX8784 step-up switching regulator operates at
1.2MHz, allowing the use of tiny surface-mount components.
The MAX8784 thin QFN package (0.8mm max
height), with low-profile external components, allows
this circuit to be less than 3mm high.
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