The MAX8784 generates supply rails for the thin-film
transistor (TFT) liquid-crystal display (LCD) panels in TVs
and monitors. It includes a step-up regulator, a regulated
positive and a negative charge-pump, three high-current
operational amplifiers, and Dual Mode™, logic-controlled,
high-voltage switch control block. HVS mode
automatically increases the output voltages of the boost
regulator and the positive charge-pump to stress test
display panels during production. The MAX8784 can
operate from input voltages of 4V to 5.5V and is optimized
for LCD TV panel and LCD monitor applications.
The step-up DC-DC regulator provides a regulated supply
voltage for TFT source drivers. The step-up regulator
is a high-frequency (1.2MHz), high-efficiency, currentmode
regulator. The step-up regulator has a built-in
110mΩ (typ) power MOSFET. The high-switching frequency
allows the use of ultra-small inductors and
ceramic capacitors. The current-mode architecture provides
fast transient response and easy compensation.
The step-up regulator features output undervoltage protection,
soft-start, internal current limit, and adjustable
output voltage by an external resistive divider.
The three operational amplifiers drive the LCD backplane
and the gamma-correction-divider string. Each
operational amplifier has a fast slew rate (45V/µs), a
wide bandwidth (20MHz), and a high-output short-circuit
current (200mA). Each op amp has rail-to-rail input
and rail-to-rail output operation.
The positive charge-pump regulator and the negative
charge-pump regulator provide regulated supply voltages
for the TFT gate drivers. The positive charge
pump is a two-stage charge pump, which requires no
external diodes. The output voltages of both charge
pumps are resistor adjustable. The logic-controlled
high-voltage switch allows the manipulation of the positive
TFT gate-driver supply.
The MAX8784 is available in a small (5mm x 5mm), low-profile
(0.8mm), 40-pin thin QFN package and operates
over the -40°C to +85°C temperature range.
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