Overview
The MAX8784 provides the various supply voltages required for thin-film transistor (TFT) liquid crystal display (LCD) panels in televisions and displays. The chip includes a boost regulator, a stable positive charge pump, a stable negative charge pump, three high-current operational amplifiers, and a Dual Mode logic-controlled high-voltage switch module. The HVS mode automatically increases the output voltage of the boost regulator and the positive charge pump for testing the display panel during mass production. It can operate from 4V to 5.5V input voltage and is optimized for LCD TV panel and LCD display applications.
The step-up DC-DC regulator provides a stable supply voltage for the source driver of the TFT. The boost regulator is a high frequency (1.2MHz), high efficiency, current mode regulator. The boost regulator has a 110mΩ (typ) built-in power MOSFET. The high switching frequency allows the use of ultra-small inductors and ceramic capacitors. The current architecture has fast transient response and is easily compensated. The boost regulator has output overvoltage protection, soft-start, internal current limit, and an output voltage that can be adjusted by an external resistor divider.
A three-way op amp drives the LCD backplane and gamma correction divider string. Each op amp has a fast slew rate (45V/μs), a wide bandwidth (20MHz), and a large output short-circuit current (200mA). Each op amp has a rail-to-rail input and a rail-to-rail output.
Positive charge pump regulators and negative charge pump regulators provide a stable supply voltage for the TFT gate driver. The positive charge pump is a two-stage charge pump that does not require any external diodes. The outputs of both charge pumps can be adjusted by resistors. A logic-controlled high voltage switch can be used to control the positive supply of the TFT gate driver.
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.
characteristic
Boost Regulator Powers LCD Panel Source Driver Provides Fast Transient Response to Pulsed Loads Built-in 18V, 4A, 0.11Ω n-Channel Power MOSFET with Lossless Current Sense Cycle-by-Cycle Current Limit Comparator
90% efficiency (5VIN to 15VOUT)
1.2MHz switching frequency three high current 19V operational amplifier
180mA output short circuit current
45V/μs slew rate
20MHz bandwidth rail-to-rail input and output regulated triple voltage charge pump with built-in diode for TFT gate conduction regulated voltage charge pump for TFT gate turn-off power supply internal sequencing circuit internal digital soft start
36V gate-on switch start timing capacitor connection overvoltage and thermal protection on AVDD and GON
4V to 5.5V input voltage range
application
LCD TV and LCD monitor
MAX8784 Typical Application Circuit
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