Simplified Block Diagram
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- Step-Up Regulator Supply for LCD Panel Source Driver
- Fast Transient Response to Pulsed Load
- Built-In 18V, 4A, 0.11Ω n-Channel Power MOSFET with Lossless Current Sensing
- Cycle-by-Cycle Current-Limit Comparator
- 90% Efficiency (5VIN to 15VOUT)
- 1.2MHz Switching Frequency
- Three High-Current 19V Operational Amplifiers
- 180mA Output Short-Circuit Current
- 45V/µs Slew Rate
- 20MHz Bandwidth
- Rail-to-Rail Input and Output Operation
- Regulated Charge-Pump Tripler with Integrated Diodes for TFT Gate-On Supply
- Regulated Charge Pump for TFT Gate-Off Supply
- Built-In Sequencing
- Internal Digital Soft-Start
- 36V Gate-On Switch
- Startup Timing Capacitors for AVDD and GON
- Undervoltage and Thermal Protection
- 4V to 5.5V Input Operating Range
- LCD TVs and LCD Monitors
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, current-mode 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 TQFN package and operates over the -40°C to +85°C temperature range.