基于MAX8784设计的TFT-LCD电源技术

本文介绍了MAX8784主要特性，方框图，典型工作电路图和所用元件列表，MAX8784评估板主要特性，电路图和评估板元件列表。

Maxim 公司的MAX8784是TV和监视器的TFT-LCD电源解决方案，包括升压稳压器，调整的正和负电荷泵，三个大电流运输放大器，以及双模式逻辑控制高压开关控制区块。输入电压4V-5.5V。效率高达90%，开关频率1.2MHz，主要用在LCD TV和LCD 监视器。

MAX8784主要特性：

_ Step-Up Regulator Supply for LCD Panel Source Driver

Fast Transient Response to Pulsed Load

Built-In 18V, 4A, 0.11n-Channel Power MOSFET with Lossless Current Sensing

Cycle-by-Cycle Current-Limit Comparator 90% Efficiency (5V In to 15V Out)

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

MAX8784应用：

LCD TVs and LCD Monitors

图1。MAX8784功能方框图

图2。MAX8784简化工作电路图

图3。MAX8784典型工作电路图

工作电路元件列表：


图4。MAX8784 HVS模式工作电路图

MAX8784评估板

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 stepup 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 stepup, 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 positivegate 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.

MAX8784评估板主要特性：

♦ +4.5V to +5.5V Input-Voltage Range

♦ Output Voltages

+14V Output at 700mA (Step-Up Switching Regulator)

+28V Output at 50mA (Positive Charge Pump)

-9V Output at 50mA (Negative Charge Pump)

Three High-Current Op Amps (±180mA)

♦ 1.2MHz Switching Frequency

♦ All Output Voltages are Resistor Adjustable

♦ Logic-Controlled, High-Voltage Switch

♦ High-Voltage Stress Mode for the Step-Up and

Positive Charge-Pump Output Voltages

♦ Capacitor-Controlled Initial Startup Delay and Positive Charge-Pump Delay

♦ Low-Profile Surface-Mount Components

♦ Fully Assembled and Tested

图5。MAX8784评估板电路图
MAX8784评估板元件列表：