基于MAX8784設(shè)計(jì)的TFT-LCD電源技術(shù)

本文介紹了MAX8784主要特性，方框圖，典型工作電路圖和所用元件列表，MAX8784評(píng)估板主要特性，電路圖和評(píng)估板元件列表。

Maxim 公司的MAX8784是TV和監(jiān)視器的TFT-LCD電源解決方案，包括升壓穩(wěn)壓器，調(diào)整的正和負(fù)電荷泵，三個(gè)大電流運(yùn)輸放大器，以及雙模式邏輯控制高壓開(kāi)關(guān)控制區(qū)塊。輸入電壓4V-5.5V。效率高達(dá)90%，開(kāi)關(guān)頻率1.2MHz，主要用在LCD TV和LCD 監(jiān)視器。

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應(yīng)用：

LCD TVs and LCD Monitors

圖1。MAX8784功能方框圖

圖2。MAX8784簡(jiǎn)化工作電路圖

圖3。MAX8784典型工作電路圖

工作電路元件列表：


圖4。MAX8784 HVS模式工作電路圖

MAX8784評(píng)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評(píng)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

圖5。MAX8784評(píng)估板電路圖
MAX8784評(píng)估板元件列表：