Maxim MAX8784 TFT-LCD电源方案解析

    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。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。

　　在生产过程中测试显示面板MAX8784工作输入电压为4V 5 5V，并且针对液晶电桃而板和液品显示器的应J}j进行了优化。该升压DC—DC稳压器为TFT僳驱动器提供丁一种稳压电源电压。该升压捌节器是一个高频率（1 2MHz）、高效率电{ifc模式稳压器该升压调节器有一个内臂110m高开关频率。允许使}}I超小型电感和陶瓷电容。该电流模式架构提供r快速的瞬态响应和方便的补偿升￡芷调节器其有输出欠压保护高带宽（20MHz的）。以及高输出短路电流（200mA） 每个运算放大器都县有轨到轨流入和轨轨输出正电荷泵稳压器和负电荷泵渊节器为TFT栅极驱动提供稳定的电源电雎正电荷泵是一个两阶段的电荷泉，它无需外部二板管l两个电荷泵输出的电眶可通过电阻调整其中的逻辑控制高压开关可以控制正TFT栅极驱动电源MAX8784封裟为小型（5mm X5ram）。簿型（0.

　　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 110m??（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 pider.

　　The three operational amplifiers drive the LCD backplane and the gamma-correction-pider 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）， lowprofile （0.8mm）， 40-pin TQFN package and operates over the -40℃ to +85℃ temperature range.

　　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 capa

　　citive 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：

　　1.+4.5V to +5.5V Input-Voltage Range

　　2. Output Voltages

　　+14V Output at 700mA

　　+28V Output at 50mA

　　-9V Output at 50mA

　　Three High-Current Op Amps

　　3. 1.2MHz Switching Frequency

　　4. All Output Voltages are Resistor Adjustable

　　5.Logic-Controlled, High-Voltage Switch

　　6. High-Voltage Stress Mode for the Step-Up and

　　Positive Charge-Pump Output Voltages

　　7. Capacitor-Controlled Initial Startup Delay and Positive Charge-Pump Delay

　　8.Low-Profile Surface-Mount Components

　　9.Fully Assembled and Tested

　　图5。MAX8784评估板电路图

　　MAX8784评估板元件列表：