TIUC1825PWM电源控制方案.doc
3页
Tl UC1825 PWM电源控制方案作者： 时间：2009-05-24 来源：TI公司的UC1825是PWM控制器件，非常适合高频开关电源应用.UC1825的特别之处是通过比较器 和逻辑电路最小化传输时延，同时最人化误差放大器的带宽和转换速率.UC1825的开关频率高达1MHz,50ns 传输时延至输出，符合QML-V认证和SMD 5962-87681以及Rad容差为30 kRad (Si) TID. UC1825具 有大电流双图腾柱输出，峰值电流1.5A,起动电流仅为1.1mA,逐个脉冲进行限流,软起动/最大占空比控制和带 滞后的欠压锁住.本文介绍了 UC1825的主妾特性，方框图以及采用UC1835的50W设计案例The UC1825 PWM control device is optimized for high-frequency switched mode power supply applications. Particular care was given to minimizing propagation delays through the comparators and logic circuitry while maximizing bandwidth and slew rate of the error amplifier. This controller is designed for use in either current-mode or voltage mode systems with the capability for input voltage feed-forward.Protection circuitry includes a current limit comparator with a 1-V threshold, a TTL compatible shutdown port, and a soft start pin which will double as a maximum duty-cycle clamp・ The logic is fully latched to provide jitter-free operation and prohibit multiple pulses at an output. An undervoltage lockout section with 800 mV of hysteresis assures low start up cur re nt. During undervoltage lockout, the outputs are high impedanee.This device features totem pole outputs designed to source and sink high peak currents from capacitive loads, such as the gate of a power MOSFET・ The on state is designed as a high level.UC1825主要特性：QML-V Qualified, SMD 5962-87681Rad-Tolerant: 30 kRad (Si) TID(1)Compatible With Voltage- or Current-Mode TopologiesPractical Operation Switching Frequencies to 1 MHz50-ns Propagation Delay-to-OutputHigh-Current Dual Totem Pole Outputs (1.5 A Peak)Wide Bandwidth Error AmplifierFully Latched Logic With Double-Pulse SuppressionPulse-by-Pulse Current LimitingSoft Start/Maximum Duty-Cycle ControlUndervoltage Lockout With HysteresisLow Start-Up Current (1.1 mA)Oon omr*卄IOu?BF'A*r GNDJrr c -=s-=2W" BanSaW* Enor ApVccEpGNDVr图1 .UC1825方框图Q50UC182527 k4OscillatorRampVcOut A1310kQ10.1 urF111a1033 ku S8E/AOut、Out BNonINV> Error ‘AmpPwr GndINV 丿GndSoft Startli IM ShutdownVref5.1V911-ox 11020图2.UC1825开环实验室测试电路42V?o56VVootSV1 A to 10 A1513i0.1 UFVccVREF2 NlOutA [W1N5820 -VA—Vc IOutB 11rl 卫一-T丄-< 4.3 kllUC28J51 nF们 inv lu^sordiij10kl212Q3.3 kQI E/A Out Rflmp 74 CLOCK Ct 65 Rt PwGnd 1Jl.5kDGnd SS Ro壬 0.1 nFUDG-iXJ2图3採用UC1835的设计案例:50 W, 48V到5V DC/DC转换器——1.5MHz时钟频率。
