UC1572
UC2572
UC3572
Negative Output Flyback Pulse Width Modulator
FEATURES
• Simple Single Inductor Flyback PWM for Negative
Voltage Generation
• Drives External PMOS Switch
• Contains UVLO Circuit
• Includes Pulse-by-Pulse Current Limit
• Low 50µA Sleep Mode Current
DESCRIPTION
The UC3572 is a negative output flyback pulse width modulator which con- verts a positive input voltage to a
regulated negative output voltage. The chip is optimized for use in a single inductor negative flyback switching con-
verter employing an external PMOS switch. The block diagram consists of a precision reference, an error amplifier
configured for voltage mode opera- tion, an oscillator, a PWM comparator with latching logic, and a 0.5A peak gate
driver. The UC3572 includes an undervoltage lockout circuit to insure sufficient input supply voltage is present
before any switching activity can occur, and a pulse-by-pulse current limit. Output current can be sensed and limited
to a user determined maximum value. The UVLO circuit turns the chip off when the input voltage is below the UVLO
threshold. In addition, a sleep comparator interfaces to the UVLO circuit to turn the chip off. This re- duces the
supply current to only 50µA, making the UC3572 ideal for battery powered applications.
负输出反激脉冲宽度调制器
特征
简单的单电感反激PWM用于产生负电压
驱动外部PMOS开关
包含UVLO电路
包括逐脉冲电流限制
低50
μA睡眠模式电流
描述
UC3572是一款负输出反激脉冲宽度调制器，它可以将正输入电压转换为稳定的负输
出电压。的该芯片经过优化，可用于单电感器负反激开关控制中使用外部PMOS开关
的转换器。框图包括一个精密基准，一个误差放大器，配置用于电压模式操作，一个
振荡器，具有锁存逻辑的PWM比较器以及0.5A峰值门驱动器。UC3572包含一个欠压
锁定电路，以确保在进行任何开关动作之前，必须有足够的输入电源电压发生，并逐
脉冲电流限制。可以检测输出电流并限制为用户确定的最大值。UVLO电路将当输入
电压低于UVLO阈值时，芯片关闭。此外，睡眠比较器与UVLO电路接口以关闭芯
片。这个重新降低电源电流只有50 ì A，使得UC3572适合于电池受支持的应用程序。
框图
SLUS275A-1999
年
3
月
-2001
年
8
月修订
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