基于UCC28C42的BiCMOS 低电流 8 引脚 PWM 电流模式控制器

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基于UCC28C42的BiCMOS 低电流 8 引脚 PWM 电流模式控制器

　　1 Features

　　Enhanced Replacement for UCx84x and UCx84xA Family With Pin-to-Pin Compatibility

　　1-MHz Operation

　　50-µA Standby Current, 100-µA Maximum

　　Low Operating Current of 2.3 mA at 52 kHz

　　Fast 35-ns Cycle-by-Cycle Over-Current Limiting

　　±1-A Peak Output Current

　　Rail-to-Rail Output Swings with 25-ns Rise and 20-ns Fall Times

　　±1% Initial Trimmed 2.5-V Error Amplifier Reference

　　Trimmed Oscillator Discharge Current

　　New Undervoltage Lockout Versions

　　VSSOP-8 Package Minimizes Board Space

　　2 Applications

　　Switch-Mode Power Supplies

　　General Purpose DC-DC or Off-Line Isolated Power Converters

　　Board Mount Power Modules

　　3 Description

　　UCCx8C4x family are high-performance, current-mode PWM controllers. The UCCx8C4x is an enhanced BiCMOS version with pin-for-pin compatibility to the industry standard UCx84xA family and UCx84x family of PWM controllers. The BiCMOS technology offers lower power consumption to improve efficiency as well as faster current sense and oscillator frequency. In addition, lower startup voltage versions of 7 V are offered as UCCx8C40 and UCCx8C41 for use in battery systems. The UCC28C4x series is specified for operation from –40°C to 105°C, and the UCC38C4x series is specified for operation from 0°C to 70°C.

　　Providing necessary features to control fixed frequency, peak current-mode power supplies, this family offers the following performance advantages. The device offers high-frequency operation up to 1 MHz, suitable for high speed applications. The trimmed discharge current enables more precise programming of the maximum duty cycle and dead-time limit when compared to the UCx84x family. Reduced start-up and operating currents minimizes start-up loss and low operating power consumption for improved efficiency. The device also features a fast current-sense-to-output delay time of 35 ns for superior overload protection at the power switch, and a ±1-A peak output current capability with improved rise and fall times for driving large external MOSFETs directly.

　　The UCC38C4x family is offered in 8-pin VSSOP (DGK), 8-pin SOIC (D), and 8-pin PDIP (P) packages.

　　The UCCx8C4x series of control integrated circuits provide the features necessary to implement AC-DC or DCto-DC fixed-frequency current-mode control schemes with a minimum number of external components. Protection circuitry includes undervoltage lockout (UVLO) and current limiting. Internally implemented circuits include a start-up current of less than 100 µA, a precision reference trimmed for accuracy at the error amplifier input, logic to ensure latched operation, a pulse-width modulation (PWM) comparator that also provides current-limit control, and an output stage designed to source or sink high-peak current. The output stage, suitable for driving N-channel MOSFETs, is low when it is in the OFF state. The oscillator contains a trimmed discharge current that enables accurate programming of the maximum duty cycle and dead time limit, making this device suitable for high-speed applications.

Major differences between members of this series are the UVLO thresholds, acceptable ambient temperature range, and maximum duty cycle. Typical UVLO thresholds of 14.5 V (ON) and 9 V (OFF) on the UCCx8C42 and UCCx8C44 devices make them ideally suited to off-line AC-DC applications. The corresponding typical thresholds for the UCCx8C43 and UCCx8C45 devices are 8.4 V (ON) and 7.6 V (OFF), making them ideal for use with regulated input voltages used in DC-DC applications. The UCCx8C40 and UCCx8C41 feature a start-up threshold of 7 V and a turnoff threshold of 6.6 V (OFF), which makes them suitable for battery-powered applications. The UCCx8C40, UCCx8C42, and UCCx8C43 devices operate to duty cycles approaching 100%. The UCCx8C41, UCCx8C44, and UCCx8C45 obtain a duty cycle from 0% to 50% by the addition of an internal toggle flip-flop, which blanks the output off every other clock cycle. The UCC28C4x series is specified for operation from –40°C to 105°C, and the UCC38C4x series is specified for operation from 0°C to 70°C.

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　　The UCC28C4x and UCC38C4x series are an enhanced replacement with pin-to-pin compatibility to the bipolar UC284x, UC384x, UC284xA, and UC384xA families. The new series offers improved performance when compared to older bipolar devices and other competitive BiCMOS devices with similar functionality. These improvements generally consist of tighter specification limits that are a subset of the older product ratings, maintaining drop-in capability. In new designs, these improvements can reduce the component count or enhance circuit performance when compared to the previously available devices.