UC2844BD1R2G Electronic IC Chips HIGH PERFORMANCE CURRENT MODE CONTROLLERS

UC3844B, UC3845B, UC2844B, UC2845B

High Performance Current Mode Controllers

The UC3844B, UC3845B series are high performance fixed frequency current mode controllers. They are specifically designed for Off−Line and dc−dc converter applications offering the designer a cost−effective solution with minimal external components. These integrated circuits feature an oscillator, a temperature compensated reference, high gain error amplifier, current sensing comparator, and a high current totem pole output ideally suited for driving a power MOSFET.

Also included are protective features consisting of input and reference undervoltage lockouts each with hysteresis, cycle−by−cycle current limiting, a latch for single pulse metering, and a flip−flop which blanks the output off every other oscillator cycle, allowing output deadtimes to be programmed from 50% to 70%.

These devices are available in an 8−pin dual−in−line and surface mount (SOIC−8) plastic package as well as the 14−pin plastic surface mount (SOIC−14). The SOIC−14 package has separate power and ground pins for the totem pole output stage.

The UCX844B has UVLO thresholds of 16 V (on) and 10 V (off), ideally suited for off−line converters. The UCX845B is tailored for lower voltage applications having UVLO thresholds of 8.5 V (on) and 7.6 V (off).

Features

• Pb−Free Packages are Available

• Trimmed Oscillator for Precise Frequency Control

• Oscillator Frequency Guaranteed at 250 kHz

• Current Mode Operation to 500 kHz Output Switching Frequency

• Output Deadtime Adjustable from 50% to 70%

• Automatic Feed Forward Compensation

• Latching PWM for Cycle−By−Cycle Current Limiting

• Internally Trimmed Reference with Undervoltage Lockout

• High Current Totem Pole Output

• Undervoltage Lockout with Hysteresis

• Low Startup and Operating Current

MAXIMUM RATINGS

Maximum ratings are those values beyond which device damage can occur. Maximum ratings applied to the device are individual stress limit values (not normal operating conditions) and are not valid simultaneously. If these limits are exceeded, device functional operation is not implied, damage may occur and reliability may be affected.

1. Maximum package power dissipation limits must be observed.

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