UC3845BN

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

 

 

 

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