Improved Current Mode PWM Controller

UC1856

UC2856

UC3856

DESCRIPTION

FEATURES

•

Pin-for-Pin Compatible With the UC3846

•

65ns Typical Delay From Shutdown to

Outputs, and 50ns Typical Delay From

Sync to Outputs

•

Improved Current Sense Amplifier With

Reduced Noise Sensitivity

•

Differential Current Sense with 3V

Common Mode Range

•

Trimmed Oscillator Discharge Current

for Accurate Deadband Control

•

Accurate 1V Shutdown Threshold

•

High Current Dual Totem Pole Outputs

(1.5A peak)

•

TTL Compatible Oscillator SYNC Pin

Thresholds

•

4kV ESD Protection

The UC3856 is a high performance version of the popular UC3846

series of current mode controllers, and is intended for both design

upgrades and new applications where speed and accuracy are impor-

tant. All input to output delays have been minimized, and the current

sense output is slew rate limited to reduce noise sensitivity. Fast 1.5A

peak output stages have been added to allow rapid switching of

power FETs.

A low impedance TTL compatible sync output has been implemented

with a tri-state function when used as a sync input.

Internal chip grounding has been improved to minimize internal

“noise” caused when driving large capacitive loads. This, in conjunc-

tion with the improved differential current sense amplifier results in

enhanced noise immunity.

Other features include a trimmed oscillator current (8%) for accurate

frequency and dead time control; a 1V, 5% shutdown threshold; and

4kV minimum ESD protection on all pins.

BLOCK DIAGRAM

9/96

UDG-96176