1 Features

1• Pin-for-Pin Compatible With the UC1846

• 65-ns Typical Delay From Shutdown to Outputs,

and 50-ns Typical Delay From SYNC to Outputs

• Improved Current-Sense Amplifier With Reduced

Noise Sensitivity

• Differential Current Sense with 3-V Common-

Mode Range

• Trimmed-Oscillator Discharge Current for

Accurate Deadband Control

• Accurate 1-V Shutdown Threshold

• High-Current Dual Totem-Pole Outputs (1.5-A

peak)

• TTL Compatible Oscillator SYNC Pin Thresholds

• 4-kV ESD Protection

2 Applications

• DC-DC Converters

• Supports Various Topologies:

– Push-Pull, Forward, Half-Bridge, Full Bridge

• Available in Military Temperature range (-55°C to

125°C)

3 Description

The UC1856 is a high-performance version of the

popular UC1846 series of current-mode controllers, and is intended for both design upgrades and new

applications where speed and accuracy are

important. All input-to-output delays have been

minimized, and the current sense output is slew-rate

limited to reduce noise sensitivity. Fast 1.5-A 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 improvement, in conjunction

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

1-V 5% shutdown threshold; and 4-kV minimum

electrostatic discharge (ESD) protection on all pins.