UC1823A,B/1825A,B

UC2823A,B/2825A,B

UC3823A,B/3825A,B

DESCRIPTION

The UC3823A & B and the UC3825A & B family of PWM control ICs are

improved versions of the standard UC3823 & UC3825 family. Performance

enhancements have been made to several of the circuit blocks. Error ampli-

fier gain bandwidth product is 12MHz while input offset voltage is 2mV. Cur-

rent limit threshold is guaranteed to a tolerance of 5%. Oscillator discharge

current is specified at 10mA for accurate dead time control. Frequency ac-

curacy is improved to 6%. Startup supply current, typically 100

µA, is ideal

for off-line applications. The output drivers are redesigned to actively sink

current during UVLO at no expense to the startup current specification. In

addition each output is capable of 2A peak currents during transitions.

Functional improvements have also been implemented in this family. The

UC3825 shutdown comparator is now a high-speed overcurrent comparator

with a threshold of 1.2V. The overcurrent comparator sets a latch that en-

sures full discharge of the soft start capacitor before allowing a restart.

While the fault latch is set, the outputs are in the low state. In the event of

continuous faults, the soft start capacitor is fully charged before discharge

to insure that the fault frequency does not exceed the designed soft start

period. The UC3825 Clock pin has become CLK/LEB. This pin combines

the functions of clock output and leading edge blanking adjustment and has

been buffered for easier interfacing.

(continued)

High Speed PWM Controller

FEATURES

• Improved versions of the

UC3823/UC3825 PWMs

• Compatible with Voltage or

Current-Mode Topologies

• Practical Operation at Switching

Frequencies to 1MHz

• 50ns Propagation Delay to Output

• High Current Dual Totem Pole

Outputs (2A Peak)

• Trimmed Oscillator Discharge Current

• Low 100µA Startup Current

• Pulse-by-Pulse Current Limiting

Comparator

• Latched Overcurrent Comparator With

Full Cycle Restart

SLUS334A - AUGUST 1995 - REVISED NOVEMBER 2000

BLOCK DIAGRAM

UDG-95101

* Note: 1823A,B Version Toggles Q and Q are always low

application

INFO

available