
UC1825
UC2825
UC3825
SLUS235A - MARCH 1997 - REVISED MARCH 2004
BLOCK DIAGRAM
Compatible with Voltage or Current Mode
Topologies
Practical Operation Switching Frequencies
to 1MHz
50ns Propagation Delay to Output
High Current Dual Totem Pole Outputs
(1.5A Peak)
Wide Bandwidth Error Amplifier
Fully Latched Logic with Double Pulse
Suppression
Pulse-by-Pulse Current Limiting
Soft Start / Max. Duty Cycle Control
Under-Voltage Lockout with Hysteresis
Low Start Up Current (1.1mA)
The UC1825 family of PWM control ICs is optimized for high fre-
quency switched mode power supply applications. Particular care
was given to minimizing propagation delays through the comparators
and logic circuitry while maximizing bandwidth and slew rate of the
error amplifier. This controller is designed for use in either cur-
rent-mode or voltage mode systems with the capability for input volt-
age feed-forward.
Protection circuitry includes a current limit comparator with a 1V
threshold, a TTL compatible shutdown port, and a soft start pin
which will double as a maximum duty cycle clamp. The logic is fully
latched to provide jitter free operation and prohibit multiple pulses at
an output. An under-voltage lockout section with 800mV of hysteresis
assures low start up current. During under-voltage lockout, the out-
puts are high impedance.
These devices feature totem pole outputs designed to source and
sink high peak currents from capacitive loads, such as the gate of a
power MOSFET. The on state is designed as a high level.
High Speed PWM Controller
FEATURES
DESCRIPTION
application
INFO
available
UDG-92030-2