UC1856
UC2856
UC3856
Improved Current Mode PWM Controller
FEATURES
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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
DESCRIPTION
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.
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BLOCK DIAGRAM
UDG-96176
9/96
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