UC1870 -1/ -2
UC2870 -1/ -2
UC3870 -1/ -2
High Efficiency, Synchronous, Step-down (Buck) Controllers
FEATURES
DESCRIPTION
• Operation to 36V Input Voltage
The UC3870 family of synchronous step-down (Buck) regulators provides
high efficiency power conversion from an input voltage range of 4.5 to 36
volts. The UC3870 is tailored for battery powered applications such as lap-
top computers, consumer products, communications systems, and aero-
space which demand high performance and long battery life. The
synchronous regulator replaces the catch diode in the standard buck regu-
lator with a low Rds(on) N-channel MOSFET switch allowing for significant
efficiency improvements. The high side N-channel MOSFET switch is
driven out of phase from the low side N-channel MOSFET switch by an
on-chip bootstrap circuit which requires only a single external capacitor to
develop the regulated gate drive. Fixed frequency, average current mode
control provides the regulator with inherent slope compensation, tight regu-
lation of the output voltage, and superior load and line transient response.
Switching frequencies up to 300kHz are possible.
• Fixed Frequency Average Current
Mode Control
• 2V to 3.5V Output Voltage when
Combined with UC3910 Precision
Reference/DAC
• Drives External N-Channel MOSFETs
for Highest Efficiency
• Sleep Mode Current <75 A
• Complementary 1 Amp Outputs with
Regulated Gate Drive Voltage
• LDO (Low Drop Out) Virtual 100%
Duty Cycle Operation
The UC3870-1,-2 is designed to interface directly with precision references
like the UC3910. When combined with the UC3910, output voltages be-
tween 2V to 3.5V in 100mV increments and 1% accuracy are attainable.
This makes the UC3870-1,-2 ideal for powering high performance micro-
processors like the Intel Pentium Pro and others.
• Non-Overlapping Gate Drives
(continued)
BLOCK DIAGRAM
UDG-96158
Pin Numbers refer to the DIL-18 Package.
SLUS288A - AUGUST 1998 - REVISED OCTOBER 2001