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A
ADVANCED INFORMATION
data sheets provide specification for products not yet complete or characterized. They provide design target infor-
mation for customer planning purposes.
www.fairchildsemi.com
Features
Combines switching regulator and low dropout linear
regulator in single chip
Enable function switches from single to dual output mode
Overvoltage and short circuit protection
Drives N-Channel MOSFETs
Precision trimmed low TC voltage reference
Soft start control during power-up
88% Efficiency for switching regulator
16 pin SOIC package
Applications
Switchable single/dual power supply for Pentium
P54C/
P55C flexible motherboard implementation
Description
The RC5035 combines a switch-mode DC-DC converter
with a low-drop-out linear regulator providing a 5V to 3.3V
and 2.8V conversion for CPUs that require split power sup-
plies. It can be configured with the proper applications cir-
cuitry to deliver load currents greater than 10 Amps. The
RC5035 is designed to operate in a “constant on-time”
(patent pending) control mode under all load conditions. Its
highly accurate low TC reference eliminates the need for
precision external components in order to achieve tight toler-
ance voltage regulation. Using on-chip precision resistors,
the RC5035A can generate the accurate output voltages
required by Intel and Cyrix processors. The programmable
oscillator can operate up to1MHz for flexibility in choosing
external components such as inductors, capacitors, and
Power MOSFETs. Short circuit current protection is pro-
vided on both the switch mode as well as the linear regulator.
Block Diagram
VOL
REF
I
O
I
ON
CONSTANT ON-TIME
OSCILLATOR
RC5035A
gm
gm
V/I
V
H
V
L
V/I
ANALOG
SWITCH
–
+
VOSW
VIN
VREF
65-5035-01
gm
ENABLE
Iset
FBSW
+12V
RC5035A
Dual Prec ision Voltage Regulators
Rev. 0.5.0