SC4901 Datasheet, PDF (1/20 Pages) Semtech Corporation – COMBI-SYNC Secondary Side Synchronous Rectifier and Regulator

SC4901
COMBI-SYNC Secondary Side
Synchronous Rectifier and Regulator
POWER MANAGEMENT
Description
SC4901 is a unique secondary side regulator designed
for implementing Semtech’s proprietary Combi-Sync
topology for isolated convertors with multiple outputs. The
Combi-Sync is a true all-MOSFET topology that allows
synchronous rectification and post regulation of
transformer isolated outputs, resulting in higher efficiency
and low component count. Details of this unique topology
are described in the Application Information section.
Multiple outputs can be synchronously rectified and
independently regulated by individual SC4901s. Each
output has its own ON/OFF control, soft start, remote sense
and current limits. They can be turned on or off without
affecting the primary or other outputs. The secondary side
control makes it much easier to design tight control loops
and implement load current sharing and hot swap
features. All devices are synchronised to the transformer
winding. The current sense can be either from the output
inductor for high efficiency or a resistor for better accuracy.
An amplified current signal is provided for external use.
Each device is capable of driving high side MOSFETs with
2A current. The forward drive is configured for direct
connection to a 1:1 pulse transformer. SC4901 has an
undervoltage lockout with typical turn-on threshold of 4.5V
and is available in a low cost TSSOP-16 package
Typical Application Circuit
Features
‹ Single controller performs synchronous rectification
and post regulation
‹ Independent regulation of multiple outputs from a
common secondary winding
‹ Turn on shoot through inherently eliminated
‹ Primary switch turns ON and OFF with zero current
‹ No synchronising or any other signals needed across
the isolation boundary
‹ Eliminates the need for a secondary bias supply
‹ Independent soft start, ON/OFF, remote sense and
current limit for each output
‹ Resistive or inductive current sensing with 2V current
signal and 2.5V reference for external applications.
‹ 4.5 to 18V operation
‹ Max operating frequency to 1 MHz
‹ Low profile 16 pin TSSOP package
‹ Based on Semtech’s patented Combi Sync
concept
Applications
‹ Telecom isolated DC to DC converters with multiple
low voltage outputs
‹ High density brick and sub brick modules with
independently regulated multiple outputs
‹ Distributed power architectures
‹ Isolated VRMs
SIN GLE
EN DED
FORWARD
C ON VER TOR
••
T1
QS
T2
R4
R5
QF
R8
L1
QR
R9
R1
R6
R7
VO UT
R2
R3
C1 C2
R10
C3
R TN
C6
D1 D2
RZ
RT
R13 D3
R14
C4
C5
U 1 S C 4901
R11 R12
CAO
D4
CT
Revision: May, 2005
C9
C8
C7
C10
R15
United States Patent 6,788,554
1
www.semtech.com