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SC1485
Dual Synchronous Buck
Power Supply Controller
POWER MANAGEMENT PRELIMINARY
Revision 1, March 2002
Description Features
Applications
Typical Application Circuit
The SC1485 is a dual output constant on synchronous-
buck PWM controller intended for use in notebook
computers and other battery operated portable devices.
Features include high efficiency and a fast dynamic
response with no minimum on time. The excellent
transient response, means that SC1485 based solutions
will require less output capacitance than competing fixed
frequency converters.
The frequency is constant until a step in load or line voltage
occurs at which time the pulse density and frequency will
increase or decrease to counter the change in output or
input voltage. After the transient event, the controller
frequency will return to steady state operation. At light
loads, Power-Save Mode enables the SC1485 to skip
PWM pulses for better efficiency.
Each output voltage can be independently adjusted from
0.5V to VCCA. Two frequency setting resistors set the
on-time for each buck controller. The frequency can thus
be tailored to minimize crosstalk. The integrated gate
drivers feature adaptive shoot-through protection and
soft switching. Additional features include cycle-by-cycle
current limit, digital soft-start, over-voltage and under-
voltage protection, and a PGOOD output for each
controller.
K Notebook computers
K CPU I/O supplies
K Handheld terminals and PDAs
K LCD monitors
K Network power supplies
K Constant on-time for fast dynamic response
K Programmable VOUT range = 0.5 VCCA
K VIN Range = 1.8V 25V
K DC current sense using low-side RDS(ON)
sensing or sense resistor
K Resistor programmable frequency
K Cycle-by-cycle current limit
K Digital soft-start
K Separate PSAVE option for each switcher
K Over-voltage/Under-voltage fault protection
K 10uA Typical shutdown current
K Low quiescent power dissipation
K Two PGOOD indicators
K 1% Reference (2% system DC accuracy)
K Efficiency >90%
K Integrated gate drivers with soft switching
K Separate enables
K 28 Lead TSSOP
K Industrial temperature range
VBAT
SC1485
1
2
4
5
6
9
12
13
15
16
18
19
2022
23
26
27
8
PGND1
DL1
ILIM1
LX1
DH1
TON2
FBK2
PGOOD2
PGND2
DL2
ILIM2
LX2
DH2EN/PSV1
TON1
FBK1
PGOOD1
EN/PSV2
VOUT2
PGND1
R3
R7
PGOOD1
EN1
R5
PGOOD2
PGND1
Q2
+
C7
R8
R2
R6
R1
Q1
L2
Q3
VBAT
VOUT1
R4
EN2
L1
+
C8
Q4
