Synchronous Buck Pseudo Fixed
Frequency Power Supply Controller
POWER MANAGEMENT
Description
The SC1470 is a single output, constant on-time
synchronous-buck PWM controller intended for use in
notebook computers and other battery operated portable
devices. Features include high efficiency and fast dynamic
response with no minimum on time. The excellent
transient response means that SC1470 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 SC1470 to skip
PWM pulses for better efficiency.
The output voltage can be adjusted from 0.5V to VCCA.
A frequency setting resistor sets the on-time for flexibility
in choosing filter components. 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 Power Good output.
SC1470
Features
Constant on-time for fast dynamic response
Programmable VOUT range = 0.5 – VCCA
VBAT range = 1.8V – 25V
DC current sense using low-side RDS(ON)
sensing or sense resistor
Resistor programmable frequency
Cycle-by-Cycle current limit
Digital soft-start
Combined EN and PSAVE functions
Over-voltage/under-voltage fault protection and
Power Good output
10µA typical shutdown current
Low quiescent power dissipation
14 Lead TSSOP package
Industrial temperature range
1% Internal reference (2% system DC accuracy)
Integrated gate drivers with soft switching
Applications
Notebook computers
CPU I/O supplies
Handheld terminals and PDAs
LCD monitors
Network power supplies
Typical Application Circuit
VBAT
5VSUS
5VSUS
VBAT
D1
R1
RTON
R2
10R
1
2
VOUT
R3
R5
3
4
5
6
R6
7
U1
EN/PSV
TON
VOUT
VCCA
FB
PGD
VSSA
SC1470
BST
DH
LX
ILIM
VDDP
DL
PGND
14
13
12
11
10
9
8
C4
1uF
R4
L1
VOUT
C3
+
Q2
C1
0.1uF
Q1
C2
10uF
PGOOD
C5
1nF
C6
1uF
Revision: April 29, 2005
1
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