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SC1470
Synchronous Buck Pseudo Fixed
Frequency Power Supply Controller
POWER MANAGEMENT
Description
Revision: April 29, 2005
Applications
Typical Application Circuit
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.
Notebook computers
CPU I/O supplies
Handheld terminals and PDAs
LCD monitors
Network power supplies
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
Features
5VSUS
5VSUS
VBAT
R3
R1
RTON
PGOOD
R4
C4
1uF
VOUT
R6
L1
R5
C2
10uF
U1
SC1470
1
2
3
4
5
6
7
8
9
10
11
12
13
14
EN/PSV
TON
VOUT
VCCA
FB
PGD
VSSA
PGND
DL
VDDP
ILIM
LX
DH
BST
C6
1uF
VOUT
D1
R2
10R
VBAT
+
C3
Q2
C1
0.1uF
Q1
C5
1nF