SC1470 Datasheet, PDF (1/25 Pages) Semtech Corporation – Synchronous Buck Pseudo Fixed Frequency Power Supply Controller

SC1470
Synchronous Buck Pseudo Fixed
Frequency Power Supply Controller
POWER MANAGEMENT
Description
Features
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.
Typical Application Circuit
‹ 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
VBAT
5VSUS
5VSUS
VBAT
PGOOD
R1
R2
RTON
10R
VOUT
R3
R5
R6
C5
C6
1nF
1uF
U1
1 _EN/PSV
2 _TON
3 _VOUT
4 _VCCA
5 _FB
6 _PGD
7 _VSSA
SC1470
BST ¹⁴
DH ¹³
LX ¹²
ILIM ¹¹
VDDP ¹⁰
DL ⁹
PGND ⁸
D1
C1 0.1uF
R4
C4
1uF
Q1
C2
10uF
L1
Q2
C3
+
VOUT
Revision: April 29, 2005
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