SC470 Datasheet, PDF (1/31 Pages) Semtech Corporation – Synchronous Buck Controller for Dynamic Load-Voltage Applications

SC470
Synchronous Buck Controller for
Dynamic Load-Voltage Applications
POWER MANAGEMENT
Description
Features
The SC470 is a single output, constant on-time
synchronous-buck, pseudo-fixed frequency, 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 SC470 based solutions will require less
output capacitance than competing fixed frequency
converters.
The SC470 is specifically targeted for graphics processor
power supplies that require dynamic voltage transition,
with a tight 0.85% DC accuracy and a 20% OVP threshold.
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 SC470 to
skip PWM pulses for better efficiency.
The output voltage can be adjusted from 0.5V to VCCA.
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 PGD 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 RSENSE in source of low-side MOSFET for
greater accuracy
‹ Resistor programmable on-time
‹ Cycle-by-cycle current limit
‹ Digital soft-start
‹ Combined EN and PSAVE functions
‹ Over-voltage/under-voltage fault protection
and PGD output
‹ 20% OVP threshold for simpler dynamic voltage
transition circuitry
‹ 5µA typical shutdown current
‹ Low quiescent power dissipation
‹ 14 lead TSSOP and 16 pin MLPQ (4mm x 4mm)
packages
‹ Industrial temperature range
‹ 0.85% DC accuracy
‹ Integrated gate drivers with soft-switching
Applications
‹ Graphics Cards
‹ Embedded Graphics Processors
‹ High Performance Processors
VBAT
5VSUS
5VSUS
VBAT
PGOOD
R1
R1
RTON
10R
VOUT
R2
R2
R4
C5
C6
1nF
1uF
U1
EN/PSV
TON
VOUT
VCCA
FB
PGD
VSSA
SC470
BST
DH
LX
ILIM
VDDP
DL
PGND
D1
C1 0.1uF
R3
C4
1uF
Q1
C2
10uF
L1
Q2
C3
+
VOUT
September 27, 2005
1
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