Synchronous Buck Pseudo-Fixed
Frequency Power Supply Controller
POWER MANAGEMENT
Description
The SC411 is a constant on-time synchronous buck PWM
controller in a space-saving MLPQ package 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 SC411 based solu-
tions will require less output capacitance than competing
fi
xed frequency converters.
The switching frequency is constant until a step-in load or
line voltage occurs. During this 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, Powersave Mode enables the SC411 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 the controller.
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, a Power Good output and
soft discharge upon shutdown.
SC411
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
Powersave option
Over-voltage/under-voltage fault protection
10μA typical shutdown current
Low quiescent power dissipation
Power good indicator
1.2% reference
Integrated gate drivers with soft switching
Enable pin
16 pin MLPQ (4mm x 4mm)
Output soft discharge upon shutdown
Applications
Notebook Computers
CPU/IO Supplies
Handheld Terminals and PDAs
LCD Monitors
Network Power Supplies
Typical Application Circuit
VBAT
5VSUS
5VSUS
VBAT
R1
RTON1
D1
C1 0.1uF
R2
15
14
10R
U1
16
EN/PSV
TON
BST
NC
13
Q1
DH
LX
12
11
10
9
R5
C2
10uF
VOUT
C3
R4
R3
1
2
3
4
VOUT
VCCA
L1
VOUT
C4
+
Q2
SC411
FB
PGD
ILIM
VDDP
PGOOD
R6
C5
1nF
C6
PGND
7
VSSA
TPAD
NC
1uF
5
6
8
DL
C7
1uF
June 2007
1
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