SC1485 Datasheet, PDF (1/17 Pages) Semtech Corporation – Dual Synchronous Buck Pseudo Fixed Frequency Power Supply Controller

SC1485
Dual Synchronous Buck Pseudo Fixed
Frequency Power Supply Controller
POWER MANAGEMENT
Description
Features
The SC1485 is a dual output constant on synchronous-
buck PWM controller 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 SC1485 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 SC1485 to skip
PWM pulses for better efficiency.
Each output voltage can be independently adjusted from
0.5V to VCCA. Two frequency setting resistors set the
on-time for each buck controller. The frequency can thus
be tailored to minimize crosstalk. 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 PGOOD output for each
controller.
Typical Application Circuit
Constant on-time for fast dynamic response
Programmable VOUT range = 0.5 – VCCA
VIN 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
Separate PSAVE option for each switcher
Over-voltage/Under-voltage fault protection
10uA Typical shutdown current
Low quiescent power dissipation
Two PGOOD indicators
1% Reference (2% system DC accuracy)
Efficiency >90%
Integrated gate drivers with soft switching
Separate enables
28 Lead TSSOP
Industrial temperature range
Applications
Notebook computers
CPU I/O supplies
Handheld terminals and PDAs
LCD monitors
Network power supplies
VBAT
VOUT1
L1
+ C7
R4
R1
R2
EN2
EN1
Q1
R3
Q2
PGND1
R5
23 _TON1
9 _TON2
8 _EN/PSV2
22 _EN/PSV1
6 _DH1
5 _LX1
4 _ILIM1
2 _DL1
1 _PGND1
PGOOD1 ²⁷
PGOOD1
SC1485
PGOOD2 ¹³
PGOOD2
VBAT
DH2 ²⁰
LX2 ¹⁹
R8
ILIM2 ¹⁸
DL2 ¹⁶
PGND2 ¹⁵
FBK2 ¹²
FBK1 ²⁶
Q4
L2
Q3
+ C8
PGND1
VOUT2
R7
R6
Revision: October 14, 2004
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