SC1485_05 Datasheet, PDF (1/27 Pages) Semtech Corporation – Dual Synchronous Buck Pseudo Fixed Frequency Power Supply Controller

SC1485
POWER MANAGEMENT
Dual Synchronous Buck Pseudo Fixed
Frequency Power Supply Controller
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 switching 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.
‹ 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
‹ Separate PSAVE option for each switcher
‹ Over-voltage/Under-voltage fault protection
‹ 10µA typical shutdown current
‹ Low quiescent power dissipation
‹ Two Power Good indicators
‹ 1% Reference (2% system DC accuracy)
‹ 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
Revision: April 26, 2005
VBAT
5VSU S
5VSU S
PGOOD
R1
R TON 1
R5
C5
1nF
R2
10R
VOU T1
R3
R7
C6
1uF
U1
22 _EN/PSV1
23 _TON1
24 _VOUT1
25 _VCCA1
26 _FB1
27 _PGD1
28 _VSSA1
SC 1485
BST1 ⁷
DH1 ⁶
LX1 ⁵
ILIM1 ⁴
VDDP1 ³
DL1 ²
PGND1 ¹
D1
C1 0.1uF
R4
C4
1uF
PGOOD
VBAT
VSSA1
5VSU S
R8
R TON 2
R9
10R
8 _EN/PSV2
9 _TON2
VOU T2
R 10
R 12
10 _VOUT2
11 _VCCA2
12 _FB2
13 _PGD2
C 11
1nF
R 14
C 12
1uF
14 _VSSA2
5VSU S
BST2 ²¹
DH2 ²⁰
LX2 ¹⁹
ILIM2 ¹⁸
VDDP2 ¹⁷
DL2 ¹⁶
PGND2 ¹⁵
D2
C7 0.1uF
R 11
C 10
1uF
VSSA2
1
VBAT
Q1
C2
10uF
L1
VOU T1
C3
+
Q2
R6 0R
VSSA1
VBAT
Q3
C8
10uF
L2
VOU T2
C9
+
Q4
R13 0R
VSSA2
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