SC1486A
Dual Synchronous Buck
DDR and DDR2 Power Supply Controller
POWER MANAGEMENT
Description
Features
The SC1486A is a dual output constant on-time 1% DC accuracy
synchronous buck PWM controller optimized for cost
effective mobile DDR and DDR2 applications. Features
include high efficiency, a fast dynamic response with no
minimum on time, a REFIN input and a buffered REFOUT
pin capable of sourcing 3mA. The excellent transient
response means that SC1486A based solutions will
require less output capacitance than competing fixed
frequency converters.
Compatible with DDR & DDR2 memory power
requirements
Constant on-time for fast dynamic response
VIN range = 1.8V – 25V
DC current sense using low-side RDS(ON) sensing
or sense resistor
Integrated reference buffer for VTT
Low power S3 state with high-Z VTT
Resistor programmable on-time
Cycle-by-cycle current limit
The output voltage of the first controller can be adjusted
from 0.5V to VCCA. In DDR applications, this voltage is
set to 2.5 volts, and in DDR2, 1.8V. A resistor divider
Digital soft-start
from this supply is used to drive the REFIN pin of the PSAVE option for VDDQ
second controller. A unity gain buffer drives the REFOUT
pin to the same potential as REFIN. The second controller
regulates its output to REFOUT. 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, requiring no gate resistors
for the top MOSFET. Additional features include cycle-
by-cycle current limit, digital soft-start, over-voltage and
under-voltage protection, and a Power Good output for
each controller.
Over-voltage/under-voltage fault protection
<20µA shutdown current
Low quiescent power dissipation
Two Power Good indicators
Separate enable for each switcher
Integrated gate drivers with soft switching - no gate
resistors required
Efficiency >90%
28 Lead TSSOP (lead free available)
Applications
Notebook computers
CPU I/O supplies
Typical Application Circuit
Handheld terminals and PDAs
VBAT
5VSUS
5VSUS
VBAT
D1
C1 0.1uF
U1
SC1486A
BST1
R1
RTON1
R2
10R
22
23
7
6
5
4
3
EN/PSV1
Q1
C2
10uF
TON1
VOUT1
VCCA1
FB1
DH1
LX1
VDDQ
24
25
26
27
28
L1
R3
R4
VDDQ
ILIM1
C3
+
R5
VDDP1
DL1
Q2
R6 0R
2
1
PGOOD
PGD1
VSSA1
VSSA1
C4
1uF
R7
PGND1
C5
C6
1nF
1uF
VSSA1
5VSUS
VBAT
5VSUS
VDDQ
5VRUN
VBAT
R8
R9
10k
10R
D2
C7 0.1uF
R10
8
9
21
20
19
18
17
16
15
REFIN
TON2
BST2
DH2
RTON2
Q3
Q4
C8
10uF
REFOUT
10
11
12
REFOUT
VCCA2
FB2
LX2
L2
R11
R12
10R
R13
VTT
ILIM2
VDDP2
DL2
C9
+
VTT
R14 0R
VSSA2
13
14
PGOOD
PGD2
VSSA2
C10
1uF
R15
10k
PGND2
C11
1nF
C12
C13
1uF
C14
1uF
100nF
VSSA2
Revision: June 22, 2004
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