SC1486A Datasheet, PDF (1/29 Pages) Semtech Corporation – Dual Synchronous Buck DDR and DDR2 Power Supply Controller

SC1486A
Dual Synchronous Buck
DDR and DDR2 Power Supply Controller
POWER MANAGEMENT
Description
The SC1486A is a dual output constant on-time
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.
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
from this supply is used to drive the REFIN pin of the
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.
Typical Application Circuit
Features
‹ 1% DC accuracy
‹ 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
‹ Digital soft-start
‹ PSAVE option for VDDQ
‹ 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
‹ Handheld terminals and PDAs
VBAT
5VSUS
5VSUS
VBAT
R1
RTON1
R5
PGOOD
C5
1nF
VBAT 5VSUS VDDQ
R2
10R
VDDQ
R3
R7
C6
1uF
VSSA1
5VSUS
U1
22
EN/PSV1
23
TON1
24
VOUT1
25
VCCA1
26
FB1
27
PGD1
28
VSSA1
SC1486A
7
BST1
6
DH1
5
LX1
4
ILIM1
3
VDDP1
2
DL1
1
PGND1
D1
C1 0.1uF
R4
C4
1uF
5VRUN
R10
RTON2
PGOOD
C11
1nF
R8
R9
10k
10R
R11
C12
100nF
REFOUT
R12
10R
VTT
R15
10k
C13
C14
1uF
1uF
VSSA2
8
REFIN
9
TON2
10
REFOUT
11
VCCA2
12
FB2
13
PGD2
14
VSSA2
21
BST2
20
DH2
19
LX2
18
ILIM2
17
VDDP2
16
DL2
15
PGND2
D2
C7 0.1uF
R13
C10
1uF
Revision: June 22, 2004
1
Q1
C2
10uF
L1
VDDQ
C3
+
Q2
R6 0R
VSSA1
VBAT
Q3
C8
10uF
L2
VTT
C9
+
Q4
R14 0R
VSSA2
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