POWER MANAGEMENT
Description
The SC488 is a combination switching regulator and lin-
ear source/sink regulator intended for DDR1/2 memory
systems. The purpose of the switching regulator is to gen-
erate the supply voltage, VDDQ, for the memory system.
It is a pseudo-fixed frequency constant on-time controller
designed for high efficiency, superior DC accuracy, and fast
transient response. The purpose of the linear source/sink
regulator is to generate the memory termination voltage,
VTT, with the ability to source and sink 2.8A peak cur-
rents.
For the VDDQ regulator, the switching frequency is constant
until a step in load or line voltage occurs at which time the
pulse density, i.e., frequency, will increase or decrease to
counter the transient change in output or input voltage.
After the transient, the frequency will return to steady-state
operation. At lighter loads, the selectable Power-Save
Mode enables the PWM converter to reduce its switching
frequency and improve efficiency. The integrated gate
drivers feature adaptive shoot-through protection and soft-
switching. Additional features include cycle-by-cycle current
limiting, digital soft-start, over-voltage and under-voltage
protection and a power good
fl
ag.
For the VTT regulator, the output voltage tracks REF, which
is �½ VDDQ to provide an accurate termination voltage.
The VTT output is generated from a 1.2V to VDDQ input by
a linear source/sink regulator which is designed for high
DC accuracy, fast transient response, and low external
component count. All three outputs (VDDQ, VTT and REF)
are actively discharged when VDDQ is disabled, reducing
external component count and cost. The SC488 is avail-
able in a 24-pin MLPQ (4x4 mm) package.
Complete DDR1/2/3
Memory Power Supply
Features
Constant On-Time Controller for Fast Dynamic
Response on VDDQ
DDR1/DDR2/DDR3 Compatible
VDDQ = Fixed 1.8V or 2.5V, or Adjustable From
1.5V to 3.0V
1.5% Internal Reference (2.5% System Accuracy)
Resistor Programmable On-Time for VDDQ
VCCA/VDDP Range = 4.5V to 5.5V
VIN Range = 2.5V to 25V
VDDQ DC Current Sense Using Low-Side R
DS(ON)
Sensing
External R
SENSE
in Series with Low-Side FET
Cycle-by-Cycle Current Limit for VDDQ
Digital Soft-Start for VDDQ
Analog Soft-Start for VTT/REF
Smart Over-Voltage VDDQ Protection
Combined EN and PSAVE Pin for VDDQ
Over-Voltage/Under-Voltage Fault Protection
Power Good Output
Separate VCCA and VDDP Supplies
VTT/REF Range = 0.75V – 1.5V
VTT Source/Sink 2.8A Peak
Internal Resistor Divider for VTT/REF
VTT is High Impedance in S3
VDDQ, VTT, REF are Actively Discharged in S4/S5
24 Lead MLPQ (4x4 mm) Lead-Free Package
Product Is Fully WEEE and RoHS Compliant
SC488
Applications
Notebook Computers
CPU I/O Supplies
Handheld Terminals and PDAs
LCD Monitors
Network Power Supplies
C2
0.1uF
Q1
VBAT
C3
2x10uF
Typical Application Circuit
5V
VDDQ
VTT
VBAT
C4
10uF
C5
10uF
C1
1uF
1
2
VTTSNS
3
4
C7
1nF
R6
10R
REF
C9
1uF
C8
0.1uF
C10
1uF
5
6
D1
24
23
22
21
20
19
LX
BST
DL
VTT
L1
Q2
18
17
16
15
14
13
PAD
R4
R7
10R
C11
1uF
RILIM
C6
VDDQ
+
PGND2
VTTS
VSSA
TON
REF
VTTIN
DH
PGND1
U1
PGND1
ILIM
VDDP
VDDP
R1
1Meg
SC488
VDDQS
VTTEN
EN/PSV
VCCA
NC
PGD
NC
PGOOD
FB
PAD
10
11
12
7
8
9
5V
VDDQ
EN/PSV
VTT_EN
September 28, 2006
1
www.semtech.com
SEMTECH [ SEMTECH CORPORATION ]
