POWER MANAGEMENT
Description
The SC480 is a combination switching regulator and
linear source/sink regulator intended for DDR1/2/3
memory systems. The purpose of the switching regulator
is to generate 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 a 3A peak current.
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 SC480
is available 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% Internal Reference (2% 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 or 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 Against Source-
Current Loads
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 3A 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
Fully WEEE and RoHS Compliant
SC480
Applications
Notebook Computers
CPU I/O Supplies
Handheld Terminals and PDAs
LCD Monitors
Network Power Supplies
C2
0.1uF
Q1
20
Typical Application Circuit
5V
D1
VDDQ
22
24
23
21
19
VBAT
C3
2x10uF
VTT
VBAT
C4
10uF
C5
10uF
C1
1uF
1
R1
1Meg
VTTSNS
2
3
4
C7
1nF
R6
10R
REF
C9
1uF
C10
1uF
5
6
VDDQ
L1
Q2
18
17
16
15
14
13
PAD
R4
R7
10R
5V
PGOOD
RILIM
C6
+
LX
VTT
BST
PGND2
VTTS
VSSA
TON
REF
VTTIN
DH
PGND1
U1
PGND1
ILIM
VDDP
VDDP
SC480
VDDQS
VCCA
NC
VTTEN
EN/PSV
DL
PGD
NC
12
FB
PAD
10
11
7
8
9
VDDQ
C8
0.1uF
EN/PSV
VTT_EN
C11
1uF
November 3, 2006
1
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