Complete DDR1/2/3
Memory Power Supply
POWER MANAGEMENT
Description
The SC486 is a combination switching regulator and linear
source/sink regulator intended for DDR1/2/3 memory
systems. The switching regulator is used 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 linear source/sink regulator
is used 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.
For the VTT regulator, the output voltage tracks VREF,
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. Additional features include
cycle-by-cycle current limiting, digital soft-start, power
good (all VDDQ only) and over-voltage and under-voltage
protection (VDDQ and VTT). All 3 outputs (VDDQ, VTT and
REF) are actively discharged when VDDQ is disabled,
reducing external component count and cost. The SC486
is available in a 24 pin MLPQ 4mmx4mm Lead-free
package.
SC486
Features
DDR1, DDR2 and DDR3 compatible
Constant on-time controller for fast dynamic
response on VDDQ
Programmable VDDQ range - 1.5V to 3V
1% Internal Reference (2% System Accuracy)
Resistor programmable on time for VDDQ
VCCA/VDDP range = 4.5V to 5.5V
VBAT 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
Combined EN and PSAVE pin for VDDQ
Over-voltage/under-voltage fault protection for
both outputs and PGD output (VDDQ only)
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 and REF are actively discharged in
S4/S5
24-pin MLPQ (4 x 4mm) Lead-free package, fully
WEEE and RoHS compliant
Applications
Notebook computers
CPU I/O supplies
Handheld terminals and PDAs
LCD monitors
Network power supplies
5VSUS
R3 470k
VBAT
Typical Application Circuit
VBAT
5VSUS
5VRUN
R1
R4 10R
C1
no-pop
REF
R6
10R
R9
C6
1uF
C7
no-pop
C2
R5
1uF
R2
10R
11
3
2
6
R7 10R
C3
no-pop
R8 0R
C8
1nF
C9
1uF
8
9
10
5
4
14
15
12
13
16
17
U1
VTTEN
VDDQS
TON
FB
REF
COMP
VTTS
VCCA
VSSA
VTT
VTT
VTTIN
VTTIN
PGND2
PGND2
PAD
SC486
PGD
EN/PSV
7
1
D1
PGOOD
VDDQ
5
BST
24
C4
0.1uF
R10
4
3
8
6
C5
10uF
DH
ILIM
LX
23
21
22
7
L1
VDDQ
+
C10
VTT
VDDQ
C11
20uF
C12
1uF
DL
VDDP
PGND1
19
20
18
C13
1uF
2
Q1
1
Revision: September 13, 2006
1
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