®
RT6551A/B
Complete DDR Memory Power Supply Controller
General Description
The RT6551A/B provides a complete power supply for
DDR2/DDR3/DDR3L/LPDDR3/DDR4 memory systems. It
integrates a synchronous PWM Buck controller with a
1.5A sink/source tracking linear regulator and buffered low
noise reference.
The PWM controller provides the low quiescent current,
high efficiency, excellent transient response, and high DC
output accuracy needed for stepping down high-voltage
batteries to generate low-voltage chipset RAM supplies
in notebook computers. The constant on-time PWM
control scheme handles wide input/output voltage ratios
with ease and provides 100ns
“instant-on”
response to
load transients while maintaining a relatively constant
switching frequency.
The RT6551A/B achieves high efficiency at a reduced cost
by eliminating the current-sense resistor found in
traditional current mode PWMs. Efficiency is further
enhanced by its ability to drive very large synchronous
rectifier MOSFETs. The Buck conversion allows this device
to directly step down high-voltage batteries for the highest
possible efficiency.
The 1.5A sink/source LDO maintains fast transient
response only requiring a 10μF ceramic output capacitor.
In addition, the LDO supply input is available externally
to significantly reduce the total power losses. The
RT6551A/B supports all of the sleep state controls placing
VTT at high-Z in S3 and discharging VDDQ, VTT and
VTTREF (soft-off) in S4/S5.
The RT6551A/B provides protections including OVP, UVP,
and thermal shutdown. The RT6551A/B is available in the
WQFN-20L 3x3 package.
Applications
DDR2/DDR3/DDR3L/LPDDR3/DDR4 Memory Power
Supplies
Notebook computers
SSTL18, SSTL15 and HSTL bus termination
Pin Configurations
(TOP VIEW)
VTT
VLDOIN
BOOT
UGATE
PHASE
20 19 18 17 16
VTTGND
VTTSNS
GND
VTTREF
VDDQ
1
2
3
4
5
6
7
8
9 10
15
14
GND
21
13
12
11
LGATE
PGND
CS
VDD
VID
WQFN-20L 3x3
Simplified Application Circuit
V
VDD
VDD
TON
RT6551A/B
UGATE
BOOT
PGOOD
VTT
VTTSNS
CS
S3
S5
VID
PHASE
LGATE
FB
VTTREF
VDDQ
GND
VLDOIN
V
IN
PGOOD
V
TT
Copyright
©
2015 Richtek Technology Corporation. All rights reserved.
is a registered trademark of Richtek Technology Corporation.
DS6551A/B-00 May 2015
FB
S3
S5
TON
PGOOD
V
VDDQ
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1
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