NB685A
28 V, 12 A, Low Iq, High Current
Synchronous Buck Converter
with +/- 1 A LDO and Buffered Reference
DESCRIPTION
The NB685A provides a complete power supply
with the highest power density for DDR3,
DDR3L, LPDDR3, and DDR4 memory. It
integrates a high-frequency, synchronous,
rectified, step-down, switch-mode converter
(VDDQ) with a 1 A sink/source LDO (VTT) and
buffered low noise reference (VTTREF).
The NB685A operates at high efficiency over a
wide output current load range based on MPS
proprietary switching loss reduction technology
and internal low Ron power MOSFETs.
Adaptive constant-on-time (COT) control mode
provides fast transient response and eases loop
stabilization. The DC auto-tune loop provides
good load and line regulation.
The VTT LDO provides 1 A sink/source current
capability and requires only a 22 μF ceramic
capacitor. The VTTREF tracks VDDQ/2 with
excellent 1% accuracy.
Full protection features include OC limit, OVP,
UVP, over-temperature warning (OTW), and
thermal shutdown.
The converter requires a minimum number of
external components and is available in a QFN
3mm x 3mm package.
TYPICAL APPLICATION
FEATURES
Wide 4.5 V to 28 V Operating Input Range
Compatible for IMVP8
135 μA Low Quiescent Current
12 A Continous Output Current
13 A Peak Output Current
Selectable Ultrasonic Mode
Selectable 500 k/700 k Switching
Frequency
Built-in +/- 1 A VTTLDO
1% Buffered VTTREF Output
Adaptive COT for Fast Transient
DC Auto-Tune Loop
Stable with POSCAP and Ceramic Output
Capacitors
Over-Temperature Warning
Internal Soft Start
Output Discharge
OCL, OVP, UVP, and Thermal Shutdown
Latch-Off Reset via EN or Power Cycle
QFN 3mm x 3mm Package
APPLICATIONS
Laptop Computers
Networking Systems
Servers
Distributed Power Systems
All MPS parts are lead-free, halogen-free, and adhere to the RoHS
directive. For MPS green status, please visit the MPS website under
Quality Assurance. “MPS” and “The Future of Analog IC Technology” are
registered trademarks of Monolithic Power Systems, Inc.
VIN
4.5 V-24 V
VIN OTW BST SW
22 μF x 1
DDR_VTT_CONTROL
FB
EN 1
EN2
EN 2 NB685A
100 kΩ
3.3 V
(Needs external 3.3 V
power supply)
1 μF
PG
VDDQ
3V3
VTT
AGND
PGND
VTTS
MODE VTTREF
0Ω
220 nF
220 nF
0.68 μH
VDDQ
1.35 V/10 A
28 kΩ
22.1 kΩ
22 μF x 3
22 μF
VTT
0.675 V/1 A
NB685A Rev. 1.02
www.MonolithicPower.com
1
7/6/2018
MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited.
© 2018 MPS. All Rights Reserved.
