Datasheet

TPS65251
C25
100pF
R22
20K
C24
4700pF
R20
40.2K
R21
32K
1.8V 2A
L2
4.7uH
GND
VIN
LX3
VIN
LX3
GND
C23
4.7nF
BST3
VIN3
EN3
FB1
SS1
SYNC
CMP1
ROSC RLIM1 CMP3 RLIM3
FB3
SS3
LX2
BST2
LX1
VIN2
LX2
EN2
VIN1
EN1
LX1
BST1
CMP2
GND
FB2
LOW_P
SS2
V7V
AGND
PGOOD
V3V
C11
22uF
R10
40.2K
R11
80.6K
1.2V 3A
L1
4.7uH
C13
4.7nF
R13
100K
C15
100pF
R12
20K
C14
4700pF
V2
V1
VIN1
C10
47nF
C27
4.7nF
C17
4.7nF
VIN
C35
100pF
R32
20K
C34
4700pF
C36
4.7nF
R1
383K
C26
4.7nF
C21
22uF
FB2
FB2LP
PG
C1
10uF
C2
3.3uF
C37
4.7nF
C31
22uF
R30
40.2K
R31
12.7K
3.3V 2A
C33
4.7nF
V3
C30
47nF
VIN3
VIN
C20
47nF
VIN2
C16
4.7nF
L3
4.7uH
R23
150K
RLIM2
R33
120K
TPS65251
SLVSAA4D –JUNE 2010–REVISED DECEMBER 2012 www.ti.com
TYPICAL APPLICATION CIRCUIT
A. VIN pins require local decoupling capacitors.
OVERVIEW
TPS65251 is a power management IC with three step-down buck converters. Both high-side and low-side
MOSFETs are integrated to provide fully synchronous conversion with higher efficiency. TPS65251 can support
4.5-V to 18-V input supply, high load current, 300-kHz to 2.2-MHz clocking. The buck converters have an
optional PSM mode, which can improve power dissipation during light loads. Alternatively, the device implements
a constant frequency mode by connecting the LOW_P pin to ground. The wide switching frequency of 300 kHz to
2.2 MHz allows for efficiency and size optimization. The switching frequency is adjustable by selecting a resistor
to ground on the ROSC pin. The SYNC pin also provides a means to synchronize the power converter to an
external signal. Input ripple is reduced by 180 degree out-of-phase operation between Buck 1 and Buck 2. Buck
3 operates in phase with Buck 2.
All three buck converters have peak current mode control which simplifies external frequency compensation. A
traditional type II compensation network can stabilize the system and achieve fast transient response. Moreover,
an optional capacitor in parallel with the upper resistor of the feedback divider provides one more zero and
makes the crossover frequency over 100 kHz.
Each buck converter has an individual current limit, which can be set up by a resistor to ground from the RLIM
pin. The adjustable current limiting enables high efficiency design with smaller and less expensive inductors.
The device has two built-in LDO regulators. During a standby mode, the 3.3-V LDO and the 6.5-V LDO can be
used to drive MCU and other active loads. By this, the system is able to turn off the three buck converters and
improve the standby efficiency.
The device has a power good comparator monitoring the output voltage. Each converter has its own soft start
and enable pins, which provide independent control and programmable soft start.
14 Submit Documentation Feedback Copyright © 2010–2012, Texas Instruments Incorporated
Product Folder Links: TPS65251