Datasheet
LDO OUT
VIN
DC-DC OUT_
AGND
PGND
CFF
R4
R5
RRT
R3
C1
CSS
C2
L1
CIN
C_DC-DC_OUT
R1
R2
C11
CBOOT
C_LDO_IN
CNR
1
OUT
2
OUT
3
FB
4
GND
5
NC
6
RT/CLK
7
PGND
8
PGND
9
PVIN
10
PVIN
11
VIN
12
VSENSE
13
COMP
14
SS
15
EN
16
PH
17
PH
18
BOOT
19
PWRGD
20
NC
21
LDOEN
22
NR
23
LDOIN
24
LDOIN
25
PWPD
U
TPS54120
COUT
SENSE
SENSE
TPS54120
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SBVS180C –JANUARY 2012–REVISED JUNE 2012
APPLICATION INFORMATION
DESIGN METHODOLOGY
The TPS54120 has a low-noise output voltage range from 0.8 V to 6.0 V with an output current of up to 1 A. To
simplify design efforts using the TPS54120, typical designs for common applications are listed in Table 1
according to the typical schematic diagram shown in Figure 34. For more details about designing with the
TPS54120, refer to Application Report SLVA506, Design Procedure for the TPS54120, and SLVC411, the
TPS54120 Design Tool Calculator.
The TPS54120 can also be configured to provide two separate power rails: one from the switching regulator and
one from the LDO. For more information on how to create a dual-rail power supply from the TPS54120, refer to
Application Report SLVA502, Design Guidelines for TPS54120 as a 3-A Switcher and 1-A Switcher Plus LDO.
Figure 34. Application Circuit
Figure 34 shows a typical application diagram for the TPS54120. The first step in the design process is to select
the switching frequency for the regulator. Higher switching frequencies may produce a smaller solution size using
lower-valued inductors and smaller output capacitors compared to a power supply that switches at a lower
frequency. However, higher switching frequencies causes additional switching losses that negatively impact
converter efficiency and thermal performance.
After a switching frequency is determined, the inductor and output capacitor values of the switcher are selected.
These two component values are related to each other and they depend on the input and output voltages of the
switcher, as well as the current rating. Choosing a high inductor-ripple current also impacts the selection of the
output capacitor because the output capacitor must have a ripple current rating equal to or greater than the
inductor ripple current.
The TPS54120 requires a high-quality ceramic, type X5R or X7R, input decoupling capacitor of 4.7 μF on each
input voltage rail. In some applications, additional bulk capacitance may also be required for the PVIN input. The
voltage rating of the input capacitor must be greater than the maximum input voltage.
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