Datasheet

P
OUT OUT
1
F =
2 L C´p
Ox
R1x
V = 0.765 V 1+
R2x
æ ö
´
ç ÷
è ø
VINx
12V ± 10%
PGND
1uF
PGND
C
4
SW1
VIN1
VBST1
EN1
VFB2
VFB1
GND
VREG5
PGND1
6
VIN2
VBST2
EN2
SW2
PG1
5
1
3
PG2
9
10
11
PGND2
2
4
7
13
12
TPS54294
HTSSOP16
14
8
15
16
PGND
SGND
SGND
C11
10 Fm
VO1
1.05 V
C21
22 F
x2
m
R11
8.25 kW
R21
22.1 kW
L11
1.5 Hm
C31
0.1 Fm
C32
0.1 Fm
L12
1.5 Hm
C12
10 Fm
VO2
1.8 V
C22
22 F
x2
m
R12
30.1 kW
R22
22.1 kW
TPS54294
www.ti.com SLVSB00D –OCTOBER 2011–REVISED SEPTEMBER 2013
DESIGN GUIDE
Step By Step Design Procedure
To begin the design process, you must know a few application parameters:
• Input voltage range
• Output voltage
• Output current
In all formulas x is used to indicate that they are valid for both converters. For the calculations the estimated
switching frequency of 700 kHz is used.
Figure 24. Schematic Diagram for the Design Example
Output Voltage Resistors Selection
The output voltage is set with a resistor divider from the output node to the VFBx pin. It is recommended to use
1% tolerance or better divider resistors. Start by using Equation 2 to calculate V
Ox
.
To improve the efficiency at very light loads consider using larger value resistors, but too high resistance values
will be more susceptible to noise and voltage errors due to the VFBx input current will be more noticeable.
(2)
Output Filter Selection
The output filter used with the TPS54294 is an LC circuit. This LC filter has double pole at:
(3)
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