Datasheet

V =
OUT
0.765 •
(1+
R1
R2
−
)
V = V
OUT OUT_SET
(0.763 + 0.0017 ) 1 +· · (
R1
R2
¾
)
1
2
P
OUT OUT
F
L Cp
=
´
TPS54425
SLVSA84C –AUGUST 2010– REVISED JULY 2011 www.ti.com
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
• Output voltage ripple
• Input voltage ripple
Figure 13. Shows the schematic diagram for this design example.
Output Voltage Resistors Selection
The output voltage is set with a resistor divider from the output node to the VFB pin. It is recommended to use
1% tolerance or better divider resistors. Start by using Equation 2 and Equation 3 to calculate V
OUT
.
To improve efficiency at very light loads consider using larger value resistors, too high of resistance will be more
susceptible to noise and voltage errors from the VFB input current will be more noticeable.
For output voltage from 0.76 V to 2.5 V:
(2)
For output voltage over 2.5 V:
(3)
Where:
V
OUT_SET
= Target V
OUT
voltage.
Output Filter Selection
The output filter used with the TPS54425 is an LC circuit. This LC filter has double pole at:
(4)
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