Datasheet

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SLVS324A − JULY 2001 REVISED NOVEMBER 2004
14
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APPLICATION INFORMATION
RC-post filter
TPS60400
OUT C1+
IN
C1− GND
1
2
3
5
4
C
(fly)
1 µF
C
O
1 µF
C
P
C
I
1 µF
V
O
(−V
I
)
GND
V
I
GND
R
P
Figure 24. TPS60400 and TPS60401 With RC-Post Filter
An output filter can easily be formed with a resistor (R
P
) and a capacitor (C
P
). Cutoff frequency is given by:
ƒ
c
+
1
2pR
P
C
P
(1)
and ratio V
O
/V
OUT
is:
Ť
V
O
V
OUT
Ť
+
1
1 )
ǒ
2pƒR
P
C
P
Ǔ
2
Ǹ
(2)
with R
P
= 50 Ω, C
P
= 0.1 µF and f = 250 kHz:
Ť
V
O
V
OUT
Ť
+ 0.125
The formula refers only to the relation between output and input of the ac ripple voltages of the filter.
LC-post filter
TPS60400
OUT C1+
IN
C1− GND
1
2
3
5
4
C
(fly)
1 µF
C
O
1 µF
C
P
C
I
1 µF
V
O
(−V
I
)
GND
V
I
GND
L
P
V
OUT
Figure 25. LC-Post Filter
Figure 25 shows a configuration with a LC-post filter to further reduce output ripple and noise.