Datasheet
10
15
20
25
30
35
40
45
0 0.5 1 1.5 2 2.5 3
1 MHz
600 kHz
Attenuation − dB
Load Current − A
GND
GND
1 3
42
GND Adj
C5
†
V
I
V
O
PTN04050C
V
I
V
O
R
SET
L1
1-5 Hm
L2
1-5 Hm
C1
22 F
Ceramic
m
C4
22 F
Ceramic
m
C2
10
*
0 F
(Required)
m
C3*
100 F
(Required)
m
* Seethe sectionforsuggestedvalueandtype.ApplicationInformation
† Recommendedforapplicationswithloadtransients.
PTN04050C
www.ti.com
SLTS251A –SEPTEMBER 2005–REVISED FEBRUARY 2011
π Filters
If a further reduction in ripple/noise level is required for an application, higher order filters must be used. A π (pi)
filter, employing a ferrite bead (Fair-Rite Part Number 2673000701 or equivalent) in series with the input or
output terminals of the regulator reduces the ripple/noise by at least 20 db (see Figure 18 and Figure 19). In
order for the inductor to be effective in reduction of ripple and noise, ceramic capacitors are required. (Note: for
additional information on vendors and component suggestions, see the capacitor recommendations for the
PTN04050C.)
These inductors plus ceramic capacitors form an excellent filter because of the rejection at the switching
frequency (650 kHz - 1 MHz). The placement of this filter is critical. It must be located as close as possible to the
input or output pins to be effective. The ferrite bead is small (12,5 mm X 3 mm) and has low dc resistance. Fair-
Rite also manufactures a surface-mount bead (Part No. 2773021447), through hole (Part Number 2673000701)
rated to 5 A. Inductors in the range of 1 μH to 5 μH can be used in place of the ferrite inductor bead.
Figure 18. Adding π Filters
Figure 19. π-Filter Attenuation vs. Load Current
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