Datasheet

+V
IN
DCH01xxxxDN7
-V
IN
+V
OUT
COM
2.2 mF
Ceramic
1 mH to 5 mH
4.7 mF
Ceramic
+V
IN
-V
IN
4.7 mF
1 mH to 5 mH
1 mF
-V
OUT
4.7 mF1 mF
1 mH to 5 mH
+V
OUT
-V
OUT
UDG-08076
π FILTERS
DCH01 START-UP
I
IN
100mA/div
V
O
5V/div
V
IN
5V/div
DCH01 Series
SBVS073H – NOVEMBER 2006 – REVISED JANUARY 2009 ........................................................................................................................................... www.ti.com
Figure 21. DCH01 Series π Filter (5 V at 1 W)
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 inductor in series with the input or output terminals of the regulator reduces the
ripple/noise by at least 20 db (see Figure 20 and Figure 21 ). Ceramic capacitors are required for the inductor to
be effective in reduction of ripple and noise.
These inductors plus ceramic capacitors form an excellent filter because of the rejection at the switching
frequency. The placement of this filter is critical. It must be located as close as possible to the input or output
pins to be efffective. The ferrite bead is small (12,5 mm x 3 mm), easy to use, low cost, and has low dc
resistance. Fair-Rite manufactures a surface-mount bead (part number 2773021447) or through hole (part
number 2673000701) rated to 5 A. Inductors with a value between 1 µ H and 5 µ H can be used in place of the
ferrite bead inductor.
Start-up waveforms.
Figure 22. Startup Waveforms
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