Datasheet

t-Time=5ms/div
V
O
(2V/div)
I
I
(1 A/div)
Q1V
GS
(10V/div)
Optional Input/Output Filters
Input/Output Capacitors
PTN78060W , PTN78060H
www.ti.com ................................................................................................................................................... SLTS229B – NOVEMBER 2004 – REVISED JUNE 2009
Figure 31. Power-Up Response From Inhibit Control
Power modules include internal input and output ceramic capacitors in all of their designs. However, some
applications require much lower levels of either input reflected or output ripple/noise. This application describes
various filters and design techniques found to be successful in reducing both input and output ripple/noise.
The easiest way to reduce output ripple and noise is to add one or more 1- µ F ceramic capacitors, such as C4
shown in Figure 32 . Ceramic capacitors should be placed close to the output power terminals. A single 2.2- µ F
capacitor reduces the output ripple/noise by 10% to 30% for modules with a rated output current of less than 3 A.
(Note: C3 is recommended to improve the regulators transient response, and does not reduce output ripple and
noise.)
Switching regulators draw current from the input line in pulses at their operating frequency. The amount of
reflected (input) ripple/noise generated is directly proportional to the equivalent source impedance of the power
source including the impedance of any input lines. The addition of C1, minimum 2.2- µ F ceramic capacitor, near
the input power pins, reduces reflected conducted ripple/noise by up to 20%.
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