TPA032D04 Class-D EVM Power Supply Decoupling Data
3-24
Details
3.7
TPA032D04 Class-D EVM Power Supply Decoupling Data
The decoupling capacitance required will depend upon the application. Pads
and through-holes have been provided on the EVM for the addition of bulk
capacitance (see the schematic). A plot showing the impact of various levels
of bulk capacitance on the voltage ripple on the power supply line is shown in
Figure 3–18. This ripple is maximum at higher frequency. The figure shows
worst-case voltage ripple for a 20-kHz, 10-W output into a 4-
Ω
load. In all
cases, two 10-
µ
F and one 1-
µ
F ceramic chip capacitors were decoupling the
power supply signal from the EVM. The 1-
µ
F unit was placed immediately
adjacent to the IC power pins, and the 10-
µ
F units were placed adjacent to
each other a little farther out.
The upper trace shows the ripple when only these capacitors are used. The
middle trace shows the impact of an additional 330-
µ
F aluminum electrolytic
capacitor rated at 25 V, 90 m
Ω
, and for 755 mA at 100 kHz. In the bottom trace,
the 330-
µ
F capacitor was replaced by a 390-
µ
F aluminum electrolytic
capacitor rated at 35 V, 65 m
Ω
, and for 1.2 A of 100 kHz ripple current.
The results indicate that for sensitive circuits where minimum voltage ripple is
required, a larger bulk capacitance with low ESR should be used. For systems
that are contained and EMI is controlled, less capacitance may be used. The
difference in the level of distortion in the output signal was very small between
each level of decoupling, with the 20-
µ
F bulk capacitance providing the least
distortion. This is attributed to the low ESR of the capacitor, which is only a few
millohms at the switching frequency of 250 kHz. The distortion is made lower
still by the parallel combination. Distortion of the output signal when only one
10-
µ
F capacitor is used is the same as for 20
µ
F. The difference is more
noticeable on the power supply line, though the distortion is increased only
slightly more than with the 20-
µ
F capacitor.
Figure 3–18. Power Supply Decoupling
V Ripple V
oltage
(2
V
per
division)
RIPPLE VOLTAGE
Time (10
µ
sec per division)
cc
Summary of Contents for TPA032D02
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