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P
SPKR
+ P
SUP
–P
SUP THEORETICAL
(at max output power)
(19)
P
SPKR
+
P
SUP
P
OUT
–
P
SUP THEORETICAL
P
OUT
(at max output power)
(20)
P
SPKR
+ P
OUT
ǒ
1
h
MEASURED
*
1
h
THEORETICAL
Ǔ
(at max output power)
(21)
hTHEORETICAL +
R
L
R
L
) 2r
DS(on)
(at max output power)
(22)
When to Use an Output Filter
1 nF
Ferrite
Chip Bead
OUTP
OUTN
Ferrite
Chip Bead
1 nF
1 µF
1 µF
33 µH
33 µH
OUTP
OUTN
TPA2010D1
SLOS417C – OCTOBER 2003 – REVISED SEPTEMBER 2007
The maximum efficiency of the TPA2010D1 with a 3.6 V supply and an 8- Ω load is 86% from Equation 22 . Using
equation Equation 21 with the efficiency at maximum power (84%), we see that there is an additional 17 mW
dissipated in the speaker. The added power dissipated in the speaker is not an issue as long as it is taken into
account when choosing the speaker.
Design the TPA2010D1 without an output filter if the traces from amplifier to speaker are short. The TPA2010D1
passed FCC and CE radiated emissions with no shielding with speaker trace wires 100 mm long or less.
Wireless handsets and PDAs are great applications for class-D without a filter.
A ferrite bead filter can often be used if the design is failing radiated emissions without an LC filter, and the
frequency sensitive circuit is greater than 1 MHz. This is good for circuits that just have to pass FCC and CE
because FCC and CE only test radiated emissions greater than 30 MHz. If choosing a ferrite bead, choose one
with high impedance at high frequencies, but very low impedance at low frequencies.
Use an LC output filter if there are low frequency (< 1 MHz) EMI sensitive circuits and/or there are long leads
from amplifier to speaker.
Figure 37 and Figure 38 show typical ferrite bead and LC output filters.
Figure 37. Typical Ferrite Chip Bead Filter (Chip bead example: NEC/Tokin: N2012ZPS121)
Figure 38. Typical LC Output Filter, Cutoff Frequency of 27 kHz
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Product Folder Link(s): TPA2010D1