Datasheet

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
TPA2005D1
www.ti.com ............................................................................................................................................................... SLOS369F – JULY 2002 – REVISED JULY 2008
The maximum efficiency of the TPA2005D1 with a 3.6 V supply and an 8- Ω load is 86% from equation
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 TPA2005D1 without an output filter if the traces from amplifier to speaker are short. The TPA2005D1
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 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 41 and Figure 42 show typical ferrite bead and LC output filters.
Figure 41. Typical Ferrite Chip Bead Filter (Chip bead example: NEC/Tokin: N2012ZPS121)
Figure 42. Typical LC Output Filter, Cutoff Frequency of 27 kHz
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Product Folder Link(s): TPA2005D1