Datasheet

Z
L
− Load Impedance − Ω
5
7
9
11
13
15
17
19
21
P
O
− Maximum Output Power − W
T
A
= 25°C,
10% THD Maximum
V
CC
= 18 V
V
CC
= 15 V
V
CC
= 12 V
3.6 4 5 6 7 8 9 10
O(avg),max L
in(pp),max
V
8P Z
V
A
´
=
V
G(dB)
A voltage gain (V/V)
20
æ ö
= =
ç ÷
è ø
P
O(10% THD)
+ P
O(1% THD)
1.25
TPA3001D1
www.ti.com SLOS398E –DECEMBER 2002–REVISED AUGUST 2010
Figure 33. Output Power
DRIVING A LOW-IMPEDANCE LOAD FROM A HIGH POWER-SUPPLY VOLTAGE
When driving low-impedance loads (e.g., a 4-Ω speaker), the output power can be limited by reducing the
maximum audio input signal level or by reducing the gain of the TPA3001D1. The maximum input voltage may
be calculated with Equation 1.
(1)
where
P
O(avg),max
= maximum continuous output power (W)
Z
L
= load impedance (Ω)
For example, consider an application in which the TPA3001D1 drives a 4-Ω speaker from an 18-V power supply.
The gain is selected to be 18 dB. The maximum allowable output power for a 4-Ω load impedance is 12.8 W.
From Equation 1, the input voltage must not exceed 2.54 V
pp
.
In this same example, however, if the maximum output voltage of audio signal source is 5 V
pp
, then the gain of
the TPA3001D1 should be reduced to 12 dB to eliminate the need for limiting the input signal.
The input voltage may be limited using a variety of methods, depending on what is known about the audio signal
source. If the maximum output voltage of the source is known, a resistive voltage divider in conjunction with
proper TPA3001D1 gain selection may be used to prevent distortion. If the maximum audio source voltage is
unknown, diodes may be used to clamp the input voltage, at the cost of distortion when the input signal level
exceeds the required clamping voltage.
DRIVING THE OUTPUT INTO CLIPPING
The output of the TPA3001D1 may be driven into clipping to attain a higher output power than is possible with no
distortion. Clipping is typically quantified by a THD measurement of 10%. The amount of additional power into
the load may be calculated with Equation 2.
(2)
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