TPA731 Datasheet, PDF (12/22 Pages) Texas Instruments – 700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER WITH DIFFERENTIAL INPUTS

TPA731
700-mW MONO LOW-VOLTAGE AUDIO POWER AMPLIFIER
WITH DIFFERENTIAL INPUTS
SLOS315B – JUNE 2000 – REVISED OCTOBER 2002
APPLICATION INFORMATION
bridged-tied load
Figure 23 shows a linear audio power amplifier (APA) in a BTL configuration. The TPA731 BTL amplifier consists
of two linear amplifiers driving both ends of the load. There are several potential benefits to this differential drive
configuration but initially consider power to the load. The differential drive to the speaker means that as one side
is slewing up, the other side is slewing down, and vice versa. This, in effect, doubles the voltage swing on the
load as compared to a ground referenced load. Plugging 2 × V_O(PP) into the power equation, where voltage is
squared, yields 4× the output power from the same supply rail and load impedance (see equation 1).
V(rms)
+
VO(PP)
2 ^Ǹ2
V_(rms)2
(1)
Power + _RL
VDD
RL
VDD
VO(PP)
2x VO(PP)
–VO(PP)
Figure 23. Bridge-Tied Load Configuration
In a typical portable handheld equipment sound channel operating at 3.3 V, bridging raises the power into an
8-Ω speaker from a singled-ended (SE, ground reference) limit of 62.5 mW to 250 mW. In sound power that is
a 6-dB improvement, which is loudness that can be heard. In addition to increased power, there are frequency
response concerns. Consider the single-supply SE configuration shown in Figure 24. A coupling capacitor is
required to block the dc offset voltage from reaching the load. These capacitors can be quite large
(approximately 33 µF to 1000 µF) so they tend to be expensive, heavy, occupy valuable PCB area, and have
the additional drawback of limiting low-frequency performance of the system. This frequency-limiting effect is
due to the high pass filter network created with the speaker impedance and the coupling capacitance and is
calculated with equation 2.
fc
+
1
2pRLCC
(2)
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