TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C – JANUARY1998 – REVISED MARCH 2000
APPLICATION INFORMATION
bridge-tied load
Figure23showsalinearaudiopoweramplifier(APA)inaBTLconfiguration. TheTPA301BTLamplifierconsists
of two linear amplifiers driving both ends of the load. There are several potential benefits to this differential drive
configuration but power to the load should be initially considered. 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
swingontheloadascomparedtoagroundreferencedload. Plugging2× V
voltage is squared, yields 4× the output power from the same supply rail and load impedance (see equation 1).
intothepowerequation, where
O(PP)
V
O(PP)
V
(rms)
2 2
2
V
(rms)
(1)
Power
R
L
V
DD
V
O(PP)
2x V
O(PP)
R
L
V
DD
–V
O(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 single-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.
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