Datasheet

TPA311
350-mW MONO AUDIO POWER AMPLIFIER
SLOS207C – JANUARY 1998 – REVISED MAY 2003
20
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
bridge-tied load versus single-ended mode (continued)
R
L
2x V
O(PP)
V
O(PP)
–V
O(PP)
V
DD
V
DD
Figure 48. Bridge-Tied Load Configuration
In typical portable handheld equipment, a sound channel operating at 3.3 V and using 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 terms of 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 49. 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), tend to be expensive, heavy, and occupy valuable PCB area. These
capacitors also 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.
f
c
+
1
2p R
L
C
C
(2)
For example, a 68-µF capacitor with an 8-Ω speaker would attenuate low frequencies below 293 Hz. The BTL
configuration cancels the dc offsets, which eliminates the need for the blocking capacitors. Low-frequency
performance is then limited only by the input network and speaker response. Cost and PCB space are also
minimized by eliminating the bulky coupling capacitor.