TPA301
350-mW MONO AUDIO POWER AMPLIFIER
SLOS208C – JANUARY1998 – REVISED MARCH 2000
APPLICATION INFORMATION
bridge-tied load versus single-ended mode (continued)
1
(2)
f
(corner)
2 R C
L
C
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, eliminating 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.
V
DD
–3 dB
V
O(PP)
C
C
V
O(PP)
R
L
f
c
Figure 24. Single-Ended Configuration and Frequency Response
Increasing power to the load does carry a penalty of increased internal power dissipation. The increased
dissipation is understandable considering that the BTL configuration produces 4× the output power of a SE
configuration. Internal dissipation versus output power is discussed further in the thermal considerations
section.
BTL amplifier efficiency
Linear amplifiers are notoriously inefficient. The primary cause of these inefficiencies is voltage drop across the
output stage transistors. There are two components of the internal voltage drop. One is the headroom or dc
voltage drop that varies inversely to output power. The second component is due to the sinewave nature of the
output. The total voltage drop can be calculated by subtracting the RMS value of the output voltage from V
.
DD
The internal voltage drop multiplied by the RMS value of the supply current, I rms, determines the internal
DD
power dissipation of the amplifier.
An easy-to-use equation to calculate efficiency starts out as being equal to the ratio of power from the power
supply to the power delivered to the load. To accurately calculate the RMS values of power in the load and in
the amplifier, the current and voltage waveform shapes must first be understood (see Figure 25).
I
V
O
DD
I
DD(RMS)
V
(LRMS)
Figure 25. Voltage and Current Waveforms for BTL Amplifiers
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