Datasheet

TPA0211
2-W MONO AUDIO POWER AMPLIFIER
SLOS275D – JANUARY 2000 – REVISED NOVEMBER 2002
15
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
bridged-tied load versus single-ended mode (continued)
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.
R
L
C
(C)
V
O(PP)
V
O(PP)
V
DD
–3 dB
f
c
Figure 23. 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 the SE
configuration. Internal dissipation versus output power is discussed further in the crest factor and thermal
considerations section.
single-ended operation
In SE mode (see Figure 22 and Figure 23), the load is driven from one amplifier output (V
O+
, terminal 5).
The amplifier switches to single-ended operation when the SE/BTL
terminal is held high.
BTL amplifier efficiency
Class-AB amplifiers are inefficient. The primary cause of inefficiencies is the 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
DD
rms, determines the internal 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 and average values of power in the
load and in the amplifier, the current and voltage waveform shapes must first be understood. See Figure 24.
V
(LRMS)
V
O
I
DD
I
DD(avg)
Figure 24. Voltage and Current Waveforms for BTL Amplifiers