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USING LOW-ESR CAPACITORS
BRIDGED-TIED LOAD vs SINGLE-ENDED LOAD
Power
V
(rms)
2
R
L
V
(rms)
V
O(PP)
2 2
(5)
R
L
2x V
O(PP)
V
O(PP)
-V
O(PP)
V
DD
V
DD
TPA6011A4
SLOS392A – FEBRUARY 2002 – REVISED JULY 2004
As Table 4 indicates, most of the bass response is attenuated into a 4-
Ω
load, an 8-
Ω
load is adequate,
headphone response is good, and drive into line level inputs (a home stereo for example) is exceptional.
Low-ESR capacitors are recommended throughout this applications section. A real (as opposed to ideal)
capacitor can be modeled simply as a resistor in series with an ideal capacitor. The voltage drop across this
resistor minimizes the beneficial effects of the capacitor in the circuit. The lower the equivalent value of this
resistance, the more the real capacitor behaves like an ideal capacitor.
Figure 36 shows a Class-AB audio power amplifier (APA) in a BTL configuration. The TPA6011A4 BTL amplifier
consists of two Class-AB 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 5).
Figure 36. Bridge-Tied Load Configuration
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