Datasheet
SLOS327C − AUGUST 2000 − REVISED MAY 2001
16
POST OFFICE BOX 655303 • DALLAS, TEXAS 75265
APPLICATION INFORMATION
output coupling capacitor, C
C
(continued)
Table 1. Common Load Impedances vs Low Frequency Output Characteristics in SE Mode
R
L
C
C
LOWEST FREQUENCY
3 Ω 330 µF 161 Hz
4 Ω 330 µF 120 Hz
8 Ω 330 µF 60 Hz
32 Ω 330 µF Ą15 Hz
10,000 Ω 330 µF 0.05 Hz
47,000 Ω 330 µF 0.01 Hz
As Table 1 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.
using low-ESR capacitors
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.
bridged-tied load versus single-ended mode
Figure 22 shows a linear audio power amplifier (APA) in a bridged-tied load (BTL) configuration. The TPA0172
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).
Power +
V
(rms)
2
R
L
(5)
V
(rms)
+
V
O(PP)
22
Ǹ