TPA0142

2-W STEREO AUDIO POWER AMPLIFIER

WITH DC VOLUME CONTROL

SLOS248B – JUNE 1999 – REVISED MARCH 2000

21

POST OFFICE BOX 655303

APPLICATION INFORMATION

bridged-tied load versus single-ended mode

Figure 33 shows a Class-AB audio power amplifier (APA) in a BTL configuration. The TPA0142 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

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

V

O(PP)

22

RL

2x VO(PP)

VO(PP)

–VO(PP)

VDD

VDD

Figure 33. Bridge-Tied Load Configuration

In a typical computer sound channel operating at 5 V, bridging raises the power into an 8-

Ω speaker from a

singled-ended (SE, ground reference) limit of 250 mW to 1 W. In 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 34. 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)

so they tend to be expensive, heavy, occupy valuable PCB area, and 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 6.

f

1

2

pR

(6)