TPA0152

2-W STEREO AUDIO POWER AMPLIFIER

WITH DIGITAL VOLUME CONTROL

SLOS246B – JUNE 1999 – REVISED MARCH 2000

21

POST OFFICE BOX 655303

APPLICATION INFORMATION

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 section.

single-ended operation

In SE mode (see Figure 32 and Figure 33), the load is driven from the primary amplifier output for each channel

(OUT+, terminals 21 and 4).

The amplifier switches single-ended operation when the SE/BTL terminal is held high. This puts the negative

outputs in a high-impedance state, and reduces the amplifier’s gain to 1 V/V.

BTL amplifier efficiency

Class-AB 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

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 34).

V(LRMS)

VO

IDD

IDD(avg)

Figure 34. Voltage and Current Waveforms for BTL Amplifiers

Although the voltages and currents for SE and BTL are sinusoidal in the load, currents from the supply are very

different between SE and BTL configurations. In an SE application the current waveform is a half-wave rectified

shape whereas in BTL it is a full-wave rectified waveform. This means RMS conversion factors are different.

Keep in mind that for most of the waveform both the push and pull transistors are not on at the same time, which

supports the fact that each amplifier in the BTL device only draws current from the supply for half the waveform.

The following equations are the basis for calculating amplifier efficiency.

Efficiency of a BTL amplifier

+

P

L

P

SUP

(7)

Where:

P

V

L

R

L

, and V

V

P

2

, therefore, P

V

P

2

2R

L

and

P

SUP +

V

DD

I

DD

avg and IDDavg +

1

p

p

0

V

P

R

L

sin(t) dt

+ 1p

V

P

R

L

p

2V

P

p R

L