TPA0213

2-W MONO AUDIO POWER AMPLIFIER

WITH HEADPHONE DRIVE

SLOS276D – JANUARY 2000 – REVISED NOVEMBER 2002

13

POST OFFICE BOX 655303

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.

RL

C(C)

VO(PP)

VO(PP)

VDD

–3 dB

fc

Figure 15. 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 14 and Figure 15), the load is driven from the primary amplifier output for each channel

(LO and RO, terminals 6 and 10)

The amplifier switches to single-ended operation when the ST/MN terminal is held high.

input MUX operation

The input MUX allows two separate inputs to be applied to the amplifier. When the ST/MN terminal is held high,

the headphone inputs (LIN and RIN) are active. When the ST/MN terminal is held low, the line BTL input

(MONO-IN) is active.

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.

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 16.