Datasheet

O(PP)

-3 dB

(LRMS)

DD(avg)

TPA6211A1

SLOS367D –AUGUST 2003– REVISED JUNE 2011

www.ti.com

For example, a 68-μF capacitor with an 8-Ω speaker subtracting the RMS value of the output voltage from

would attenuate low frequencies below 293 Hz. The V

. The internal voltage drop multiplied by the

BTL configuration cancels the dc offsets, which average value of the supply current, I

(avg),

eliminates the need for the blocking capacitors. determines the internal power dissipation of the

Low-frequency performance is then limited only by amplifier.

the input network and speaker response. Cost and

An easy-to-use equation to calculate efficiency starts

PCB space are also minimized by eliminating the

out as being equal to the ratio of power from the

bulky coupling capacitor.

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 35).

Figure 34. Single-Ended Output and Frequency Figure 35. Voltage and Current Waveforms for

Response BTL Amplifiers

Increasing power to the load does carry a penalty of Although the voltages and currents for SE and BTL

increased internal power dissipation. The increased are sinusoidal in the load, currents from the supply

dissipation is understandable considering that the are different between SE and BTL configurations. In

BTL configuration produces 4× the output power of an SE application the current waveform is a

the SE configuration. 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

FULLY DIFFERENTIAL AMPLIFIER

most of the waveform both the push and pull

EFFICIENCY AND THERMAL INFORMATION

transistors are not on at the same time, which

Class-AB amplifiers are inefficient, primarily because

supports the fact that each amplifier in the BTL

of voltage drop across the output-stage transistors.

device only draws current from the supply for half the

The two components of this internal voltage drop are

waveform. The following equations are the basis for

the headroom or dc voltage drop that varies inversely

calculating amplifier efficiency.

to output power, and the sinewave nature of the

output. The total voltage drop can be calculated by