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APPLICATION INFORMATION

Headphone Amplifiers

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TPA4411

TPA4411M

SLOS430E – AUGUST 2004 – REVISED MARCH 2008

Single-supply headphone amplifiers typically require dc-blocking capacitors. The capacitors are required because

most headphone amplifiers have a dc bias on the outputs pin. If the dc bias is not removed, the output signal is

severely clipped, and large amounts of dc current rush through the headphones, potentially damaging them. The

top drawing in Figure 64 illustrates the conventional headphone amplifier connection to the headphone jack and

output signal.

DC blocking capacitors are often large in value. The headphone speakers (typical resistive values of 16

Ω or 32

Ω) combine with the dc blocking capacitors to form a high-pass filter. Equation 1 shows the relationship between

values require large package sizes. Large package sizes consume PCB area, stand high above the PCB,

increase cost of assembly, and can reduce the fidelity of the audio output signal.

Two different headphone amplifier applications are available that allow for the removal of the output dc blocking

capacitors. The Capless amplifier architecture is implemented in the same manner as the conventional amplifier

with the exception of the headphone jack shield pin. This amplifier provides a reference voltage, which is

connected to the headphone jack shield pin. This is the voltage on which the audio output signals are centered.

This voltage reference is half of the amplifier power supply to allow symmetrical swing of the output voltages. Do

not connect the shield to any GND reference or large currents will result. The scenario can happen if, for

example, an accessory other than a floating GND headphone is plugged into the headphone connector. See the

second block diagram and waveform in Figure 64.

Copyright © 2004–2008, Texas Instruments Incorporated

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