TPA3003D2

SLOS406A − FEBRUARY 2003 − REVISED MARCH 2003

22

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APPLICATION INFORMATION

internal 2.5-V bias generator capacitor selection

The internal 2.5-V bias generator (V2P5) provides the internal bias for the preamplifier stage. The external input

capacitors and this internal reference allow the inputs to be biased within the optimal common-mode range of

the input preamplifiers.

The selection of the capacitor value on the V2P5 terminal is critical for achieving the best device performance.

During startup or recovery from the shutdown state, the V2P5 capacitor determines the rate at which the

amplifier starts up. When the voltage on the V2P5 capacitor equals 0.75 x V2P5, or 75% of its final value, the

device turns on and the class-D outputs start switching. The startup time is not critical for the best depop

performance since any pop sound that is heard is the result of the class-D outputs switching on and not the

startup time. However, at least a 0.47-

µF capacitor is recommended for the V2P5 capacitor.

A secondary function of the V2P5 capacitor is to filter high frequency noise on the internal 2.5-V bias generator.

input resistance

Each gain setting is achieved by varying the input resistance of the amplifier, which can range from its smallest

value to over six times that value. As a result, if a single capacitor is used in the input high-pass filter, the −3 dB

or cutoff frequency also changes by over six times.

Ci

IN

Zi

Zf

Input

Signal

The −3-dB frequency can be calculated using equation 5.

1

2

p Z

a high-pass filter with the corner frequency determined in equation 6.

1

2

pZ

i

C

i

−3 dB

fc

(6)

(5)