Philips Semiconductors

AN10327

TDA856x ,TDA8571J

2. Application Information

2.1 Input capacitors

The amplifiers need capacitors on the inputs to get a DC decoupling of the input source

(pre-amplifier stage). The impedance of the input stage together with the input

capacitors, create a low frequency roll-off point. A larger input capacitor means a lower

frequency roll-off point. The values that should be used are mentioned in the datasheet

of the amplifier type.

The following figure shows the influence of the input capacitors on the frequency roll-off

point for the TDA8566TH.

(A) Input capacitor 470nF

(B) Input capacitor 220nF

(C) Input capacitor 100nF

Fig 1. Roll-off frequency at different input capacitor values

The low frequency roll-off point can easily be calculated :

tot

in

in

dB

low

C

Z

f

_

3

_

2

1

⋅

⋅

⋅

=

−

π

<12NC>

© Koninklijke Philips Electronics N.V. 2004. All rights reserved.

Application note

Rev. 01.00 — 15 October 2004

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