Datasheet

LM48820

www.ti.com

SNAS370B –MAY 2007–REVISED MAY 2013

Input Capacitor Value Selection

Amplifying the lowest audio frequencies requires high value input coupling capacitors (C

INL

and C

INR

in Figure 1).

A high value capacitor can be expensive and may compromise space efficiency in portable designs. In many

cases, however, the speakers used in portable systems, whether internal or external, have little ability to

reproduce signals below 150Hz. Applications using speakers with this limited frequency response reap little

improvement by using high value input and output capacitors.

Besides affecting system cost and size, the input coupling capacitor has an effect on the LM48820's click and

pop performance. The magnitude of the pop is directly proportional to the input capacitor's size. Thus, pops can

be minimized by selecting an input capacitor value that is no higher than necessary to meet the desired −3dB

frequency.

As shown in Figure 1, the internal input resistor, R

and the input capacitor, C

INL

and C

INR

, produce a -3dB high

pass filter cutoff frequency that is found using Equation 4.

–3dB

= 1 / 2πR

(Hz) (4)

Also, careful consideration must be taken in selecting a certain type of capacitor to be used in the system.

Different types of capacitors (tantalum, electrolytic, ceramic) have unique performance characteristics and may

affect overall system performance.

REVISION HISTORY

Rev Date Description

1.0 05/09/07 Initial release.

1.1 05/15/07 Added the BOM table.

1.2 06/25/07 Deleted and replaced some curves. Input text edits also.

B 05/02/2013 Changed layout of National Data Sheet to TI format

Product Folder Links: LM48820