LM48411

SNAS399G – SEPTEMBER 2007 – REVISED MAY 2013

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AUDIO AMPLIFIER INPUT CAPACITOR SELECTION

Input capacitors may be required for some applications, or when the audio source is single-ended. Input

capacitors block the DC component of the audio signal, eliminating any conflict between the DC component of

the audio source and the bias voltage of the LM48411. The input capacitors create a high-pass filter with the

input resistance Ri. The -3dB point of the high pass filter is found using Equation 2 below.

f = 1 / 2

πRiCi

(2)

The values for Ri can be found in the EC table for each gain setting.

The input capacitors can also be used to remove low frequency content from the audio signal. Small speakers

cannot reproduce, and may even be damaged by low frequencies. High pass filtering the audio signal helps

protect the speakers. When the LM48411 is using a single-ended source, power supply noise on the ground is

seen as an input signal. Setting the high-pass filter point above the power supply noise frequencies, 217 Hz in a

GSM phone, for example, filters out the noise such that it is not amplified and heard on the output. Capacitors

with a tolerance of 10% or better are recommended for impedance matching and improved CMRR and PSRR.

AUDIO AMPLIFIER GAIN SETTING

The LM48411 features four internally configured gain settings. The device gain is selected through the two logic

inputs, G0 and G1. The gain settings are as shown in the following table.

LOGIC INPUT

GAIN

G1

G0

V/V

dB

0

0

2

6

0

1

4

12

1

0

8

18

1

1

16

24

Build of Materials

Designator

Description

Footprint

Quantity

C1, C2

Ceramic Capacitor 0.1

μF, 50V, 10%

805

2

C3 – C6

Tantalum Capacitors 1

μF 20V, 10%, Size A

1206

4

C11

Tantalum Capacitors 10

μF 20V, 10% Size B

1411

1

JP1–5, JP8–11

Jumper Header Vertical Mount 2X1 0.100

9

JP6, JP7

Jumper Header Vertical Mount 3x1 0.100

2

14

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