PAM8124

Document number: DS36627 Rev. 1 - 2

8 of 15

www.diodes.com

October 2013

© Diodes Incorporated

PAM8124

A Product Line of

Diodes Incorporated

Input Resistance

Changing the gain setting can vary the input resistance of the amplifier from its smallest value (6.67kΩ ±20%) to the largest value (40kΩ ±20%).

As a result, if a single capacitor is used in the input high-pass filter, the –3dB cutoff frequency may change when changing gain steps.

The –3dB frequency can be calculated using the following Equation. Use the Ri values given in Table 1.

()

C

1

f

2RiCi

π

=

Single-Ended Output Capacitor

In single-ended (SE) applications, the dc blocking capacitor forms a high-pass filter with the speaker impedance. The frequency response rolls off

with decreasing frequency at a rate of 20dB/decade. The cutoff frequency is determined by:

SE

L

coh

C

R

f

π

2

1

=

Table 2 shows some common component values and the associated cutoff frequencies:

Table 2: Common Filter Responses

CSE-DC Blocking Capacitor (µF)

fc = 60Hz (-3dB)

fc = 40Hz (-3dB)

fc = 20Hz (-3dB)

4

680

1000

2200

6

470

680

1500

8

330

470

1000

Output Filter and Frequency Response

For the best frequency response, a flat pass band output filter (second-order Butterworth) may be used. The output filter components consist of

the series inductor and capacitor to ground at the LOUT and ROUT pins. There are several possible configurations, depending on the speaker

impedance and whether the output configuration is single-ended (SE) or bridge-tied load (BTL). Table 3 lists the recommended values for the filter

components. It is important to use a high-quality capacitor in this application. A rating of at least X7R is required.

Table 3: Recommended Filter Output Components

Output Configuration

Speaker Impedance(Ω)

Filter Inductor(µH)

Filter Capacitor(nF)

Single Ended (SE)

4

22

680

8

33

220

Bridge Tied Load (BTL)

8

22

680