PAM8124

Document number: DS36627 Rev. 1 - 2

7 of 15

www.diodes.com

October 2013

© Diodes Incorporated

PAM8124

A Product Line of

Diodes Incorporated

Application Information

Input Capacitors (Ci)

In the typical application, an input capacitor Ci, is required to allow the amplifier to bias the input signal to the proper DC level for optimum

operation. In this case, Ci and the minimum input impedance Ri form is a high-pass filter with the corner frequency determined in the follow

equation:

()

C

1

f

2RiCi

π

=

It is important to consider the value of Ci as it directly affects the low frequency performance of the circuit. For example, when Ri is 40kΩ and the

specification calls for a flat bass response are down to 20Hz. Equation is reconfigured as followed:

()

ic

1

Ci

2R f

π

=

When input resistance variation is considered Ci is 200nF, so one would likely choose a value of 220nF. A further consideration for this capacitor

is the leakage path from the input source through the input network (Ci, Ri + Rf) to the load. This leakage current creates a DC offset voltage at

the input to the amplifier that reduces useful headroom, especially in high gain applications. For this reason, a low-leakage tantalum or ceramic

capacitor is the best choice.

Gain Setting Control

The gain of the PAM8124 is set by two input terminals, GAIN0 and GAIN1.

The gains listed in following table are realized by changing the taps on the input resistors inside the amplifier. This causes the input impedance to

be dependent on the gain setting. The actual gain settings are controlled by ratios of resistors, so the gain variation from part-to-part is small.

However, the input impedance from part-to-part at the same gain may shift by ±20% due to shifts in the actual resistance of the input resistors.

Table 1: Gain Setting

Gain1

Gain0

Amplifier Gain (dB),

Typical

Input Impedance (kΩ),

Typical (Ri)

0

0

20

40

0

1

26

20

1

0

30

10

1

1

36

6.67

Two Channels Driving

Two Channels Driving