Diodes PAM8015 - Manual (Page 6)

PAM8013/PAM8015
Document number: DS36979 Rev. 2 - 2
6 of 9
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May 2014
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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:
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 150kΩ and the
specification calls for a flat bass response are down to 150Hz. Equation is reconfigured as followed:
When input resistance variation is considered, the Ci is 7nF, so one would likely choose a value of 10nF. 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. When polarized capacitors are used, the positive side of the capacitor should face the amplifier input in most
applications as the DC level is held at VDD/2, which is likely higher than the source DC level. Please note that it is important to confirm the
capacitor polarity in the application.
Decoupling Capacitor (CS )
The PAM8013/PAM8015 is a high-performance CMOS audio amplifier that requires adequate power supply decoupling to ensure the output total
harmonic distortion (THD) as low as possible. Power supply decoupling also prevents the oscillations causing by long lead length between the
amplifier and the speaker.
The optimum decoupling is achieved by using two different types of capacitors that target on different types of noise on the power supply leads. For
higher frequency transients, spikes, or digital hash on the line, a good low equivalent-series-resistance (ESR) ceramic capacitor, typically 1μF, is
placed as close as possible to the device VDD pin for the best operation. For filtering lower frequency noise signals, a large ceramic capacitor of
10μF or greater placed near the audio power amplifier is recommended.
How to Reduce EMI
Most applications require a ferrite bead filter for EMI elimination shown at Figure 1. The ferrite filter reduces EMI around 1MHz and higher. When
selecting a ferrite bead, choose one with high impedance at high frequencies, but low impedance at low frequencies.
200pF
200pF
OUT+
OUT-
Ferrite Bead
Ferrite Bead
Figure 1 Ferrite Bead Filter to Reduce EMI
  C
1
f
2 RiCi 

 
i c
1
Ci
2 R f 
