PAM8304
Document number: DS36589 Rev. 1 - 2
6 of 11
www.diodes.com
October 2013
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PAM8304
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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 a high-pass filter with the corner frequency determined in the follow equation:
C
1
f
2RiCi
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 down to 150Hz. The equation is reconfigured as followed to determine the value of Ci:
ic
1
Ci
2Rf
When input resistance variation is considered, if Ci is 7nF 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 and 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 PAM8304 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.
Optimum decoupling is achieved by using two different types of capacitors that target different types of noise on the power supply leads. Higher
frequency transients, spikes or digital hash should be filtered with a good low equivalent-series-resistance (ESR) ceramic capacitor with a value of
typically 1μF. This capacitor should be placed as close as possible to the VDD pin of the device. Lower frequency noise signals should be filtered
with a large ceramic capacitor of 10μF or greater. It's recommended to place this capacitor near the audio power amplifier.
How to Reduce EMI
Most applications require a ferrite bead filter for EMI elimination as shown in Figure 1. The ferrite filter reduces EMI around 1MHz and higher.
When selecting a ferrite bead it should be chosen 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
