PAM8320 Datasheet, PDF (6/11 Pages) Diodes Incorporated – 20W Mono Class D Audio Amplifier

Application Information
A PRODUCT LINE OF
DIODES INCORPORATED
PAM8320
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:
fC


2
1
RiCi
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. The equation is reconfigured as followed to determine the value of Ci:
Ci

1
 2 Rifc

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 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.
Input Resistance
The value of the input resistance (Ri) of the amplifier is 40kΩ ±20%. If a single capacitor is added to the input of the high-pass filter the –3dB
cutoff frequency can be calculated using equation:
fC

2
1
RiCi
Gain Formula with External Input Resistor
The default gain of PAM8320 is 26dB. The gain can be reduced by adding one external resistor between input decoupling capacitor and IN PIN.
The gain formula is as below:
A_v

20
1

14

R_x
400k
Note: Rx is external input resistor
Power and Heat Dissipation
Speakers must be chosen to withstand the large output power from the PAM8320, otherwise speaker damage may occur.
Heat dissipation is very important when the device works in full power operation. Two factors affect the heat dissipation, the efficiency of the
device that determines the dissipation power and the thermal resistance of the package that determines the heat dissipation capability.
The PAM8320 class-D amplifier is highly efficiency and should not need heat sink. Operating at higher powers a heat sink still may not be
necessary if the PCB is carefully designed to achieve good thermal dissipation.
PAM8320
Document number: DS36610 Rev. 1 - 2
6 of 11
www.diodes.com
October 2013
© Diodes Incorporated