PAM8320

Document number: DS36610 Rev. 1 - 2

6 of 11

www.diodes.com

October 2013

© Diodes Incorporated

PAM8320

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





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:



ic

1

Ci

2R f





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:



C

1

f

2RiCi





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:

k

R

A

x

v

400

14

1

20







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.