PAM8303DASC datasheet(12/17 Pages) PAM

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Input Resistance (Ri)

Input Capacitors (Ci )

Decoupling Capacitor (C )

How to Reduce EMI

The input resistors (Ri) set the gain of the

amplifier according to Equation 1.

Resistor matching is very important in fully

differential amplifiers. The balance of the output

on the reference voltage depends on matched

ratios of the resistors. CMRR, PSRR, and

cancellation of the second harmonic distortion

diminish if resistor mismatch occurs. Therefore,

it is recommended to use 1% tolerance resistors

or better to keep the performance optimized.

Matching is more important than overall

tolerance. Resistor arrays with 1% matching can

be used with a tolerance greater than 1%.

Place the input resistors very close to the

PAM8303D to limit noise injection on the high-

impedance nodes.

For optimal performance the gain should be set

to 2X(Ri=150k) or lower. Lower gain allows the

PAM8303D to operate at its best, and keeps a

high voltage at the input making the inputs less

susceptible to noise. In addition to these

features, higher value of Ri minimizes pop noise.

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 150k

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 (

) 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 V /2,

which is likely higher than the source DC level.

Please note that it is important to confirm the

capacitor polarity in the application.

The PAM8303D 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 1 F, is placed as close as possible to

the device each VDD and PVDD pin for the best

operation. For filtering lower frequency noise

signals, a large ceramic capacitor of 10 F or

greater placed near the audio power amplifier is

recommended.

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.

Figure 1: Ferrite Bead Filter to Reduce EMI

Ci Ri + Rf

In order to reduce power consumption while not

in use, the PAM8303D contains shutdown

circuitry that is used to turn off the amplifier’s

bias circuitry. This shutdown feature turns the

Shutdown operation

Application Information

PAM8303D

Ultra Low EMI, 3W Filterless

Mono Class-D Audio Power Amplifier

Power Analog Microelectronics Inc

www.poweranalog.com

2 150k

Gain

´W æö

ç÷

èø

()

2RiCi

()

2R f

200pF

OUT+

OUT-

Ferrite Bead

09/2008 Rev 1.4

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