PAM8012

Mono 2.0W Anti-saturation Class D

Audio Power Amplifier with Power Limit

8

,

Power Analog Microelectronics Inc

www.poweranalog.com

06/2012 Rev1.3

Input Capacitors (Ci )

Decoupling Capacitor (C )

How to Reduce EMI

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

co rne r fre quency 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,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 34nF, so one would likely choose a value

of 33nF. 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 PAM8012 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-re sista nce (ESR) ceram ic cap acit or,

typically 1 F, is placed as close as possible to

VDD pin for the best operation. For filtering lower

f r e q u e n c y n o i s e s i g n a ls , a l a r g e c e r a m i c

c apacitor 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

DD

S

μ

Ci Ri + Rf

amplifier off when logic low is placed on the EN

pin. By switching the EN pin connected to GND,

th e PAM801 2 su pply curre nt draw will be

minimized in idle mode.

Th e PAM8 01 2 h as sh ort circuit p ro te ction

circuitry on the outputs to prevent the device

from damage when output-to-output shorts or

output-to-GND shorts occur. When a short circuit

o cc u rs , t h e d e v ice i m m e d ia t e l y g o e s in t o

shutdown state. Once the short is removed, the

device will be reactivated.

μ

Short Circuit Protection (SCP)

Shutdown operation

In order to reduce power consumption while not

in use, the PAM8012 contains shutdown circuitry

that is used to turn off the amplifier’

s bias

c ircu it r y. Th is sh u td o w n f e a tu r e tu r n s th e

Application Information

20 0p F

20 0p F

OUT+

OUT-

Fe rrit e Bea d

Fe rrit e Be ad

RiCi

fc

p

2

1

=

Rifc

Ci

p

2

1

=