PAM8803 datasheet(10/13 Pages) PAM

10 / 13 page

Power supply decoupling

Input Capacitor (C )

Analog Reference Bypass Capacitor (C

)

The PAM8803 is a high performance CMOS

audio amplifier that requires adequate power

supply decoupling to ensure the output THD and

PSRR are as low as possible. Power supply

decoupling is affecting low frequency response.

Optimum decoupling is achieved by using two

capacitors of different types that target 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

1.0μF, placed as close as possible to the device

terminal works best. For filtering lower-

frequency noise signals, a larger capacitor of

or greater placed near the audio

power amplifier is recommended.

Large input capacitors are both expensive and

space hungry for portable designs. Clearly, a

certain sized capacitor is needed to couple in low

frequencies without severe attenu ation. But in

many cases the speakers used in portable

systems, whether internal or external, have little

ability to reproduce signals below 100Hz to

150Hz. Thus, using a large input capacitor may

not increase actual system perfor mance. In this

case, input capacitor (C ) and input resistance

(R ) of the amplifier form a high-pass filter with

the corner frequency determined equation below,

In addition to system cost and size, click and pop

perfor mance is affected by the size of the input

coupling capacitor, C . A larger input coupling

capacitor requires more charge to reach its

quiescent DC voltage (nominally 1/2 V ). This

charge comes from the internal circuit via the

feedback and is apt to create pops upon device

enable. Thus, by minimizing the capacitor size

based on necessary low frequency response,

turn-on pops can be minimized.

The Analog Reference Bypass Capacitor (C

) is

the most critical capacitor and serves several

important functions. During start-up or recovery

from shutdown mode, C

determines the rate at

which the amplifier starts up. The second

function is to reduce noise produced by the

power supply caused by coupling into the output

drive signal. This noise is from the internal

analog reference to the amplifier, which appears

as degraded PSRR and THD+N.

Bypass capacitor (C

) values of 0.47μF to

1.0μF ceramic is recommended for the best THD

and noise performance. Increasing the bypass

capacitor reduces clicking and popping noise

from power on/off and entering and leaving

shutdown.

BYP

10μF (ceramic)

The PAM8803 incorporates circuitry designed to

detect when the supply voltage is low. When the

supply voltage drops to 1.85V or below, the

PAM8803 outputs are disable, and the device

comes out of this state and starts to normal

functional when the supply voltage increases.

The PAM8803 has short circuit protection

circuitry on the outputs that prevents damage to

the device during

output-to-output and output-

to-GND short. When a short circuit is detected on

the outputs, the outputs are disable immediately.

If the short was removed, the device activates

again.

Thermal protection on the PAM8803 prevents

damage to the device when the internal die

temperature exceeds 150°C. There is a 15

degree tolerance on this trip point from device to

device. Once the die temperature exceeds the

thermal set point, the device outputs are

disabled. This is not a latched fault. The thermal

fault is cleared once the temperature of the die is

reduced by 60°C. This large hysteresis will

prevent motor boating sound well and the device

begins normal operation at this point with no

external system interaction.

A simple solution is to put an additional capacitor

1000uF at power supply terminal for power line

coupling if the traces from amplifier to speakers

are short (<20cm).

Under Voltage Lock-out (UVLO)

Short Circuit Protection (SCP)

Over Temperature Protection

How t o Reduce EMI (Electro Magnetic

Interference)

2πR C

Power Analog Microelectronics Inc

www.poweranalog.com

PAM8803

3W Filterless Stereo Class-D Audio Amplifier

with Digital Volume Control

12/2009 Rev 1.4

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