PAM8008

Document number: DSxxxxx Rev. 1 - 0

10 of 14

www.diodes.com

October 2012

© Diodes Incorporated

PAM8008

A Product Line of

Diodes Incorporated

Power Supply Decoupling

The PAM8008 is a high performance CMOS audio amplifier that requires adequate power supply decoupling to ensure the output THD and

PSRR as low as possible. Power supply decoupling also prevents oscillations caused by long lead between the amplifier and the speaker. The

optimum decoupling is achieved by using two capacitiors 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 resisitance (ESR) ceramic capacitor, typically 0.1µF,

(ceramic) or greater placed near the audio power amplifier is recommended.

Large input capacitors are both expensive and spce hungrt for portale designs. Clearly, a certain sized capacitor is needed to couple in low

frequencies without severe attenuation. 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 inout capacitior may not increase actual system performance. In this case, input

capacitor (CI) and input resisitance (RI) of the amplifier form a high-pass filter with the corner frequency determined equation below,

C

R

2

1

f

I

I

C

Π

=

In addition to system cost and size, click and pop performance is affected by the size of the input coupling capacitor requires more charge to

device enable. Thus, by minimizing the capacitor size based on necessary low frequency response, turn-on pops can be minimized.

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.

capacitor reduces clicking and popping noise from power on/off and entering and leaving shutdown.

Under Voltage Lock-Out

The PAM8008 incorporates circuitry designed to detect when the supply voltage is low. When the supply voltage drops to 2.2V or below, the

Short Circuit Protection (SCP)

The PAM8008 has short circuit protection circuitry on the outputs that prevents the device from damage when output-to-output and output-to-

GND short. When a short circuit is detected on the outputs, the outputs are disabled immediately. If the short was removed, the device activates

again.

Over Temperature Protection

Thermal protection on the PAM8008 prevents the device from damage 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 +40°C. This large hysteresis will prevent motor

boating sound well. The device begins normal operation at this point without external system interaction.

How to Reduce EMI (Electro Magnetic Interference)

A simple solution is to put an additional capacitor 1000µF at power supply terminal for power line coupling if the traces from amplifier to speakers

are short (< 20CM).