PAM8408

Document number: DS36992 Rev. 1 - 2

8 of 11

www.diodes.com

June 2014

© Diodes Incorporated

PAM8408

A PRODUCT LINE OF

DIODES INCORPORATED

Input Capacitor (Ci)

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 (Ci) and input resistance (Ri) of the amplifier form a high-pass filter with the corner frequency determined equation below,

C

ii

1

f=

2πRC

In addition to system cost and size, click and pop perfor-mance is affected by the size of the input coupling capacitor, Ci. A larger input coupling

capacitor requires more charge to reach its quiescent DC voltage (nominally 1/2 VDD). 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.

Under Voltage Lock-Out (UVLO)

The PAM8408 incorporates circuitry designed to detect when the supply voltage is low. When the supply voltage drops to 2.4V or below, the

PAM8408 outputs are disable, and the device comes out of this state and starts to normal functional when the supply voltage increases.

Short Circuit Protection (SCP)

The PAM8408 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.

Over Temperature Protection

Thermal protection on the PAM8408 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.

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). Most applications require a ferrite bead filter which shows at Figure 3. The ferrite filter reduces EMI around 1 MHz and higher.

When selecting a ferrite bead, choose one with high impedance at high frequencies, but low impedance at low frequencies.

220pF

220pF

OUT+

OUT-

Ferrite Bead

Ferrite Bead

Figure 3 Ferrite Bead Filter to Reduce EMI