Diodes PAM8404 - Manual (Page 13)

PAM8404
Document number: DSxxxxx Rev. 1 - 1
13 of 18
www.diodes.com
November 2012
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PAM8404
A Product Line of
Diodes Incorporated
Application Information
Input Capacitors (C
I
) (cont.)
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
DD
/2, which is likely higher than the source DC level.
Please note that it is important to confirm the capacitor polarity in the application.
If the corner frequency is within the audio band, the capacitors should have a tolerance ±10% or better, because any mismatch in capacitance
cause an impedance mismatch at the corner frequency and below.
Decoupling Capacitor (CS)
The PAM8404 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
1µF, is placed as close as possible to the device each V
DD
and PV
DD
pin for the best operation. For filtering lower frequency noise signals, a
large ceramic capacitor of 10µF or greater placed near the audio power amplifier is recommended.
How to Reduce EMI
Most applications require a ferrite bead filter for EMI elimination as shown at Figure 1. The ferrite filter reduces EMI of around 1MHz and higher.
When selecting a ferrite bead, choose one with high impedance at high frequencies and low impedance at low frequencies.
Figure 1. Ferrite Bead Filter to Reduce EMI
Shutdown Operation
In order to reduce power consumption while not in use, the PAM8404 contains shutdown circuitry to turn off the amplifier's bias circuitry. It
features independent shutdown controls for each channel. This shutdown turns the amplifier off when logic low is placed on the
SDx pin. By
switching the shutdown pin to GND, the PAM8404 supply current draw will be minimized in idle mode.
Short Circuit Protectrion (SCP)
The PAM8404 has short circuit protection 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 occurs, the device immediately goes into shutdown state. Once the short is removed, the device will be
reactivated.
Over Temperature Protection (OTP)
Thermal protection on the PAM8404 prevents the device from damage when the internal die temperature exceeds +150°C. There is a +15°C
tolerance on this trip point from device to device. Once the die temperature exceeds the set point, the device will enter the shutdown state and
the outputs are disabled. This is not a latched fault. The thermal fault is cleared once the temperature of the die decreased by 50°C. This large
hysteresis will prevent motor boating sound well and the device begins normal operation at this point with no external system interaction.