Diodes PAM8803 - Manual (Page 9)

PAM8803
Document number: DSxxxxx Rev. 1 - 4
9 of 14
www.diodes.com
November 2012
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PAM8803
A Product Line of
Diodes Incorporated
Application Information
(cont.)
Power Supply Decoupling
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-seriesresistance (ESR) ceramic capacitor, typically 1.0μF, placed as close as possible to the device V
DD
terminal works best. For filtering lowerfrequency noise signals, a larger capacitor of 10µF (ceramic) or greater placed near the audio power
amplifier is recommended.
Input Capacitor (C
J
)
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 performance. In this case, input
capacitor (C
J
) and input resistance (R
J
) of the amplifier form a high-pass filter with the corner frequency determined equation below,
C R 2
1
f
J J
C


In addition to system cost and size, click and pop performance is affected by the size of the input coupling capacitor, C
J
. A larger input coupling
capacitor requires more charge to reach its quiescent DC voltage (nominally 1/2 V
DD
). 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.
Analog Reference Bypass Capacitor (C
BYP
)
The Analog Reference Bypass Capacitor (C
BYP
) is the most critical capacitor and serves several important functions. During start-up or recovery
from shutdown mode, C
BYP
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
BYP
) 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.
Under Voltage Lock-Out (UVLO)
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.
Short Circuit Protection (SCP)
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.
Over Temperature Protection
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.
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).