PAM8008 Datasheet, PDF (10/14 Pages) Diodes Incorporated – 3W STEREO CLASS-D with DC VOLUME, POWER LIMIT and ANTI-SATURATION

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PAM8008
Application Information (cont.)
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,
is recommended, placing as close as possible to the device’s V_DD lead. For filtering lower-frequency noise signals, a large capacitor of 10µF
(ceramic) or greater placed near the audio power amplifier is recommended.
Input Capacitior (C_I)
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,
fC
=
1
2ΠRI CI
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
reach its quiescent DC voltage (norminally ½ 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)
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.
A ceramic bypass capacitor (C_BYP) of 0.47µF to 1.0µF 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
The PAM8008 incorporates circuitry designed to detect when the supply voltage is low. When the supply voltage drops to 2.2V or below, the
PAM8008 outputs are disable, and the device comes out of this state and starts to normal functional once V_DD ≥ 2.4V.
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).
PAM8008
Document number: DSxxxxx Rev. 1 - 0
10 of 14
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October 2012
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