Diodes PAM8010 - Manual (Page 13)

PAM8010
Document number: DSxxxxx Rev. 1 - 0
13 of 17
www.diodes.com
November 2012
© Diodes Incorporated
PAM8010
A Product Line of
Diodes Incorporated
Application Information
Power Supply Decoupling
The PAM8010 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 affects low frequency on the power supply leads for higher frey response. Optimum
decoupling is achieved by using two capacitors of different types that target different types of noise frequency transients, spike, or digital hash
on the line, a good low equivalent-series-resisitance (ESR) ceramic capacitor, typically 1.0µF, placed as close as possible to the device V
DD
terminal works best. For filtering lower-frequency noise signals, a large capacitor of 10µF (ceramic) or greater placed near the audio power
amplifier is recommended.
Input Capacitor (C
I
)
Large input capaciitors are both expensive and spce hungry for portable designs. Clearly, a certain sized capacitor is needed to capacitor is
needed to couple in low frequencies wothout 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 input capacitor may not increase actual system
performance. In this case, input capacitor (C
I
) and input resisitance (R
I
) of the amplifier form a high-pass filter with the corner frequency
determined equation below,
C R 2
1
f
I I
C


In addition to system cost and size, click and pop perfomance is affected by the size of the input coupling capacitor, CI. A larger inout coupling
capacitor requires more charge to reach its quiescent DC voltage (nominally ½ VDD). This charge comes from the internall circuit via the
feedback and is apt to creat pops upon device enable. Thus, by minimizing the capacitor size based on necessary low frequency response,
turn-on pops can be minimized.
Analog Refernce Bypass Capacitor (C
BYP
)
Analog Refernce 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.
Over Temperature Protection
Thermal protection on the PAM8010 prevents the device from damage when the internal die temperature exceeds +150°C. There is a 15
degree tolerance on this 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. Before thermal shutdown, gain
of the PAM8010 will drop -3dB when the chip temperature reaches +120°C.
How to Reduce EMI (Electro Magnetic Interference)
A simple solution is to put an additional capacitor 1000uF 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 as shown at Figure 1. The ferrite filter reduces EMI around 1MHz
and higher. When selecting a ferrite bead, choose one with high impedance at high frequencies, and low impedance at low frequencies
(MH2012HM221-T).
Figure 1. Ferrite Bead Filter to Reduce EMI