PAM8007 Datasheet, PDF (13/16 Pages) Power Analog Micoelectronics – Filterless 3W Class-D Stereo Audio Amplifier with DC Volume Control and Headphone Output

PAM8007
Filterless 3W Class-D Stereo Audio Amplifier
with DC Volume Control and Headphone Output
Application Information(continued)
Over Temperature Protection
Thermal protection on the PAM8007 prevents the
device from damage when the internal die
temperature exceeds 150℃. 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
30℃ . 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
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 1 MHz and higher. When selecting a
ferrite bead, choose one with high impedance at
high frequencies, and low impedance at low
frequencies (MH2012HM221-T).
channel amplifier has two seperate channels and
consequently must have two seperate output
noise ground traces. The layout of the PAM8007
offers separate PGND connections for each
channel and in some cases each side of the
bridge. Output noise grounds must be tied to
system ground at the power in exclusively. Signal
currents for the inputs, reference, etc need to be
returned to quite ground. This ground is only tied
to the signal components and the GND pin, and
GND then tied to system ground.
PCB Layout Example
OUT +
Fe rrite Bea d
22 0p F
OUT-
Fe rrite Bea d
22 0p F
Figure 1: Ferrite Bead Filter to reduce EMI
PCB Layout Guidelines Grounding
At this stage it is paramount to notice the
necessity of separate grounds. Noise currents in
the output power stage need to be returned to
output noise ground and nowhere else. Were
these currents to circulate elsewhere, they may
get into the power supply, the signal ground, etc,
worse yet, they may form a loop and radiate
noise. Any of these cases results in degraded
amplifier performance. The logical returns for the
output noise currents associated with Class D
switching are the respective PGND pins for each
channel. The switch state diagram illustrates that
PGND is instrumental in nearly every switch
state. This is the perfect point to which the output
noise ground trace should return. Also note that
output noise ground is channel specific. A two
Power Analog Microelectronics, Inc
www.poweranalog.com
13
Figure 2: Top Layer
Figure 3: Bottom Layer
01/2012 Rev1.2