PAM8007DHR datasheet(13/16 Pages) PAM

13 / 16 page

Power Analog Microelectronics Inc

PAM8007

Filterless 3W Class-D Stereo Audio Amplifier

with DC Volume Control and Headphone Output

www.poweranalog.com

Application Information(continued)

Over Temperature Protection

H o w t o R e d u c e E M I ( E l e c t r o M a g n e t i c

Interference)

PCB Layout Guidelines Grounding

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

. This large hysteresis will prevent motor

boating sound well. The device begins normal

operation at this point without external system

interaction.

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).

Figure 1: Ferrite Bead Filter to reduce EMI

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

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

Figure 2: Top Layer

Figure 3: Bottom Layer

22 0p F

OUT+

OUT-

Fe rrite Bea d

01/2012 Rev1.2

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