Diodes PAM8404 - Manual (Page 14)

PAM8404
Document number: DSxxxxx Rev. 1 - 1
14 of 18
www.diodes.com
November 2012
© Diodes Incorporated
PAM8404
A Product Line of
Diodes Incorporated
Application Information
POP and Click Circuitry
The PAM8404 contains circuitry to minimize turnon and turn-off transients or “click and pops”, where turn-on refers to either power supply turnon
or device recover from shutdown mode. When the device is turned on, the amplifiers are internally muted. An internal current source ramps up
the internal reference voltage. The device will remain in mute mode until the reference voltage reach half supply voltage V
DD
/2. As soon as the
reference voltage is stable, the device will begin full operation. For the best power-off pop performance, the amplifier should be set in shutdown
mode prior to removing the power supply voltage.
PCB Layout Guidelines
Grouding
It is recommended to use plane grounding or separate grounds. Do not use one line connecting power GND and analog GND. Noise currents in
the output power stage need to be returned to output noise ground and nowhere else. When these currents circulate elsewhere, they may get
into the power supply, or the signal ground, etc, even worse, they may form a loop and radiate noise. Any of these instances results in degraded
amplifier performance. The output noise ground that the logical returns for the output noise currents associated with Class-D switching must tie
to system ground at the power exclusively. Signal currents for the inputs, reference need to be returned to quite ground. This ground only ties to
the signal components and the GND pin. GND then ties to system ground.
Power Supply Line
Same as the ground, V
DD
and PV
DD
need to be separately connected to the system power supply. It is recommended that all the trace could be
routed as short and thick as possible. For the power line layout, just imagine water stream, any barricade placed in the trace (shown in Figure 2)
could result in the bad performance of the amplifier.
Figure 2. Power Line
Component Placement
Decoupling capacitors-As previously described, the high-frequency 1μF decoupling capacitors should be placed as close to the power supply
terminals (V
DD
and PV
DD
) as possible. Large bulk power supply decoupling capacitors (10μF or greater) should be placed near the PAM8404 on
the PV
DD
terminal.
Input capacitors need to be placed very close to input pins.
Output filter - The ferrite EMI filter should be placed as close to the output terminals as possible for the best EMI performance, and the capacitors
used in the filters should be grounded to system ground.