PAM8404
3W/CH Filterless Stereo Class-D Audio Amplifier
Shutdown operation
PCB Layout Guidelines
In order to reduce power consumption while not in
use, the PAM8404 contains shutdown circuitry to
turn off the amplifier's bias circuitry. It features
independent shutdown controls for each channel.
This shutdown turns the amplifier off when logic
low is placed on the SDx pin. By switching the
shutdown pin to GND, the PAM8404 supply
current draw will be minimized in idle mode.
Grounding
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.
Short Circuit Protection (SCP)
The PAM8404 has short circuit protection circuitry
on the outputs to prevent the device from damage
when output-to-output shorts or output-to-GND
shorts occur. When a short circuit occurs, the
device immediately goes into shutdown state.
Once the short is removed, the device will be
reactivated.
Over Temperature Protection (OTP)
Power Supply Line
Thermal protection on the PAM8404 prevents the
device from damage when the internal die
temperature exceeds 150°C. There is a 15°C
tolerance on this trip point from device to device.
Once the die temperature exceeds the set point,
the device will enter the shutdown state and the
outputs are disabled. This is not a latched fault.
The thermal fault is cleared once the temperature
of the die decreased by 50°C. This large
hysteresis will prevent motor boating sound well
and the device begins normal operation at this
point with no external system interaction.
Same as the ground, VDD and PVDD 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.
POP and Click Circuitry
Figure 2: Power Line
The PAM8404 contains circuitry to minimize turn-
on and turn-off transients or “click and pops”,
where turn-on refers to either power supply turn-
on 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 VDD/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.
Components Placement
Decoupling capacitors-As previously described,
the high-frequency 1μF decoupling capacitors
should be placed as close to the power supply
terminals (VDD and PVDD) as possible. Large
bulk power supply decoupling capacitors (10μF or
greater) should be placed near the PAM8404 on
the PVDD 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.
Power Analog Microelectronics,Inc
www.poweranalog.com
03/2009 Rev 1.1
15
PAM [ POWER ANALOG MICOELECTRONICS ]
