PAM8404 datasheet(15/18 Pages) PAM

15 / 18 page

Shutdown operation

Short Circuit Protection (SCP)

Over Temperature Protection (OTP)

POP and Click Circuitry

PCB Layout Guidelines

Grounding

Power Supply Line

Figure 2:

Components Placement

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

pin. By switching the

shutdown pin to GND, the PAM8404 supply

current draw will be minimized in idle mode.

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.

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.

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

/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.

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.

Same a

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.

Power Line

404 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.

SDx

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 PAM8

Power Analog Microelectronics Inc

www.poweranalog.com

PAM8404

3W/CH Filterless Stereo Class-D Audio Amplifier

03/2009 Rev 1.1

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