MAX9879 datasheet(21/32 Pages) AD

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MAX9879

Stereo Class D Audio Subsystem

with DirectDrive Headphone Amplifier

Maxim Integrated

1) The sleeve is typically grounded to the chassis.

Using the midrail biasing approach, the sleeve

must be isolated from system ground, complicating

product design.

2) During an ESD strike, the amplifier’s ESD structures

are the only path to system ground. Thus, the

amplifier must be able to withstand the full energy

from an ESD strike.

3) When using the headphone jack as a line out to

other equipment, the bias voltage on the sleeve

may conflict with the ground potential from other

equipment, resulting in possible damage to the

amplifiers.

The MAX9879 features a low-noise charge pump. The

switching frequency of the charge pump is 1/2 of the

Class D switching frequency, regardless of the operating

mode. Since the Class D amplifiers are operated in

spread-spectrum mode, the charge pump also switches

with a spread-spectrum pattern. The nominal switching

frequency is well beyond the audio range, and thus does

not interfere with audio signals. The switch drivers fea-

ture a controlled switching speed that minimizes noise

generated by turn-on and turn-off transients. By limiting

the switching speed of the charge pump, the di/dt noise

caused by the parasitic trace inductance is minimized.

Although not typically required, additional high-frequen-

cy noise attenuation can be achieved by increasing the

size of C2 (see the

Typical Application Circuit). The

charge pump is active only in headphone modes.

Headphone Current Limit

The headphone amplifier current is limited to 140mA (typ).

The current limit clamps the output current, which appears

as clipping when the maximum current is exceeded.

Shutdown Mode

The MAX9879 features two ways of entering low-power

shutdown:

• The device can be placed in shutdown mode by writ-

ing to the SHDN bit in the Output Control Register.

• The device can be placed in an ultra-low power shut-

down mode by setting the SHDN pin to 0V. This com-

pletely disables the MAX9879 including the I2C

interface.

Click-and-Pop Suppression

The MAX9879 features click-and-pop suppression that

eliminates audible transients from occurring at startup

and shutdown.

Use the following procedure to start up the MAX9879:

1) Configure the desired output mode and pream-

plifier gain.

2) Set the SHDN bit to 1 to start up the amplifier.

3) Wait 10ms for the startup time to pass.

4) Increase the output volume to the desired level.

To disable the device simply set SHDN to 0.

During the startup period, the MAX9879 precharges the

input capacitors to prevent clicks and pops. If the output

amplifiers have been programmed to be active they are

held in shutdown until the precharge period is complete.

When power is initially applied to the MAX9879, the

power-on-reset state of all three volume control registers

is mute. For most applications, the volume can be set to

the desired level once the device is active. If the click-

and-pop is too high, step through intermediate volume

settings with zero-crossing detection disabled. Stepping

through higher volume settings has a greater impact on

click-and-pop than lower volume settings.

For the lowest possible click and pop, start up the device

at minimum volume and then step through each volume

setting until the desired setting is reached. Disable zero-

crossing detection if no input signal is expected.

VDD

VDD/2

GND

CONVENTIONAL DRIVER BIASING SCHEME

DirectDrive BIASING SCHEME

+VDD

GND

-VDD

VOUT

Figure 5. Traditional Amplifier Output vs. MAX9879 DirectDrive

Output

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