MAX9879 Maxim Integrated Products, MAX9879 Datasheet - Page 21

• Manufacturer Part Number: MAX9879
• Description: Stereo Class D Audio Subsystem
• Manufacturer: Maxim Integrated Products

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1) The sleeve is typically grounded to the chassis.
2) During an ESD strike, the amplifier’s ESD structures
3) When using the headphone jack as a line out to
The MAX9879 features a low-noise charge pump. The
switching frequency of the charge pump is
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
Figure 5. Traditional Amplifier Output vs. MAX9879 DirectDrive
Output
V
V
OUT
OUT
Using the midrail biasing approach, the sleeve
must be isolated from system ground, complicating
product design.
are the only path to system ground. Thus, the
amplifier must be able to withstand the full energy
from an ESD strike.
other equipment, the bias voltage on the sleeve
may conflict with the ground potential from other
equipment, resulting in possible damage to the
amplifiers.
DirectDrive BIASING SCHEME
CONVENTIONAL DRIVER BIASING SCHEME
______________________________________________________________________________________
with DirectDrive Headphone Amplifier
Stereo Class D Audio Subsystem
1
/
2
of the
V
V
GND
+V
GND
-V
DD
DD
DD
DD
/2
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.
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.
The MAX9879 features two ways of entering low-power
shutdown:
• The device can be placed in shutdown mode by writ-
• The device can be placed in an ultra-low power shut-
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:
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.
1) Configure the desired output mode and pream-
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.
ing to the SHDN bit in the Output Control Register.
down mode by setting the SHDN pin to 0V. This com-
pletely disables the MAX9879 including the I
interface.
plifier gain.
Click-and-Pop Suppression
Headphone Current Limit
Shutdown Mode
2
21
C