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Circuits > APP 4449

Jun 30, 2009

Keywords: click-and-pop, MAX9890, MAX9892

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APPLICATION NOTE 4449

How to Pick a Click-and-Pop Suppressor

Abstract: This
application note presents the MAX9890 and MAX9892 which use
different approaches to remove audible click and pop from
headphones. Each device is uniquely suited to different
applications.

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Introduction
Click-and-pop suppressors are unique
devices that can be added to a system late in the design
process to eliminate click-and-pop issues without
substantially changing the design. Two devices, the MAX9890 and MAX9892, are
primarily focused on eliminating clicks and pops from
headphone playback systems. The devices reflect different
approaches, and thereby solve click and pop generated at
different times and by different sources in the
design.

The Series-Switch Method of the MAX9890
The MAX9890
(Figure 1) only addresses click and pop that originates
from output-coupling capacitors. Many headphone playback
systems rely upon DC-blocking capacitors to couple the
headphone amplifier
to the transducer. In these systems the main source
of click and pop is the charging and discharging of the
coupling capacitors at turn-on and turn-off. Capacitors in the
100µF to 330µF range are typically used. The "pop" resulting
from charging such capacitors is generally quite
large.

Figure
1. MAX9890 click-and-pop suppressor.

To address the
click and pop caused by coupling capacitors, the MAX9890
allows the capacitors to charge and discharge slowly, at a
rate below the audible frequency range. To do this, the
MAX9890 is placed between the amplifier and the coupling
capacitors. At turn-on the device uses two analog switches to
slowly apply the DC bias from the headphone amplifier to the
capacitor. At turn-off, resistors are then used to slowly
discharge the coupling capacitors.

This series-switch
method of the MAX9890 quite effectively eliminates click and
pop caused by coupling capacitors; it does nothing for other
sources of click and pop. In addition, this approach assumes a
low impedance
to ground through the headphone transducer at the output side
of the coupling capacitor. Consequently, the design does not
work effectively for line outputs where the expected load is
typically greater than 10kΩ.

The Shunt-Mode of the MAX9892
In systems either where
the source of click and pop is not output-coupling capacitors
or where the output is a line output, then the MAX9892 is the
ideal solution. The MAX9892 places a switch
between each output and ground, causing the power-up and
power-down transients to be shunted to ground. While the
switches are closed, the output is completely muted,
eliminating all clicks and pops.

Figure
2. MAX9892 click-and-pop suppressor.

To achieve
sufficient attenuation, the MAX9892 requires series resistors
between the amplifier and the jack. Combined with the
MAX9892's switches, these resistors create a voltage-divider
on the output that attenuates any clicks and pops generated by
the amplifier. When the click and pops are finished, the
MAX9892 can be disabled and will have no impact on the output
signal.

Conclusion
There are multiple devices to suppress
audible click and pop in designs. The devices function
differently, so not every IC is ideal for every application.
When selecting a click-and-pop suppression device, ask the
following basic questions to determine which device is best
for the design. Is the expected load headphones? Is the
charging of coupling capacitors the only source of click and
pop in the system?

If the answer to both questions is
yes, then the MAX9890 is the ideal solution to eliminating
click and pop. In all other cases, the MAX9892 will provide
the best results.

Related parts

MAX9890

Audio Click-Pop
Suppressor

Free
samples

MAX9892

Shunt Mode Audio
Click-and-Pop Eliminator

Free
samples

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Download,
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APP 4449: Jun 30, 2009

AN4449, AN 4449, APP4449,
Appnote4449, Appnote 4449

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