Max9892 shunt mode audio click-and-pop eliminator, Detailed description, Applications information – Rainbow Electronics MAX9892 User Manual

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Detailed Description

The MAX9892 is the second-generation click-and-pop
eliminator designed to be used with conventional head-
phone amplifiers. The MAX9892 works by adding a low-
impedance current path from the headphone side of
the DC-blocking capacitor to ground. Drive MUTE low
when turning off the amplifier, and high when enabling
the amplifier. A short turn-on time allows the switches in
the MAX9892 to close before the DC-blocking capaci-
tors have significantly discharged, eliminating clicks
and pops at amplifier turn-off. An adjustable turn-off
time allows the delay to be set to mask all clicks and
pops during amplifier turn-on.

Setting the Turn-Off Time

The MAX9892 features a SET input that allows the turn-
off time to be adjusted from 1ms to 1000ms to match
the click-and-pop profile of the amplifier startup. The
value of an external capacitor sets the switch open
delay, as shown in the following equation:

(ms) = 0.02 x C

SET

(pF)

When the headphone amplifier is enabled, the
MAX9892 automatically waits the set delay time before
opening the analog switches. This allows amplifier turn-
on click and pop to be eliminated.

Applications Information

Setting the Supply Voltage

The MAX9892 operates from 1.7V to 3.6V supply volt-
age. The inputs, INL and INR, accept voltage swings
from V

to V

- 5.5V. The audio signal applied to a

headphone is ground biased, meaning that the signal
swings just as much negative as positive. Since the
MAX9892 input voltage is limited to V

- 5.5V on the

negative side, the voltage on V

must be set properly

to pass the audio signal when the switch is open
(Figure 2).

A voltage-divider can be used to scale down an avail-
able supply voltage as shown in Figure 3. The voltage-
divider allows the creation of a supply voltage for the
MAX9892 that is low enough to allow the negative por-
tion of the audio signal to pass. When using large resis-
tances for the voltage-divider, the supply current
affects what resistors to use. Select R

between 10k

to 1M

Ω for a given supply voltage. Use the following

equation to calculate the R

where V

AMP

is the supply voltage of the amplifier, and

is the current through R

. For a signal of ±2V in refer-

ence to GND, the MAX9892 supply can be set from 2V
to 3.5V.

Selecting Series Resistors

A series resistor (R

SERIES

), as shown in the

Typical

Operating Circuit

, is necessary to achieve optimal click-

and-pop reduction. See the Click and Pop vs. R

SERIES

graph in the

Typical Operating Characteristics

for

details on how much click-and-pop reduction to expect
for a given series resistor.

Layout Considerations

Bypass V

to GND with a 0.1µF capacitor. The 0.1µF

bypass capacitor should be positioned as close as
possible to V

. Minimize trace length from GND to

solid system ground plane to ensure optimum perfor-
mance.

Refer to the MAX9892 Evaluation Kit for a proven PCB
layout.

AMP

−

(

)

MAX9892

Shunt Mode Audio Click-and-Pop Eliminator

_______________________________________________________________________________________

IN_

- 5.5V

GND

IN_

GND

- 5.5V

Figure 2. Proper Supply Selected for a Given Input Signal.
A: Supply Voltage with a Large Signal;
B: Supply Voltage with a Small Signal