Rainbow Electronics MAX9892 - Manual (Page 5)

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:
t ON (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
DD to V DD - 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
DD - 5.5V on the
negative side, the voltage on V DD 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
2 between 10k
Ω
to 1M
Ω for a given supply voltage. Use the following
equation to calculate the R
1
:
where V AMP is the supply voltage of the amplifier, and
I 2 is the current through R 2 . 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 DD to GND with a 0.1µF capacitor. The 0.1µF
bypass capacitor should be positioned as close as
possible to V
DD . 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.
R
V V
I I
AMP DD
DD
1
2
=
−
+
( )
MAX9892
Shunt Mode Audio Click-and-Pop Eliminator
_______________________________________________________________________________________ 5
IN_
V DD - 5.5V
GND
V DD
IN_ GND
V DD
A
B
V DD - 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