MAX9890
Detailed Description
The MAX9890 provides click-and-pop suppression for
single-supply devices such as CODECs and other
headphone amplifiers that do not have click-and-pop
suppression. Single-supply audio amplifier outputs
have a DC bias voltage, V
CC
/ 2, and require large out-
put-coupling capacitors to block the DC voltage from
the speaker. During startup or shutdown, the DC bias
voltage is quickly raised or lowered (Figure 1), resulting
in an audible transient through the headphone load.
The MAX9890 prevents the audible transient by slowly
ramping the DC bias in an S-shaped waveform (Figure
2), suppressing the large transient at the output of the
coupling capacitor. The S-shaped waveform shapes
the frequency spectrum, minimizing the amount of
audible components present at the output.
Internal switches couple the inputs to the outputs after
the coupling capacitors have fully charged to the input
common-mode bias voltage. When power is removed or
the device is put into shutdown, the internal switches in
the MAX9890 immediately disconnect the output and
slowly discharge the coupling capacitors through
220kΩ resistors.
The MAX9890 has an undervoltage lockout (UVLO) that
prevents device operation when V
CC
is below the
power-down threshold (2.5V, typ). The MAX9890 fea-
tures ±8kV ESD (Human Body Model) protection on the
audio outputs.
Startup
The MAX9890 monitors V
CC
and SHDN. The UVLO
holds the device off when V
CC
is below the power-
down threshold (V
UVLO
) or SHDN is held low. The
device needs both V
CC
above the power-down thresh-
old and SHDN = high for the part to start up. Once the
supply voltage is above the power-down threshold and
SHDN is high, the device charges the coupling capaci-
tors to the input DC bias voltage using CEXT to control
the ramp. After the DC bias ramp, the internal switches
close, coupling the audio input to the output. The
MAX9890 provides click-pop suppression even if the
output blocking capacitors are already partially or fully
charged.
The MAX9890A features a 200ms switch turn-on time,
enabling the use of up to 100µF coupling capacitors at
the output for applications requiring only a limited low-
frequency response and a rapid turn-on time. The
MAX9890B features a 330ms switch turn-on time,
enabling the use of >100µF coupling capacitors at the
output for extended low-frequency response applica-
tions. For optional click-pop suppression, mute the
audio signal until after the turn-on time has elapsed.
The internal switches stay closed as long as V
CC
is
above the power-down threshold voltage and SHDN is
high. Figures 1 and 2 show typical startup/power-up
sequences with and without click-pop suppression.
Shutdown
If the supply voltage falls below the UVLO threshold or
if SHDN is driven low, the device enters low-power
shutdown mode. In low-power shutdown mode, quies-
cent current reduces to 0.001µA. The switches are
immediately turned off and 220kΩ resistors slowly
bleed the charge off the coupling capacitors. Figures 3
and 4 show typical shutdown/power-down sequences
with and without click-pop suppression. For optimal
click-pop performance, mute the audio signal before
shutting down the MAX9890.
Audio Click-Pop Suppressor
6 _______________________________________________________________________________________
Pin Description
