MAX9720 Maxim, MAX9720 Datasheet - Page 14

• Manufacturer Part Number: MAX9720
• Description: 50mW / DirectDrive / Stereo Headphone Amplifier with SmartSense and Shutdown
• Manufacturer: Maxim

For automatic headphone detection, connect HPS to the
control pin of a 3-wire headphone jack, as shown in
Figure 7. With no headphone present, the output imped-
ance of the amplifier pulls HPS to less than 0.8 x V
When a headphone plug is inserted into the jack, the
control pin is disconnected from the tip contact, and
HPS is pulled to V
A debounce delay controls the time between HPS going
high and the initiation of the SmartSense test sequence.
This time is controlled by an external capacitor on the
TIME pin and allows the user to customize the de-
bounce time (see the TIME Capacitor section).
Driving MODE1 and MODE2 to GND shuts down the
MAX9720, disconnects the internal HPS pullup resistor,
disables the charge pump and amplifiers, sets the
amplifier output impedance to 1kΩ, and reduces sup-
ply current to less than 6µA.
In forced left mono mode (MODE1 = high, MODE2 =
low), the right channel is disabled and OUTR goes high
impedance. The stereo signal inputs are combined
through the mixer/attenuator and output on the left
channel. In forced mono mode, the SmartSense routine
is disabled.
In forced stereo mode (MODE1 = low, MODE2 = high),
the device operates as a stereo headphone amplifier.
In forced stereo mode, the SmartSense routine is dis-
abled.
The MAX9720 includes an active-low, open-drain
ALERT output that indicates to the master device that
SmartSense has detected a fault condition. ALERT trig-
gers when an output short circuit is detected through
the SmartSense routine. During normal operation,
ALERT idles high. If a fault condition is detected,
ALERT pulls the line low. ALERT remains low until
MODE1 is toggled from high to low.
In conventional single-supply audio amplifiers, the out-
put-coupling capacitor is a major contributor of audible
clicks and pops. Upon startup, the amplifier charges
the coupling capacitor to its bias voltage, typically half
the supply. Likewise, during shutdown, the capacitor is
discharged to GND. A DC shift across the capacitor
results, which in turn appears as an audible transient at
the speaker. Since the MAX9720 does not require out-
put-coupling capacitors, no audible transient occurs.
50mW, DirectDrive, Stereo Headphone
Amplifier with SmartSense and Shutdown
14
______________________________________________________________________________________
DD
Click-and-Pop Suppression
through the internal 100kΩ pullup.
Forced Stereo Mode
Forced Mono Mode
A A L L E E R R T T Output
Shutdown
DD
.
Additionally, the MAX9720 features extensive click-and-
pop suppression that eliminates any audible transient
sources internal to the device. The Power-Up/Down
Waveform in the Typical Operating Characteristics
shows that there are minimal spectral components in
the audible range at the output upon startup and shut-
down.
In most applications, the preamplifier output driving the
MAX9720 has a DC bias of typically half the supply.
During startup, the input-coupling capacitor is charged
to the preamplifier’s DC bias voltage through the input
resistor of the MAX9720, resulting in a DC shift across
the capacitor and an audible click/pop. Delaying the
startup of the MAX9720 by 4 to 5 time constants (80ms
to 100ms) based on R
of the preamplifier, eliminates this click/pop caused by
the input filter.
If the SmartSense routine occurs during normal opera-
tion, a low-level audible transient may be heard. To pre-
vent this, a host-controlled SmartSense routine should
only be executed when ALERT asserts.
Figure 6. Typical 2-Wire (Mono) Headphone Plug
Figure 7. HPS Configuration
(SIGNAL)
TIP
MAX9720
100kΩ
OUTR
OUTL
HPS
SLEEVE
(GND)
R1
IN
V
DD
and C
15
16
14
IN
, relative to the startup