MAX9777/MAX9778
Stereo 3W Audio Power Amplifiers with
Headphone Drive and Input Mux
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13
Headphone Sense Input (HPS)
With headphone sense enabled, a voltage on HPS less
than 0.7 x V
DD
sets the device to speaker mode. A volt-
age greater than 0.9 x V
DD
disables the inverting
bridge amplifier (OUT_-), which mutes the speaker
amplifier and sets the device into headphone mode.
For automatic headphone detection, enable headphone
sense and connect HPS to the control pin of a 3-wire
headphone jack as shown in Figure 2. With no head-
phone present, the resistive voltage-divider created by
R1 and R2 sets the voltage on HPS to be less than 0.7 x
V
DD
, setting the device to speaker mode and the gain
setting defaults to GAINA (MAX9777). When a head-
phone plug is inserted into the jack, the control pin is dis-
connected from the tip contact, and HPS is pulled to V
DD
through R1, setting the device into headphone mode and
the gain-setting defaults to GAINB (MAX9777) (see the
Gain Select section). Place a resistor in series with the
control pin and HPS (R3) to prevent any audio signal from
coupling into HPS when the device is in speaker mode.
Shutdown
The MAX9777/MAX9778 feature a 10µA, low-power
shutdown mode that reduces quiescent current con-
sumption and extends battery life. The drive amplifiers
and bias circuitry are disabled, the amplifier outputs
(OUT_) go high impedance, and BIAS is driven to
GND. Driving
SHDN
low places the devices into shut-
down mode, disables the interface, and resets the I
2
C
registers to a default state. A logic-high on
SHDN
enables the devices.
MAX9777 Software Shutdown
A logic-high on bit 0 of the SHDN register places the
MAX9777 in shutdown mode. A logic-low enables the
device. The digital section of the MAX9777 remains
active when the device is shut down through the inter-
face. All devices feature a logic-low on the
SHDN
input.
MUTE
The MAX9777/MAX9778 feature a mute mode. When
the device is muted, the input is disconnected from the
amplifiers. MUTE does not shut down the device.
MAX9777 MUTE
The MAX9777 MUTE mode is selected by writing to the
MUTE register (see the
Mute Register section). The left
and right channels can be independently muted.
MAX9778 MUTE
The MAX9778 features an active-high MUTE input that
mutes all channels.
Click-and-Pop Suppression
The MAX9777/MAX9778 feature Maxim’s comprehen-
sive click-and-pop suppression. When entering or exit-
ing shutdown, the common-mode bias voltage of the
amplifiers is slowly ramped to and from the DC bias
point using an S-shaped waveform. In headphone
mode, this waveform shapes the frequency spectrum,
minimizing the amount of audible components present
at the headphone. In speaker mode, the BTL amplifiers
start up in the same fashion as in headphone mode.
When entering shutdown, both amplifier outputs ramp
to GND quickly and simultaneously. To maximize click-
and-pop suppression, drive
SHDN
to 0V before power-
up or power-down transitions.
MAX9777
MAX9778
R3
47k
Ω
R1
680k
Ω
R2
10k
Ω
R2
10k
Ω
HPS
V
DD
OUTL+
OUTR+
Figure 2. HPS Configuration Circuit
INPUTS
HPS_EN
HPS
MODE
GAIN PATH*
0
X
BTL
A or B
1
0
BTL
A or B
1
1
SE
A or B
Table 1b. MAX9778 HPS Setting
*Note:
A or B—Gain path selected by external GAINAB
