max9761 Maxim Integrated Products, Inc., max9761 Datasheet - Page 13

• Manufacturer Part Number: max9761
• Description: Stereo 3w Audio Power Amplifiers With Headphone Drive And Input Mux
• Manufacturer: Maxim Integrated Products, Inc.

When configured as a headphone (single-ended) ampli-
fier, the slave amplifier is disabled, muting the speaker
and the main amplifier drives the headphone. The
MAX9760–MAX9763 can deliver 3W of continuous aver-
age power into a 3Ω load with less than 1% THD+N in
speaker mode, and 200mW of continuous average
power into a 16Ω load with less than 1% THD+N in
headphone mode. These devices also feature thermal
overload protection.
The MAX9762/MAX9763 are 3W mono speaker ampli-
fiers, 200mW stereo headphone amplifiers, and a
mixer/attenuator (see the MAX9762/MAX9763 Functional
Diagram). In speaker (mono) mode, the mixer/attenuator
combines the two stereo inputs (INL_ and INR_) and
attenuates the resultant signal by a factor of 2. This
allows for full reproduction of a stereo signal through a
single speaker, while maintaining optimum headroom.
The resistor connected between GAINM and OUTR+,
sets the gain of the devices in speaker mode (see the
MAX9762 Functional Diagram). This allows the speaker
amplifier to have a different gain and feedback network
from the headphone amplifier.
These devices operate from a single 5V supply, and
feature an internally generated, power-supply indepen-
dent, common-mode bias voltage of 2.5V referenced to
GND. BIAS provides both click-and-pop suppression
and sets the DC bias level for the audio outputs. BIAS
is internally connected to the noninverting input of each
speaker amplifier (see Typical Application Circuit/
Functional Diagram). Choose the value of the bypass
capacitor as described in the BIAS Capacitor section.
No external load should be applied to BIAS. Any load
lowers the BIAS voltage, affecting the overall perfor-
mance of the device.
Figure 1. Using the Input Multiplexer for Gain Setting
AUDIO
INPUT
______________________________________________________________________________________
Stereo 3W Audio Power Amplifiers with
15kΩ
30kΩ
IN_1
IN_2
MAX9760
Headphone Drive and Input Mux
Mono Mode
BIAS
Each amplifier features a 2:1 input multiplexer, allowing
input selection between two stereo sources. Both multi-
plexers are controlled by bit 1 in the control register
(MAX9760/MAX9762) or by the IN1/2 pin (MAX9761/
MAX9763). A logic low selects input IN_1 and a logic
high selects input IN_2.
The input multiplexer can also be used to further
expand the number of gain options available from the
MAX9760–MAX9763 family. Connecting the audio
source to the device through two different input resis-
tors (Figure 1) increases the number of gain options
from two to four (MAX9760/MAX9761) and from three to
six (MAX9762/MAX9763). Additionally, the input multi-
plexer allows a speaker equalization network to be
switched into the speaker signal path. This is typically
useful in optimizing acoustic response from speakers
with small physical dimensions.
The HPS pin is enabled by HPS_EN (MAX9762/
MAX9763) or the HPSD bit (MAX9760/MAX9761).
HPSD or HPS_EN determines whether the device is in
automatic detection mode or fixed mode operation (see
Tables 1a and 1b).
A voltage on HPS less than 0.7
to speaker mode. A voltage greater than 0.9
ables the inverting bridge amplifier (OUT_-), which
mutes the speaker amplifier and sets the device into
headphone mode.
For automatic headphone detection, connect HPS to the
control pin of a 3-wire headphone jack as shown in
Figure 2. With no headphone present, the resistive volt-
age-divider created by R1 and R2 sets the voltage on
HPS to be less than 0.7
speaker mode and the gain setting defaults to GAINA
(MAX9760/MAX9762). When a headphone plug is insert-
ed into the jack, the control pin is disconnected from the
tip contact, and HPS is pulled to V
the device into headphone mode and the gain-setting
defaults to GAINB (MAX9760/MAX9762) (see Gain
Select section). Place a resistor in series with the control
pin and HPS (R3) to prevent any audio signal from cou-
pling into HPS when the device is in speaker mode.
The MAX9760–MAX9763 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
Headphone Sense Input (HPS)
Headphone Sense Enable
✕
V
DD
, setting the device to
✕
Input Multiplexer
DD
V
DD
through R1, setting
sets the device
Shutdown
✕
V
DD
dis-
13