Rainbow Electronics MAX9755 - Manual (Page 15)

MAX9750/MAX9751/MAX9755
2.6W Stereo Audio Power Amplifiers and
DirectDrive Headphone Amplifiers
______________________________________________________________________________________ 15
BEEP Input
The MAX9750 features an audible alert beep input
(BEEP) that accepts a mono system alert signal and
mixes it into the stereo audio path. When the amplitude
of V
BEEP(OUT)
exceeds 800mV
P-P
(Figure 8) and the
frequency of the beep signal is greater than 400Hz, the
beep signal is mixed into the active audio path (speaker
or headphone). If the signal at V
BEEP(OUT) is either
<800mV P-P or <400Hz, the BEEP signal is not mixed into
the audio path. The amplitude of the BEEP signal at the
device output is roughly the amplitude of V
BEEP(OUT)
times the gain of the selected signal path.
The input resistor (R B ) sets the gain of the BEEP input
amplifier, and thus the amplitude of V BEEP(OUT) . Choose
R B based on:
where R
INT
is the value of the BEEP amplifier feedback
resistor (47kΩ) and V IN is the BEEP input amplitude.
Note that the BEEP amplifier can be set up as either an
attenuator, if the original alert signal amplitude is too
large, or set to gain up the alert signal if it is below
800mV
P-P . AC couple the alert signal to BEEP. Choose
the value of the coupling capacitor as described in the
Input Filtering section. Multiple beep inputs can be
summed (Figure 8).
Input Multiplexer
The MAX9751 features a 2:1 input multiplexer on each
amplifier, allowing input selection between two stereo
sources. The logic input IN1/2 controls both multiplex-
ers. A logic high selects input IN_1 and a logic low
selects input IN_2.
Shutdown
The MAX9750/MAX9751/MAX9755 features a 0.2µA,
low-power shutdown mode that reduces quiescent cur-
rent consumption and extends battery life. Driving
SHDN low disables the drive amplifiers, bias circuitry,
and charge pump, and drives BIAS and all outputs to
GND. Connect SHDN to V
DD for normal operation.
Click-and-Pop Suppression
Speaker Amplifier
The MAX9750/MAX9751/MAX9755 speaker amplifiers
feature Maxim’s comprehensive, industry-leading click-
and-pop suppression. During startup, the click-pop
suppression circuitry eliminates any audible transient
sources internal to the device. When entering shut-
down, both amplifier outputs ramp to GND quickly and
simultaneously.
R
V R
B
IN INT
.
≤
×
0 8
MAX9750
V REF
DAC
HPV DD
VOL
Figure 6. Volume Control Circuit
GAIN
SPEAKER MODE
GAIN (dB)
HEADPHONE
MODE GAIN (dB)
0 10.5 0
1 9 3
Table 2. MAX9751 Gain Settings
SPEAKER MODE GAIN (dB)
GAIN1 GAIN2
MAX9750A MAX9750B MAX9750C
HEADPHONE MODE GAIN (dB)
0 0 9 15 6 0
0 1 12 18 9 3
1 0 10.5 16.5 7.5 0
1 1 13.5 19.5 10.5 3
Table 1. MAX9750 Maximum Gain Settings