MAX9750CEUI datasheet(14/30 Pages) MAXIM

14 / 30 page

2.6W Stereo Audio Power Amplifiers and

DirectDrive Headphone Amplifiers

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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 VBEEP(OUT) exceeds 800mVP-P (Figure 8) and the

frequency of the beep signal is greater than 300Hz, the

beep signal is mixed into the active audio path (speaker

or headphone). If the signal at VBEEP(OUT) is either

<800mVP-P or <300Hz, 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 VBEEP(OUT)

times the gain of the selected signal path.

The input resistor (RB) sets the gain of the BEEP input

amplifier, and thus the amplitude of VBEEP(OUT). Choose

RB based on:

where RINT is the value of the BEEP amplifier feedback

resistor (47k

Ω) and VIN 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

800mVP-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 VDD 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.

INT

≤

MAX9750

VREF

DAC

HPVDD

VOL

Figure 6. Volume Control Circuit

GAIN

SPEAKER MODE

GAIN (dB)

HEADPHONE

MODE GAIN (dB)

10.5

Table 2. MAX9751 Gain Settings

SPEAKER MODE GAIN (dB)

GAIN1

GAIN2

MAX9750A

MAX9750B

MAX9750C

HEADPHONE MODE GAIN (dB)

10.5

16.5

7.5

13.5

19.5

10.5

Table 1. MAX9750 Maximum Gain Settings

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