MAX9720 查看數據表（PDF） - Maxim Integrated

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MAX9720

50mW, DirectDrive, Stereo Headphone Amplifier with SmartSense and Shutdown

Maxim Integrated 

50mW, DirectDrive, Stereo Headphone

Amplifier with SmartSense and Shutdown

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 VDD.

When a headphone plug is inserted into the jack, the

control pin is disconnected from the tip contact, and

HPS is pulled to VDD through the internal 100kΩ pullup.

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).

Shutdown

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.

Forced Mono Mode

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.

Forced Stereo Mode

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.

ALERT Output

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.

Click-and-Pop Suppression

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.

TIP

(SIGNAL)

SLEEVE

(GND)

Figure 6. Typical 2-Wire (Mono) Headphone Plug

VDD

MAX9720

R1

100kΩ

HPS

15

OUTL

16

OUTR

14

Figure 7. HPS Configuration

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 RIN and CIN, relative to the startup

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.

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