Shutdown

The MAX9770 features a 0.1µA, low-power shutdown

mode that reduces quiescent current consumption and

extends battery life. Drive SHDN low to disable the

drive amplifiers, bias circuitry, and charge pump. Bias

is driven to GND and the headphone amplifier output

impedance is 10k

Ω in shutdown. Connect SHDN to

Click-and-Pop Suppression

Speaker Amplifier

The MAX9770 speaker amplifier features comprehensive

click-and-pop suppression that eliminates audible tran-

sients on startup and shutdown. While in shutdown, the

H-bridge is in a high-impedance state. During startup or

power-up, the input amplifiers are muted and an internal

loop sets the modulator bias voltages to the correct lev-

els, preventing clicks and pops when the H-bridge is

subsequently enabled. For 30ms following startup, a

soft-start function gradually unmutes the input amplifiers.

Headphone Amplifier

In conventional single-supply headphone drivers, the

output-coupling capacitor is a major contributor of

audible clicks and pops. Upon startup, the driver

charges the coupling capacitor to its bias voltage, typi-

cally half the supply. Likewise, during shutdown, the

capacitor is discharged to GND. This results in a DC

shift across the capacitor, which in turn, appears as an

audible transient at the speaker. Since the MAX9770

headphone amplifier does not require output-coupling

capacitors, this does not arise.

Additionally, the MAX9770 features extensive click-and-

pop suppression that eliminates any audible transient

sources internal to the device. The Power-Up/Power-

Down Waveform in the Typical Operating Characteristics

shows that there are minimal spectral components in the

audible range at the output upon startup or shutdown.

In most applications, the output of the preamplifier dri-

ving the MAX9770 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

capacitor and an audible click/pop. An internal delay of

50ms eliminates the click/pop caused by the input filter.

Applications Information

Filterless Operation

Traditional Class D amplifiers require an output filter to

recover the audio signal from the amplifier’s output. The

filters add cost, increase the solution size of the amplifi-

er, and can decrease efficiency. The traditional PWM

peak-to-peak) at idle and causes large ripple currents.

Any parasitic resistance in the filter components results

in a loss of power, lowering efficiency.

1.2W Low-EMI, Filterless, Mono Class D Amplifier

with Stereo DirectDrive Headphone Amplifiers

16

______________________________________________________________________________________

Table 3. Gain Selection

GAIN1

GAIN2

SPEAKER

GAIN

(dB)

HEADPHONE

GAIN

(dB)

SPEAKER

OUTPUT

POWER

(mW)

SPEAKER

OUTPUT

POWER

(mW)

HEADPHONE

OUTPUT

POWER

(mW)

HEADPHONE

OUTPUT

POWER

(mW)

0

0

6

7

500 / 4

Ω

500 / 8

Ω

60* / 32

Ω

60* / 32

Ω

0

1

3

4

250 / 4

Ω

500 / 4

Ω

78 / 16

Ω

60* / 32

Ω

1

0

9

-2

500 / 8

Ω

1000 / 8

Ω

19 / 16

Ω

39 / 16

Ω

1

1

0

1

124 / 4

Ω

250 / 4

Ω

39 / 16

Ω

78 / 16

Ω

*Output power limited to 60mW due to output voltage swing.

Table 4. Gain Settings with HPS

Connection

GAIN1

GAIN2

SPEAKER MODE

GAIN

(HPS = 0)

HEADPHONE

MODE GAIN

(HPS = 1)

HPS

0

6

-2

HPS

1

3

1

0

HPS

6

4

1

HPS

9

1

HPS

HPS

6

1

00

6

7

01

3

4

10

9

-2

11

0

1