2.6W Stereo Audio Power Amplifiers and

DirectDrive Headphone Amplifiers

______________________________________________________________________________________

13

parasitic bond wire and trace inductance. Although not

typically required, additional high-frequency ripple atten-

uation can be achieved by increasing the size of C2 (see

the Typical Application Circuit).

Headphone Sense Input (HPS)

The headphone sense input (HPS) monitors the head-

phone jack and automatically configures the device

based upon the voltage applied at HPS. A voltage of

less than 0.8V sets the device to speaker mode. A volt-

age of greater than 2V disables the bridge amplifiers

and enables the headphone amplifiers.

For automatic headphone detection, connect HPS to the

control pin of a 3-wire headphone jack as shown in

Figure 5. With no headphone present, the output imped-

ance of the headphone amplifier pulls HPS low. When a

headphone plug is inserted into the jack, the control pin

is disconnected from the tip contact and HPS is pulled

BIAS

The MAX9750/MAX9751/MAX9755 feature an internally

generated, power-supply independent, common-mode

bias voltage of 1.8V referenced to GND. BIAS provides

both click-and-pop suppression and sets the DC bias

level for the amplifiers. 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.

Gain Selection

MAX9750

The MAX9750 features an internally set, selectable gain.

The GAIN1 and GAIN2 inputs set the maximum gain of

the MAX9750 speaker and headphone amplifiers (Table

1). The gain of the device can vary based upon the volt-

age at VOL (see the Analog Volume Control section).

However, the maximum gain cannot be exceeded.

MAX9751/MAX9755

The gain of the MAX9751/MAX9755 is set by the GAIN

input. Driving GAIN high sets the gain of the speaker

amplifiers to 9dB and the gain of the headphone ampli-

fiers to 0dB. Driving GAIN low sets the gain of the

speaker amplifiers to 10.5dB, and the gain of the head-

phone amplifiers to 3dB (Table 2).

Analog Volume Control (VOL)

The MAX9750 features an analog volume control that

varies the gain of the device in 31 discrete steps based

upon the DC voltage applied to VOL. The input range of

with example step sizes shown in Table 3. Connect the

are not constant; the step sizes are 0.5dB/step at the

upper extreme, 2dB/step in the midrange, and 4dB/step

at the lower extreme. Figure 7 shows the transfer function

of the volume control for a 3.3V supply.

ADDITIONAL THD+N DUE

TO DC-BLOCKING CAPACITORS

FREQUENCY (Hz)

10k

1k

100

0.001

0.01

0.1

1

10

0.0001

10

100k

TANTALUM

ALUM/ELEC

Figure 4. Distortion Contributed by DC-Blocking Capacitors

MAX9750/

MAX9751/

MAX9755

10

µA

1k

Ω

1k

Ω

20

14

13

HPS

HPOUTL

HPOUTR

SHUTDOWN

CONTROL

Figure 5. HPS Configuration