MAX9723(2005) 查看數據表（PDF） - Maxim Integrated

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MAX9723
(Rev.:2005)

Stereo DirectDrive Headphone Amplifier with BassMax, Volume Control, and I2C

Maxim Integrated 

Stereo DirectDrive Headphone Amplifier with

BassMax, Volume Control, and I2C

COMMAND BYTE IS STORED ON

RECEIPT OF STOP CONDITION

ACKNOWLEDGE FROM MAX9723

B7 B6 B5 B4 B3 B2 B1 B0

S SLAVE ADDRESS

0 ACK COMMAND BYTE

ACK P

R/W

ACKNOWLEDGE

FROM MAX9723

Figure 6. Write Data Format Example

The MAX9723A and MAX9723B have a maximum gain

setting of -5dB or 0dB, while the MAX9723C and

MAX9723D have a maximum gain setting of +1dB or

+6dB. B5 in the command register programs the maxi-

mum gain (see Tables 5 and 6).

Adjust the MAX9723’s amplifier gain with the volume

control bits [4:0]. The gain is adjustable to one of 32

steps ranging from full mute to the maximum gain pro-

grammed by B5. Tables 7–10 list all the possible gain

settings for the MAX9723. Figures 7–10 show the vol-

ume control transfer functions for the MAX9723.

Power-On Reset

The contents of the MAX9723’s command register at

power-on are shown in Table 11.

Applications Information

Power Dissipation and Heat Sinking

Linear power amplifiers can dissipate a significant

amount of power under normal operating conditions.

The maximum power dissipation for each package is

given in the Absolute Maximum Ratings section under

Continuous Power Dissipation or can be calculated by

the following equation:

PD(MAX)

=

TJ(MAX) −

θJA

TA

where TJ(MAX) is +150°C, TA is the ambient tempera-

ture, and θJA is the reciprocal of the derating factor in

°C/W as specified in the Absolute Maximum Ratings

section. For example, θJA for the thin QFN package is

+59°C/W.

The MAX9723 has two power dissipation sources, the

charge pump and the two output amplifiers. If the

power dissipation exceeds the rated package dissipa-

Table 5. MAX9723A and MAX9723B

Maximum Gain Control

MAXIMUM GAIN (dB)

B5

-5

0

0

1

Table 6. MAX9723C and MAX9723D

Maximum Range Control

MAXIMUM GAIN (dB)

B5

+1

0

+6

1

tion, reduce VDD, increase load impedance, decrease

the ambient temperature, or add heatsinking. Large

output, supply, and ground traces decrease θJA, allow-

ing more heat to be transferred from the package to

surrounding air.

Output Dynamic Range

Dynamic range is the difference between the noise

floor of the system and the output level at 1% THD+N. It

is essential that a system’s dynamic range be known

before setting the maximum output gain. Output clip-

ping will occur if the output signal is greater than the

dynamic range of the system. The DirectDrive architec-

ture of the MAX9723 has increased dynamic range

compared to other single-supply amplifiers.

Use the THD+N vs. Output Power in the Typical

Operating Characteristics to identify the system’s

dynamic range. Find the output power that causes 1%

THD+N for a given load. This point will indicate what

output power causes the output to begin to clip. Use

the following equation to determine the peak output

voltage that causes 1% THD+N for a given load.

VOUT _(P−P) = 2 2(POUT _1% × RL)

where POUT_1% is the output power that causes 1%

THD+N, RL is the load resistance, and VOUT_(P-P) is the

peak output voltage. After VOUT_(P-P) is identified,

determine the peak input voltage that can be amplified

without clipping:

VIN_(P−P)

=

VOUT _(P−P)



10

AV

20





where VIN_(P-P) is the largest peak voltage that can be

amplified without clipping, and AV is the voltage gain of

14 ______________________________________________________________________________________

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