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5

MAX9723D Evaluation Kit/Evaluation System

Detailed Description of Hardware

BassMax Component Selection

PCB components R5, R6, and C9 set the bass boost for

the left channel, while components R4, R3, and C10 set

the bass boost for the right channel (see Figure 6). The

default bass boost is +8.8dB. Changing the components

listed above modifies the bass-boost gain and frequency

response. For example, when bass boost is enabled, the

ratio of R5 and R6 sets the left-channel bass boost gain

tion. Adjust resistors R4 and R3 to set the right-channel

bass boost.

To maintain circuit stability, the ratio:

must not exceed 1/2 (a ratio of 1/3 is recommended).

The switch that shorts BB_ to SGND, when BassMax is

disabled, can have an on-resistance as high as 300Ω.

Choose a value for R5 (R3) greater than 40kΩ to ensure

that positive feedback is negligible when BassMax is

disabled. Table 3 contains a list of R6 (R3) values, with

R5 (R4) = 47kΩ, and the corresponding low-frequency

gain.

The low-frequency boost attained by the BassMax cir-

cuit is added to the gain realized by the volume setting.

Select the BassMax gain so that the output signal

remains within the dynamic range of the MAX9723.

Output signal clipping occurs at low frequencies if the

BassMax gain boost is excessively large (refer to the

Output Dynamic Range section in the MAX9723 data

sheet).

R

RR

6

56

+

A

RR

RR

V BOOSTL

_

log

=×

+

⎛

⎝

⎜

⎞

⎠

⎟

−

20

56

56

MAX9723D

R

R

OUT_

BB_

R5

(R4)

*REFERENCE DESIGNATORS IN PARENTHESIS INDICATE RIGHT-CHANNEL COMPONENTS.

R6

(R3)

AUDIO INPUT

BASSMAX

ENABLE

C9

(C10)

Figure 6. Bass Boost External Components for Left Channel

R6 (R3) (k

Ω)

AV GAIN (dB)

39

20.6

33

15.1

27

11.3

22

8.8

15

5.7

10

3.7

Note: Reference designators in parenthesis indicate right-

channel components.

Table 3. BassMax Gain Examples—R5

(R4) = 47kΩ

GAIN PROFILE WITH AND

FREQUENCY (Hz)

10,000

1000

100

-2

0

2

4

6

8

10

12

14

16

MAX9723D

R5(R3) = 47kΩ

R6 (R4) = 22.1kΩ

C9 (C10) = 0.1µF

-4

10

100,000

Figure 7. BassMax, Gain Profile Example for AV_VOL = +6dB