Technical Note

7/16

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2010.09 - Rev.A

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BU7831KN

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Detail explanation of each function blocks

・

Reference Voltage (Bias part)

The reference voltage occurrence part that decides the operating point of a group of internal amplifiers is the following.

CVCOM_OUT, CSTART_OUT, all is about 1/2VDD[V], and therefore the level of internal signal becomes about 1/2VDD[V],

too. CVCOM has a pre-charge function, and it is possible to shorten of rising time of the bias in ON.

(As for the CVCOM, ON/OFF of the pre-charge function is possible with a register bit.)

CSTART terminal is used as a reference voltage of the output amplifier of the headphone, and it included pop sound low

stage function in headphone path ON/ OFF, too.

Capacitor value with the outside in the figure is recommended to make the PSRR character of both standard voltages the

same. Choose the thing whose character is good in Capacitor with the outside because it becomes the reference voltage

of the internal circuit.

Pre

Pre

charge

charge

CVCOM

CSTART

30k

30k

4.7μF

140k

140k

1μF

Fig.22 CVCOM, CSTRT equivalent circuit

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Analog input part

The following is about each analog. Input. Please use the coupling capacitor with the outside in consideration of frequency

characteristic of input. Input DC level is about 1/2VDD[V]. Input impedance on off (input non-choice) becomes Hi-z. When

an input terminal isn’t used (when an input path isn’t set up) is open, and there is no problem. But, be careful that noise

from the outside and so on doesn’t turn because it becomes Hi-z. When it is anxious, pull-down in about 100kΩ.

ST1L and ST1R inputs change input impedance by setting of ATT1L and ATT1R respectively.

ST1L(R) input impedance

ATT1 L (R) setting

200kΩ(TYP)

0dB setting

400kΩ(TYP)

Mute setting

CVCOM_OUT

200k

200k

ST1L

ST1R

ST2L

ST2R

ST3L

ST3R

CVCOM_OUT

100k

100k

100k

Fig.23 Input pins equivalent circui

CSTART_OUT

To the headphone amplifier output step

CVCOM_OUT

To the one except for the headphone amplifier output step