BU7831KN_06 Datasheet, PDF (7/17 Pages) Rohm – Voice/Audio Mixer & Selector

●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.
CVCOM
4.7μF
CSTART
1μF
Pre
charge
30k
30k
Pre
charge
140k
140k
CVCOM_OUT
To the one except for the headphone
amplifier output step
CSTART_OUT
To the headphone amplifier output step
Fig.22 CVCOM, CSTRT equivalent circuit
・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
200kΩ(TYP)
400kΩ(TYP)
ATT1 L (R) setting
0dB setting
Mute setting
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