lc75412e Sanyo Semiconductor Corporation, lc75412e Datasheet - Page 19

• Manufacturer Part Number: lc75412e
• Description: Electronic Volume Controller For Car Audio Systems
• Manufacturer: Sanyo Semiconductor Corporation

Usage Cautions
(1) Data transmission at power ON
(2) Description of zero-cross switching circuit operation
(3) Zero-cross switching control method
(4) Zero-cross timer setting
The LC75412E and 75412W have a function to switch zero-cross comparator signal detection locations, enabling the
selection of the optimum detection location for blocks whose data is to be updated. Basically, the switching noise can
be minimized by inputting the signal immediately following the block whose data is to be updated to the zero-cross
comparator, so it is necessary to switch the detection location every time.
The zero-cross switching control method consists of setting the zero-cross control bits to the zero-cross detection
mode (D36, D37 = 0), and specifying the detection blocks (D38, D39) before transmitting the data. These control bits
are latched immediately following data transfer, that is to say beforehand in sync with the falling edge of CE, so when
updating data of volumes, etc., it is possible to perform mode setting and zero-cross switching with one data transfer.
An example of control when updating the data of the volume block is shown below.
If the input signal becomes lower than the zero-cross comparator detection sensitivity, or if only low-frequency
signals are input, zero-cross detection continues to be impossible, and data is not latched during this time.
The zero-cross timer can set a time for forcible latch during such a status when zero-cross detection is not possible.
For example, to set 25 ms,
using T = 0.69CR and C = 0.033 µF,
we obtain
Normally, a value between 10 ms and 50 ms is set.
• The status of internal analog switches is unstable at power ON. Therefore, perform muting or some other
R=
countermeasure until the data has been set.
Zero-cross detection
D36
0
0.69
mode setting
25 10
0.033
D37
0
Selector
–3
10
–6
D38
LC75412E, 75412W Zero-Cross Detection Circuit
1
Volume block
1.1 M
setting
D39
0
Volume
LC75412E, 75412W
Tone
Switch
comparator
Zero-cross
Fader
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