SM5846AP datasheet(21/36 Pages) NPC

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SM5846AP

NIPPON PRECISION CIRCUITS—21

"0"

bit1

bit2

bit3

bit4

bit5

bit6

bit7

bit8

MSB

LSB

DATT attenation data (7bit)

Attenuation setting

The data stored in the D-ATT attenuation register,

accessed through the microprocessor interface,

determines the attenuation setting of the digital

attenuator. The D-ATT register data format is shown

below.

The attenuation setting is given by the following

equations.

The attenuation for a selection of values is given in

the following table.

DATT register

value

Microprocess

or command

(hex)

Attenuation

(dB)

Relative gain

00H

× 1.0

01H

−0.137

× 0.984375

02H

−0.206

× 0.9765625

↓↓↓↓

3FH

−6.021

× 0.5

40H

−6.157

× 0.4921875

↓↓↓↓

125

7DH

−36.12

× 0.015625

126

7EH

−42.14

× 0.0078125

127

7FH

−∞

× 0

Attenuation

0 [dB]

Attenuation

20log

127

DATT

–

128

-------------------------------





[dB]

Attenuation

∞

–

DATT = 0

()

0 < DATT <127

()

DATT = 127

()

Digital attenuator operation

The attenuation register is reset to 0 (attenuation = 0

dB) after a system reset signal.

When data is written to the attenuation register,

through the microprocessor interface, the attenuation

changes from the current value to the new value at

the speed shown in the following table.

Soft muting operation

Soft muting ON/OFF is controlled by the MUTE

ﬂag, accessed through the microprocessor interface.

When muting is ON, the attenuation ramps down to

−∞ at the speed shown in the table. Similarly when

muting is OFF, the attenuation level returns to the

original value at the same speed.

If the contents of the DATT attenuation register are

changed while muting is ON (attenuation =

−∞),

only the register contents are replaced. If muting is

subsequently turned OFF, the attenuation value

changes to the new value at the same speed as shown

in the table.

Operating speed

Speed of

attenuation change

Time from min. to

max. attenuation

Normal-speed

sampling

8/fs per step change

1016/fs (23.0 ms at

44.1 kHz)

High-speed sampling

16/fs per step change

2032/fs (23.0 ms at

88.2 kHz)

MUTE

Muting

Notes

HIGH

OFF

The MUTE ﬂag is set HIGH (default) after a

system reset.

LOW

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