SM5846AP datasheet(22/36 Pages) NPC

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SM5846AP

NIPPON PRECISION CIRCUITS—22

Output data round-off

Output data round-off processing is required because

the internal data length of the digital ﬁlter is different

from the output data length (internal data processing

width > output data width).

The SM5846AP can select either normal round-off

or dither round-off on the output data. Round-off

processing can be selected either by input pin or con-

trol ﬂag settings.

Normal round-off

Normal round-off is carried out by adding 1/2 LSB

to the ﬁlter output data to form 20/24-bit output data,

depending on the selected output data length.

MDS

DITH

ﬂag

Output

data

round-off

Notes

HIGH

Dither

round-off

The DITH ﬂag is set

HIGH (default) after a

system reset.

LOW

Normal

round-off

LOW

HIGH

Normal

round-off

LOW

Dither

round-off

Dither round-off

Dither round-off is carried out by adding a pseudo-

random number between 0 and 1 LSB, derived from

a rectangular distribution, to the ﬁlter output data to

form 20/24-bit output data, depending on the

selected output data length. The random number

rectangular distribution is shown below (average =

1/2 LSB).

Probavility

1/2

(LSB)

,,,,,,,,

Overﬂow limiter

If an overﬂow or underﬂow condition occurs after

round-off or ﬁlter arithmetic processing, the output

data will be ﬁxed at positive or negative maximum

value.

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