SM5849F datasheet(17/26 Pages) NPC

17 / 26 page

SM5849AF

NIPPON PRECISION CIRCUITS—17

Attenuation (MDT, MCK, MLEN)

The digital attenuator coefﬁcients are read in as

serial data on the microcontroller interface. Data on

MDT is read into the internal shift register on the ris-

ing edge of MCK, and then 12 bits are latched inter-

nally on the rising edge of MLEN.

When the leading bit is 0 (D1 = LOW), the following

11 bits are read into the attenuation register and used

as an unsigned integer in MSB ﬁrst format. See ﬁg-

ure 3.

Although the attenuation data comprises 11 bits,

only 1025 levels are valid as given by the following.

The gain of the attenuator for values of DATT from

001H to 400H are given by the following equations.

Note that when the F12DB ﬂag is HIGH, the gain is

shifted by a ﬁxed +12.0412dB.

After a system reset initialization, DATT is set to

400H and the F12DB ﬂag is LOW, corresponding to

0dB gain. (The F12DB ﬂag is described in table 3.)

Figure 3. Attenuation data format (microcontroller interface)

MCK

MDT

MLEN

MSB

LSB

D10

D11

D12

,,,,,

,,,,,,,,,

,,,,,

B10

"L"

DATT

–

()

∑

Gain

DATT

1024

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





log

[dB]

DATT

256

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





log

[dB]

when F12DB = LOW

when F12DB = HIGH

Table 6. Attenuator settings

Attenuation data

DAT T

F12DB = LOW (default)

F12DB = HIGH

Gain (dB)

Linear expression

Gain (dB)

Linear expression

LO W

000H

−∞

0.0

−∞

0.0

001H

−60.206

1/1024

−48.165

1/256

↓↓↓↓↓

100H

−12.041

256/1024

0.0

256/256

↓↓↓↓↓

3FFH

−0.0085

1023/1024

12.032

1023/256

400H (to 7FFH)

1.0

12.041

4.0

SM5849F Datasheet(PDF) 17 Page - Nippon Precision Circuits Inc

SM5849F Datasheet(HTML) 17 Page - Nippon Precision Circuits Inc

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Datasheet Download

Link URL