SM5849F Datasheet, PDF (17/26 Pages) Nippon Precision Circuits Inc – Asynchronous Sample Rate Converter

SM5849AF
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.
MLEN
MMCD_,,,,,,KT _{,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,}
1
D1
D2
D3
D4
D5
D6
D7
D8
D9
D10
D11
D1212^{,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,}
MSB
LSB
"L"
B0
B1
B2
B3
B4
B5
B6
B7
B8
B9
B10
Figure 3. Attenuation data format (microcontroller interface)
Although the attenuation data comprises 11 bits,
only 1025 levels are valid as given by the following.
10
∑ ^{DATT =}
a_i × 2^{(10 – i)}
i=0
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.
Gain
=
20
×
log


D--1---A0---2-T--4--T--_
[dB]
when F12DB = LOW
=
20
×
log


D----2-A--5--T-6---T--_
[dB]
when F12DB = HIGH
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.)
Table 6. Attenuator settings
D1
Attenuation data
DATT
F12DB = LOW (default)
Gain (dB)
Linear expression
F12DB = HIGH
Gain (dB)
Linear expression
000H
−∞
0.0
−∞
0.0
001H
−6 0 . 2 0 6
1/1024
−4 8 . 1 6 5
1/256
↓
↓
↓
↓
↓
LOW
100H
−1 2 . 0 4 1
256/1024
0.0
256/256
↓
↓
↓
↓
↓
3FFH
−0 . 0 0 8 5
1023/1024
12.032
1023/256
400H (to 7FFH)
0
1.0
12.041
4.0
NIPPON PRECISION CIRCUITS—17