Datasheet
LTC2630
17
2630ff
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 27 28 29 30 31 32
C2 C1 C0 X X X X D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 X X X XC3XXXXXXXX
CS/LD
SCK
SDI
COMMAND WORD DATA WORD
8 DON’T-CARE BITS 4 DON’T-CARE BITS
2630 F03b
32-BIT INPUT WORD
Figure 3b. 32-Bit Load Sequence
LTC2630-12 SDI Data Word: 12-Bit Input Code + 4 Don’t-Care Bits (Shown);
LTC2630-10 SDI Data Word: 10-Bit Input Code + 6 Don’t-Care Bits;
LTC2630-8 SDI Data Word: 8-Bit Input Code + 8 Don’t-Care Bits
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
C2 C1 C0 X X X X D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 X X X XC3
CS/LD
SCK
SDI
COMMAND WORD 4 DON’T-CARE BITS DATA WORD
24-BIT INPUT WORD
2630 F03a
Figure 3a. 24-Bit Load Sequence (Minimum Input Word)
LTC2630-12 SDI Data Word: 12-Bit Input Code + 4 Don’t-Care Bits (Shown);
LTC2630-10 SDI Data Word: 10-Bit Input Code + 6 Don’t-Care Bits;
LTC2630-8 SDI Data Word: 8-Bit Input Code + 8 Don’t-Care Bits
operation
Optoisolated 4mA to 20mA Process Controller
Figure 5 shows how to use an LTC2630HZ to make an
optoisolated, digitally-controlled 4mA to 20mA transmit-
ter. The transmitter circuitry, including optoisolation, is
powered by the loop voltage which has a wide range of
5.4V to 80V. The 5V output of the LT
®
3010-5 is used to
set the 4mA offset current and V
OUT
is used to digitally
control the 0mA to 16mA signal current. The supply cur-
rent for the regulator, DAC, and op amp is well below
the 4mA budget at zero scale. R
S
senses the total loop
current, which includes the quiescent supply current and
additional current through Q1. Note that at the maximum
loop voltage of 80V, Q1 will dissipate 1.6W when I
OUT
=
20mA and must have an appropriate heat sink.
R
OFFSET
and R
GAIN
are the closest 0.1% values to ideal
for controlling a 4mA to 20mA output as the digital input
varies
from zero scale to full scale. Alternatively, R
OFFSET
can be a 365k, 1% resistor in series with a 20k trim pot
and R
GAIN
can be a 75.0k, 1% resistor in series with a 5k
trim pot. The optoisolators shown will limit the speed of
the serial bus; the 6N139 is an alternative that will allow
higher data rates.