LTC2630-HM10 Просмотр технического описания (PDF) - Linear Technology

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LTC2630-HM10

Single 12-/10-/8-Bit Rail-to-Rail DACs with Integrated Reference in SC70

Linear Technology 

LTC2630

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 VOUT 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. RS 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 IOUT =

20mA and must have an appropriate heat sink.

ROFFSET and RGAIN 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, ROFFSET

can be a 365k, 1% resistor in series with a 20k trim pot

and RGAIN 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.

CS/LD

SCK

SDI

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

C3 C2 C1 C0 X X X X D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 X X X X

2630 F03a

COMMAND WORD

4 DON’T-CARE BITS

DATA WORD

24-BIT INPUT WORD

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

CS/LD

SCK

SDI

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

X X X X X X X X C3 C2 C1 C0 X X X X D11 D10 D9 D8 D7 D6 D5 D4 D3 D2 D1 D0 X X X X

8 DON’T-CARE BITS

COMMAND WORD

4 DON’T-CARE BITS

32-BIT INPUT WORD

DATA WORD

2630 F03b

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

2630f

16

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