LTC1655C Ver la hoja de datos (PDF) - Linear Technology

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Fabricante

LTC1655C

16-Bit Rail-to-Rail Micropower DACs in SO-8 Package

Linear Technology 

LTC1655/LTC1655L

TYPICAL APPLICATIONS

This circuit shows how to use an LTC1655 to make an

optoisolated digitally controlled 4mA to 20mA process

controller. The controller circuitry, including the

optoisolation, is powered by the loop voltage that can have

a wide range of 6V to 30V. The 2.048V reference output of

the LTC1655 is used for the 4mA offset current and VOUT

is used for the digitally controlled 0mA to 16mA current.

RS is a sense resistor and the op amp modulates the

transistor Q1 to provide the 4mA to 20mA current through

this resistor. The potentiometers allow for offset and full-

scale adjustment. The control circuitry dissipates well

under the 4mA budget at zero scale.

An Isolated 4mA to 20mA Process Controller

LT®1121-5

IN OUT

1µF

FROM

OPTOISOLATED

INPUTS

150k

1% 20k

8

6

1

VCC

CLK

VREF

75k

2

DIN

LTC1655 VOUT 7 1%

5k

3 CS/LD

GND

5

3+

7

LT®1077

3k 2 –

4

6 1k

CLK

DIN

CS/LD

5V

OPTOISOLATORS

500Ω

4N28

10k

CLK

DIN

CS/LD

VLOOP

6V TO 30V

Q1

2N3440

RS

10Ω

IOUT

1655/55L TA03

11

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