DAC7750IPWPR datasheet(35/53 Pages) TI1

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DAC

ISET-R

HART

Signal

Conditioning

(ON Only in 4-mA

to 20-mA Range)

Cin

HART SIGNAL

RSET

NŸ

Rin

CAP2

AVDD

CAP1

BOOST

R3-SENSE

IOUT

HART-IN

DAC7750, DAC8750

www.ti.com

SBAS538B – DECEMBER 2013 – REVISED JUNE 2016

Product Folder Links: DAC7750 DAC8750

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Application Information (continued)

9.1.1.2 Using the ISET-R Pin

The second method to implement HART is to couple the HART signal through the ISET-R terminal when IOUT is

operated using an external RSET resistor. The FSK signal from the modem is ac-coupled into the terminal through

a series combination of Rin and Cin as shown in Figure 61.

Figure 61. Implementing HART with the ISET-R Terminal

The magnitude of the ac-current output is calculated with Equation 6.

(VHART × k) / Rin

where

•

VHART is the amplitude of the HART FSK signal from the modem

•

k is a constant that represents the gain transfer function from the ISET-R terminal to the IOUT terminal and

depends on the selected current output range as follows:

–

k = 60 for the 4-mA to 20-mA range

–

k = 75 for the 0-mA to 20-mA range

–

k = 90 for the 0-mA to 24-mA range

(6)

The series input resistor and capacitor form a high-pass filter at the ISET-R terminal. Select Cin to make sure

that all signals in the HART extended-frequency band pass through unattenuated.

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