DAC8750IPWPR datasheet(29/56 Pages) TI2

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8.4.6 HART Interface

For the DACx750, HART digital communication can be modulated onto the input signal by the methods shown in

the following subsections. For more detail, see Implementing HART Communication with the DAC8760 Family.

8.4.6.1 Implementing HART in 4-mA to 20-mA Mode

This method is limited to the case where the RANGE bits of the Control Register are programmed to the 4-mA

to 20-mA range. Some applications require going beyond the 4-mA to 20-mA range. In those cases, see the

methods described in the next subsection.

The external HART signal (ac voltage; 500 mVPP, 1200 Hz, and 2200 Hz) can be capacitively coupled in through

the HART-IN pin and transferred to a current that is superimposed on the 4-mA to 20-mA current output. The

HART-IN pin has a typical input impedance of 35 kΩ that together with the input capacitor used to couple the

external HART signal, forms a filter to attenuate frequencies beyond the HART band-pass region. In addition

to this filter, an external passive filter is recommended to complete the filtering requirements of the HART

specifications. Figure 8-7 shows the output current versus time operation for a typical HART signal. Table 8-6

specifies the performance of the HART-IN pin.

Bit

Boundary

Phase

Continuous

2200 Hz

(space)

1200 Hz

(mark)

Time

5.5 mA

6.5 mA

6.0 mA

Bit Cell Time = 833 s

DC current = 6 mA.

Figure 8-7. Output Current vs Time

Table 8-6. HART-IN Pin Characteristics

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX UNIT

Input impedance

HART signal ac-coupled into pin

kΩ

Output current (peak-to-peak)

Input signal of 500 mV (peak-to-peak)

0.9

1.1

8.4.6.2 Implementing HART in All Current Output Modes

The use of the HART-IN pin to implement HART modulation is limited to the case where the RANGE bits of the

Section 8.6.1.1 are set to the 4-mA to 20-mA range. If it is desirable to implement HART in all current-output

modes, see Section 9.1.1.

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DAC7750, DAC8750

SBAS538D – DECEMBER 2013 – REVISED DECEMBER 2021

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