DAC8760IPWPR datasheet(39/69 Pages) TI2

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8.4.4 HART Interface

On the DACx760, HART digital communication can be modulated onto the input signal by two methods:

8.4.4.1 For 4-mA to 20-mA Mode

This method is limited to the case where the RANGE bits of Table 8-17 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 second method

described in this section.

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 8-8 illustrates the output current versus time operation for a typical HART signal.

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

NOTE: DC current = 6 mA.

Figure 8-8. Output Current vs Time

Table 8-11 specifies the performance of the HART-IN pin.

Table 8-11. 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

8.4.4.2 For 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

Table 8-17 are set to the 4-mA to 20-mA range. To implement HART in all current-output modes, see Section

9.1.2.

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DAC7760, DAC8760

SBAS528D – JUNE 2013 – REVISED DECEMBER 2021

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