ZHCSBX4D June 2013 – December 2021 DAC7760 , DAC8760
PRODUCTION DATA
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.
Table 8-11 specifies the performance of the HART-IN pin.
PARAMETER | TEST CONDITIONS | MIN | TYP | MAX | UNIT |
---|---|---|---|---|---|
Input impedance | HART signal ac-coupled into pin | 35 | kΩ | ||
Output current (peak-to-peak) | Input signal of 500 mV (peak-to-peak) | 0.9 | 1 | 1.1 | mA |