ZHCSHP3 February 2018 DAC8771
PRODUCTION DATA.
On the DAC8771, digital communication such as HART can be modulated onto the current output signal.
If the RANGE (address 0x04) bits are programmed such that the IOUT is enabled, the external HART signal (ac voltage; 500 mVPP, 1200 Hz and 2200 Hz) can be capacitively coupled in through the HARTIN pin and transferred to a current that is superimposed on the current output. The HARTIN pin has a typical input impedance of 20 kΩ to 30 kΩ, depending on the selected current output range, which together with the input capacitor used to couple the external HART signal into the HARTIN pin can be used to form a high-pass filter to attenuate frequencies below the HART bandpass region. In addition to this filter, an external passive filter is recommended to complete the filtering requirements of the HART specifications. Figure 101 illustrates the output current vs time operation for a typical HART interface.
NOTE:
DC current = 6 mA.The HART pin for the selected channel can be enabled by writing logic '1' to the HTEN bit at address 0x04 (Table 4 and Table 5).