In order to acquire readings from one or more HART-enabled Loop-Powered Smart Transmitters, we are planning to use AD5700 in HART Master Mode. It would be of immense help, if one can give us a reference circuit using AD5700 in HART Master Mode. At high-level the functional diagram is as shown below. Thanks a lot !
Hi Corvid Team,
1. Yes, you can use the circuit in Fig 28 to interface one or more HART Field Instruments in Multi-drop mode if all HART Field Instruments communicate only through HART.
2. Yes, you must…
Please take a look at the following reference designs: CN0414, CN0418, or CN0435 (PLC/DCS system example).
1. Please check out the schematic of EVAL-AD5700-1EBZ. Probably this is a mistake in the mentioned figure.That capacitor should be 22nF like is mentioned also in datasheet.
2. For low impedance…
Thank you for the quick response. We went through all the reference circuits. It gave us a fair bit of idea. It helped us to understand that the circuit given in page #17 of AD5700/AD5700-1 data sheet, may also fit our requirement.
Thank youCorvid Team
Thanks a lot, Mihai !!
We have 2 follow-up questions:
1. We trying the above circuit using AD5700 evaluation board (EVAL-AD5700-1EBZ). We noticed that in the evaluation board, there is a 22nF capacitor instead of 10nF near the HART_OUT pin. Is it fine to use 22nF in place of 10nF as is without changing rest of the circuit components ? Please advice.
2. Our MCU has an in-built 12-bit ADC and it works with 3.3V. So we are using 165Ω resistor instead of 250Ω resistor. Do we need to change 20kΩ resistor and 10μF capacitor as well ? Please advice.
2. For low impedance devices, the RLOAD range is typically 230 Ω to 600 Ω.
The circuit worked as per our expectation.
Great. We are glad that we were able to help you.