HART Modem AD5700

AD5700_5700-1.pdf (549.9 KB)

Hi everyone, I am researching upon HART modems and transmitters, looking to build my own. However, I have a question upon reading the AD5700 Datasheet (attached).

In the pdf I attached, on page 19 & 20, are Figures 31 & 32 the same diagram?
Because Fig.32 has omitted many resistor & capacitor values while Fig.31 labels all of them.

For example, in Fig.32 are the values under Regin and VLoop in AD5421 the same as the ones for AD5421 in Fig.31?

Is there any difference between Fig.31 and Fig.32 other than Fig.32 zooming into the internals?

Thank you. Appreciate any help on this!

Hello bryank00h,

After reviewing the diagrams for Figure 31 & 32, I believe they’re demonstrating different but similar things. That is to say Figure 31 is showing an actual complete circuit that the part could be used in. Figure 32 is more abstract, showing the block diagram of an application, the part could be designed in. I believe the second diagram exists to show more of the intelligence that could be applied, however they do state the following:

Figure 31 shows how the AD5700/AD5700-1 HART modem
can be interfaced with the AD5421(4 mA to 20 mA loop-powered
DAC) and the ADuCM360 microcontroller to construct a loop
powered transmitter circuit. The HART signal from
HART_OUT is introduced to the AD5421 via the CIN pin.

The HART enabled smart transmitter reference demo circuit
(the block diagram shown in Figure 32) was developed by
Analog Devices and uses the AD5421, a 16-bit, loop-powered,
4 mA to 20 mA DAC, the ADuCM360 microcontroller and the
AD5700 modem. This circuit has been compliance tested,
verified, and registered as an approved HART solution by the
HART Communication Foundation.

This statement implies that it might be generally the same circuit but with the emphasis on the communication. It does note that you should reach out to them if you want specification of the demo circuit, which also alludes to the thought that there may be more to the circuit not displayed in Figure 32. As such, if you’re using these as references in your own build, I highly recommend you reach out to them directly for the full schematic.

Regards,
Klint