AD74115 Simultaneous Input and Output, Either Current or Voltage

Hi BillyTheFish ,

thank you for your querry.  In principle you are right.

Main channel function/mode would be available at terminals I/OP and I/ON. 

In parallel you can use SENSE_EXT1 (SENSE_EXT2) as single ended voltage input (or differential input).

AD74115 ADC allows to have configured two conversions. These conversion are then measured in single ADC sequence. (Conversion 1 - Main channel function/mode conversion, Conversion 2 - conversion related to SENSE_EXTn)

Probably following figure highlights, that SENSE_EXT1 (SENSE_EXT2) pins are not used for all channel functions/modes.

Please have in mind, SENSE_EXT1 and SENSE_EXT2 pins are used for 3W and 4W RTD measurements.

Please let me know, if there is anything else I can assist you further. 

Regards,

Arnost

Thanks, the scenario would be to use the AD74115H as a signal replacement controller, so would not be in parallel.

The idea being that the SENSE_EXT would be used to read incoming signals and the other circuit would be used to generate required output, thus 'replacing' the signal. ie 5mA replaced with 7mA.

Billy..

Thanks, the scenario would be to use the AD74115H as a signal replacement controller, so would not be in parallel.

The idea being that the SENSE_EXT would be used to read incoming signals and the other circuit would be used to generate required output, thus 'replacing' the signal. ie 5mA replaced with 7mA.

Billy..

Hi BillyTheFish ,

I am not sure, if I entirely understand your application. Maybe you might sketch the scenario or elaborate on it bit more?

However if you are looking for monitoring "output voltage" (or "current") you can use ADC filtered inputs SENSELF and SENSEHF (Not necessarily EXT pins.) ADC will take care of the measurements and DAC can be configured to drive output current as in the example. (Please note that Channel MUX is connected to ADC - "MAIN ADC" - MAIN DAC is typo in Datasheet.) 

For reference see: https://www.analog.com/media/en/technical-documentation/data-sheets/ad74115.pdf

Regards,

Arnost

Arnost,

I appreciate your help and what I'm asking is a very unusual indeed. I have made a simple diagram in an attempt to help explain.

The idea is that the controller may be sending a signal which due to external factors needs to be changed to improve performance. A controller may be opening a valve 50% but another related process is unable to support the increased flow so the valve should be momentarily only opened 30%. The original signal could be 10mA which would be changed to say 7mA.

Hi BillyTheFish ,

Thank you for your explanation of the challenge.

It is not clear to me what is the function of the "Signal Switching" block in your configuration could you elaborate on the function of this block, please? 

How is the Signal+ and Signal- (on Actuator side) affected by "Signal Switching" block? 

Does the change on Actuator side translates also to Controller side? 

Regards,

Arnost 

Thanks, it is a hopefully simple thing but I keep assuming I've missed something obvious.

If I change the drawing to be more like below it should simplify the problem (I hope). The switching would be used to interrupt the flow of 'normal' signals and output alternatives only when required, but if we work with the idea of input signal and output signal simultaneously, eg 5v input signal would be read and the MCU would generate a 5v output signal or whatever it required based on some logic.

Hi BillyTheFish ,

such a system will certainly work. 

Note:

SENSE inputs are in the end "ADC voltage inputs".

VIOUT is output of the DAC, which can generate output voltage or output Current.

Probably points of interest for your application (I believe you probably considered the same, alerady):

# Current output function can only source current - out of VIOUT pin.

# Voltage Output and current output is referenced towards GND. This means Signal- will be connected to GND of the SWIO.

Your application looks interesting to me.

Let me know, if there is anything else I can help you with.

Regards,

Arnost

Thanks, I was just doubting myself as it felt like I've missed something obvious.