Using 2 shunts only

[PCama.1]

I designed my own motor controller board and it works fine. For the next revision, I am looking into reducing parts count and simplifying schematics a bit.

In the sense control area, I have tested the option of using the internal gain for the OpAmps and it works great. Digging into the code, I noticed that there are only two OpAmps being used. So is it possible to eliminate the third shunt?

I noticed an input for the positive side from a third shunt (generated by the 5.Y.4. MC Workbench). That is the M1_CURR_SHUNT_W which is a signal on OPAMPV2_VINP_SEC and COMP4.

Is it possible to eliminate it? I really wanted that pin if available for one of my Hall sensors input.

[KnarfB]

There are variants calculating the 3rd value by Kirchhoff's current law, and there are even 1 shunt variants. They might be more difficult to use or show some tradeoffs.

hth

KnarfB

[PCama.1]

@KnarfB​ thank you.

That's my question: I want to calculate the 3rd value based on the other two. Do you have any implementation ideas?

[KnarfB]

No, not really. Haven't done that in practice. The idea is Ia+Ib+Ic=0, but it is also important to measure Ia Ib at the right moment. There are app notes and tutorials by a number of different chip vendors.

hth

KnarfB

[PCama.1]

You are right, timing of measure is critical. Maybe that is why in ST implementation they still use the input from the third shunt. I will look into it and dig into the code. Thank you again.

In the meantime, if anyone has implemented it, I welcome comments.