Hall current sensor simulation

Feb 22, 2015 3 Replies
P

Hello all,



I am trying to simulate in LTSpice a circuit which contains a Hall effect current sensor (ACS758 for that matter). I don't have its model, but the simulation doesn't need to cover all the corner cases, even a simplified model would be enough:



There is a 100uOhm resistor R. The voltage drop across it should produce isolated voltage 2.5V+40[mV/A]*I(R).



I can handicraft an opamp-based network which does more or less what needed, but I consider it to be a workaround. So, what is the simplest way to express such a circuit in LTSpice? The "voltage" library node doesn't contain the "expression" mode or whatever its name should be. Is there a four-terminal abstract block to do this kind of transformations?



Best regards, Piotr


Vote
Twitter Facebook LinkedIn
P

Found it under the very descriptive name "E", LOL! :-D

Best regard, Piotr

Vote
Twitter Facebook LinkedIn
T

Hey Piotr, why are you doing this with a current sense resistor? AFAIK the Hall sensor more or less acts like a current-controlled voltage source, which Spice provides, and calls "H". IIRC, you put a voltage source in series, with the voltage set to zero, then you put the "H" block wherever you need it, with a reference to the voltage source you placed.

If the Hall sensor has some specified internal resistance (that 100u-ohm? ), I think I'd still simulate it as a resistor in series with the sensing voltage source, and use an "H" block.

Just a simple H block won't simulate any output impedance, frequency- dependence, nonlinear behaviors, etc. But you knew that.

Tim Wescott Wescott Design Services http://www.wescottdesign.com
Vote
Twitter Facebook LinkedIn
P

Because the the ACS758 datasheet says that the resistance of the current path is ~100uOhm. So, since there is this "resistor" already, I simply decided to use this fact. I am still learning Spice, so I didn't know about its more advanced primitive blocks. Let alone about how to use them correctly.

Since I've already mastered "E", there is time to learn "H". ;-)

Yes, but that doesn't matter here. The frequency is 100Hz, the currents are within the specified range and I simply wanted to check whether the Hall sensor could be used to correctly drive a synchronous rectifier. And Spice says it can, much better than the standard comparator-based approach, as there are no oscillations. Its primary purpose was overcurrent protection, but since the signal is already available, I wanted to see what would happen. I set the threshold to 0.25A and combined its output with the outputs of the sign detector -- voila, it works and seems to be very robust.

One stupid thing about the ACS75* and similar sensors design: three output terminals. The output voltage is specified to be VCC/2 + V(I), but they do not expose their VCC/2 in order to allow accurate differential measurements. And they say that the drift can be +-25mV, which is half an amp of an error...

Best regards, Piotr

Vote
Twitter Facebook LinkedIn

Join the Discussion

Have something to add? Share your thoughts — no account required.

Didn't find your answer?

Ask the community — no account required