Couple of points, I set the copper up to allow a person to have an easier choice of sense resistors buy using parallel resistors. You don't have to use parallel resistors. For the sake of discussion, I will refer to one sense resistor, Rsense. If a person uses parallel resistors, consider the parallel electrical equavalent as Rsense.
For the SLA7062 Itrip=Vref/RS i.e. ohms law I=E/R. The voltage at the sense input needs to be less than 2V at Itrip (coil current rating) and no less than .1V (Allegro's recommendation). Above 2V the SLA7062 goes into sleep mode. Say you can get four 1ohm 1W resistors. The parallel value is .5ohm at 2W. At 3A you will develop 1.5V across the sense resistor, but it would require 4.5W total. So that would be a bad choice. So lets say you can get 1/2ohm 1 watt resistors. the electrical equavalent is .25ohm 2 W 3A at .25ohm is 2.25W still a bad choice but close.
For 1A the minimum sense resistance is 1 , max 2 ohm. 2W
For 2A the minimum sense resistance is .5ohm, max 1 ohm. 4W
For 3A the minimum sense resistance is .34ohm, max is .66ohm. 6W
For 3A I would recommend two .5ohm 2W resistors for each coil. (electrical equavalent of one .25ohm 4W resistor) or one .2ohm 2W resistor.
For 2A, one .5ohm 2W resistor for each coil, etc.
Vref voltage should be adjusted to Rsense * Itrip. So if your motor is 1.5A, and Rsense is .2 ohm, Vref should be set to .75V
Postscript. Don't use wirewound resistors.
Now using resistors to limit current in the linear sense (no chopper or electronics current limiting). You are on the right track with your power resistor calculation, but it's just a tiny bit more complicated depending on full step/half step/wave drive......
Phil, Still too many interests, too many projects, and not enough time!!!!!!!!
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