Part Number:DRV8313
Hi,
We have a project to measure the brushless motor torque through phase current.
We tried two methods:
1)Measure current through the low side resistor:
See DRV8313 datasheet on page12 Figure 12 shows connections to use the comparator to sense current for implementing a current limit. Current from all three low-side FETs is sensed using a single low-side sense resistor.
We measure the current through the Rsense, and then calculate the torque. But we found that under a same torque at different speed the motor has a different current value, which is incorrect.
1)Measure the current through a high side resistor:
Connect a small resistor (0.1 ohm) in-line with a motor phase(between a Vout and a motor phase) and measure the average current through the resistor, we did have the current proportional to speed under same torque, it seems correct but the current is quite unstable, fluctuate about 2%(we need to achieve 0.1% or better).
And the current through the three phases added together is not equal to or proportional to the current in the Rsense. I would think all the three phases' current should added together and eventually went to ground through Rsense.
Could anyone please explain this to me? Any suggestions please?
Thanks and regards,