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DRV8830: Current sense resistor over 1 ohm

Part Number: DRV8830

In the data sheet for the DRV8830, the maximum current limit sense resistor is listed as 1 ohm. Is this because the accuracy of the current limit will be out of spec with higher resistance and lower current? Or because of minimum on-time limits of the PWM? Or will some internal feedback become unstable? Basically I'm just wondering if we could set a low value for the current limit if we were willing to have reduced accuracy.

  • Hello Michael,

    Thank you for reaching out! The resistor used to set the current limit must be less than or equal to 1 ohm. 

    The reason for this is that any voltage above 0.2V on ISENSE will trigger the overcurrent protection setting. If you use a higher resistor, the device will allow for a higher voltage on this pin, and you will perpetually trigger the OCP fault condition. 

    Please let me know if you still have questions.

  • The current through the sense resistor is proportional to the motor current, and the choice of current limit resistor allows you to set the point where current limiting occurs. OCP is fixed at a higher level to protect the device, and it is independent of the sense resistor choice.

    I'm interested in why the sense resistor is limited to 1 ohm.

  • Hello Michael,

    Ultimately, this is a design choice. The device is not designed to operate with any resistor higher than 1 Ohm. 

    Thank you!

  • Hello Michael,

    I am checking with my team internally and I will get back to you.

  • Hello Michael,

    The low-side FETs gates are driven with respect to GND, while their sources are tied to the ISEN node. Because of this a fast rise < 3us in ISEN node voltage would be limiting the Vgs drive voltage of LSFETs (Vgs minus V_ISEN) and render an 'in-rush or short to VM' event current to lower than OCP threshold for ISEN resistors > 1 ohms. OCP may never happen and potentially may damage the FETs under these conditions because Itrip takes >3us to react.