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DRV10970: CURRENT LIMIT FUNCTION

Part Number: DRV10970

Good Morning,

I have a question concerning the current limit function of the DRV10970 part number.

Inside the datasheet it is stated that the maximum output peak current is 1.5A; also, the current limit threshold can be set by connecting an external resistor to the CS pin; if the CS pin is put to GND, the current limit function is disabled; also, the minimum threshold for OverCurrent Protection is 3A.

Therefore, is it possible to set the current limit threshold to a value which is higher than 1.5A and lower than 3A, by selecting an appropriate CS resistor value?

If I put CS to GND, which is the maximum output current that the driver is able to provide? Is the driver able to provide e.g. 2.5A peak current (being such value lower than the OCP threshold)?

Thank you so much. Kind regards.

  • Hi Alessandro,

    Thanks for posting your question in MD forum. Equation 1 in the datasheet holds good only when Rcs is 20 kOhms and above, so it is not possible to set the current threshold to a value above 1.5A.

    Regards,

    Vishnu   

  • Thank you for your answer!

    This means that if I disable the current limit function by putting CS pin to GND, will the driver be able to deliver peak currents up to 3A before the OCP triggers?

  • Hi Alessandro,

    I want to highlight the difference between the current limit function and over current protection (OCP). When you tie CS directly to ground it disables the current limit threshold. If you look at equation 1, making rcs zero, aka ground, makes this equation indeterminate. 

    OCP is different. OCP has a fixed threshold, I_OCP, which protects the device from phase to ground shorts, phase to VM shorts, and phase to phase shorts. The difference between IOCP and the current limit is that when IOCP crosses the ICP threshold (3A),  the device will shut down the FETS, wait 2 seconds before it starts to drive the motor again. On page 14 of the datasheet you can read more about this.

    This being said we do not recommend operating over 1.5A, OCP is there as a backup just incase there is a large current spike that reaches up to 3A.

    Thanks,

    Michael

  • Good Morning Michael,

    Thank you for the reply.
    I understand the difference between the current limit function and overcurrent protection.

    Therefore, if the current limit function is disabled, the current may actually increase up to ca.3A without any limit function nor the overcurrent protection to be triggered, am I right?

    However, I understand that is not recommended to operate over 1.5A.

    Therefore, if I want to use you driver for our application, I need to reduce the current consumptions. I asked about the disabling of the current limit function since I want to have a certain safety margin in our application. As you can see in the picture I'm attaching, we have a quasi-sinusoidal current profile, with RMS value of ca.0.65A and peaks that may go above the upper limit of 1.5A of your driver (that's why I would need to disable the current limit function). This waveform is applied at 5Hz and may go on continuously for up to 5minutes/day. I want to avoid the driver to be damaged in a short life-time.

      

    Do you think that your driver can whitstand such type of stimulation without being damaged?

    Thank you so much. Kind regards.

  • Hi Alessandro,

    Can you try to set the current limit threshold to 1.5A and see if it triggers a fault? If no fault is triggered then we don't recommend disabling the current limit. 

    Thanks,

    Michael

  • Good Morning Michael,

    thanks for the reply.

    My questions were needed for a preliminary evaluation. We'll now consider to purchase the evaluation board for an actual evaluation of the behaviour of the driven given our current consumption profile.

    Thank you. Regards.

  • Hi Alessandro,

    OK sounds good. 

    I'll provide a link to our DRV10970EVM.

    If you have any more questions let us know.

    Regards,

    Michael