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DRV8434S: Open load detection specifications

Part Number: DRV8434S

Tool/software:

Hello,

My customer has been investigating DRV8434S, but their target full scale current is 10-20mA or so.  Therefore they're wondering the open load detection.  Would you please give me your comments for these?

1. How much would the open load detection current be?  Is it still 75mA(typ) or can it be lower like 15mA if FS=20mA?  I fit is still 75mA, does it mean the open load detection doesn't work at FS=20mA?

2. Would you please tell me the open load detection time in minimum?  The datasheet says only 50ms(max).

Best Regards,

Yoshikazu Kawasaki

  • Hi Kawasaki-san,

    Please allow me some time to look into this. I'll have more information next week.

    Best,

    David

  • Hi Kawasaki-san,

    1. How much would the open load detection current be?  Is it still 75mA(typ) or can it be lower like 15mA if FS=20mA?  I fit is still 75mA, does it mean the open load detection doesn't work at FS=20mA?

    The OL threshold will be close to 75 mA regardless of the IFS setting. With only 20 mA IFS, if OL detect is enabled it will report a false OL.

    My customer has been investigating DRV8434S, but their target full scale current is 10-20mA or so.

    To drive an IFS 20 mA stepper motor the DRV8434S is overkill. Besides the current sensing and regulation accuracy will not be as accurate as with operating the device with its full-scale max. current setting. For 20 mA IFS the VREF input must be around 26 mV. For this low current motor the stall detection feature in the DRV8434S will not be operational as well. 

    2. Would you please tell me the open load detection time in minimum?  The datasheet says only 50ms(max).

    We do not have a minimum specification for this parameter because in an application the maximum detection time is what matters. Thank you.

    Regards, Murugavel 

  • Hello Murugavel-san,

    Thank you very much for your comments.

    With only 20 mA IFS, if OL detect is enabled it will report a false OL.

    Do you mean DRV8434S will report false OL all the time if OL_MODE=1 and there is no way to detect the open load correctly when IFS=20mA?  If so, it's meaningless to use at OL_MODE=1.

    For this low current motor the stall detection feature in the DRV8434S will not be operational as well. 

    The main purpose my customer will use DRV8434S is stall detection.  Which device would you recommend for IFS=20mA then?  What would be the minimum IFS for DRV8434S to work stall detection correctly?

    Best Regards,

    Yoshikazu Kawasaki

  • Hi Kawasaki-san,

    Do you mean DRV8434S will report false OL all the time if OL_MODE=1 and there is no way to detect the open load correctly when IFS=20mA?  If so, it's meaningless to use at OL_MODE=1.

    Yes, you are correct. The device looks for minimum load current threshold and 20 mA is less than the threshold specification.

    The main purpose my customer will use DRV8434S is stall detection.  Which device would you recommend for IFS=20mA then?  What would be the minimum IFS for DRV8434S to work stall detection correctly?

    The DRV8434S would need around 200 to 250 mA IFS and Stepper motor DCR around 20 ohms or less for stall detection to work reliably. For stall detection with IFS 20 mA we do not have a device currently that can support this. Thank you.

    Regards, Murugavel  

  • Hello Murugavel-san,

    Thank you very much for your quick reply.  I understand how it works.  Please let me open another thread if I get more questions.

    Best Regards,

    Yoshikazu Kawasaki