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DRV110 min/typ/max specs for "external settings"

JONATHAN GRAHAM98068
Prodigy 90 points
Other Parts Discussed in Thread: DRV110

I'm using the DRV110 in a medical design (trying to), but I'm running into difficulty trying to guarantee operation.  We're using external resistors to program the peak and hold currents, trying to target 3A and 700mA respectively.  The spec sheet does not define a min or max for the tolerance on the programmed current levels.  Should I use the -20%/+30% tolerance reported for the "internal settings"?  That will likely cook my solenoid if I design for the -20% case and we get some chips that are +30%...  Any advice from the factory?

Thanks!

-Jonathan

  • 0
    TI__Genius 9975 points

    Hello Jonathan,

    Thank you for your question.

    I will ask the person responsible for support of this product to reply to your inquiry.

    Best regards,

    Jose

  • 0 in reply to Jose Duenas
    TI__Intellectual 1915 points

    Hi Jonathan, I have contacted the design team to get these info; I'll come back to you when I have a reply, likely beginning of next week.

    Best regards, Alain. 

  • 0 in reply to AlainC
    TI__Intellectual 1915 points

    Jonathan,: the internal reference for Ipeak and Ihold is specified in datasheet as 300mA+/-10% for Ipeak and 50mA+/-10% for Ihold. On top of that you need to take into account tolerance of Rpeak and Rhold.

    Best regards, Alain.

  • 0 in reply to AlainC
    Prodigy 90 points

    The "internal settings" are 300mA +/- 10% for Ipeak and 50mA +30/-20% for Ihold, however I'm looking for clarification on the undocumented min/max numbers for the "external settings".  The current sources are likely nano-amps, not milliamps.  

    300mA through my 100k Rpeak resistor would be 30kV, I don't think the chip is doing that.
    (or I'll need a much higher wattage resistor)

  • 0 in reply to JONATHAN GRAHAM98068
    TI__Intellectual 1915 points

    Yes, I understand; the way it has been specified is to describe the tolerance of the reference, i.e. +/-10%. Whatever program you will program will have the same internal precision.

    Best regards, Alain.

  • 0 in reply to AlainC
    Prodigy 90 points

    +/-10% for Ipeak is fine

    +30/-20% for Ihold is terrible...  

    Unless we can get some information on the source of this error (maybe the temperature coefficient past 85C is a major factor?) we will likely need to replace this circuit before we go into production.  Are you sure that this is the case?  From my (albeit limited) understanding of semiconductor processes, current sources are easier than internal resistors as far as tight tolerances go, so one of our assumptions when initially choosing this chip was that the major contributor to the +30/-20% error was the internal resistor in the DRV110, so we were hoping that removing the internal resistor would tighten the tolerances significantly.

  • 0 in reply to JONATHAN GRAHAM98068
    TI__Intellectual 1915 points

    Jonathan, this is not a current source internally but a voltage source; its internal resistor limits the output current to the maximum specified value. I think that precision on Ihold is less stringeant than Ipeak as based on your original comment it won't harm the solenoid since it is lower than max allowable current. What matters for this state is to have enough current to avoid losing the hold state.

    Best regards, Alain.