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DRV10987: Open loop current settings.

Matt Storey
Intellectual 525 points
Part Number: DRV10987
Other Parts Discussed in Thread: DRV8301, DRV8332

I know this may seem like an odd question, given the datasheet. But is there any way to increase the open loop current beyond the limit in the given register settings? Some hidden register commands perhaps?

I'm asking because I'm trying to get a motor, with a very low winding resistance, to spin. And the amount of drive, the chip gives out, isn't large enough to actually get the thing going.

I can fudge the thing by incorrectly setting the motor parameters, and this gets it spinning, but obviously doesn't work beyond that as closed loop control fails.

With other motors it's absolutely fine, it's just these small ***** RC motors that are a pain. Not that I'm wanting to use it at a high power level either. I get the impression that the DRV10987 would be absolutely fine with this motor if I could increase the open loop current to get the thing started. It's parameters are otherwise encompassed by the selectable values, it just needs more of an initial kick.

I have used this motor with Instaspin/Piccolo + a DRV8301 and it works great at lower power levels and I'm sure I characterised it with far less than the max open loop current limit of the drv10987 too. It just seems that the combination of motor parameters saps the initial drive from the motor.

This leads me to my next question. The DRV10987, and the other parts in the family are great but do you have any plans to release bigger versions of them?

Something like the DRV8332 but with the integrated control set of the 10987?

Many thanks,

Matt.

  • 0
    TI__Mastermind 18900 points

    Hey Matt,

    Unfortunately, there is not a way to increase the current besides fudging the motor parameters like you have said. Though, I do find it strange our device is not able spin up a motor with lower resistance (assuming it is within the application range table from the datasheet that I've copied below).

    Please take a look at the application range table below to ensure everything is within the specifications.

    As for your follow up question. Yes, we are looking into higher voltage/current devices that have similar integrated technology as the DRV10987. In fact, this area is our current focus and we are evaluating the market. If you have any suggestions for specs specifically you'd like to see (maybe in context of thhe DRV8301), please feel free to leave it here.

    Thanks,

    -Cole

  • 0 in reply to Cole Macias
    Intellectual 525 points

    Yes, the obvious issue is that the motors winding resistance is outside of the recommended range. It's 0.09 ohm, even though the selection table allows you to configure lower than the recommended 0.3 minimum.

    I could get the motor to spin, but with the fudged parameters it didn't operate particularly well. Given the chips inherent maximum programmable current limits it would be feasible for it to have a higher open loop current setting, but as that's rather inefficient I can imagine that thermal issues might be encountered if the part were asked to do things it's not really capable of.

    Specifications-wise, towards the products under development, what the DRV10987 does is pretty great considering its simplicity, especially when you compare it to the system complexity of a complete Instaspin setup. Of course the two aren't exactly comparable, but for spinning fans there's not a lot that it does wrong. One simple feature would be a direction reversal setting so that you can make the motor spin backwards. From a fan spinning point of view this may seem pointless, but as far as I am aware some 'anti-dust' systems work by instructing the fan to spin in the wrong direction for a few seconds in an attempt to shift dust and blow it out from where it came.

    Another feature that would be nice would be for the motor to be able to start up under closed loop control. Given that the device has EEPROM, and is apparently measuring certain motor parameters as it spins, would it be possible for the device to store data from the 'previous device spun' and use that to start up closed loop instead of open? That might be too complicated for the control system to work with, but theoretically it should give more freedom with regards to the end system. Such as starting up under partial load, or allowing for greater inertial loading under start up too. Maybe this is just wishful thinking and turning the part into something that it's not though!