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DRV8834: Facing production issues. Question regarding a missing part

Part Number: DRV8834

Hi, 

I have a project which is in production right now. Our company has not worked on the design but we are building production units for this project. 

One of the recent issues which came up was a component getting knocked off while hand soldering one of the parts into 4 through holes (motor gets assembled here). On few boards the the circled capacitor got moved or even removed. These boards were caught during visual inspection.

But there were a good 300 boards on which the motors were assembled and product was already created. But we know there was a visual inspection check performed on all of those 300 boards. 

  

We want to know if by mistake on any of those 300 boards this capacitor is still missing then what error it may cause to the motor driver IC. 

I would say C6 is a decoupling capacitor so unless the system power is very noisy the motor driver is going to function ok. 

We also need a experts opinion, as this is a medical product and we have to document the reasoning. 

I also wanted to know if there a test which can be performed after the motor assembly to check if C6 is present or not, just by programing the MCU and communicating with the driver. 

Lastly we have almost 3000 of these assembled boards with us(with the motors not assembled) so re-spinning or design change is not an option.

Thank you,

Bhavya

  • Bhavya,

    If I am reading the schematic correctly, 18pF is the value of the component?  This is very, very small and if anything would filter out very high frequency noise.  The device internal circuits would not be able to respond to this high frequency noise.  VREF essentially feeds a comparator that is used to set output current.  

    If anything, you might see some variation in the output current, but I don't expect to see any difference with such a small capacitor.  

    Regards,

    Ryan

  • Thank you Ryan. 

    I have another concern about R6 which is pulled down to gnd. 

    This resistor is placed just below the circled capacitor. As this is a pull down resistor and also connected to MCU there shouldn't be much of an issue if R6 gets displaced. Is that correct?

  • Bhavya,

    The device already has an internal pull-down on this pin, so this resistor is not necessary.  Please see figure 8-2 in the datasheet.

    Regards,

    Ryan

  • I see it now. Thank you Ryan.