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Original question:

DRV425: Plane GND under DRV425

DRV425: getting fried

Ravi Ganesh
Prodigy 90 points
Part Number: DRV425

I am developing a new design and at first power on in my custom board the part draws about 0.3A at 3V and gets heated and fails thereafter.

There are no blunders in my design (it is a faithful reproduction of linear position sensing circuit in the datasheet), but I would like to know answers for these questions:

1. Can leaving the center paddle unsoldered damage the part?  Is there any electrical test to verify if the paddle go soldered?

2. Can I solder the part by hand or does it need reflow soldering only?

3. Can the BSEL pin be left floating. (Does a floating digital Input pin indeed damage the part).

Any advise is greatly appreciated.

  • 0
    TI__Mastermind 32210 points
    Hello Ravi,

    Thanks for using the forum to answer your questions. I have seen issues with QFN parts and building them by hand. I have seen unseen shorts under the device that have caused issues. I normally limit the power supply to see these

    1. You should not have issues with leaving this floating, but we do recommend it to be grounded. Please make sure there is no other potential on this pad. There is no electrical test to verify this connection.

    2. Soldering any QFN package by had can be difficult and can lead to solder bridges and other problems. I would not do it by hand but I have other qualified people that can get it done with high success rate.

    3. Beside not knowing the state of BSEL I would not see this as an issue.
  • 0 in reply to Javier Contreras4
    Prodigy 90 points
    Hi Javier
    Thank you so much.
    What current limit would be safe for the part? 10mA at 3V?
    Regarding QFN package soldering we have quite a long experience. Except for one Atmel part whose pads gets electrically open after say cleaning by manual soldering after reflow, we have had no problems. And for
    this part we concluded that the wire bond from pad to die gets molten due to the thermal spike from a soldering iron!
    After failure of DRV425, the Vcc-Ground shows 2 ohm resistance and COMP1 and 2 show short. Before power on there are no abnormal shorts as seen in continuity test using a multimeter.
    I have exhausted my 3 nos. and after the next order comes I will update. Also I am ordering the EVM for reference testing.
    Ravi
  • 0 in reply to Ravi Ganesh
    TI__Mastermind 32210 points

    Ravi,

    I would do 10mA + MaxField Expected * 12.2 mA/mT.  So for example if you are expecting if you are expecting a max field of 1.2mT I would place a max current of 10mA + 12.2mA/mT* 1.2mT = 24.64mA.   

    You may want to add a little head room as well.

    I have provided a layout from our EVM right under the device for your reference.

    Please let me know if you have further questions.