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TPL7407L: sometime driver is failing while switching

Goutam Maji
Prodigy 190 points
Part Number: TPL7407L

I am using TPL7407L driver to drive few relays as per the attached circuit. Two relay coil current is 250mA and other relay takes around 30mA. The driver is working fine for most of the time, but some time white switching ON one 250mA coil relay this driver used blown off, with sound and visible hole on the top of the IC. I am unable to repeat the failure as it is not failing even after 100 times switching.

We need your advice on this failure urgently, and let us know at what condition this kind of failure may come. I have captured all outputs-to-gnd pin voltages, but unable to see any voltage spike. we are operating with 24V supply voltage.

let me know if you need any more information to understand the failure modes.

Thanks and Regards

Goutam

  • 0
    TI__Genius 10855 points

    Hi Goutam,

    Thanks for reaching out on E2E.

    Could you provide some additional details for me regarding the application:

    1. Do you have the COM pin connected to the same VCC supply as the output loads?
    2. Can you share the rest of the schematic?
    3. What operating temperature are you running the system at?
    4. How many ICs have failed in your tests? Can you clarify the "failing even after 100 times switching" statement?

    Thanks,

    Arthur Huang

  • 0 in reply to Alpha H
    Prodigy 190 points

    Hi Arthur,

    1. Do you have the COM pin connected to the same VCC supply as the output loads? yes, it is same 24V Power supply
    2. Can you share the rest of the schematic? attached one relay connection
    3. What operating temperature are you running the system at? Currently we are testing at 25C, but actual requirement is 5-40C
    4. How many ICs have failed in your tests? 6 ics Can you clarify the "failing even after 100 times switching" statement? it is not failing even after 100 times switching when we are trying to simulate the fault
    5. Is there any chance of such failure due to 24V bus ripple ?
  • 0 in reply to Goutam Maji
    Prodigy 190 points
    Is it possible to visit our location for details understanding? it will be helpful that way.
  • 0 in reply to Goutam Maji
    TI__Genius 10855 points

    Hi Goutam,

    What type of load are you driving on OUT7, is it inductive? The TPL7407L requires a diode to be used on OUt7 to protect the pin from negative current transients during inductive load switching. I recommend moving to the TPL7407LA if possible, which does not require an external diode on OUT7 for inductive loads.

    Thanks,

    Arthur Huang

  • 0 in reply to Alpha H
    Prodigy 190 points

    Hi Arthur,

    Thanks for the response.

    We are driving a 250mA coil ( part of an contactor ) using OUT7. Please see the connected load details in the attached documents.

    Please let us know to drive these load, TPL7407L with diode or TPL7007LA should be ok or not?

    Regards

    Goutam

  • 0 in reply to Goutam Maji
    Prodigy 190 points

    Hi Arthur,

    Please find the attachment.

  • 0 in reply to Goutam Maji
    TI__Genius 10855 points

    Hi Goutam,

    Thanks for the update. With the information you provided, I recommend switching to the TPL7407LA to protect OUT7 from negative current transients. Please let me know if you still experience the failures after switching to the different device.

    Thanks,

    Arthur Huang

  • 0 in reply to Alpha H
    Prodigy 190 points

    Hi Arthur,

    Thanks for the recommendation to use TPL7407LA. Do you sure the route cause for the problem is not using diode for OUT07 pin and drawing more than 250mA current of TPL7407L. Is these any other reason which can be taken care in the design. Do you think total 587mA is ok to draw combining all channels or required to reduce load in that case we can use other ICs to share the load. Other ics we are using for LED drive.

    Thanks and Regards

    Goutam

  • 0 in reply to Goutam Maji
    TI__Genius 10855 points

    Hi Goutam,

    The TPL7407L requires an external diode on OUT7 to protect the pin from negative current transients during inductive load switching, like the situation you have. We were noticing that the OUT7 was exhibiting failures when connected to a inductive load, thus the TPL7407LA was created to address these issues.  

    Looking at your calculations, it looks like the device will dissipate around 0.3W. Depending on which package you're using, the thetaja can be 113.1C/W or 88C/W. Multiplying power * thethja, you'll be getting either a 33.9C or 26.4C increase. As long as you don't exceed the junction temperature (150C), you should be ok.

    Thank you,

    Arthur Huang

  • 0 in reply to Alpha H
    Prodigy 190 points

    Hi Arthur,

    Thanks for the response.

    I will let you know how the LA series is working for us.

    Another question, if the diode would be issue why it is not failing everytime, it is failing may be around once in 200 or more number of switching.

    Regards

    Goutam

  • 0 in reply to Goutam Maji
    Prodigy 190 points
    Hi Arthur,
    Please share your TI id for more discussion, I am seeing a sourcing issue for the TPL7407LA part. Element14 doesn't have this part.

    Regards
    Goutam
  • 0 in reply to Goutam Maji
    TI__Genius 10855 points

    Hi Goutam, 

    Please email me at a-huang@ti.com with any questions.

    Thanks,

    Arthur