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Relay Driver IC ULN2003V12 Failure

Ars
Intellectual 950 points
Other Parts Discussed in Thread: ULN2003V12

Hello ,

I have a msp430 based application where  7 Relays  are driving  7 contactors which inturn drive loads consisting of several capacitor banks & motor.

The coil resistance is about 1200 ohm of each Relay and voltage is 12 V DC  i.e each relay takes  about  10mA.

The operations of relay are frequent.

These 7 relays are driven by TI's ULN2003V12 ( IC's top side marking u2003v12) .After running for few days it was found that driver ic uln became faulty.

The ic was then taken out from the application board and checked. it was found that resistance between one of the IN & OUT pin is approx 5 ohm and between rest of  IN and OUT pins are of 200 k ohm. whereas it is noted for a non-faulty ic the resistance between IN & OUT pins are in Mega Ohms.

IN pins were driving by MSP430 gpios.The MCU pins were not found faulty.

I would like to know from the experts here , what could be the real cause of the failure of the IC pins. And what precautionary steps should be taken in design to prevent this kind of issue 

rgds,

Ars

  • 0
    TI__Guru** 114905 points
    Hi Ars,

    Our experts have been notified and should reply soon.

    Do you have the COM pin connected to 12V?
  • 0 in reply to Rick Duncan
    Intellectual 950 points
    Hi Rick,
    Thanks. Yes COM pin is connected to +12V DC , which is connected to one end of all the relay coils.

    rgds,
    Ars
  • 0 in reply to Ars
    TI__Mastermind 24975 points
    Hello Ars,

    This is an issue I have not seen before.
    Have you had this issue on multiple devices? What channel has failed in this experiment?

    Best,
    Michael
  • 0 in reply to Michael J Schultis
    Intellectual 950 points

    Hello Michael,

    This was not an experiment . It was a failure of one of my product installed at field.And the relays in it was driven by this particular part .Please read my original post for my detailed observation.Out of 7 Channels 6 Channels were faulty ( The value of resistance was

    This IC having 7 Channels were driving 7 Relays as described in my post.My finding was that on power up the device ,N/O contact of relays show N/C by default.This observation leads me to check the ULN2003V12 .And the MSP430 MCU.Though potential at IN pins were at low level , the 6 OUT pins were at in mV level..... N/O contacts of Relay became N/C   whereas 7th Channel of the IC was at 12V. 

    I replaced the IC and board was working.

    Now I would like to know from TI's expert team and other experts here that ......what could be possible cause for this failure. And what precautionary design steps can be taken to prevent future failure.

    Please Note :

    a.    I have not used any external Free-wheeling Diodes considering IC has it internally.

    b.    In my application the relays will be switching frequently.

    Hope I have given my observation in complete and let me know if i could give more to find the root cause of the failure in any way.....

    Regards,

    Ars

  • 0 in reply to Ars
    TI__Mastermind 24975 points

    Hello Ars, 

    It is very difficult to try to determine the cause for failure. 

    Based on the way you describe the setup, I do not see anything that stands out, but  a failure this severe is typically caused by an electrical overstress or ESD event, which is very hard to pinpoint.

    Are there a number of devices that are currently being used, and is this the only one to fail or have you found multiple devices to fail in the same scenario?
    Do you have an idea of how long it took to fail? 

    I could review a complete schematic (although I have a pretty clear picture already) to see if anything is out of the ordinary, or I could take a look at a layout to see if there is anything there (if you feel comfortable sharing either of these on a public forum). 

    As you mentioned the free-wheeling diodes should handle any inductive kickback from the inductors, so there really isn't much that can be done for precautionary design steps outside of putting clamping diodes to ensure that the voltage on each output doesn't exceed 20V or putting schottky diodes in parallel with the COM diodes of the device. Both of these are too much to ask in a design like this honestly.

    Best,
    Michael