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INA146

John Perlick
Prodigy 65 points
Other Parts Discussed in Thread: INA146

Hello

I am having a problem with the INA146. I get a constant 2-4 VDC out, even with both input terminals shorted together, or with both input terminals shorted to ground.  I am running the part on +12VDC  single-ended for VCC.  The output is set for a gain of 60, and the output amp seems to be working.  The input to A2 (pin 8) is around 30-40 mV when the output is abt 2 VDC.  When I first turn on the part, the output voltage--always DC--slowly rises from maybe 1.5 or 2 Volts up to about 3.5-4 VDC.  It makes no difference what I do with the inputs.  I swapped in a couple of new parts and no change.  Pin 1, Pin 4 are both grounded.  In fact, if I short pis 1-2-3-4 all to ground, I get the same result.

Any ideas on what is wrong?

THe part is marked:

 

BB INA

146UA

01VN4

Does this imply a date code of 2001?  This is a brand new board, our sub must have used some old parts!

Any help or ideas would be much appreciated!  Can't seem to get any answers from TI.

 

  • 0
    TI__Mastermind 25805 points

    Hello John,

    Sorry for the delay.  I am working on this and will get back with you shortly.

     

  • 0
    TI__Prodigy 280 points

    Hi John,

    Topside symbol marking information can be found on the TI product description website: http://www.ti.com/product/ina146

    In this case the lot trace code is 01VN4. The first two characters are the year-month (YM). The last three characters are part of the lot identifier (LLL). So this device was manufactured January 2010. Note the YM is re-cycled every 10 years. However it is very unlikely 10 year old devices remain in inventory unused, certainly not with TI approved distributors. If you purchase from an authorized TI distributor you can be assured the material is fresh, conforms to the datasheet specs, and fully warranted.

    Regards,

    Fred Nakovic - CQE

  • 0
    TI__Mastermind 25805 points

    Hello John,

    Are the devices that you’re testing coming from field failures?  If so, I recommend ordering some samples and verifying a test setup before testing the failed units.  You stated that you tried ‘new’ units, but I’m not sure if those are recent samples from TI.

    My recommendation for a test setup is to place the device in a known linear operation configuration.  For example, I would use a dual-supply (+/-15V with Ref connected to ground) and set the overall gain to 10 (output stage gain is 100).  You can then apply a 1Vpp input sine wave (100Hz, for example) and should expect to see ~10Vpp sine wave at the output.  I have attached a TINA simulation to this effect.  I have also attached a single-supply TINA simulation.  To keep it simple I used a 5V supply with 2.5V reference.  I also put A2 in a non-inverting buffer configuration.  This ensures that the reference voltage is not gained.

    The issue with grounding the inputs is that A1 is probably not operating very linearly.  The output stage of the amplifier is trying to reach ground but cannot do so.  Then, A2 gains up the output voltage of A1.

     

    Please let me know if you have any further questions.

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