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TLV521: Negative Voltage on IN+ Pin

hideyuki sakai
Mastermind 6250 points

Part Number: TLV521

Dear, Sir.

My customer is considering to apply TLV521 for their system, now.

The circuit is similar as Figure34 on the datasheet(using single power supply).

They are concerning the negative voltage around -0.3V on IN+ pin will be cretaed

due to the sensor behavior.

-0.3V is the absolute maximum ratings for TLV521. Please give your advice.

1. I wonder above negative voltage would influenced to output voltage, such as

    output inverting?

2. I think the putting series resistors on both IN+ & IN-to limit the input current

    could be one of the solution because input offset current is quite small, 50fA.

    How do you think about this idea?

3. Please give your advice if you have the better solution?

Best Regards,

H. Sakai

 

  • 0
    TI__Guru**** 174396 points
    Hello H. Sakai,

    Even -1uA of input current due to either input being negative voltage was enough for the op amp to no longer follow the input voltage difference on a test sample. The output did go low on that sample and it is probable but not certain that all devices will have an low output with the negative input current.

    Adding a series resistance to non-inverting input should be added to limit current to less than 1mA to protect the op amp. Also be prepared for a possible output at V+ if input is negative and all samples do not go low.

    Vos, offset voltage, is up to 3mV at 25C temperature and this can be 101* +/-3mV = +/-303mV of error at the output
    Anytime output goes to 0V, overload recovery overload delay may occur, see Fig 27 in data sheet
  • 0 in reply to Ron Michallick
    Mastermind 6250 points

    Dear, Ron-san. 

    Thank you so much for your valuable advice. 

    Regarding #3 about my previous question(better solution to protect negative

    input voltage), Please give your advice about it. 

    How about to put the Schottky diode which VF is smaller than 0.3V

    could be helpful? 

    Best Regards, 

    H. Sakai

  • 0 in reply to hideyuki sakai
    TI__Guru**** 174396 points
    Sakai-san,

    Yes, a Schottky diode that limits voltage to less than 300mV is helpful.