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OPA2171: about OPA2171

Vera Mao
Expert 5065 points
Part Number: OPA2171

Hi dear supporting team,

when customer  use OPA2171 with 3.3V single supply, they will find there is lower than -0.5V voltage showing up at Vin+ for more than 10ms.  by adjusting the circuit, they could control the input current to be lower than 10mA, so want to double check with you:

1. if the current does not exceed 10mA, what' the max negative voltage it could bare?

2. if the current does not exceed 10mA, Vin+=-1V,  how long time could it last without damaging the part? (or withouth causing potential damage)

tks a lot!

  • 0
    Guru 140200 points
    Hi Vera,

    have a look at figure 40 of datasheet to see how the inputs of OPA2171 are clamped by protection diodes. If the input voltage exceeds the supply rails by more than 0.5V, the input current must be limited to under 10mA. Just insert a suited current limiting resistor at the input(s) and you will be fine. The usual recommendation is to limit the input current to about 1mA.

    Kai
  • 0 in reply to kai klaas69
    TI__Mastermind 30600 points
    Hi Vera,

    Kai is correct. You should size your series protection resistor such that you have less 10mA or less of input current for your worst case input voltage. If you expect the input to exceed the supply frequently, then limit the current to 1mA. It is difficult to say precisely how much time it will take to cause damage as each device will be a little different and the damage can accumulate over time. That is why we say limit to 1mA if you are going to do this frequently.

    Thanks,
    Paul
  • 0 in reply to Paul Goedeke
    TI__Expert 5065 points

    HI Kai, Pual,

    thank you for your reply!

    so double check with you, if Vin+ has frequently -0.7V shown up which  current limited to 1mA,  is it ok without potential damage? tks a lot!

  • 0 in reply to Vera Mao
    Guru 140200 points
    Hi Vera,

    provided the input voltage does not exceed the supply rails by more than 1V, insert a 1k resistor at the +input of OPA2171 and you will be fine.

    Kai
  • 0 in reply to kai klaas69
    TI__Mastermind 30600 points
    Hi Vera,

    "If Vin+ has frequently -0.7V shown up which current limited to 1mA, is it ok without potential damage? tks a lot!"
    --> Yes, this will be okay with at least a 1k resistor as Kai mentioned.

    Best,
    Paul