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Original question:

OPA189: Vf value of internal diode

OPA189: About input protection

Taroimo
Intellectual 630 points
Part Number: OPA189

Dear TI team

 

I have a question related to the content of the thread below.

https://e2e.ti.com/support/amplifiers-group/amplifiers/f/amplifiers-forum/898699/opa189-vf-value-of-internal-diode/3328628?tisearch=e2e-sitesearch&keymatch=OPA189%20absolute#3328628

 

Since the supply voltage of the amplifier in front of the OPA189 is ±10V, -5.5V, which exceeds the absolute maximum rating, may be momentarily applied to the -input via a 1kΩ resistor.

So I have the following two questions.

 

(1)There is a clamp diode at the input of the OPA189. What is the Vf of this diode?

(If the Vf of this diode is sufficiently high, I believe that the absolute maximum rating can be avoided. I was able to confirm through simulation that the absolute maximum rating is not exceeded.)

 

(2) Please let me know if there are any points to note when adding an external 5V clamp circuit to the front stage of R1 (1kΩ) in the attached circuit.

 

Best Regards,

Taroimo

  • +1
    TI__Guru 54416 points

    Hi Taroimo,

    Per the Absolute Maximum Ratings, the OPAx189 can withstand up to ±10mA of current at the device inputs during a fault condition. 

    Please see the Absolute Maximum Ratings table below.

    On the circuit above, the OPAx189 is powered with ±5V supplies in the inverting configuration. Since the signal during a fault can be ±10V, the 1kΩ resistor will limit the current to about (-10V - (-5V)) / 1kΩ =  ~-5mA.  This current is less than the 10mA absolute maximum rating current on the inputs of the amplfier, so the device will be to withstand this condition during a temporary fault.

    Thank you and Regards,

    Luis

  • 0 in reply to Luis Chioye
    Intellectual 630 points

    Hi Luis,

     

    Thanks for your prompt reply.

    I was relieved that my worries were gone.

     

    Best Regards,

    Taroimo

  • 0 in reply to Taroimo
    TI__Guru 54416 points

    HI Taroimo,

    Thank you and Kind Regards,

    Luis