• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 47 subscribers
  • Views 704 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TLE2062: Output Impedance when both Power Rails are Grounded

Richard Elmquist
Mastermind 45250 points
Part Number: TLE2062

My customer is asking the following about the TLE2062:

I am using the TLE2062AMDREP in an application where, in certain circumstances, I ground the VCC  and VCC– rails in order to guarantee that the output is driven to zero. I had made the assumption that when I do this the output pin goes high impedance, but lab tests have shown that is not the case. Can you provide any more information about the impedance of the output with respect to the rails when there is no voltage applied?

I am wondering if maybe the impedance path I am seeing has to do with any ESD protection diodes. I am not sure if those are shown in the equivalent schematic in the datasheet (D1 and D2), or if those were omitted for clarity.

I cannot tell from looking at the diagram where the current path would be other than the feedback circuits that would be used in the circuit. Can you go into detail to answer the customer’s questions.

Thanks for your help with this!

Richard Elmquist

  • 0
    TI__Guru 62825 points
    Hello,

    Unfortunately this is not an effective method to achieve a high-impedance output from an op amp. Selecting an op amp with shutdown and a HI-Z output is the best option for this type of design.

    Even though VCC+ and VCC- are connected to GND, all of the circuitry shown in the datasheet is still connected to the OUT pin and when a voltage is applied some current will likely flow into the output of the amp.

    You're correct and on any modern op amp ESD cells would be located from OUT to VCC+ and VCC- which would conduct when a voltage was applied to OUT with the supplies connected to GND. I'm not immediately sure about the ESD protection methods used on the TLE2062 device but we'll look into the ESD ratings which will give us some indication of the protection structures used. Either way another solution is likely required.
  • 0 in reply to Collin Wells
    TI__Mastermind 45250 points

    Collin,

    Thanks so much for your response!

    I will let you know if the customer has any further questions.

    Have a great day.

    Richard Elmquist