• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 49 subscribers
  • Views 288 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.

LT1014D: behavior at low -40C

Aaron Spaete
Expert 4290 points
Part Number: LT1014D

Team, 

My customer has the following question:

We are using this part with Vcc+ = 5V and Vcc- = GND.  Its configured as a typical inverting amplifier and we are applying about -3.5V to -2.3V  to pin 2.  The issue we are seeing is that in a few cases we are not seeing the correct output from the part at -40C.

 

Page 8 of the data sheet implies that we are using the part in an unintended manner because we appear to be violating the common mode input voltage range but sheet 18 seems to state the part was designed to work this way.

 

Are we using the part in an unspecified manner?      

Regards,

Aaron

  • 0
    TI__Guru* 93105 points

    Hi Aaron,

    I don't know the exact circuit configuration, but based on your description I constructed the TINA circuit shown below having the LT1014D connected as an inverting amplifier.

    The LT1014D VICR range is listed in the Electrical Characteristics table on Pg. 8 as 0 to 3 V, for the full temperature range. The non-inverting input is connected to 0 V, which is within the VICR range listed. This places the inverting input, the summing node, near 0 V as well. If the -2.3 V to -3.5 V is applied to the input resistor as shown, the common-mode voltage range VICR, does not get exercised in the inverting amplifier mode. There may be some other dc parameter that is temperature sensitive that changes enough at -40C to alter the amplifier's performance level.

    Can you provide a bit more information regarding, "The issue we are seeing is that in a few cases we are not seeing the correct output from the part at -40C."

    Regards, Thomas

    Precision Amplifiers Applications Engineering

  • 0
    TI__Genius 10850 points

    Hi Aaron,

    We haven't heard from you in a while. We hope the issue was resolved. I am going to close this thread now. You may reply to re-open.

    -Tamara

  • 0 in reply to Tamara M Alani
    TI__Expert 4290 points

    Tamara,

    Thank you for the response, the failure we’re observing at -40C is that the output of the Op Amp gets stuck low (@-0.5V) until the device warms up.  One concern we had is that when the power supplies come up, the 5V rail which supplies Vcc to the op amp lags the -15V supply by @1mS which causes a negative voltage to be applied to the inverting input of the Op Amp before Vcc comes up on the Op Amp.  We suspect this is causing current through the ESD diodes which is causing the behavior of the device.  A schematic and scope plots of the behavior we’re observing can be found below:

    This is a sample of the circuit where we’re utilizing a LT1014D Op Amp. 

    Channel 1 (Yellow) is connected to the inverting input of the Op Amp:

    Normal power up at ambient where the failure is not observed:

    Power up at -40C where the failure is observed: