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LM5112: Clarity on IN_REF/VEE and absolute maximum ratings.

Michael Ciuffo1
Prodigy 20 points
Part Number: LM5112

I am working on a design using the LM5112 on a dual-supply (+6 and -8V) application.  I would like to connect the IN_REF pin to ground to allow for simple TTL control. The recommended operating conditions specify that VCC to IN_REF must be less than 14V (it is) and that VCC to VEE must be less than 14V (it also is, barely).

My concern is the absolute maximum ratings specify that IN_REF to VEE must be less than 5V which would be violated in this design. It's strange that there is no recommended operating condition regarding the IN_REF-VEE voltage.

I learned about the LM5112 from another design where it is successfully being used with a VEE of -8V without apparent issue. Can you clarify if this absolute maximum rating is real? What is the recommended operating voltage of IN_REF-VEE?

  • 0
    TI__Guru**** 189399 points
    Hi, Michael, Thanks for your question on the LM5112. Our application engineer supporting that device is out for the holidays. He’ll get back to you later this week when he returns to the office.
  • 0
    TI__Mastermind 21465 points

    Hello Michael,

    The VCC to VEE in your application will be OK with the 14V total as you mentioned. The IN_REF to VEE is rated at 5V maximum as shown in the datasheet table 6.1  which is beyond the 8V that you mention. There are internal devices in which the worst case voltage ratings result in the datasheet specification of 5V.

    It is possible with typical devices and/or operating temperatures that are not at the minimum or maximum temperature range will result in typical operation that exceeds the absolute maximum ratings. TI can only guarantee operation within the datasheet parameter maximum ratings however.

    Can the design be modified to operate within the 5V IN_REF to VEE rating?

    Confirm if this addresses your question, or you can post additional questions on this thread.

    Regards,

  • 0 in reply to Richard Herring
    Prodigy 20 points

    Hi Richard,

    Thanks for the response. Unfortunately, I cannot change the -8V spec as it is required for the CCD I am trying to operate. Do you know of any similar parts that can support a -8V to 5V output?

  • 0 in reply to Michael Ciuffo1
    TI__Mastermind 21465 points

    Hello Michael,

    The small low side drivers I found with the split ground feature seem to have a similar limitation on the voltage rating from the input to driver ground.

    There is a simple method to level shift the input signal to a driver with its ground referenced to a negative bias supply. It only requires a small signal PNP and a couple of resistors. This would allow you to use the LM5112 with a higher negative bias.

    The app note explaining the level shift can be found here:

    https://www.ti.com/lit/an/slua994/slua994.pdf

    Regards,