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LOG112 gets hot when input is open

Jesus Vasquez
Prodigy 80 points
Other Parts Discussed in Thread: LOG112

Hello,

I designed a acquisition board for current measurement using the LOG112. The board reads 40 signal so it has 40 LOG112. In normal operation the input current are all near zero, and I notice that in this situation (as the LOG112 output with zero input current goes to saturation) the LOG112s get hot, around 50°C. Could this be a problem on a long time period? 

Thanks!

  • 0
    TI__Guru* 93105 points

    Hi Jesus,

    I wouldn't expect the LOG112 to become very hot considering its relatively low quiescent current, unless maybe the log amplifier and/or output amplifier is driving maximum current into a load. Have you checked the VLOGOUT and VO3 outputs to see if anything is oscillating and causing the current to be higher than expected?

    Even if the LOG112 is getting up to 50 C, that is well within the operating temperature range for the product. Anytime a semiconductor is operated at elevated temperature it does reduce the lifetime of the device. How much depends on the temperature and other factors. You can find more information about failure rates vs. time and temperature here:

    http://focus.ti.com/en/download/qlty/A9R7E1F.pdf

    Operating the LOG112 at 50 C, vs. 25 C, shouldn't degrade the lifetime to the point where it becomes unusable in any reasonable time span. But I would try and understand why the device is getting hot and remedy the situation.

    Regards, Thomas

    PA - Linear Applications Engineering