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LOG2112 Over heating problem

Katsuhiko Kaizawa
Intellectual 2045 points
Other Parts Discussed in Thread: LOG2112

Hello support team,

We have a problem on the LOG2112 over heating. Could you please give us your feedback for this phenomena?

[Back ground]

Supply voltage is +/-12V.

When the input current are almost "0", the log output is saturated around 11V. I think this is normal operation.

But the high supply current around 70mA to 80mA is observed when both of 2ch of LOG2112 are saturated. At that time, the package temperature is 80~90 degC.  

[Questions]

1. In the data sheet, input current is spcified from 100pA. Is the input current below 100pA acceptable for this device?

2. Is it correct operation such a 70mA supply current?

3. If this is correct operation on LOG2112, is there any workaround to prevent the high supply currennt when the input current is "0".

Thanks and best regards,

Kaizawa

  • 0
    TI__Guru* 93105 points

    Kaizawa-san,

    To answer your questions:

    When the input current are almost "0", the log output is saturated around 11V. I think this is normal operation.

    If the input current I2 is close to zero, the VLOGOUT equation indicates the output will be driven towards the positive supply rail. 

    [Questions]

    1. In the data sheet, input current is spcified from 100pA. Is the input current below 100pA acceptable for this device?

    A smaller input current can be applied, but the output accuracy is not specified. The smaller the current is made the more inaccurate the output level will become.

    2. Is it correct operation such a 70mA supply current?

    No, that seems way too high. Check the VOUTLOG and Vo3 outputs with a 10x probe and DSO. Look for evidence of oscillation.

    3. If this is correct operation on LOG2112, is there any workaround to prevent the high supply currennt when the input current is "0".

    Is the supply current high when the input current is at a level above 100 pA?

    Would it be possible to view the customer's circuit diagram? If it is confidential send it to:

    Precisionamps@list.ti.com

    Regards, Thomas

    PA - Linear Applications Engineering