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LM34: Temperature Sensor with Increased Current Source/Sink

Charles Gervasi
Expert 2270 points

Part Number: LM34
Other Parts Discussed in Thread: LMT84, TMP235

LM34's output stage can only source 16uA and sink 1uA.  This is from Page 11 of the LM34 datasheet:

Why can the Class-A output amp only source 16uA if it has an output impedance of 0.5 ohms?

  • 0
    TI__Expert 7855 points
    Charles,

    Good question, let me check with the team. This is an old device so it may take some time to get the answer.

    -Kelvin
  • 0 in reply to Kelvin Le THS
    Expert 2270 points

    Kelvin Le THS said:
    Good question, let me check with the team.

    Thank you for looking into it.  I appreciate any suggestions of other devices we could use.  

    BTW, I figured Kelvin was your handle on the Temperature Sensors Forum.  I figured Kelvin Le THS stood for Kelvin, Lord Thomas.  Thanks again for helping me.  

  • 0 in reply to Charles Gervasi
    TI__Expert 7855 points
    Charles,

    Please give me more information about your application and requirements.

    Here are some alternative analog sensors with a strong output drive:
    LMT84/87 (50uA)
    TMP235/236 (500uA)

    -Kelvin
  • 0 in reply to Kelvin Le THS
    Expert 2270 points

    Kelvin Le THS said:
    Please give me more information about your application and requirements.

    Here are some alternative analog sensors with a strong output drive:
    LMT84/87 (50uA)
    TMP235/236 (500uA)

    Thank you for finding these.  I think we may be stuck, though, because we don't to change the software to support a new voltage vs temperature function.  I doubt there's anything that we could scale to read in the same units as LM34.  Next time we may design in something digital so if we change it software would detect that rather than reading the wrong value.  

  • 0 in reply to Charles Gervasi
    TI__Expert 7855 points
    Charles,

    How much current drive strength do you need for your application? Worst-case, if you really need more drive you can add a buffer but this will certainly add cost.

    -Kevlin
  • 0 in reply to Kelvin Le THS
    Expert 2270 points

    Kelvin Le THS said:


    How much current drive strength do you need for your application? Worst-case, if you really need more drive you can add a buffer but this will certainly add cost.

    It depends on how we change other things in the circuit.  Depending how how we do it. even 100uA could be an issue, which means we need a buffer.