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LM35: LM35 negative temperature sensing with single supply

Wei-Hao Chen (TW-FAE)
Expert 3260 points
Part Number: LM35
Other Parts Discussed in Thread: TL431, LMV431

Hi team,

Is it possible to achieve negative temperature sensing using LM35 with only single VS supply? I saw Figure 18 in the datasheet, does this circuit support full range temperature sensing? If yes, is the output voltage still = 0 ± 10mV/°C?

Thanks a lot.

  • 0
    TI__Expert 7355 points
    Hi Wei-Hoa,

    Please look at this post:

    e2e.ti.com/.../2155043 user:230186#2155043

    Vout ("+" node relative to supply GND) = 2*Vd+10mV/oC, where Vd is the forward voltage of the diode.
    The diode is an inexpensive way to produce a voltage reference but it's not a stable reference over temperature.

    -Kelvin
  • 0 in reply to Kelvin Le THS
    TI__Expert 3260 points
    Hi Kelvin,

    Got it, thanks for your answer. This is really helpful.

    Wei-Hao
  • 0 in reply to Kelvin Le THS
    TI__Expert 3260 points
    Hi Kelvin,

    One more follow up question, as you mentioned the diode Vf is not a stable voltage reference over a large temperature range, is it possible to use precision voltage reference like TL431 to the GND pin of the LM35 to create a headroom for negative temperatures?

    Could you please provide any reference circuit using precision voltage references device?

    Thank a lot.
  • 0 in reply to Wei-Hao Chen (TW-FAE)
    TI__Expert 7355 points

    Wei-Hao,

    Looking the TL431, the Vref variation over temperature can vary by as much as 30mV from 25C to -40C or 125C.

    LM35 has a gain of 10mV/C.  So you're looking at a min error of 3C due to Vref temperature variation. 

    Try searching for examples of voltage references on ti.com.  There are plenty of examples in the applications section of those devices.  You are literally creating a virtual ground for LM35 with a voltage source.

    You will need to find voltage reference with a temp coefficient that you're willing to accept.  The cost increases with performance so you will have to decide where to draw the line.

    Maybe look into LMV431 as starting point and do the same analysis I did with TL431.

    -Kelvin

  • 0 in reply to Kelvin Le THS
    TI__Expert 3260 points

    Understood, thanks a lot!

    Best Regards,

    Wei-Hao