LM35: LM35 negative temperature sensing with single supply

Wei-Hao Chen (TW-FAE)

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.

over 6 years ago

0 Kelvin Le THS over 6 years ago

TI__Expert 6475 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 Wei-Hao Chen (TW-FAE) over 6 years ago 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 Wei-Hao Chen (TW-FAE) over 6 years ago 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 Kelvin Le THS over 6 years ago in reply to Wei-Hao Chen (TW-FAE)

TI__Expert 6475 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 Wei-Hao Chen (TW-FAE) over 6 years ago in reply to Kelvin Le THS

TI__Expert 3260 points

Understood, thanks a lot!

Best Regards,

Wei-Hao

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LM35: LM35 negative temperature sensing with single supply