LM26: Correct transfer function for VTEMP output

Danilo A.

Part Number: LM26

Hi Team,

We would like to ask your help on the customer's inquiry below.

We are currently using the LM26CIM5-DPB/NOPB and we are having issues properly calculating the VTEMP output for our measurements to engineering values. On the forum I found that one of your team said the datasheet equation was wrong and to change a value from positive to negative but we are still not getting reasonable readings... Would you be able to tell me the correct transfer function for VTEMP output for this chip?

Thank you for your support.

Regards,

Danilo

over 3 years ago

0 Josh Wyatt over 3 years ago

TI__Guru* 91166 points

Dear Danilo -

Thanks for posting. Formula 3 on page 9 does appear to be missing a negative sign on the 1.082E-2 term. Formula 4 is correct. I just went through the exercises, using both formulas 3&4 to cross check them against each other, using 85C first, then made sure -20C, -40C also worked out correctly.

Formula 3 should be: Vtemp = (−3.479E-6 * (T−30)^2 ) + (−1.082E-2 * (T−30)) + 1.8015

Confirmation was also found in the original datasheet from National, too ==> http://pdf.datasheetcatalog.com/datasheet/nationalsemiconductor/LM26.pdf

I also made an excel sheet for this - which I have attached here, which shows output you should see over temp, which corresponds to the formulas (one of which is of course corrected as mentioned).