Team,
We are using the TMP275 and it seems to be working fine at positive temperatures. When we went cold like -25 we started to get readings like 242.
I am assuming this is a software problem and that the neg temp = 245- 2^8 = 242-256 = -14 degC.
Is this correct?
Hi Go Bravos,
Thank you for your post. The TMP275 reports temperature as in table 1 of the datasheet. Your reading of 242 would be equivalent to 3872 in unsigned decimal, or 0xF20. This would be -224 as unweighted two's complement, or -14C when the bits are properly weighted, as you correctly calculated.
You can interpret its output (after shifting out the unused 4 lower bits) as a 12 bit two's complement number, with the lower 4 bits being fractional (the LSB has a value of 0.0625C).
So at -25C, you would expect a value of 0xE70 (as shown in the table). If not interpreted as a two's complement number, then you would see this as 231C.
Best Regards,
Brandon Fisher
