TMP75: Replace Onsemi NCT75DR2G

Hi Shu-Cheng Lin,

The hardware will be the same, as the devices are pin compatible. The devices also have compatible register maps if all you are doing is reading temperature, but there are some differences in the configuration register due to differing feature sets. 

For the TMP75 the config register looks like this:

For the NCT75 it looks like this:

The key differences here are as follows:

The One-shot mode bits of these devices are different bit locations (D5 vs D7) and do not have the same function. On the TMP75 you would set the shutdown mode bit and write to the one-shot mode bit to trigger a single conversion. On the NCT75 you have a redundant shutdown mode and one-shot mode with different functions. As well as a one-shot register added to the register map for triggering conversions.

The TMP75 also includes a configurable temperature resolution between 9 to 12 bits (D6 and D5), with different conversion timings with each resolution. The default for the TMP75 is 9 bits, and the default for the NCT75 is 12 bits. It would still work but you would not get the full resolution using the TMP75 in default mode. I would recommend using the TMP1075 instead, as you will not have the difference in default resolution. 

Overall I would say you could do this with no differences in the code if you are working under default configuration settings. Otherwise you would just need to change the value that you write to the configuration register in your code. I would still recommend taking a look at the TMP1075, as it will have better performance than both these devices with comparable pricing. 

Best Regards,
Brandon Fisher