Temperature sensor interface

Hi johnpritchard ,

I will reach out to product owner of the LTM4702 to find out more details.

AD7293 have two external sensors with offset adjustment by register, let me find out, if that would be enough to be used with LTM4702. Note: AD7293 is calibrated to be used with 2N3906 external transistor. 

Regards,

Arnost

Thanks for your help, I await further information.

Hi Arnost

Do you have any answers for me?

Thanks

John

Hi John,

my apologies, it took couple of e-mail exchanges to figure the same out.

Based on the discussion, we believe AD7293 and LTM4702 is possible to use together for temperature sensor measurement. 

From LTM4702 support I got feedback that: "LTM4702 uses a diode connected NPN transistor that is similar to the 2N3904", 2N3904 is listed as sensor in AD7293 datasheet also. Based on the same, it should work well. 

When it comes to accuracy AD7293 is calibrated to "2n3906", so it may require slight calibration, depending on required accuracy. 

Following notes from my colleague should help you reason the same:

"It looks like the typical IDF (something like ideality factor) of the 2N3904 is around 1.004, whereas the 2N3906 is typically around 1.013.  Armed with this, the temperature can be ‘corrected’ for the difference in IDF.

 As an exercise, and ignoring any offsets,
IDF_3906 * T_actual = IDF_3904 * T_ad7293, where T is in Kelvin.

Lets say the actual temp is 100C, or (273.15 + 100) = 373.15

 T_ad7293 = IDF_3906 * T_actual / IDF_3904 = 1.013/1.004 * (100 + 273.15) = 376.49K, or 103.3C, so an error of 3.3C due to the difference in IDF.

At 0C, the error due to the difference in IDF between the 2n3906 and the 2N3904 is ~2.45C.

If the Temp region of interest is 0C – 100C, then the customer could set the offset to be –((3.3C – 2.45C)/2 + 2.45C) = -2.875C"

Regards,

Arnost

Hi Arnost

Thanks very much that is good news.

Thanks

John