TMP421: n-factor correction

Hi Lars,

How much error do you see between the expected temperature and the TMP421 reading?  Also, how are you forcing the device temperature?

Thanks,

Hei

When setting 0x21 = 0x06  I get app 10C too low reading.

The FPGA has an internal register for temperature reading.  This is my comparison.

When setting 0x21 = 0x00 I get app 5C too low reading.

The connection to the sense pins in the FPGA is 100 Ohm series on both and 100pF between.

BR

Lars Petter

Hi Lars,

There are a couple possibilities that could cause this error.  This junction could have a low beta that could be causing this error or their could be noise on the DXP/DXN pins.  Can you please let me know what the temperature the FPGA is reading and what temperature the TMP421 is reading with the default setting 0x21 = 0x00?  Also, please send an oscilloscope shot of the DXP pin and DXN pins. Please make sure the oscope shot is zoomed in enough to tell the different voltage levels with the different injected currents from the device.

Thanks,

Hi Lars Petter,

Do you have an update on this or have resolved your issue?  

Thanks,

Hi

I have not resolved this issue, but I have not been able to measure the differential voltage levels yet.

However, I have done some temperature measurements:

When 0x21=0x00 i get  4-5C lower reading than the internal sensor.

When setting 0x21=0x06, (setting a compensation factor), I get 9-10C lower reading.

BR

Lars Petter

Hi Lars,

Ok, please let me know when you can get the oscilloscope screen shots.  Meanwhile, is the 4-5C and 9-10C consistent over the temperature range or does the temperature have a slope error (the error gets worse across temperature).

Thanks,

Hi Lars,

In while getting the oscilloscope waveforms, can you also send me the schematic?

Thanks,