Hi,
Following discussion we had here.
I am using a TMS570LC4357 and according to the TI Application note SPNA216, I made the following assumption: the measurable temperature range using the internal calibration sensor directly depends on the ADC reference voltage.
To illustrate this, I used calibration data from a TMS that we have here, and I computed the slope and offset according to the application note, using direct OTP values then using scaled OTP values to 1.15V.
Assuming ADREFLO is 0, the result shows that the temperature range when ADREFHI equals 3.3V is approximately [-40K; 862K], but with a reference of 1.15V, the range is [-40K; 211K].
Can you confirm that this assumption is correct? If not, could you provide some explanation of where the misunderstanding would be?
| OTP Calibration Values (no scaling): | ||||
| conv | temp | conv*temp | conv*conv | temp*temp |
| 1936 | 303 | 586608 | 3748096 | 91809 |
| 1556 | 233 | 362548 | 2421136 | 54289 |
| 2490 | 398 | 991020 | 6200100 | 158404 |
| Slope | 0.176352104 | |||
| Offset | 228.5924666 | |||
| OTP Calibration Values (scaling to 1.15V): | ||||
| conv (scaled to 1.15V) | temp_kelvin | conv*temp | conv*conv | temp*temp |
| 5555.478261 | 303 | 1683309.913 | 30863338.71 | 91809 |
| 4465.043478 | 233 | 1040355.13 | 19936613.26 | 54289 |
| 7145.217391 | 398 | 2843796.522 | 51054131.57 | 158404 |
| Slope | 0.061456036 | |||
| Offset | 655.9609911 | |||
| Methods results comparison: | ||||
| thermistor_read: | conv | temp computed using direct OTP conv values (ADREF = 3.3V) |
temp computed using scaled OTP conv values (ADREF = 1.15V) |
|
| 0 | -40.31276249 | -40.31276249 | ||
| 1556 | 234.0911117 | 55.31283002 | ||
| 1936 | 301.1049113 | 78.66612383 | ||
| 2490 | 398.803977 | 112.7127679 | ||
| 4095 | 681.8491043 | 211.3497062 | ||
Best regards,
Gael
