Clarifications on TSENS calculations on MPC5675K

[chethanvenkates]

Hello,

I had few questions on the TSENS calculations on MPC5675K

1) As per  MPC5675K TRM, TSENS calibration constants will retrieved from test sector  of flash

Constant Description for TSENS calculations using Formula:

P1 Code from the ADC converting VTSENS in PTAT mode at 145 C

P2 Code from the ADC converting VTSENS in PTAT mode at -40 C

C1 Code from the ADC converting VTSENS in CTAT mode at 145 C

C2 Code from the ADC converting VTSENS in CTAT mode at -40 C

Test flash memory information:

0x0000 TSENS1_CAL W1/W2 Temperature sensor Calibration data W1 and W2

0x0004 TSENS1_CAL W3/W4 Temperature sensor Calibration data W3 and W4

Question here is Calibration data TSENS1_CAL W1/W2/W3/W4 is interpreted as P1/P2/C1/C2 Respectively? Or is there any alternative correlation to interpret the calibration constants TSENS1_CAL W1/W2/W3/W4 w.r.t P1/P2/C1/C2?

2)Temperature sensor Calibration data (TSENS1_CAL W1/W2/W3/W4) retrieved from test sector is of 16 bit data for each constant.

  Whether we need to use all 16 bit Calibration constant Data for TSENS calculations or we need to use only 12 Bit data?  Since the ADC conversion values will be of 12 bit from the Channel Data Register n (CDRn) of ADC  for getting current PTAT or CTAT values at Generic temperature.

if I use 16 Bit Data then I am getting incorrect temperature as output from the formula, but if I use 12 bit then I am getting correct temperature as output. Refer below example and data.

Example:  Case 1 output is 37.4112341632604 ◦C using 12 bit Calibration Const Data

                    Case 2 output is 1728.62365481082 ◦C using 16 bit Calibration Const Data.

	CASE 1: Using 12 Bit Calibration Const Data	CASE 2: Using 16 Bit Calibration Const Data
T2	-40	-40
T1	145	145
PX	1229	1229
CX	1225	1225
P1	2575	47631
P2	1429	46485
C1	1515	62955
C2	2181	63621
A	918944	21246084
B	1295320	-19023720
T	37.4112341632604	1728.62365481082

Request to clarify above questions

Thanks

Chethan

[laurayindra]

using this method, we are consistently seeing temperature readings that are 10 degrees higher than what would be expected based on the thermal gun.  Why?

[davidtosenovjan · Accepted solution]

1) Yes, that's right.

2) I think you answered yourself. 16-bit TSENS1_CAL Wx code must be ANDed by 0x0FFF before use.

[chethanvenkates]

Thanks for the clarifying questions . Information on "16-bit TSENS1_CAL Wx code must be ANDed by 0x0FFF before use" is missed in the TRM , shouldn't we add this note in TRM ?