Clarifications on TSENS calculations on    MPC5675K

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Clarifications on TSENS calculations on    MPC5675K

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chethanvenkates
Contributor I

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

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davidtosenovjan
NXP TechSupport
NXP TechSupport

1) Yes, that's right.

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

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laurayindra
Contributor I

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?

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davidtosenovjan
NXP TechSupport
NXP TechSupport

1) Yes, that's right.

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

View solution in original post

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chethanvenkates
Contributor I

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 ?

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