Nick Guzzardo

SG8 / SH8 Temperature Sensor Specification Errors

Discussion created by Nick Guzzardo on May 12, 2008
Latest reply on May 13, 2008 by bigmac
My application requires the calculation of temperature from the internal temperature sensor of the S08.  We plan on using the SG8 since it is aimed at automotive apps, but we are starting with the SH8 since it is nearly equivalent, and the chips are readily available for prototypes.  The processor supply will be 5V.
 
Due to the significant similarities between the SG8 and SH8 I will only refer to the SH8 from here on out unless there is a specific difference.
 
The following excerpt is from section "9.1.4 Temperature Sensor" of the SH8 datasheet Rev.1 11/2007:
 

"Equation 9-1 provides an approximate transfer function of the on-chip temperature sensor for VDD = 5.0V, Temp = 25°C, using the ADC1 at fADCK = 1.0MHz and configured for long sample.

 
TempC = 25 - ( (VTEMP - 0.7013) / 0.0017 ) Eqn. 9-1
 
0.0017 is the uncalibrated voltage versus temperature slope in V/°C. Uncalibrated accuracy of the temperature sensor is approximately ± 12°C, using Equation 9-1."
 
 
The following is my understanding of the preceding excerpt so please reply if I am off in any way...
  1. The constant 0.0017 (1.7mV/C) is supposed to be the temperature sensors slope with VDD = 5V.
  2. The constant 0.7013V is supposed to be the voltage of the temp sensor at 25C with VDD = 5V.

Contrary to these 2 points is the data at the bottom of "Table A-12. ADC Characteristics".a

  1. The temp sensor slopes are 3.266 and 3.638mV/C for -40 to 25C and 25 to 125C respectively with VDD = 5V.
  2. The temp sensor voltage is supposed to be 1.396V at 25C with VDD = 5V.

Both of these data pairs cannot be correct.  As it turns out, the numbers used in Equation 9-1 of the SH8/SG8 datasheet are incorrect for VDD = 5V, but would be correct for 3V.  The data in Table A-12 is correct (with the exception that the 25C/5V temp senor voltage is shown as 1.396mV instead of 1.396V).

 

My local FAE has confirmed that the numbers in Table A-12 are correct, and the numbers in Equation 9-1 are incorrect for VDD = 5V; however my FAE also thought that the SH8 was a 3V part when it is actually a 5V part.

 

So to double check, can anyone confirm that for an S08 part (preferably an SH8 or SG8) that with VDD = 5V, that the 25C temp-sensor voltage is ~1.396V and that the slope(s) are near 3.4mV/C?

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