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ADuC7061 Internal Temperature Sensor Error

Question asked by jbuckf50 on May 8, 2017
Latest reply on Sep 22, 2017 by barryzhang

Hello.  I'm picking up an error with use of the internal temperature sensor on the ADuC7061.  It consistently reads about 10-15C too low.  I see this error across multiple parts and multiple PCB revisions.


Below are the settings I'm using for ADC1CON:

ADC1CON = (BIT15+BIT11)+(BIT10+BIT8+BIT7);


And the engineering-unit conversion:

temp_7061 = ((aux_result[3]/16777216.0*1.2)-0.096)/0.00028;

where 'aux_result[3]' is the result from the ADC register. 


For debug, I also looked at the raw voltage:

temp_7061 = ((aux_result[3]/16777216.0*1.2));


Room temperature here is about 22C, and using a thermal imager I measured a rough package temperature at 33C in my application, once things are warmed up.  I'd expect the die to be in the mid to high 30s of Celsius, but instead it tops out at around 0.1014V (~19C). 


My aux ADC is single ended and I've grounded the ADC5 pin, so I also tried:


but got the same results. 


Any idea what I might be doing wrong here?