The MC33978 / 34978 has a temp diode for measuring junction temperature that can be output on the AMUX. The data sheet gives a coefficient of 8mV per degree C. That is the only information that I can find on how to use this feature. Is this merely a matter of applying a linear equation? If so what is the slope intercept value?
If anyone can supply some guidance here I would greatly appreciate it.
Regards,
Tom
Solved! Go to Solution.
Hi Tom,
I have asked our device group to comment on this, here is the answer.
The temperature sensor is 4 series diodes.
At room temp,
Vbe = ~ 0.65V (one diode only)
4*Vbe = ~ 2.6V
TC of Vbe is ~ -2mV/degC
TC of the temp sensor = 4*TC(Vbe) = ~ -8mV/degC
Die temp is approximated by the equation of a line y = mx +b where
y is the voltage as a function of temperature
m is -8mV/degC
x = temp
b is the voltage @ 0 degC
Y(0) = -8mV/degC x 0 degC + b => b = 2.6V + (0-25C)(-8mV/degC) = 2.8V
So the equation is:
Vtemp = (-8mV/degC)(Temp) +2.8V
More practical is to solve for Temp = (Vtemp-2.8)/(-8mV)
I hope it helps.
Regards,
Tomas
Hi Tom,
I have asked our device group to comment on this, here is the answer.
The temperature sensor is 4 series diodes.
At room temp,
Vbe = ~ 0.65V (one diode only)
4*Vbe = ~ 2.6V
TC of Vbe is ~ -2mV/degC
TC of the temp sensor = 4*TC(Vbe) = ~ -8mV/degC
Die temp is approximated by the equation of a line y = mx +b where
y is the voltage as a function of temperature
m is -8mV/degC
x = temp
b is the voltage @ 0 degC
Y(0) = -8mV/degC x 0 degC + b => b = 2.6V + (0-25C)(-8mV/degC) = 2.8V
So the equation is:
Vtemp = (-8mV/degC)(Temp) +2.8V
More practical is to solve for Temp = (Vtemp-2.8)/(-8mV)
I hope it helps.
Regards,
Tomas