MC33771B - Temperature Measurement

[Patrick_Pavle]

Dear Community, 

Can the MC33771B also measure the temperature of the individual cells?
I have only been able to find out that the IC can measure undertemperature, overtemperature and the IC temperature.

best regards,

Patrick 

[TomasVaverka · Accepted solution]

Hello Patrick,

Yes, the MC33771B (Advanced and Premium) provides 7 GPIOs which can be used as analog inputs for temperature measurement as described and illustrated in the Temperature channels section of the datasheet or in the Temperature measurement design section of the AN12963.

The conversion results are available in MEAS_ANx registers.

BR, Tomas

[Patrick_Pavle]

Dear @TomasVaverka.,

if there are only 7 NTCs, how can the MC33771B monitor 14 cells?

if i read out the register, how do i convert the value into temperature?

regards,

Patrick

[TomasVaverka]

Hello Patrick,

It is usually not mandatory to monitor the temperature of all cells in the battery pack.

Temperature measurements are typically done with an NTC with a polarization resistor (10K recommended in our datasheets) connected to Vcom. Using a ratiometric measurement mode will allow to remove any error that could be coming from a variation of the Vcom voltage. Thus, better temperature measurement accuracy is achieved.

In ratiometric mode, the content of the GPIO measurement register (Code(Hexa) in the formulas below) depends only on the NTC resistor value (hence its temperature) and not on Vcom at all.

To calculate the NTC resistor value, one should use the following formula:

BR, Tomas

[Patrick_Pavle]

Dear @TomasVaverka ,

I'm sorry but I don't understand exactly how to apply the formula.
if i read the register MEAS_AN0 i get the value 0x800E. but how do i get the temperature value?

BR, Patrick

[TomasVaverka]

Hello Patrick,

The most common method to get the actual temperature based on the calculated NTC resistor value uses a lookup table (LUT), also known as a resistance table, normally provided by the thermistor manufacturer.

BR, Tomas

[Patrick_Pavle]

Dear @TomasVaverka ,

so is there no other method for this? because i have an unknown battery module where i don't know what kind of ntc is used.

BR, Patrick

[TomasVaverka]

Hello Patrick,

I am not aware of another simpler method, I am afraid you will need the specification of the RTC used in your battery pack.

BR, Tomas