MC33771B NTC Thermistor Input Filter

[jriley]

Hello,

I am reviewing the component sizing for the MC3371B NTC thermistor input filters, following the MC3311B datasheet, section 13.2.5.  When I use the provided component values from Table 99 with the equations 17-20 to find the signal cutoff frequency, I find the bandwidth result to be much larger than the bandwidth calculated for the cell voltage measurements.

Temperature signal cutoff frequency calculation:

Cell voltage signal cutoff frequency calculation:

The datasheet notes that these bandwidths should be equal.  Is there a problem with my calculations or the values I am using?

Thanks,

Jess

[reyes · Accepted solution]

Hi Jess,

Your calculated result is okay.

Actually, there is no relationship between the bandwidth of the cell voltage channel and that of the temperature channel. The latter is kept much greater than it would be needed only for readiness reasons (when temporarily exiting the sleep mode to perform a temperature measurement). 

Have a great day,
Jose

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