MC33771C capacitve isolation

[Vladimir_A]

Hello,

I see that new version of BMS AFE support capacitive isolation (table 1. https://www.nxp.com/docs/en/application-note/AN12633.pdf ). But, I can't find details about implementation. Application note AN12626 https://www.nxp.com/docs/en/application-note/AN12626.pdf describe TPL over transformer only.
Could you please provide me the requirements for the capacitors in case of capacitive isolation?

[ErikaC · Accepted solution]

Hello, sorry for the delay in replaying. 

For capacitor selection, the voltage rate depends on the application/ The customer should select X7R or X7S dielectric for automotive temperature range. No need of specific low ESL/ESR.

Safety capacitors (soft termination from TDK), or two capacitors in series, should be considered for capacitors connected to high voltage and low impedance nets (batterry cells, TPL isolation, ...)

Hope this helps.

[Vladimir_A]

Hi Erika, thank you for the answer.
I just checked this part of documentation and see that there are only high level requirements are provide - capacitance, resistance and voltage of ESD. One characteristics for each component.
I think that the type, class, voltage of capacitor should determined at least. Maybe some type of frequecy characteristics. Due to high frequency and high voltage operation bad choice of capacitor and ESD may affect on the result.

[ErikaC]

Hello,

The requirements for the capacitors in case of capacitive isolation are described in the MC33771C datasheet, please refer to section 13.

Hope this helps.