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BCTLC goes to 12V

Question asked by Manish Sangram on Jun 2, 2016
Latest reply on Jun 13, 2016 by Radek Sestak

Hi,

 

We are using S12ZVMC128 which has the ability to generate power supply for CAN chip using an external ballast transistor. we are using BC53PA transistor with 5.6K biasing resistor (also tried 10K). We have lost as many as 20 CAN chips till date because the output of the ballast randomly goes to 12V instead of 5V (on power up).

 

We have been in touch with the local support group and we can assure you that this is not a software problem because we are using PE to generate the code which also is simply setting the the bit EXTCON right at the beginning.

 

We are very frustrated with this problem as it is just not getting solved. We are having to use a 5V LDO to test our system.

 

The important things to note are that this issue is seen when connecting to battery input and not when connecting to a lab power supply. Also note that we do not have reverse protection as we have physical means of ensuring that so no mosfet/diode exists between battery input and VSUP to MCU and to both ballast transistors.

 

Schematic attached.

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