Do I always have to use a ballast transistor with the built in CAN physical layer?

[kevinerickson]

I have a design that is operating on a regulated 5V supply and the design is space constrained.  So the PCB area is very small.  Adding a recommended ballast transistor to the design for CAN support does not fit very well into the design.  Do I always have to use a ballast transistor with the built in CAN physical layer?  Can I provide a regulated 5V supply to VDDC for power?

[RadekS]

Hi Kevin,

I suppose that you want use S12ZVC MCU. I am right?

In fact, you don’t need use external PNP transistor for generating CANPHY power supply.

If you don’t use external PNP transistor for generation VDDC power supply, you should disable regulator in CPMUVREGCTL register.

Note: This register could be written just once in normal mode.

Unfortunately I am afraid that internal VDDX regulator itself isn’t suitable for powering CANPHY.

There should not be any problem in case of standard communication, however current during fault states could be simply too high.

I hope it helps you.

Have a great day,
RadekS

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