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mpc5744p pmc external voltage regulator

Question asked by Luka Škorić on Mar 5, 2019
Latest reply on Mar 8, 2019 by Peter Vlna

Hello, Peter Vlna

I have a question regarding implementation of the requirement SM_089 in Safety Manual for MPC5744P, Rev. 4, 02/2018.

 

"Assumption under certain conditions: [SM_089] When the system requires robustness
regarding 1.25 V over voltage failures, the external VREG mode is preferably selected.
The internal VREG mode uses a single pass transistor and, therefore, over voltage can not
be shut off redundantly."

 

What is the exact procedure for this implementation?

 

In our system we use MC33907/08 System Basis Chip that does what is described in Safety Requirement [SAG_MPC5744P_042] (from document Integrating the MPC5774P and MC33907/08 for Safety Applications Rev. 004/2015) but without any modifications done to PMC registers of MCP5744P controller.

Is the above mentioned Safety Manual requirement (SM_089) covered by the fact that the SBC monitors voltage levels? Is there anything to be done in relation to PMC_PMCCR register INT_REG_BYPASS flag?

 

When tried to modify that register in order to activate external voltage regulator, which was done by the following code:

 

        // Enable writing to PMC Control Register
        PMC.PMCCR.B.PMCCR_EN = 1u;
        // Disable internal regulator, external regulator is active
        PMC.PMCCR.B.INT_REG_BYPASS = 1u;

 

a series of resets crash the system.

 

Is there anything that has to be configured previous to disabling internal regulator? Does this register even have to be modified in order to satisfy requirement SM_089 from Safety Manual? What is the overall procedure for implementation of that requirement?

 

Thank you in advance.

Kind Regards

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