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MC33907 Vcore UV and CAN transciever

Question asked by sanwal saleem on Nov 1, 2017

Hi Guys,


From many days I am trying to make this chip works. We have two different projects based on MPC5744P+MC33907. On earlier project MC33907 works like a charm but on new hardware it is not working with the same schematics. 


Following things happens:


By reading registers of SBC it states that there is always UV condition on VCORE, VAUX and VCCA but i have measured all the power supplies generated by SBC they are well within their specification. Another problem is CAN transceiver is not working. On power up SBC is in debug mode. CAN5V pin has 5V. 


Whenever MPC5744 sends something on CAN0TX SBC doesnt acknowledge anything on CAN0RX line. We have tried similar code on previous project and it is working fine on them. Even i tried to connect CAN0RX and CAN1TX to another CAN transceiver and its working fine. 


I checked all the CAN diagnostic registers there are no errors. 

Following is the status:

1. CAN MODE: NORMAL operation

2. CAN autowake up 120usec

3. CAN wakeup confg: 3 dominant pulses


I tried to read ESR register of MPC5744P and it shows BUS OFF and not sync whenever we tried to send something from MCU to CAN. Things are different when we send DATA from PC to MCU, ESR register states that CAN is sync, CAN is receiving data, BIT1 ERROR and passive error in FLTCONF. 


I have checked there are not shorts either to VCC or GND. 


We run the very same code on other project and it works fine. 



I really need help here.