MPC55xx power sequencing

[ypchen]

hello,I'm developing a new board based on MPC5554,the board has three power supply:+1.5V,+3.3V,+5V.

In my design,VRC33 is connected to the +3.3 V supply,and the internal regulator controller is not being used.

What is the power-sequencing in +1.5V,+3.3V and +5V ?

[ypchen]

Hi  David：

VRC33 is  connected to the 3.3 V supply, thus it removes power sequencing requirements.

But,if it is  to GND,what is the benefit?To reduce power consumption，and what else？

[davidtosenovjan]

Actually I don't see any benefit, power consumption saving will be negligible. It is recommended to have VRC33 connected to 3.3V.

[ypchen]

So,why not connect VRC33 to  +3.3V plane in the 5554 package ? in this way,it can simplify our designe.

[davidtosenovjan · Accepted solution]

Yes, you are right, it would be simpler. Unfortunately I don't know why it was implemented this way.

[davidtosenovjan]

You have connected VRC33 to the 3.3 V supply thus it removes power sequencing requirements. If internal regulator is not used, VRCCTL should be left unconnected and this pin will float high internally.

For details, read following document:

http://cache.freescale.com/files/microcontrollers/doc/app_note/AN3254.pdf