MPC5644A VDDREG operating range?

[cthhk]

Dear Support:

According to datasheet, VDDREG should be within 4.75~5.25V. The question is, what happens if it falls to lower than 4.75V?

We are using internal 3.3V regulator and internal 1.2V regulator so we need to make sure if they still work normally till LVD happens.

Your quick response would be highly appreciated!

Best Regards,

WY

[davidtosenovjan · Accepted solution]

AN4291, chapter 3.1.1 says:

“If VDDREG is less than 4.5 V, then the 3.3 V regulator is disabled”

There will some safety margin, but in my opinion disabling of 3.3 V regulator can happen is VDDREG it falls to lower than 4.75V.

http://cache.nxp.com/files/32bit/doc/app_note/AN4291.pdf

[cthhk]

hi David:

I need to append one more question: If we use 5V for all GPIO, 3.3V is only connected to NEXUS module. Then can we say 3.3V can be ignored and won't affect anything else in normal mode?

I'm asking this because we need to design the external reset circuit to guarantee that the whole system is always working before reset asserted... If 3.3V could be ignored in such case, the external circuit will be much simpler.

Best Regards,

WY.

[davidtosenovjan]

Even though VDDEH7 voltage is being powered by 5V, when nexus functionality for nexus pads is selected, these pads will have 3.3V level (MultiV output in low-swing mode).

So yes, you can build 5V only system (considering core voltage powered by internal regulator).

[cthhk]

hi David:

Clear and thank you very much!

Best Regards,

WY