Why intrenal regulator o/p (VDDA) of MC13213 is 2.23V isntead of 1.8V?

[lekkal]

Hi all,

 I am getting output of internal regulator of MC1321x is 2.23V i.e., pin No 32, VDDA. It is suppose to be 1.8V. When I removed the external crystal oscilltor(16MHz) the internal regulator output is 1.8V. I am unable to get the same 1.8V output with external crystal oscillator is introducing on the board. 3 modules are assembled and found the same problem in all of them.

The board contains:
1. MC13213
2.16MHz Crystal Oscillator


1. No extrenal baluns
2. No external switch

Why I am getting VDDA 2.23V istead of 1.8V, how the crystal effects regulator output?

Thanks inadvance.

[Denn]

Hello,

Also refer the AN on Improving the Transient Immunity Performance of Microcontroller-Based Applications

http://www.freescale.com/files/microcontrollers/doc/app_note/AN2764.pdf

Regards,

Denn

[bigmac]

Hello,

It would seem that VddA is pin 33, rather than pin32.  So possibly you might be measuring the wrong pin.  Pin 32 is Vbat.

Have you used all the supply bypass capacitors as specified in the datasheet, and do you have proper grounding to a ground plane layer? The only explanation I can think of is that you are "picking up" some of the RF signal from the crystal, and this is imposing itself on your voltage measurement.  This would be more likely to occur with poor bypassing or grounding.

Regards,

Mac