Recommended AVcc supply for G2955?

[paulpthcom 19]

Anyone have a recommend analog power supply for the G2955? Didn't see anything in the docs and the closest I came up with is the below from a TI note (8Ohm ferrite bead chosen because it was cheap at digikey).

 

[ILAMtitan 86]

I typically just decouple DVcc and AVcc with a low impedance resistor.  10ohms is typically good enough to reduce the noise carryover to an acceptable level for high performance analog applications.  Depending on the accuracy you need though, you may not have to even do that.

 

Any reason for the extra 22uF cap?  The standard bulk and bypass caps should be sufficient for this part.

[paulpthcom 19]

I typically just decouple DVcc and AVcc with a low impedance resistor.  10ohms is typically good enough to reduce the noise carryover to an acceptable level for high performance analog applications.  Depending on the accuracy you need though, you may not have to even do that.

Thanks for the response, any reason for the resistor instead of inductor/ferrite bead (cheaper and works good enough)?

 

Any reason for the extra 22uF cap?  The standard bulk and bypass caps should be sufficient for this part.

This was straight out of one of the schematics from that TI document. No clue if it'd actually make much of a difference vs a 10uF.

[ILAMtitan 86]

 

Thanks for the response, any reason for the resistor instead of inductor/ferrite bead (cheaper and works good enough)?

 

This was straight out of one of the schematics from that TI document. No clue if it'd actually make much of a difference vs a 10uF.

 

 

I use a 10Ohm resistor to make a small low pass filter, which the bead won't achieve.

 

Which schematic are you referencing?  The hardware users guide for the associated target board just has the two caps on it.  You can check out pg57 of slau278m.

[paulpthcom 19]

Which schematic are you referencing?  The hardware users guide for the associated target board just has the two caps on it.  You can check out pg57 of slau278m.

 

The one listed here http://www.ti.com/lit/an/scaa048/scaa048.pdf. I do see that the target board doesn't even have separate caps for AVcc so seems like its not particularly important, thanks for pointing that out.

[ILAMtitan 86]

The one listed here http://www.ti.com/lit/an/scaa048/scaa048.pdf. I do see that the target board doesn't even have separate caps for AVcc so seems like its not particularly important, thanks for pointing that out.

 

The separate bypass caps aren't required for operation, however I would recommend a set on both VCC inputs in order to help stabilize the AVcc line from digital noise.  I do a lot of work with the analog side the MSP, and stable analog power is very important.  I'm not familiar with the ADCs on the G2xx parts however, so they might not actually be accurate enough to matter.  Your best bet might be to just proto it up and see how it performs.  Worst case, you can pop a 0ohm rather than a 10, and no-pop the bypass caps.