Andy Kunz says:
[We should separately bypass/isolate the AVcc and AGND]
It came about as a result of using a 17C756 (in which they are labelled as AVcc/AGND) while having poor results with a '74. One day, a lightbulb went off, and all of a sudden it worked with the new power layout. Ever since then I've used a fixed part (separated the two power/ground systems) in the schematic package and have not had such problems any more.
I think it's an oversight on their part NOT to tell us this. What I can't figure is how they get a '73/76 to work well, since it's the same die as the 40-pin part just a different bonding.
I never thought of it until just now, but I wonder how much resistance is between the two grounds and two power supply pins.
Dan Michaels says:
This is most unfortunate. Exactly the other side of the "AGnd" are the oscillator pins, so this gnd pin makes a really great place to return the little gnd-trace-island that you draw around the xtal/cap/cap area on your pcb to help isolate and confine the hi-freq stuff.
So, instead of reducing overall noise, you end up directing it straight into your AGnd. Gakkk. Wrost of all possible worlds.
|file: /Techref/microchip/a2dvccgnd.htm, 1KB, , updated: 2004/2/13 15:40, local time: 2021/10/21 02:11,
|©2021 These pages are served without commercial sponsorship. (No popup ads, etc...).Bandwidth abuse increases hosting cost forcing sponsorship or shutdown. This server aggressively defends against automated copying for any reason including offline viewing, duplication, etc... Please respect this requirement and DO NOT RIP THIS SITE. Questions?|
<A HREF="http://www.piclist.com/techref/microchip/a2dvccgnd.htm"> Seperating the Vcc and Gnd for the A/D converter</A>
|Did you find what you needed?|
PICList 2021 contributors:
o List host: MIT, Site host massmind.org, Top posters @20211021 Neil, Harold Hallikainen, Alan Pearce, RussellMc, Bob Blick, Allen Mulvey, Dwayne Reid, madscientistatlarge, Sean Breheny, Justin Richards,
* Page Editors: James Newton, David Cary, and YOU!
* Roman Black of Black Robotics donates from sales of Linistep stepper controller kits.
* Ashley Roll of Digital Nemesis donates from sales of RCL-1 RS232 to TTL converters.
* Monthly Subscribers: Gregg Rew. on-going support is MOST appreciated!
* Contributors: Richard Seriani, Sr.
Welcome to www.piclist.com!