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Kai Klaas
06/25/08 08:48
Read: 546 times
Germany


 
Msg Score: +1
 +1 Good Answer/Helpful		 #156199 - Again, do not add any impedance in the GND line
Responding to: Richard Erlacher's previous message
Richard said:
If even a very small part of that total resistance is in the GND path between the two bypass cap's, then much less current will flow through the R in the GND rail than through the local cap.

You mean something like that?



Sorry, Richard, again, the current is entirely limited by the resistor R in the Vcc line. Inserting "even a very small part of that resistance in the GND line", as you wrote, will not have any relevant influence. What counts is the total impedance in the left, blue marked loop, which is best provided by the shown R only.

Please do not add any impedance in the GND line. This would be totally counter-productive and violate all design rules dealing with decoupling.

Kai

List of 31 messages in thread
TopicAuthorDate
Resistance in the supply rails      Richard Erlacher      06/15/08 11:04      
   inductor instead of resistor      Kalpak Dabir      06/15/08 12:02      
      yes, and no and I think the theory is flawed      Erik Malund      06/15/08 12:43      
         Spice?      Russ Cooper      06/15/08 15:11      
            That would probably help, but ...      Richard Erlacher      06/15/08 16:30      
      That's what I said      Richard Erlacher      06/15/08 16:21      
         Not in the gnd path!        Russell Bull      06/15/08 18:57      
            Well ... this normally doesn't work so well, but      Richard Erlacher      06/15/08 19:35      
   If this scheme is used it would also be well to...        Michael Karas      06/15/08 23:38      
      This does increase the supply impedance      Richard Erlacher      06/16/08 10:03      
         please clarify with a simple schematic      Erik Malund      06/16/08 10:22      
            the bypass cap\'s always go between Vcc and Gnd      Richard Erlacher      06/16/08 14:00      
               Which Vcc, Which gnd      Erik Malund      06/16/08 14:04      
                  There's a cap on either side of the resistor(s)      Richard Erlacher      06/16/08 14:28      
                     is it      Erik Malund      06/16/08 15:47      
                        Not quite ...      Richard Erlacher      06/16/08 17:43      
                           don't use a resistor in the GND connection        Frieder Ferlemann      06/19/08 14:03      
                              What >good reason< could this be??      Kai Klaas      06/19/08 19:31      
                                 What good reason could this be??      Erik Malund      06/19/08 19:33      
                                    Using a resistor in the GND connection...        Kai Klaas      06/19/08 19:37      
                              How would that come to pass?      Richard Erlacher      06/19/08 21:24      
                                 Why should I insert a resistor in the GND line??      Kai Klaas      06/20/08 19:24      
                                    Seldom andonly if it is of benefit      Richard Erlacher      06/21/08 11:50      
                                       No disagree, but ...        Kai Klaas      06/22/08 19:42      
                                          The regulator can't pull the Vcc down      Richard Erlacher      06/22/08 23:54      
                                             This has nothing to do with imbalance!        Kai Klaas      06/23/08 15:29      
                                                Kai, I don\'t disagree ...      Richard Erlacher      06/24/08 10:55      
                                                   Again, do not add any impedance in the GND line        Kai Klaas      06/25/08 08:48      
   tantalum capacitor across the MAX232 power pins      Gary Peek      06/16/08 11:51      
      It's a matter of careful choice      Richard Erlacher      06/16/08 14:25      
      Yes they does      Kalpak Dabir      06/19/08 09:19      

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