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???
07/06/09 19:57
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 		 #166811 - OK, more
Responding to: ???'s previous message
theoritically an open drain and a resistor can be used with any voltage the port pin is rated for (in your case 5V).
HOWEVER, on a silicon die many parasitic diodes (diodes that "have no function and present no problem", but are a result of the process) exist. It is posible that there will be a parasitic diode from the drain to Vdd, if so, you can not pull the pin higher than VDD plus a diode drop.

The easy way is to connect the pin to 5V through a resistor, configure it for open drain without pullup and measure. If you get 5V there is no problem ANYTHING less will indicate a parasitic/protection diode.

Erik

List of 33 messages in thread
TopicAuthorDate
Driving a 5 v PNP with 3.3 volts pin            01/01/70 00:00      
   Diagram ?            01/01/70 00:00      
      Sketch..            01/01/70 00:00      
         Steve..            01/01/70 00:00      
            Why push-pull?            01/01/70 00:00      
               Thanks Rob            01/01/70 00:00      
               Very much depending on chip            01/01/70 00:00      
                  Yeah, but ...            01/01/70 00:00      
                     Better always add a note for potentially dangerous methods            01/01/70 00:00      
                        Is that my responsability?            01/01/70 00:00      
                  Westermark            01/01/70 00:00      
                     Erik did exmplain            01/01/70 00:00      
                        Sorry Westermark..            01/01/70 00:00      
         KISS            01/01/70 00:00      
   If it has not to be a PNP...            01/01/70 00:00      
      Relay has to be driven..            01/01/70 00:00      
         since I would never do that ...            01/01/70 00:00      
            Open drain pulled up to 5V..            01/01/70 00:00      
               did you read my post            01/01/70 00:00      
                  Deep waters            01/01/70 00:00      
                     OK, more            01/01/70 00:00      
                        I missed this post..            01/01/70 00:00      
      BC556 would turn on, wouldn't it?            01/01/70 00:00      
         It wouldn't. Sorry.            01/01/70 00:00      
   Have you considered a pMOSFET?            01/01/70 00:00      
      Yep, I second that! Use a FET            01/01/70 00:00      
         Have you considered that he must drive a 5V relay?            01/01/70 00:00      
            Does that really matter?            01/01/70 00:00      
               To what do you connect the source of this pMOSFET??            01/01/70 00:00      
                  It's the switched drain current that does the work            01/01/70 00:00      
                     Of course, it does! But...            01/01/70 00:00      
                        One could also use a "switch" ...            01/01/70 00:00      
                           Yes, that's safe!            01/01/70 00:00      

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