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Topic: disadvantages to not wiring up all the power pins on a 328p? (Read 681 times) previous topic - next topic

dtokez

I guess it it good practice to wire both the grounds and 5v signals on this type of IC, but I have made simple projects before and only connected 5v and gnd on one side of the chip, what are the potential issues with this? I guess they are internally connected so I can't really see the point in connecting them all unless you will be drawing any power through it?


Docedison

Most do see the sense in it besides it being a factory recommendation
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dtokez

So are you likely to come up against issues if you don't do it?

Thanks

fungus


I guess it it good practice to wire both the grounds and 5v signals on this type of IC, but I have made simple projects before and only connected 5v and gnd on one side of the chip, what are the potential issues with this? I guess they are internally connected so I can't really see the point in connecting them all unless you will be drawing any power through it?


Try reading the datasheet.

a) Each VCC/GND pin can only handle 200mA. You'll do damage if you only connect one power supply pin then load up the chip I/O pins.

b) The pins may be connected internally but each VCC/GND pin feeds a different set of I/O pins. If you only connect one power pin then load up the "wrong" I/O pins then again, you'll doing damage.

No, I don't answer questions sent in private messages (but I do accept thank-you notes...)

dtokez

Thanks, I'll bear that in mind for future projects. Luckily all of the projects that I have made and only connected one side are still working :)

GilchristT


a) Each VCC/GND pin can only handle 200mA. You'll do damage if you only connect one power supply pin then load up the chip I/O pins.

b) The pins may be connected internally but each VCC/GND pin feeds a different set of I/O pins. If you only connect one power pin then load up the "wrong" I/O pins then again, you'll doing damage.


I've often wondered about this question myself, that's a useful explanation, thanks.

dc42

More importantly, if you connect Vcc to the supply but don't connect Avcc, then I have heard that the chip sometimes doesn't work correctly, even if you are not using the ADC.
Formal verification of safety-critical software, software development, and electronic design and prototyping. See http://www.eschertech.com. Please do not ask for unpaid help via PM, use the forum.

MarkT


I guess it it good practice to wire both the grounds and 5v signals on this type of IC, but I have made simple projects before and only connected 5v and gnd on one side of the chip, what are the potential issues with this? I guess they are internally connected so I can't really see the point in connecting them all unless you will be drawing any power through it?



Wire them all, decouple them all.  The decoupling is the important point, the multiple leads means
a lower inductance path to the first decoupling capacitor, this is why multiple power and ground pins are needed.
[ I won't respond to messages, use the forum please ]

sparkylabs

remember that the chip inside the IC is also a circuit with it's connection and grounding requirements.
My shop: www.sparkylabs.co.uk/shop

RoyK

Every pin that a manufacturer uses costs him. It's a good assumption that if fewer power and ground pins would work satisfactorily he would use fewer power and ground pins, don't ya think?

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