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'[PICLIST] Sink / Source? Whats the diff?'
2000\06\17@225738 by Greg Hastings

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The PIC 16F84 spec says it can

sink 25mA max
and
source 20mA max

What is the difference between the two?

Greg
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2000\06\17@232630 by Dale Botkin

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face
On Sat, 17 Jun 2000, Greg Hastings wrote:

> The PIC 16F84 spec says it can
>
> sink 25mA max
> and
> source 20mA max
>
> What is the difference between the two?

Sink:
Current flows into the PIC from an external source...
------
PIC  |--/\/\/\------ GND
------

Source:
Current flows out from the PIC to an external load...
------
PIC  |--/\/\/\------ +V
------

Somebody please tell me I didn't get that bass-ackwards, it's been a long
day.

Dale
---
The most exciting phrase to hear in science, the one that heralds new
discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
               -- Isaac Asimov

2000\06\17@233913 by Scott Dattalo

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flavicon
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On Sat, 17 Jun 2000, Dale Botkin wrote:

{Quote hidden}

Actually, the difference is 5mA :).

I think Greg is really asking WHY there's a difference. I'm about 99% sure that
it's because there's an N-channel FET sinking current and there's a P-channel
sourcing. N-channel devices have lower on-resistances than P-channel devices for
the same amount of silicon area. So in all likelihood, the silicon area devoted
to the P-channel is not large enough so that it mirrors the N-channel's specs.

Scott

2000\06\18@052417 by Brent Brown

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{Quote hidden}

Sorry Dale, it's bass-ackwards. Your description is perfect but your
diagrams are muxed ip. Swap GND and +V and it's right. Good
effort though for a long day. Just to make sure:

Sinking current is when you connect one end of your load to +V
and the PIC pulls the other end to ground (current flows into PIC).

Sourcing current is when you connect one end of your load to GND
and the PIC drives the other end to +Vdd (current flows out of PIC).


Brent Brown
Electronic Design Solutions
16 English Street
Hamilton, New Zealand
Ph/fax: +64 7 849 0069
Mobile: 025 334 069
eMail:  spam_OUTbrent.brownTakeThisOuTspamclear.net.nz

2000\06\18@084046 by Bob Ammerman

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> > Sink:
> > Current flows into the PIC from an external source...
> > ------
> > PIC  |--/\/\/\------ GND
> > ------
> >
> > Source:
> > Current flows out from the PIC to an external load...
> > ------
> > PIC  |--/\/\/\------ +V
> > ------
> >
> > Somebody please tell me I didn't get that bass-ackwards, it's been a
long
> > day.

Actually, you do have it backwards :-)

Bob Ammerman
RAm Systems
(high performance, high function, low-level software)

2000\06\18@125831 by David VanHorn

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>
>Sorry Dale, it's bass-ackwards. Your description is perfect but your
>diagrams are muxed ip. Swap GND and +V and it's right. Good
>effort though for a long day. Just to make sure:
>
>Sinking current is when you connect one end of your load to +V
>and the PIC pulls the other end to ground (current flows into PIC).
>
>Sourcing current is when you connect one end of your load to GND
>and the PIC drives the other end to +Vdd (current flows out of PIC).

And, that it can source/sink this while maintaining a legal logic one or
zero respectively.
The source/sink values are not the maximum current limits.

2000\06\18@135811 by Dale Botkin

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On Sun, 18 Jun 2000, Brent Brown wrote:

> Sinking current is when you connect one end of your load to +V
> and the PIC pulls the other end to ground (current flows into PIC).
>
> Sourcing current is when you connect one end of your load to GND
> and the PIC drives the other end to +Vdd (current flows out of PIC).

Yeah, see it's that old electron flow vs. current flow thing again.  I
need to remember to whack myself sharply on the head right before engaging
in thoughs about current flow to remind myself to forget about the
electrons.

Tougher to forget about it now, though, when ground is often labeled "Vss"
since it's the source of electrons.

Dale
---
The most exciting phrase to hear in science, the one that heralds new
discoveries, is not "Eureka!" (I found it!) but "That's funny ..."
               -- Isaac Asimov

2000\06\18@140209 by Spehro Pefhany

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At 12:57 PM 6/18/00 -0500, you wrote:

>
>Tougher to forget about it now, though, when ground is often labeled "Vss"
>since it's the source of electrons.

It's kind of a holdover from the old NMOS days, these days with CMOS,
Vss is connected to about as many drains as sources, and ditto with Vdd.

;-)

Best regards,

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