Pic's pins current limited?

Are the microchip pic's pins current limit? Specifically for the pic24F family. I have all the IO pins going to offboard connectors and I'm wondering what would happen if the connectors were accidently shorted(say a wire fell on them). I believe the pic's have thermal protection so it's a matter of simply saving the individual pins. I can add in some series resistance to limit the current in this application but wondering if they are needed? (it's not prefered though because some of these pins are going to be for general use)

Reply to
Jon Slaughter
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Most parts will have two specs:

#1: Total current through a short on a single output pin.

#2: Total current through Vcc or ground pin.

Note that if you have shorts on multiple output pins, you can exceed #2 very quickly without actually exceeding #1.

Physically #1 is related to current dissipation in the output buffers, but usually #2 is related to the tiny wire that bonds to the chip.

It is exceedingly unlikely that PIC's have thermal protection on normal I/O pins the way say a 7805 does. An individual output buffer simply poops out above a certain current. On chips with many outputs there is often a limit (#3) on total current drawn from all outputs simultaneously. This is a thermal limit but do not count on anything shutting down above that limit, typically the whole chip overheats.

In the Microchip data sheets, these numbers are called (#1) "maximum output current sourced (sinked) by any I/O pin", (#2) "maximum current out of Vss/into Vdd", and (#3) "maximum current sunk(sourced) by all ports".

You can start adding fuses, resistors, etc. to protect your PIC chip, but on a chip with a lot of I/O's the cost and bulk of the protection very quickly exceeds the cost of the chip. Way back in the 70's, output buffers became sacrificial chips in the case of multiple shorts. Today you just throw away the whole board.

Tim.

Reply to
Tim Shoppa

Except for the "magic" pins for external programming and the oscillator, i put a 1K resistor in series with every pin and a 1 Meg to ground. They have no effect on input pin levels and the 1K does decent current limiting; the 1Meg prevents any static buildup on unused/unconnected pins.

Reply to
Robert Baer

Around 50 0402 1K resistors is NO WAY more expensive than these $5 and UP PICs.

Reply to
Robert Baer

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