Quick pic input question...

[2camjohn]

If I have an input to my chip which is supposed to drive a high load will this damage the pic in any way? or is the pics input impedance very high?

If so what do i do to stop this?

Thanks

 

[Nigel Goodwin]

If I have an input to my chip which is supposed to drive a high load will this damage the pic in any way? or is the pics input impedance very high?

If so what do i do to stop this?

Thanks

The PIC's input impedance is very high, but you need to be more explicit about what you are feeding into to be sure you're not going to damage it.

 

[2camjohn]

I am using an output from another board whic would normally source 1A as an input to my pic. The output is driven by a transistor.

I was just wondering if it will damage my pic in any way and if i needed a protection resistor or something.

Thanks

 

[motion]

If the output from the other board does not go above the PIC's Vcc supply rail nor go below GND voltage, then the PIC's input will remain in high impedance.

If the limits are exceeded, the protective diodes will start to conduct and will be destroyed if the currents are excessive. Adding series resistors to limit this current would be advisable.

 

[Nigel Goodwin]

If the output from the other board does not go above the PIC's Vcc supply rail nor go below GND voltage, then the PIC's input will remain in high impedance.

If the limits are exceeded, the protective diodes will start to conduct and will be destroyed if the currents are excessive. Adding series resistors to limit this current would be advisable.

Exactly, it may not be required (depending on the output of the other board), but a series resistor won't do any harm in any case.

 

[Oznog]

Beware

Oh it gets worse than that.

A +5V reg may not be designed to sink current if something else tries to raise the voltage. So if the diode to Vdd conducts, it can raise Vdd above 5v, which will mess with your ADC readings, and if it goes above 7v, total latchup that even the WDT can't fix.