protecting analog input of microcontroller

[fuseshut]

I have a dual schottky diode connected to my analog input of my microcontroller. Is the only component that can be used to protect the IO pin from voltage spikes or ESD?

 

[melone]

No, you can use a cap to shunt a voltage spike to ground. Size your cap based on the frequency that you want shunted.

 

[felixc]

Place a series resistor before the diodes. The resistor will limit the peak current while the diodes clamp the voltage spikes. What value? It depends if you have any bandwidth requirement for the analog input.

 

[MrBananas]

A cap will help with high frequency transient spikes, but in the case of (relatively) low frequency transients you would be wise to have some zener diodes of the appropriate zener voltage there as well.

When the voltage on the input pin exceeds the zener voltage they "clamp" the pin voltage to the zener voltage. Make sure you size it correctly for current carrying ability if you think there could be the potential for a high-current spike. Otherwise if it is just a signal you would probably be fine with the standard small signal diode package.

 

[fuseshut]

Mr Bananas it's a 0-5VDC analog input. Small signal diode could be a 1n4152 maybe? or something of the sort?

 

[itsmoked]

You said you have schottky diodes on the processor if they are ones you have added externally do check for leakage current...

 

[fuseshut]

Itsmoked this thread is similar to the other you replied to. Check for Leakage current? Is it as simple as removing the SMT component from the circuit board, hooking up 5V to Cathode and Ammeter in series of anode and power supply common to measure current when diode is powered?

 

[zeitghost]

Yes. You can check diode leakage like that.

Schottky diodes are much leakier than signal diodes...

Have a look a the spec sheet for your device & compare it with a 1n4148 or whatever.

 

[itsmoked]

Yep that is the way to test it. Also the leakage changes a lot with temperature. Cold may be no problem, room temp may BE a problem.

I still say u rarely need them in that service. I have never used them in dozens of projects that have lots of handling.

If your analog source originates on your board you absolutely don't need them.

 

[fuseshut]

My analog source 0-5vdc comes from another location. It's fed from an analog output card.

 

[itsmoked]

Then it was wise to consider...

And decide;

1) This micro has beafy Schottkys inside. I don't need to add external ones.

2) To cut ANY Schottkys a break I should have some series impedance on that input. Is there some already due to whatever, like a voltage divider, etc. If not, I should add some being careful not to add too much if the signal is rapidly varying or the R-C this protection resistor teamed with the processor's pin capacitance will start causing other problems.

 

[fuseshut]

.2) There's a voltage divider at the input. I am just going to pull them out. thanks.