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level shifting between 3.3V and 3.6V

 
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runtime



Joined: 15 Sep 2003
Posts: 36

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level shifting between 3.3V and 3.6V
PostPosted: Wed Aug 17, 2005 10:50 am     Reply with quote
Hello All,

I would like your help on the following:

I have to connect a 3.6V device to a PIC(PIC18F252) at 3.3V, the manual for the 3.6V device says I can use a diode/resistor level shifting for this.

There is an image that shows a schematic circuit with a 4.7K resistor and a shotky diode, what would be the value for this diode? any shotky diode will do?

Thank you in advance
Peter
eaton2
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PostPosted: Wed Aug 17, 2005 11:25 am     Reply with quote
Without seeing the circuit i can't tell you any particulars but the voltage drop across a schottky is nominally .3V. I would imagine the 4.7K is used as a current limiter
asmallri



Joined: 12 Aug 2004
Posts: 1634
Location: Perth, Australia

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Re: level shifting between 3.3V and 3.6V
PostPosted: Fri Aug 19, 2005 1:44 am     Reply with quote
runtime wrote:
Hello All,

I would like your help on the following:

I have to connect a 3.6V device to a PIC(PIC18F252) at 3.3V, the manual for the 3.6V device says I can use a diode/resistor level shifting for this.

There is an image that shows a schematic circuit with a 4.7K resistor and a shotky diode, what would be the value for this diode? any shotky diode will do?

Thank you in advance
Peter


I assume you mean you are using a PIC18LF252 not a PIC18F252. The easiest way to solve this would be to run the PIC at 3.6volts. If for some reason you cannot then there are a couple of simple ways you can go about this.

Method one (diode forward volt drop):
Device output to PIC input
Cathode of Shottky diode to PIC
Anode of Shottky diode to Device
4K7 resistor from Cathode to ground

PIC output to device input - directly connected.

Method two (voltage divider method)
Device output to PIC input
390R resistor from Device output to PIC input
4K7 resistor from PIC input to ground

PIC output to device input - directly connected.
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