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3.3 volt current limits

Posted: Tue Mar 27, 2018 11:43 pm
by sekinn
Hello. I am a new user and I am just starting to plan my I/O.

I have a Kanalog expansion board and I will have quite a few inputs so I would like to use KFLOP JP4 and JP6 as well. My question is, what is the max allowable current draw from the 3.3 volt pins ? Since 8 of the inputs on Kflop JP4 and JP6 have a 150 ohm pull down, each input will draw at least 22 ma which can really add up. Does each plug have an independent 3.3v supply that can handle all of it inputs, or is it a single supply that goes to all KFLOP and Kanalog pins? What are the limitations ?


S E Kinn

Re: 3.3 volt current limits

Posted: Wed Mar 28, 2018 9:13 pm
by dynomotion
Hi S E Kinn,

The 20 pins with the 150 Ohm pulldown/termination should only be used to source < 1ma of current.

The outputs are rated for 16ma which is enough for a valid LVTTL high. The 3.3V is generated on KFLOP from the 5V supply with a single regulator. Make sure the 5V supply can provide the necessary current. 2Amps should be sufficient.


Re: 3.3 volt current limits

Posted: Tue Dec 10, 2019 11:02 am
by cadline
Dear Dynamotion, i have a problem driving 150 ohm resistor, why a so low value? may i remove the pulldown from the board ?
thank you.

Re: 3.3 volt current limits

Posted: Tue Dec 10, 2019 5:37 pm
by TomKerekes
Hi S E Kinn,

The 150ohm termination avoids signal ringing with high speed signals.

Please don’t make modifications to KFLOP. Consider adding a buffer if necessary.