Dynomotion

Group: DynoMotion Message: 10006 From: nbrobot Date: 8/20/2014
Subject: +5V tolerant Inputs

Hello,

When I switch the +5V from JP6-pin1 to any single input on JP7, they turn on and off in pairs when viewed in the KMotion Digital IO panel.


However, if I switch the +3.3V from JP7-pin1, only the input I'm connected to turns on and off (as expected).


I'm wondering if the JP7 inputs are really 5V tolerant...I'm not sure how this behavior is possible (i.e., why is there crosstalk between IO channels at higher voltages?)


Is this behavior normal?  Are the inputs actually usable with 5V?


Thanks,

Neville
Group: DynoMotion Message: 10007 From: Tom Kerekes Date: 8/20/2014
Subject: Re: +5V tolerant Inputs
Hi Neville,

The KFLOP IO are Xilinix FPGA IO which are internally diode clamped to the 3.3V Power Supply.  Avoid driving KFLOP IO Pins above 3.8V.  Most 5V TTL Outputs do not drive above 3.8V (especially under load) as they are only required to drive above 2.8V.  We add 47 ohm series resistors on 16 of KFLOP's IO to avoid damage if those are hard driven all the way to +5V.  Due to a documented quirk in the way the Xilinx clamping works combined with their High Speed Low Voltage Differential Pair driving mode, when clamping relatively high currents some current can leak into the opposite differential input.  This is normal.

In summary: Please avoid driving any KFLOP Input hard above 3.8V.

Regards
TK


Group: DynoMotion Message: 10008 From: nbrobot Date: 8/20/2014
Subject: Re: +5V tolerant Inputs
Hi Tom,
Thanks for the explanation.  What about using 5V with outputs?  I have the +5V from JP7 going to a number of external solid state switches and the return legs from the switches going to the KFLOP JP7 outputs.

I turn on any given output from the KMotion I/O panel and it sinks the voltage to ground and activates the external solid state switch.

It seems to be working just fine.  Is there any long-term risk of damage to the KFLOP in doing this?  The solid state switches don't operate with the +3.3V source, otherwise I would use that.

Thanks,
Neville
Group: DynoMotion Message: 10009 From: Tom Kerekes Date: 8/20/2014
Subject: Re: +5V tolerant Inputs
Hi Neville,

There is no risk of damage to KFLOP in doing that.  The solid state relays should draw less than 16ma at 5V.

Regards
TK

Group: DynoMotion Message: 10010 From: nbrobot Date: 8/21/2014
Subject: Re: +5V tolerant Inputs
Super!  Thank you!
-Neville