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Visitor asammanoj
Visitor
418 Views
Registered: ‎09-25-2018

CPLD voltage issue

Hi ,

We are using a Cool runner II CPLD (XC2C64A-7VQG100C) , We are facing a problem in it, below is the problem statement:

As per the attached schematics, we are using a weak pull up (10Meg ohm) for pins LATPUMP1 with R303 respectively.

LATPUMP1 is getting 1.6 v as input because of 10Meg ohm resistor. This voltage is in transition region(logic’0’-> -0.3 to 0.8, logic ‘1’ -> 2 to 3.9v). Because of this we are not getting the proper output.

Please note that this design was working and proven for the CPLD (XCR3128XL-10VQG100C).LATPUMP1 pin is getting 2.4 v input in this CPLD(XCR3128XL-10VQG100C) .But it isn’t working in the new CPLD (XC2C64A-7VQG100C), when the same logic code is written form old CPLD to new CPLD.

can we configure anything in the tool for this kind of situation? Can you please help us on this issue?cpld_issue.PNG

cpld_issue.PNG
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2 Replies
Scholar u4223374
Scholar
372 Views
Registered: ‎04-26-2015

Re: CPLD voltage issue

One possibility I can see is that it's actually in "keeper" mode (UG445 says this is the default for inputs). Forcing it to float mode would certainly help.

 

Alternatively, you can turn on the pull-up option for that pin, which effectively gives you a 100K pull-up in parallel with R303.

 

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Explorer
Explorer
315 Views
Registered: ‎09-17-2018

Re: CPLD voltage issue

10 M,

Is too large a value for reliable pull up.  Salts from water wash during pcb assembly will create leakage paths.  10K ohms is sometimes required for a reliable pull up.