Continue to Site

Welcome to

Welcome to our site! is an international Electronics Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

[SOLVED] ATF1508ASV(L) operation with VCCIO=5V

Not open for further replies.


Newbie level 3
Jun 21, 2011
Reaction score
Trophy points
Activity points
I've been working with the Atmel ATF1508AS CPLD which supports different power supplies for the internal power (VCCINT, always 5V) and I/O pin power (VCCIO, can be 5V or 3.3V). I've developed several designs that work as expected with it.

Now I'd like to use the nearly identical Atmel ATF1508ASV CPLD which requires VCCINT=3.3V. The data sheet only describes VCCIO operation at 3.3V, but lists several timing parameters taken when VCCIO=5V. So I am making the assumption VCCIO can be 5V, though this is not explicitly stated in the datasheet.

In this case (VCCINT=3.3V, VCCIO=5.0V) the same designs randomly fail at power-up. When they do work, they continue to work (even after several hours of operation). So there is some kind of fault happening during power-up. The CPLD is somewhat warm but nothing excessive during correct operation.

Could it be a power sequencing issue? I use a 7805 regulator to provide 5V (VCCIO) and a 3.3V LDO regulator chained off that for 3.3V (VCCINT), so I suppose it's possible that VCCIO reaches 5V before VCCINT reaches 3.3V.

Any other ideas? Now I realize it's possible the chip does not support VCCIO=5V and the timing parameters in the datasheet with VCCIO=5V are a cut-and-paste error on Atmel's behalf, as the ATF1508ASV(L) data sheet is derived from the ATF1508AS(L) data sheet.

Conversely are there any special considerations when working with any part that has a lower internal voltage than its I/O voltage?

the V version support up to 3.3V
Power sequencing is not an issue with Atmel CPLDs. The only thing that you can come across with is hot socketing. I've seen only once this was an issue.

There are no real issues with lower core voltages - except that the tolerances are tighter.

the V version support up to 3.3V

That sounds right, VCCINT is supposed to be 3.3V but the datasheet seems ambiguous about how high VCCIO can go, as they show it being used at 3.3V and 5.0V in their measurements. That's the part I'm trying to figure out.

Have you checked the latest datasheet?

The DS states clearly operating range 3.0V to 3.6V.

The figures referencing 5V are most probably a copy/paste error.

Thanks, it's totally clear now. :)

Not open for further replies.

Part and Inventory Search

Welcome to