Interpreting datasheet

[Alex Eisenhut]

Hi all,
p/n ADS5292
http://www.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=ads5292&fileType=pdf

Under absolute max ratings pg 5, for digital inputs, it says "min[2.2, AVDD+0.3]". I've never seen that before but I guess it means pick the least between the two.
So with AVDD at 1.8V, it would mean that 2.1V is the absolute max for a digital input?

But on pg 9, "DIGITAL CHARACTERISTICS", it says "All digital inputs support 1.8-V and 3.3-V CMOS logic levels."

So, um, now what?

Any ideas? What am I seeing wrong here? Can I skip level converters here or will the chip explode into a shower of sparks?

TIA
Alex

[T3sl4co1l]

Guessing they mean the usual 0.8/2.0V thresholds typical of CMOS.  So you'd have to use a limiter, say a current limiting resistor and schottky diode clamp, to connect 3.3V outputs to it.  But you're otherwise guaranteed to get correct logic states.

Yeah, they could've written that better.

A proper level translator will probably use less current and offer slightly better switching performance, if that's a concern.  Of course, you'll need one to go from 1.8 to 3.3, regardless.

Tim

[Alex Eisenhut]

Guessing they mean the usual 0.8/2.0V thresholds typical of CMOS.  So you'd have to use a limiter, say a current limiting resistor and schottky diode clamp, to connect 3.3V outputs to it.  But you're otherwise guaranteed to get correct logic states.

Yeah, they could've written that better.

A proper level translator will probably use less current and offer slightly better switching performance, if that's a concern.  Of course, you'll need one to go from 1.8 to 3.3, regardless.

Tim

Thanks, I see what you mean and I'll stick a level translator on there.

[David Hess]

I agree.  It supports 1.8 volt and 3.3 volt CMOS logic levels because the minimum logic high input voltage is 1.3 volts but is *not* 3.3 volt tolerant.

What a useless statement in a datasheet given that they do not specify maximum permitted input current.  They might as well have said it supports 5.0 volt CMOS logic levels as well.

I actually expect this kind of thing from TI.  They have a long history of such shenanigans.