SN74AVC16827: Modeling AVC DOC in IBIS

Ned Dempsher1

Part Number: SN74AVC16827

Hi TI,

My question for you involves the following:

I am using your IBIS model for this part that has DOC and am driving a memory over 2.5" of trace and there is A LOT of overshoot at the load, roughly 2V.

Is the IBIS model you provide able to model accurately the turning on and off of the output FETs to implement DOC?

I am thinking that this is not the case based on the large amount of overshoot that I am getting and the fact that this dynamic behavior may be difficult to model with IBIS 3.2, 2004 which is what I am seeing in the IBIS model.

For example, it has to sense the output reaching a certain value before turning off the 2nd PFET.

BUT, that being said of course, I am far from being an expert on this hence my question to you all.

If I know that the model is accurate then I'll be able to deal with this appropriately.

Thanks Very Much TI,

Ned

over 4 years ago

0 Chad Crosby over 4 years ago

TI__Expert 6680 points

Hi Ned,

On first glance, I'd say you're probably right - I'm not entirely sure if it's possible to model DOC for devices in IBIS.

Let me take a look into this and get back to you.

Thanks!

Chad Crosby

0 Chad Crosby over 4 years ago in reply to Chad Crosby

TI__Expert 6680 points

Hi Ned,

On closer look, the notes section of the IBIS itself says this:

- IBIS 3.2 SYNTAX CANNOT DESCRIBE THE CHARACTERISTICS OF
ANY OUTPUT STRUCTURES THAT DYNAMICALLY CHANGES THE
IMPEDANCES DURING THE TRANSITION. THIS DEVICE USE SIMILAR
OUTPUT STRUCTURE AND THEREFORE THE SIMULATION RESULTS
MAY NOT BE ACCURATE. TI RECOMMENDS THE USE OF SPICE
SIMULATION WHEN SIMULATION ACCURACY IS IMPORTANT.

This more has to do with the way that IBIS models are created - there's not really a good way to mimic DOC in IBIS. If you're interested more in how TI creates IBIS models, I'd recommend this appnote: https://www.ti.com/lit/an/szza034/szza034.pdf

Thanks!

Chad Crosby

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SN74AVC16827: Modeling AVC DOC in IBIS