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# ADS5400: request for clarification on the meaning of absolute maximum ratings

Hello,

I'd like to understand better the numbers given in the absolute maximum ratings table for the ADS5400. If I am reading this correctly, in the table below, it is speficied that the maximum voltage *between AINP and AINN* is between 1.75V and 3.25V for a continuous DC signal. However, isn't it correct that a zero signal in this case would have 0V between AINP and AINN? Wouldn't we allow something that is somewhat below -2V and somewhat above +2V for this voltage?

If what is meant is actually the voltage between the pins and ground (which is not completely unreasonable since typically AVDD5/2 is 2.5V and the full range of the ADC is 2V, meaning that for +2V input we would have 3.5V on AINP and 1.5V on AINN, and the opoosite for -2V input), how can I make it consistent with the "AINP, AINN to GND" voltage difference speficied 2 lines above?

Thank you very much in advance,

Lior

• Hi Lior,

With a 2.0Vpp differential signal applied, the swing on either analog input pin is 1.0Vpp, which means with a +2.5VCM, the input signal on each pin will swing +/-0.5V.

therefore, the typical signal applied will go between +3.0V and +2.0V.

Hopefully, this will help the confusion.

I also copied a link to an article on wrote on this subject to hopefully help as well, see below....

Regards,

Rob

https://www.doeeet.com/content/eee-components/actives/designing-of-analog-to-digital-input-drive-of-rf-converters/

• Hi Rob, thanks a lot for the quick reply!

I think this is fairly clear, what I'm a bit stumped about is the way the absolute maximum ratings are defined in the enclosed picture. I think I understand "AINP, AINN to GND -> Voltage differenence between pin and ground". But how could the voltage difference between AINP and AINN be only 1.25 to 3.75 in the AC case an 1.75 and 3.25 in the DC case? If it is indeed V_AINP - V_AINN, it must be able to swing negative, and if it's AINP - GND or AINN - GND, how is it not 0.5 to 4.5?

I'm sure there's a simple explanation, but in the end my question is simple but cruical: what voltage can I put on those pins without worrying about damage?

Thanks,

Lior

• Hi Lior,

I understand your point better, let me do some digging and get back to you.

Regards,

Rob

• Hi Lior,

I apologize for the delay.

I spoke the designer on this part and we thought maybe if you can describe your application a bit more, maybe we can help guide you with a good absolute max power that can applied to the analog inputs.

Regards,

Rob