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Tool/software:
One customer is considering using the ADS4128 and ADS4149 differently with the same circuit configuration depending on the resolution.
Please let me know about two points below
1. The pin assignment differs in the following parts.
Is there any problem with connecting the NC pins in the same way as the ADS4149?
Or, if there is a possibility of noise leakage, is it necessary to leave the NC pin unconnected?
ADS4128 / ADS4149
33pin NC / D0
34pin NC / D1
2. Although the resolution is different, the ENOB appears to be roughly the same under the same conditions.
Would you please let me know the reason for this?
Is it necessary to conditions or create circuits to improve the resolution with ADS4149?
If there are any related application notes, please let me know.
Best regards,
Satoshi
Hi Satoshi,
1) Yes, you will definitely, have noise, unless you terminate the two LSBs on the ADS4149. I wouldn't advise to leave these two pins floating.
2) Not exactly, the ADS4149 is a 14bit device running at 250MSPS and has 1.5dB more SNR. Therefore, it would be about +2dB more if running at 200MSPS like the ADS4128.
Keep in mind these two devices are two different designs as one of them came from the Nat Semi acquisition. There are tradeoffs designers will do internally to the sample and hold circuits in order to achieve certain SNR/ENOB specifications.
Regards,
Rob
Hi Rob
Thank you for kind reply,
I understood that your answer of 2).
I'm sorry for my typo, would you let me know about revised 1) again?
1)' Are ADS4128's 33~34pin (NC) OK to connecting any output side?
(To reuse the same wiring as the ADS4149's D0 and D1 output.)
Or, is it necessary to leave the NC pin unconnected?
Best regards,
Satoshi
HI Satoshi,
Please terminate those two pins to ground thru a 0.1uF capacitor on the ADS4149.
You can then reuse the same wiring if you put in an ADS4128.
From a pin to pin standpoint that should work.
However, if you really plan to do this, let me double check with design to make sure I am not missing anything.
Give me a few days to confirm and get back with you.
Regards,
Rob
Hi Satoshi,
I heard back from design, there should be not problem substituting the ADS4149 for the ADS4128 as you propose.
Just need to terminate the two LSBs as specified above.
Regards,
Rob
Hi Rob,
Thank you very much for reply and confirming,
These question was cleared.
Best regards,
Satoshi