12-05-2018 12:45 PM
For Kintex-7, we have VCCAUX = 1.8V, VCCAUX_IO = 2.0V (for DDR3L performance), and we are using 3.3V for some HR banks and configuration Bank 0.
The Power-On/Off Power Supply Sequencing section of DS182 (v2.16.1) August 7, 2018 defines TVCCO2VCCAUX as "Allowed time per power cycle for VCCO – VCCAUX > 2.625V." It does not define TVCCO2VCCAUX as "Allowed time per power cycle for VCCO – VCCAUX_IO > 2.625V." This is important in our application because VCCAUX is not equal to VCCAUX_IO (they come from different regulators). So in our application, do we need to ensure VCCO – VCCAUX_IO > 2.625V for some maximum duration out of device reliability concerns the same way we must for VCCAUX vs. VCCO?
To be sure, we are not asking about power sequencing here. We understand the recommended power-on sequence is VCCINT, VCCBRAM, VCCAUX, VCCAUX_IO, and VCCO, and we will follow that. We'll also take steps to have the rails collapse in reverse order at power down.
We are asking if there is time limit between VCCAUX_IO vs. VCCO analogous to TVCCO2VCCAUX (which is a time limit between VCCAUX vs. VCCO).
Thanks in advance.
12-05-2018 11:23 PM
@rkriner Good question and believe it is applicable to VCCAUX_IO as well. However, I will check this internally to confirm and get back to you.
We understand the recommended power-on sequence is VCCINT, VCCBRAM, VCCAUX, VCCAUX_IO, and VCCO, and we will follow that. We'll also take steps to have the rails collapse in reverse order at power down.
Since you mention, you will be following the sequence, any reason you are concerned about VCCO -> VCCAUX_IO violation? Is it more for your understanding to make sure of the spec?
12-06-2018 12:19 AM
If you follow the sequence I guess there is no issue.
It is something we will have to check internally since VCCAUX_IO is an Aux rail that can be bumped up to 2V to enhance MIG performance.(Otherwise it is connected to VCCAUX at the board level)
This suggests it is separate to the VCCAUX rail altogether.
Let us check the point and confirm.
12-06-2018 02:17 PM - edited 12-06-2018 02:19 PM
So which Kintex-7 package are you using? If FBG, the VCCAUX_IO pins are not connected to the die. If FFG, VCCAUX_IO pins are only used for HP IO banks whose VCCO are limited only to 1.8V max so there should be no issues with TVCCO2VCCAUX. So as long as your main VCCAUX and VCCAUX_IO are not tied together VCCAUX_IO does not have anything to do with TVCCO2VCCAUX.