Ultrazed IOCC Power-on & Power-off sequence

Question

I have a question about the Ultrazed IOCC Power-on & Power-off sequence.

On p. 30 of the SOM Designer’s guide, it says:

Once the SOM_PG_OUT signal is asserted, the Carrier Card must turn on the above voltage rails in the following sequence (the reverse sequence must be maintained on turn off):

1. PS MGTRAVCC rail followed by the PS MGTRAVTT rail.

2. PS bank 501 and PL banks 26, 64, 65, and 66 VCCO in any sequence before or after the MGTRAVCC/ MGTRAVTT rails.

However, on p. 41 of the Hardware User’s Guide, Figure 15 & 16 show the Ultrazed Power-on and –off sequences. It shows VCCO_ALL & MGTRAVCC powering on at the same time and followed by MGTRAVTT, and then all three powering off at the same time.

Does the power on sequence of VCCO relative to the MGTRAVCC & MGTRAVTT rails actually matter?

Does the reverse sequence actually need to be maintained for the MGTRAVCC, MGTRAVTT, and VCCO rails relative to each other? Or do they just need to be powered off before the other rails on the SOM?

ctammann · Accepted Answer

The sequencing for the MGT rails is independent of the VCCO rails so they have no relative sequencing requirement.

As far as power down sequencing, that becomes important when parts of the system are shut down while others stay active. If all rails are turned off at the same time you are ok. The voltage differential between rails isn't substantial enough during their decay after power is removed to do any damage. Bottom line, either kill power to everything at once or follow the shut down sequencing.

Thanks

Chris