LS1012A unused USB power supply and power-up sequence

[luka_pirnat]

Hi,

I have two LS1012 power supply related questions:
   1.) What happens when USB is unused and only USB_SVDD is powered (HVDD, SDVDD tied to GND)? If I understand AN5192 correctly, only USB boundary scan doesn't work then. Everything else (including other functions on the pins shared with USB) functions normally. Is this right?

   2.) Regarding power up sequencing: Do the power rails in the same group (from data sheet) need to be powered up simultaneously? I'd like to have all the power rails from group 1 ramp up at the same time, except the 3.3V EVDD, which would start immediately after they finish. Afterwards group 2 power rails would ramp up all together. Is this okay?

Thanks,
Luka

[Bulat · Accepted solution]

1) The app note states following: if USB is unused and only USB_SVDD is powered, then boundary scan tests will fail with the USB boundary cells (i.e. USB I/O pins). All other cells can be read/controlled by EXTEST, EXTEST_PULSE, EXTEST_TRAIN, CLAMP and SAMPLE instructions.

2) Yes, it is ok.

Regards,

Bulat