I have a specific power-on sequencing question on the TI XIO2001 PCEe-to-PCI bridge we are using that is unclear in the datasheet of course.
Here it is if you happen to know the answer:
Question - According to the XIO2001 datasheet (SCPS212F, May 2012) in Section 3.1.1 it says to turn on the 1.5V and 3.3V voltages before applying PCIR. Is there an electrical reason why PCIR can’t be turned on before 1.5V and 3.3V (the PCI clamp voltage shouldn’t have anything to do with anything else in the part I wouldn’t think)? Basically what we want to do is exactly what is shown in Section 3.1.1 and for power-down in Section 3.1.2 except we want to leave the PCIR voltage on all of the time. According to the datasheet as long as PCIR is applied the XIO2001 can take the signals as the input voltage range is spec’d as “-0.5 to PCIR + 0.5V” … and this is stated independent of any other power rails (there is nothing on the PCI bus that depends on the 3.3V and 1.5V rails except for outputs … which will not be active on the XIO2001 when we power it down).
Why? -- We would like to power the 3.3V and 1.5V power down in sleep states and leave the PCIR voltage on since there could be live (but inactive) signals on the PCI bus. Because of the stated voltage sequencing requirements in the datasheet we would be unable to ever turn off the power to the bridge since the devices on the PCI side remain powered beyond our control (but inactive when held in reset).
Thanks,