Do any power supply sequencing issues exist for Virtex-E/Spartan-IIE devices?
Power Sequencing Conditions in Virtex-E/Spartan-IIE Devices
When VCCO is applied prior to VCCINT, a portion of the output driver is On, Pulling Down, Up, or both. This can last a few ms or until VCCINT is applied, depending upon the process and temperature. If many I/Os are pulled up and down simultaneously, a significant current ICCO might occur. While this alone will not damage the device, the heat dissipation might cause the part to exceed specified temperature operating conditions if VCCINT remains off for a long period (>1s). If the device is exposed longer than the specified operating conditions, it will be damaged by overheating. Once VCCINT is up, all outputs go into a 3-state condition.
NOTE: The issue noted above (significant current draw when VCCO is powered prior to VCCINT) does not apply to updated Virtex-E/Spartan-IIE devices as specified in the following PCNs as the new version of the silicon fixes the I/O driving issue:
The updated Virtex-E/Spartan-IIE devices are marked with a 3-letter AMT or AGT on the second line as specified in the PCNs.
If VCCINT is powered-up prior to VCCO, the I/Os always come up in a 3-state condition. When VCCINT is powered up but VCCO is not, there are some ICCINT until VCCO is powered up. The amount is dependent on the part size: approximately 1 mA per 1000 system gates.
- A V50E/2S50E will have about ~50 mA.
- A V300E/2S300E will have ~300 mA.
- A V2000E will have about 2 A.
NOTE: This is on top of a standby current of about 100 mA for an unconfigured part.
This applies only to Virtex-E devices, and not Virtex devices. The current goes away once VCCO (specifically Vcco_2, the one connected to the POR circuit) reaches about 0.8-1V. If VCCO drops below this voltage, the current returns. This current is evenly distributed, and the part is not damaged by this current.
If VCCINT is lost after the device is fully powered, the I/Os are placed into a 3-state condition.
NOTE: For Virtex/Spartan-II device power supply sequencing information, see (Xilinx Answer 5133).
Power-On Power Supply Requirements
For power-on power supply requirement information, see the Virtex-E and Spartan-IIE data sheets: DC and Switching characteristics -> DC specifications -> Power-On (Power Supply) Requirements: