Article ID: 000084148 Content Type: Troubleshooting Last Reviewed: 09/11/2012

What are my options if I cannot meet the minimum supply current required for VCCPD and VCCIO in Stratix IV devices?



The power estimation tools such as the Stratix® IV device Early Power Estimator, and Quartus® II software PowerPlay Power Analyzer report both user mode current requirements and minimum current requirements for each supply. In most cases these two values are the same. However, some supplies have a power up current requirement which may be higher than the user mode requirements of the device. VCCPD and VCCIO have a specific power up current requirement, and Altera recommends the board power supply design be able to meet the minimum power requirements for all supplies.

There are points to consider for designs which are limited in the amount of current that can be supplied. In some cases, you may have the same voltage level for both VCCIO and VCCPD such as 2.5V. When you combine supplies, you must meet the additive minimum current requirement for both rails as reported in the power estimation tools. The power up current requirement will continue until the Power On Reset (POR) event has completed.

VCCPD is a POR monitored supply, it must be ramped along with VCC, VCCAUX, VCCPT, and VCCPGM for the device to enter POR (VCC must ramp before VCCAUX). Table 9-1 in Hot Socketing and Power-On Reset in Stratix IV Devices (PDF) lists the POR monitored supplies. All of these supplies must ramp monotonically and meet their respective minimum supply current requirements. After the device exits POR, the VCCPD current will drop to static current levels until after the device has configured and enters user mode. At this point, the power requirements will be dependent on the design activity as reported by the "User Mode Requirements" in the power estimation tools. 

VCCIO is not a POR monitored supply, so you have some flexibility in how you design this power supply. When VCCIO is the same voltage as VCCPD, such as when VCCIO is 2.5V, then VCCPD must be 2.5V, or when VCCIO is 3.0V, then VCCPD must be 3.0V, designers often choose to power VCCIO and VCCPD from the same regulator. This is fine if the supply can meet the combined minimum current requirement of both rails. If not, then the device will never exit POR, and the power up current consumption will continue.

If you cannot meet the combined power up current requirement of VCCIO and VCCPD, then you must separate these supplies to ensure you can ramp VCCPD. 

Also note, VCCPGM often has the same voltage level as VCCIO or VCCPD.  VCCPGM is a POR monitored supply, do not combine it with VCCIO in current limited power supplies that cannot meet the VCCIO minimum current requirement. This would prevent VCCPGM from achieving its required voltage for the device to enter POR.

When VCCIO is not the same voltage as VCCPD, such as for 1.2V, 1.5V, and 1.8V usage, or when you do not combine supplies when VCCIO and VCCPD have the same voltage level, you do not necessarily need to meet the power up current requirements for VCCIO. You can leave VCCIO powered off until after POR exits. The device will still be able to power up and configure when VCCIO is not powered, however, Altera does not characterize device behavior when supplies are not within their recommended operating range.

You do need to consider how other devices on your board will be affected if they share the same supply as VCCIO in current limited situations. When a power supply cannot meet the current loading demands, it typically will not ramp to its specied voltage level. This will not affect the Stratix IV device and its ability to configure, but you need to be sure other devices sharing that supply can tolerate this condition. After the Stratix IV device exits POR, the power up current requirement for VCCIO and VCCPD will pass. You need to ensure your regulator can recover after the power up current reduces down to static current levels. Consult your power supply datasheet or vendor to understand the power supply behavior in over current conditions.

All power supplies have a ramp time specified in the Stratix IV Device Datasheet (PDF). If you cannot meet the tRAMP specification for any power supply, you should hold nCONFIG low to prevent the device from attempting to initiate a configuration cycle. You should ensure that all power supplies have ramped prior to releasing nCONFIG so the device can configure and enter user mode with all supplies within their recommended operating conditions.  For further information on the nCONFIG pin and other configuration details, refer to Configuration, Design Security, and Remote System Upgrades in Stratix IV Devices (PDF).



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