SPRUI97E May 2017 – September 2025
During early investigation of power shut-down sequencing, it was determined that clamps were required on every 3.3V supply to the dual-voltage I/O cell supplies (VDDSHVx). This enforces the requirement shown in Figure 5-3 of the AM571x Sitara Processors Silicon Revision 2.0 Data Manual (SPRS957) that states that the 3.3V supply inputs must never be more than 2.0V above the VDDS18V supply, even during ramping up or ramping down. The AM571x IDK EVM design contains these clamp circuits on both V3_3D, that powers almost all VDDSHVx supplies, and VSDMMC, that powers VDDSHV8 used with the SDCARD on MMC1. Later it was determined that the only method to maintain device reliability was to fully enforce the supply sequence requirements shown in Figures 5-1 and 5-2 of the AM571x Sitara Processors Silicon Revision 2.0 Data Manual (SPRS957). The companion PMIC, TPS6590377, was enhanced to provide a shortened shut-down sequence that enforces the DM requirements in a time period (~1ms) that the PMIC input can hold up the supplies. The PMIC also has supply discharge resistors to pull down the supplies quickly when they are turning off. These two capabilities in the companion PMIC make the clamp circuits superfluous. However, designs that use REGEN1 to power the VDDSHVx supplies through a power switch will still need the clamp circuit. The power switches available do not discharge the supplies quick enough.