The datasheets for the various AM57xx requires a certain power-down sequencing. Specifically, it seems that all devices in the family require during power-down for the various VDDSHVx rails to be no more than +2V above the VDDS18V rail.
I have a customer designing with the PMIC and AM57xx. In their design, the VDDSHV1 to VDDSHV11 rails are all powered by an external +3.3V DC-DC converter. The VDDS18V rail is powered by the +1.8V LDO2 output of the companion PMIC TPS6590379. The PMIC itself, however, is NOT powered by the +3.3V DC-DC converter but is powered by yet another +5V DC-DC converter. The +3.3V DC-DC converter is to be enabled (sequenced) by either the +3.3V SMPS9 or the REGEN1 PMIC outputs.
In the appendices of the various AM57xx Evaluation Module User Guides there are references to a series of 2 voltage clamp circuits. They are mentioned here:
AM571x IDK EVM User Guide (SPRUI97B)---APPENDIX A.10 (Page 39)
AM572x IDK EVM User Guide (SPRUI64C)---APPENDIX A.14 (Page 39)
AM574x IDK EVM User Guide (SPRUIJ9A)---APPENDIX A.13 (Page 40)
An excerpt from the above goes something like this...
The companion PMIC, TPS6590379, 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 2 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."
As mentioned above, in their design, they do not power the VDDSHVx rails through a power switch but via a separate external +3.3V DC-DC converter (NOTE: this is NOT the PMIC SMPS9 +3.3V output) that is, however, enabled/sequenced by either the PMIC SMPS9 +3.3V rail or REGEN1 outputs). Are they correct to assume that they would still need to include the clamp circuit in their design?
