AM5728 EVM power related circuit question

Hi Yicheng,

Here is explanation from the design team:

"The 3.3-V IO power supplies should never exceed the 1.8-V IO supply by more than 2 volts. These clamp circuits will hold up the 1.8-IO supply when it tries to drop below the clamp voltage as the power supplies ramp down."

This was recently updated with the following information:

"Dual voltage IO cells have two power supplies. One is a constant 1.8 volt bias supply that is provided via VDSS terminals. The other power supply sources power to the input/output buffer of the IO cell and it provided via one of the VDDSHVx terminals.

The VDDSHVx terminals should never exceed the voltage applied to VDDS by more than 2 volts. The clamp circuits were placed on the board to hold the VDDS supply up until the last VDDSHVx supply falls during power down.

We recently learned the voltage clamp circuit connected between VDD_SD and VDD_1V8 is not necessary.

The dual voltage IO cells powered by the AM572x VDDSHV8 terminals were designed to support dynamic supply voltage changes as required for the SD card. The other dual voltage IO cells powered by the other VDDSHVx terminals were designed to only support static supply voltages. The IO cells that support dynamic supply voltage changes have an internal bias supply without any connection to an device terminal. Therefore, the external voltage clamp circuit connected to VDDSHV8 will not be effective since it is not possible for it to hold up the respective bias supply during the power down sequence.

This requires a AM572x based product to follow the VDDSHV8 power down sequence requirements defined in the data sheet."