[FAQ] AM6421:VDD_CORE Voltage selection

Hello Song Xue, 

Thank you for the query.

Q.1 VDD_ Core can use 0.75V and 0.85v power supply

There are no operational differences depending on the VDD_CORE voltage. If you wish to reduce the power solution cost then you can combine VDD_CORE and VDDR_CORE on the same 0.85V supply. If you wish to reduce heat output and power draw then VDD_CORE on 0.75V supply is better (VDDR_CORE remains on 0.85V).

Two operating voltages are supported for VDD_CORE. Use of 0.75V or 0.85V provides design flexibility to designers.

Operating VDD_CORE at 0.85V reduces the number of power rails and eliminates the supply sequencing concern between VDD_CORE and VDDA_CORE.  However, operating the core at 0.85V increases power dissipation relative to operating the core at 0.75V. 

Providing two core operating ranges allows the system designer to decide if they prefer to decrease power dissipation at the cost of providing the additional 0.75V power rail.

There is no effect on the OPP with the change in core voltage.

Please refer below related links

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/980301/am6442-vdd_core-and-vdds_ddr-related-to-opp

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1068128/am6442-powering-with-the-single-pmic-solution/3955919?tisearch=e2e-sitesearch&keymatch=AM6442%2525252525252520VDD_CORE#3955919

https://e2e.ti.com/support/processors-group/processors/f/processors-forum/1043152/am6442-powering-with-lp87334d-pmic

Q.2 Can VDD_CORE, VDDR_CORE, VDD_MMC0,VDD_DLL_MMC0, VDDA_0P85_SERDES0, VDDA_0P85_USB0 all be powered by the same set of DC-DC (0.85V)?

I would recommend you to read through the below sections of the datasheet to understand the allowed power sequencing

7.10.2 Power Supply Requirements

7.10.2.1 Power Supply Slew Rate Requirement

7.10.2.2 Power Supply Sequencing

7.10.2.2.1 Power-Up Sequencing

7.10.2.2.2 Power-Down Sequencing

Regards,

Sreenivasa