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AM5706: VDD_DDR load switch in reference design

Ryan.Bishop
Expert 3900 points
Part Number: AM5706
Other Parts Discussed in Thread: TPS22965

This is in regards to the DRA71x/DRA79x/TDA2E-17/AM570x EVM CPU Board" design on the Technical Documents tab of AM5706 product folder.

  • Is the TPS22965 load switch required for the VDD_DDR_CPU rail.  It looks like this just creates a slightly delayed copy of the VPO_S4_DDR rail (and goes to the DDR3L termination regulator and the CPU VDDS_DDR1 pins).
  • The other branch of the DDR rail (VPO_S4_DDR) turns into VDD_DDR after a current sense chip (U51) and then powers the DDR chips.
  • Is this so the rails are separated for current measurements or so the DDR rail to the CPU is delayed the small amount it takes for the load switch to turn on?

Thanks!

Ryan B

  • 0
    TI__Mastermind 42545 points
    Hi Ryan,
    The load switch was not added for the delay. The switch was added to test a low power mode in which the AM570x is powered down while a software image is maintained in the DDR memory in self-refresh mode. Since the control of the switch is pulled high, the switch will be on by default. I don't think this feature was ever supported by the software for the board. Normally the VDD_DDR voltage can be connected directly to both the memory components and the SoC.
    Regards,
    Bill