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Combining 1.8V supplies

Michael Hallak-Stamler
Prodigy 205 points


Hi,

There are numerous 1.8V supplies on the board, all supplied from separate regulators on the EVM. Is it possible to combine them? Are they separated  because of noise isolation issues? If so then what are the requirements? Can they be separated using passive means, such as a ferrite+cap?

In our design there is no need to control voltages for power management.

Here is the list I have:

     VDDA_HDMI_1P8 VDDA_CSI2_1P8 VDDA_ARMPLL_1P8 VDDA_DSPPLL_1P8 VDDA_VID0PLL_1P8 VDDA_VID1PLL_1P8 VDDA_AUDIOPLL_1P8 VDDA_DDRPLL_1P8 VDDA_L3PLL_1P8 VDDA_VDAC_1P8 VDDA_USB_3P3 VDDA_USB_3P3_1 VDDA_PCIE_1P81 VDDA_PCIE_1P82 VDDA_SATA_1P8 VDDA_1P8 VDDA_USB0_1P8 VDDA_USB1_1P8

 

Many Thanks

Michael Stamler

 

  • 0
    TI__Mastermind 25055 points

    Michael,

    Many of the I/O supplies are separated to reduce noise from other peripherals. If you are confident that you can isolate noise in your design then you can group I/O supplies. We recommend that PLL supplies be driven by their own LDO if possible or at the very least have dedicated filters. It is a good practice to isolate the high speed peripheral supplies (HDMI, PCIe, SATA, VIDEO, USB) but there is some leeway if you aren't using these peripherals or you are confident in your power supply to power these from a single LDO.  The device EVM schematics are a good reference.

    Regards,
    Marc

  • 0 in reply to MarcPyne
    Prodigy 205 points

    Hi Marc,

    Your advice about separate high speed peripheral supplies is not consistent with the following forum reply:

    http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/716/p/142155/513035.aspx

    I would like to minimize the number of supplies on the board. I am willing to implement what is needed to get to a stable design. How should I separate the supplies to get a working, stable board? i.e. what combination of separate LDOs/supplies or ferrite bead separated supplies for all multiple supplies?

    Regards

    Michael

     

  • 0 in reply to Michael Hallak-Stamler
    TI__Mastermind 25055 points

    Hi Michael,

    The other forum post you refer to is in regards to the 4 core voltage power rails on the DM814x devices.  That is not applicable to the DM816x devices.

    The first place to start is to follow the design guidelines for the high speed peripherals in the device datasheet, and please refer to the Power-Supply Decoupling section. 

    A lot of good reference information is on the Hardware Design Guide wiki: http://processors.wiki.ti.com/index.php/AM389x_C6A816x_DM816x_Hardware_Design_Guide

    The EVM schematics are also a good reference.

    Regards,
    Marc

  • 0 in reply to MarcPyne
    Prodigy 205 points

    Hi Marc,

    I am designing with the DM8148 and not the DM8168, so my question  is still open. Thanks

  • 0 in reply to Michael Hallak-Stamler
    TI__Mastermind 25055 points

    Michael,

    I moved this to the DM814x Forum so that there won't be any confusion.

    In summary for the DM8148:

    The datasheet contains some power supply filter information, and you need to follow the recommendations in the Power-Supply Decoupling section of the datasheet.

    The "core" rails (CVDD, CVDD_ARM, CVDD_DSP, CVDD_HDVICP) are separate to allow for optimal power consumption.  If you are not planning on using AVS or concerned about power consumption then you can connect the four "core" rails to the same regulator. Of course this means that all of the rails will have to run at the highest voltage required to achieve the performance needed.

    Many of the I/O supplies are separated to reduce noise from other peripherals.  If you are confident that you can isolate noise in your design then you can also group I/O supplies. We recommend that PLL supplies be driven by their own LDO if possible or at the very least have dedicated filters.  It is a good practice to isolate the high speed peripheral supplies (HDMI, PCIe, SATA, VIDEO, USB) but there is some leeway if you aren't using these peripherals or you are confident in your power supply to power these from a single LDO.

    Regards,
    Marc