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AM2432: Unused SDIO VDDSHV5 decoupling capacitors and connections

Munan Xu
Expert 5800 points

Part Number: AM2432

Hello,

For unused supply rails like SDIO (if customer is not using) what's the recommendation on these supply rails? Is it necessary to still connect this supply rail? Are decoupling capacitors needed if not connected?

Munan

  • 0
    TI__Guru 64655 points

    The VDDSHV5 IO power rail supports being turned off for short periods of time and supports dynamic voltage change as required when cycling power to reset an SD Card or when changing the IO operating voltage of an SD Card. However, the VDDSHV5 IO power rail is expected to be always powered for any other use or non-use cases. VDDSHV5 should always be connected to a valid 1.8V or 3.3V IO power supply.

    Decoupling capacitors are still required on the VDDSHV5 power rail even when the associated IOs are not used because each IO power rail sources an internal IO bias LDO.

    A decoupling capacitor is also required on CAP_VDDS5 when VDDSHV5 is connected to a 3.3V power source. See the note associated with the CAP_VDDS5 signal description in the AM243x datasheet for more information on decoupling capacitor requirements for the CAP_VDDS5 pin.

    Regards,
    Paul

  • 0 in reply to peaves
    Prodigy 210 points

    Hi Paul,

    The custom board design being worked on will not have SDIO MMC1. Reviewing the Connectivity requirements i have the following understanding:

    MMC1 Unused. All pins on this interface default GPIO off/off/off. Thes pins will be left as No connects.

    SDIO_LDO will not be used. VDDA_3P3_SDIO and CAP_VDDSHV_MMC1 must be connected to Ground. 

    VDDSHV5 Looks like it is for MMC1 module. If the MMC1 module is not used How should this Power rail be connected?

    Regards,

    Jim

  • 0 in reply to James Panko
    TI__Guru 64655 points

    Yes. As I mentioned in my previous reply, each power rail is supplying power to an internal IO bias LDO. This is a different LDO than SDIO_LDO which is powered from the VDDA_3P3_SDIO power rail.  It is not possible to leave the internal IO bias LDO unpowered for long durations. We only support it being powered off for a short duration when the VDDSHV5 IO bank is connected to an SD Card and the only way to reset an SD Card is cycle its power. The SD Card pins are not fail-safe so we must turn off the AM243x IOs and any pull-ups connected to the SD Card when its power is cycled off for a short duration to reset the SD Card. This use case is the only time we allow the VDDSHV5 to be powered off while other portions of the device remain powered.

    Regards,
    Paul