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AM3354: Internal RTC LDO handling when Extenral RTC mode

Jack Cha
Mastermind 8011 points
Part Number: AM3354
Other Parts Discussed in Thread: TPS65910, TPS65218D0

Hi TI

A customer would like to use external RTC mode. 

So they want to check how to handle Internal RTC LDO.
Three use cases were described in the TRM as follows, but if the external RTC mode is used, are the following three types? Or please let me know if I need to process Not Used.

Please clarify how to manage intenral RTC LDO when use external RTC circuit, not from AM335x Internal RTC or PMIC RTC (TPS65218D0 or TPS65910).

  • 0
    TI__Guru*** 149139 points

    Hello Jack_ArrowFAE

    Thank you for the external query.

    The 8.1.4.3.6 Internal RTC LDO of the TRM does not consider usage of external RTC.

    The 3 cases present use case for the RTC present internal to the processor.

    If power is a concern, never uses the RTC functionality can be considered.

    If design flexibility is required: configuration that uses the RTC functionality and never needs RTC-only mode. 

    I do not see the need for uses the RTC functionality and requires RTC-only mode since an external RTC is available.

    Regards,

    Sreenivasa

  • 0 in reply to Kallikuppa Sreenivasa
    Mastermind 8011 points

    Hi Kallikuppa

    Thanks for your kind answer.

    If the external RTC would be applied, Can we disable the RTC related power domain and functional pins for unused feature & pins handling ?

    We need some reference example design for external RTC mode, and with disabled AM335x internal RTC.

    They may need to implement external RTC like below diagram, not using PMIC RTC and AM335x itenral RTC as well.

    In case of External RTC use case, what should be appropriately applied to PMIC and AM335x sides.

    Thanks.

    Regards, 

    Jack

  • 0 in reply to Jack Cha
    TI__Guru*** 149139 points

    Hello Iack, 

    Thank you for the inputs.

    Jack Cha said:
    In case of External RTC use case, what should be appropriately applied to PMIC and AM335x sides.

    Customer will have to follow the termination recommendations in the data sheet for the processor as well as the PMIC.

    Jack Cha said:
    If the external RTC would be applied, Can we disable the RTC related power domain and functional pins for unused feature & pins handling ?

    This should be possible. 

    Jack Cha said:
    We need some reference example design for external RTC mode, and with disabled AM335x internal RTC.

    Please elaborate your requirement.

    Regards,

    Sreenivasa

  • 0 in reply to Kallikuppa Sreenivasa
    Prodigy 10 points

    Can you provide an example design for using RTC functionality but never using RTC-only mode with TPS65910? We are using the RTC on the PMIC but would like to maintain the flexibility to use the RTC on the CPU (but never RTC-only mode). 

    Based on what I have interpreted from the snippet in the original message, I have tested the second configuration show in this schematic:

    -- VDD-CORE is the 1.1V from the PMIC. VDDS-RTC is 1.8V from the PMIC. RTC_PWRONRSTn is connected to PWRONRSTn via a voltage divider. 

    I was able to successfully bring up one unit with this config, but on subsequent units I'm now seeing an issue where VDD-CORE is not correctly coming up in this configuration.