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AM335X Power Up Sequence with RTC Disabled with 1.8 and 3.3V IO

Cary Davis
Prodigy 115 points
Other Parts Discussed in Thread: AM3352

I am designing the power supply to an AM3352. I am not intending to use the RTC on the AM3352.

Question 1: For disabling the RTC I follow the instructions in the "AM335x Schematic Checklist" under "RTC internal oscillator is not used...", correct?

Question2: While using an AM335X with a disabled RTC do I follow Figure 4-5 "Power-Supply Sequencing with RTC Feature Disabled" on page 95 of the datasheet? I am assuming I do, but what if I use 1.8V and 3.3V I/O? There is no specific mention of the mixed voltage I/O where there is in the previous Power Up Sequence figures such as Figure 4-2.

Thanks.

  • 0
    TI__Expert 4690 points

    Hi Cary,

    Cary Davis said:

    Question 1: For disabling the RTC I follow the instructions in the "AM335x Schematic Checklist" under "RTC internal oscillator is not used...", correct?

    Yes, you are correct. Just make sure you make the right connections based on your use case (digital clock source is provided on OSC1_IN or internal RTC is not used).

    Cary Davis said:

    Question2: While using an AM335X with a disabled RTC do I follow Figure 4-5 "Power-Supply Sequencing with RTC Feature Disabled" on page 95 of the datasheet? I am assuming I do, but what if I use 1.8V and 3.3V I/O? There is no specific mention of the mixed voltage I/O where there is in the previous Power Up Sequence figures such as Figure 4-2.

    Could you provide a little bit more information on how your voltages are mixed in your system? One way to deal with mixed voltages is to use the Pin Mux Utility that will ask you to define the voltage of each VDDSHV power domain and will throw warnings if you attempt to split peripherals across VDDSHV with different voltages. the Pin Mux utility can be download from this link:

    http://software-dl.ti.com/dsps/dsps_public_sw/am_bu/ampinmux/latest/index_FDS.html

    The Power-On Sequence on the AM335x device is in the following order:
    1.- 1.8V Analog and I/O
    2.- 3.3V Analog and I/O
    3.- 1.1V Core

    Hope this helps

  • 0
    Prodigy 115 points

    When not using the AM335X RTC, I have followed the suggestion of connecting CAP_VDD_RTC to ground. However, no mention in datasheets or any previous E2E posts show what shall be done with RTC_KALDO_EN. Since I am not using the RTC LDO I am assuming I tie RTC_KALDO_EN high to disable the RTCs LDO. Is this the correct assumption.

    Cary