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AM3356: Schematic questions

Guru 15210 points

Replies: 4

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Part Number: AM3356

Hi,

I have questions about AM335x.

Q1.
From schematic of AM335x StarterKit Board, AND logic(SN74AUP2G08) are used for RTC Reset CKT.
Are these AND logic used for making delay of RTC_PORZ deassertion?
And is it because RTC_PORZ need to be asserted for at least 1 ms to provide enough time for
the internal RTC LDO output to reach a valid level before RTC reset is released?

If AND Logic are only for the delay, can I use CR circuit instead of AND Logic?

Q2.
In AM335x datasheet(SPRS717J)page.171 Figure 7-47, "49.9ohm(+/- 1%)" is connected to DDR_VTP.
Do I must to use 49.9ohm(+/- 1%) or can I use 50ohm(+/- 1%)?

best regards,
g.f.

  • Hi,

    Q1. It's not recommended to connect an RC circuit directly to the RTC_PORZ input because of the very slow rise time it will present to the input. If you use the TPS65217 PMIC, it has a dedicated RTC reset signal.

    Q2. 49.9Ohm +/- 1% is used because it's a standard resistor value. You can use 50Ohm with 1% tolerance, if you can find such resistors.

     

    Best Regards
    Biser
  • Guru 15210 points

    In reply to Biser Gatchev-XID:

    Hi Biser,

    Thank you for your support.

    About Q1, my customer are planning to use TPS65910A31. So, it doesn't have dedicated RTC reset signal.
    In such case, they need to use RC circuit + AND logic for delaying the RTC_POR deassertion, is it correct?

    I understood about the DDR_VTP resistor, thank you.

    best regards,
    g.f.
  • In reply to g.f.:

    Yes, you understood correctly about Q1.

     

    Best Regards
    Biser
  • Guru 15210 points

    In reply to Biser Gatchev-XID:

    Hi Biser,

    Thank you for the reply and I'm sorry for the delay of response from me.
    I understood.

    best regards,
    g.f.

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