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AM572x RTC connections - schematic checklist

Michi Yama
Guru 10030 points
Other Parts Discussed in Thread: AM5728

Hi,

I have one question regarding TI wiki of AM572x.

According to TI Wiki (http://processors.wiki.ti.com/index.php/AM572x_Schematic_Checklist ) , it is written in the below.

If RTC feature is not used,

RTC_ISO pin should be connected to PORZ.

RTC_PORZ pin should be connected to VSS.

However, according to the AM5728 data manual "Table 4-1.  Unused Balls Specific Connection Requirements", it is written in the below.

AF14(rtc_iso)  must be connect to the corresponding power supply through an external pull resister if unused.

AB17(rtc_porz) must be connected to F22(porz) if unused.

Which is correct, checklist ? or data manual?

Please advise me.

I appreciate your quick reply.

Best regards,

Michi

  • 0
    TI__Guru**** 393215 points
    I will ask the factory team to check this.
  • 0 in reply to Biser Gatchev-XID
    TI__Guru 62945 points

    Please read Notes 2 and 3 in the RTC section of the schematic checklist. The notes provide more detail about connecting the RTC. Note 3 provides an alternate option of pulling RTC_ISO up to VDDSHV5.

    I will need to ask about RTC_PORZ.

    Regards,
    Paul

  • 0 in reply to peaves
    TI__Guru 62945 points
    The person I need to ask is on vacation this week. So it will be next week before we get an answer why the recommendations are different.

    Both recommendations for RTC_PORZ may be acceptable. The RTC circuits will be held in reset when RTC_PORZ is connected to VSS. The RTC circuits will receive a valid reset after power is applied when RTC_PORZ is connected to the same reset source as PORZ. I do not know why one would be preferred over the other, but will let you know once I get the answer.

    Regards,
    Paul
  • 0 in reply to peaves
    Guru 10030 points
    Dear peaves-san,

    Thank you for your reply.

    Please let me know as soon as you get the information for handling RTC_PORZ when unused RTC.

    Then, I have one more question.

    As to my customer board, RTC_ISO pin is connected to PORZ now because I didn't check Note3.
    When RTC unused, is this any problem? Some internal circuit has damaged?

    Please advise me .

    Best regards,
    Michi
  • 0 in reply to Michi Yama
    TI__Guru 62945 points
    Does your customer board source VDDSHV3 and VDDSHV5 from the same supply? If VDDSHV3 and VDDSHV5 are not powered from the same source, are they operating at the same voltage? If powered from different supplies of the same voltage, are both supplies sequenced on and off at the same time?

    If you answered, "No", to any of these questions you may have damaged the device by connecting them together.

    Regards,
    Paul
  • 0 in reply to peaves
    TI__Mastermind 46460 points

    Paul,

    VDDSHV3 and VDDSHV5 must be connected to the same voltage to allow these pins to be directly connected.  However, they do not need to be sequenced on and off simultaneously.  This is because PORz must always be driven low whenever supplies are ramping up or ramping down.

    Tom

  • 0 in reply to Tom Johnson 16214
    TI__Mastermind 46460 points
    Michi-san,

    The datasheet does not list all of the options in these summary tables. There is discussion elsewhere (i.e. on page 152 for RTC_ISO) that mentions other options. We will add footnotes on page 10 that state:
    RTC_ISO can also be connected to PORz when RTC unused (level translation may be needed)
    RTC_PORz can also tie to VSS when RTC unused

    Tom
  • 0 in reply to Tom Johnson 16214
    Guru 10030 points
    Dear Tom-san,

    Thank you for your answer.

    > We will add footnotes on page 10 that state:
    > RTC_ISO can also be connected to PORz when RTC unused (level translation may be needed)
    > RTC_PORz can also tie to VSS when RTC unused

    Do you mean you will add the above two comments in the data manual at next revision?

    I appreciate your quick reply.

    Best regards,
    Michi
  • 0 in reply to Michi Yama
    TI__Mastermind 46460 points
    Michi-san,

    Yes, these3 statements will be added in the next revision.

    Tom
  • 0 in reply to Tom Johnson 16214
    Guru 10030 points

    Dear Tom-san,

    Thank you for your quick reply.

    You said "three statements".

    > RTC_ISO can also be connected to PORz when RTC unused (level translation may be needed)

    > RTC_PORz can also tie to VSS when RTC unused

    what is other one?

    And please confirm me again. 

    RTC_ISO : PORZ or VDDSHV5

    RTC_PORz : PORz or VSS

    RTC_OSC_XI_CLKIN32(AE14) :  VSS   <-  There is no written in Schematic Check list.

    The above is correct?


    Best regards,

    Michi

  • 0 in reply to Michi Yama
    TI__Mastermind 46460 points

    Michi-san,

    The '3' was a typing error.  Only 2 footnotes will be added as stated.

    Tom

  • 0 in reply to Tom Johnson 16214
    TI__Mastermind 46460 points

    Michi-san,

    Unused crystal clock inputs can be connected to ground.  That is correctly stated in the DM.

    Tom

  • 0 in reply to Tom Johnson 16214
    Guru 10030 points

    Dear Tom-san,

    Thank you for your support.

    I have one more question.

     The below shows that my customer's current connection.

    Pin Number                Signal Name                                      Connected to                               Recommendation

    AE14                          RTC_OSC_XI_CLKIN32                   CLK32KGO(PMIC-M11pin)        VSS
    AD17                          WAKEUP_0                                       OPEN                                          VSS
    AC17                          WAKEUP_1                                       OPEN                                          VSS
    AB16                          WAKEUP_2                                       OPEN                                          VSS
    AC16                          WAKEUP_3                                       OPEN                                          VSS
    AB17                          RTC_PORZ                                       PORZ AM5728（F22）                  VSS

    I know RTC_PORz can be connected to both pins (PORz or VSS). 

    How abou RTC_OSC_XI_CLKIN32? Now it is connected to CLK32KGO of PMIC. And customer' PMIC output the clock from this pin. Is current connection no problem if RTC is not used?

    Also how about WAKEUP_x pin? I thnik this is no problem, but Noise immunity is not good.

    Please advise me.

    Best regards,

    Michi

  • 0 in reply to Michi Yama
    TI__Mastermind 46460 points

    Michi-san,

    The connection on a clock input is not a problem.  Similar to the PORz connection to RTC_PORz, this is not a problem.  Also, you can enable the RTC functionality with this hook-up.

    The floating WAKEUP pins are not ideal.  However, this can be resolved by enabling the PD in the input pad configuration register.

    Tom

     

  • 0 in reply to Tom Johnson 16214
    Guru 10030 points

    Dear Tom-san,

    Thank you for your continuous support.

    I have one more question.

    When RTC feature is not used, Is the below pin handling possible?

    Please advise me again.

    I appreciate your quick reply.

    Best regards,

    Michi

  • 0 in reply to Michi Yama
    TI__Guru**** 393215 points
    It's not recommended to short I/O pins to each other. These particular pins will be safe initially, but if they are accidentally configured as outputs with different drive levels, this will directly lead to I/O cells failure and very likely to processor failure too. If you require them to be grounded you should do it through separate pulldown resistors.
  • 0 in reply to Biser Gatchev-XID
    TI__Mastermind 46460 points

    Michi-san,

    Biser provided a good explanation.  Please also see Table 4-1 in the Data Manual that provides the same guidance.

    Tom

  • 0 in reply to Tom Johnson 16214
    Guru 10030 points

    Dear Biser-san, Tom-san,

    Thank you for your advice.

    Do you have a recommendation for value of pull-down resistor?

    I confirmed 10kohm pull-down resistor is used in TI EVM. Is it reasonable value?

     

    I appreciate your quick reply.

    Best regards.

    Michi

  • 0 in reply to Michi Yama
    TI__Mastermind 46460 points

    Michi,

    Yes, 10K ohms is a reasonable value.

    Tom