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AM335x RTC-only mode + wakeup

AFM
Intellectual 560 points
Other Parts Discussed in Thread: TPS65910A

i m working on a custom board based on TPS65910A3+AM335x.

the board has no power button : the system start with applying a voltage on VCC7 of PMIC (external charger 5V 3A) and switch to OFF when there is no power.

we plan now to use the VRTC + coin cell of PMIC (removing the old LDO of VRTC) with the REV2.0 of processor for timekeeping 

when there is a problem on the external charger. Questions : 

1- does the processor switch to the RTC-Only mode when no power on VCC7 of PMIC and only VRTC is enabled (due to the existence of the coin cell ) ?  this a self-acting of AM335x to switch to the RTC-only mode 

2-when applying again a power on VCC7 of PMIC: does the system start up directly ? no need in this case to have an external wakeup for the processor to switch from the rtc-only mode to active mode ?

3-the external power is a charger and not a battery : when there is a power failure : can the PMIC switch quickly to make the VRTC ON when we remove the power on VCC7 ? is there a response time on PMIC to verify ?

thanks for your help

  • 0
    TI__Guru**** 393215 points
    Hi Mokh,
     
    Please check sections 8.1.4.3.5 and 8.1.4.3.6 of the AM335X TRM Rev. I. You should also check the TPS65910A datasheet - there are timing diagrams there for the different scenarios (Figure 4).
  • 0 in reply to Biser Gatchev-XID
    Intellectual 560 points

    HI Biser,

    switching to the RTC-only mode is done by soft ? According to 8.1.3.4.5 : "Only the RTC power supply must be ON. All the remaining supplies must be OFF." and "Wakeup from RTC-only mode can only be achieved using the ext_wakeup0 signal"

    in our system there is no power button or wakeup ? which the best configuration in our case ?

    in the PMIC datasheet, there is only some conditions threshold related to the main battery (and we are using an external charger ). 

    with Rev2.0 of processor, and if we are using the evaluation board "AM335X EVM 15x15 Baseboard rev1.1, how we can use the RTC of AM335x ?

    thanks again 

  • 0 in reply to AFM
    TI__Guru**** 393215 points
    Quoting from another post on the same subject:
     

    RTC only mode assumes the product always provides a valid power source to the RTC while operating in this mode.

    When power is first applied, the RTC will automatically turn-on the other AM335x power supplies via the PMIC_POWER_EN output going high.  After the AM335x has booted the application software, the application can configure the RTC to generate periodic interrupts as well as turn-on and turn-off events. Once the RTC is initialized, it will continue to run as long as it has a valid power source, a 32.768 KHz clock source, and RTC_PWRONRSTn is not asserted.

    To enter RTC only mode, the application software will schedule a turn-off event in the RTC which causes the PMIC_POWER_EN output to go low and this turns off all AM335x power supplies except the RTC power supply.

    This mode of operation requires the RTC to always have power applied.  If the product has an unexpected power failure that affects the RTC power source, the RTC would not be able to retain its configuration. In this case, once power is restored the product would restart and go through the same start up process described above.   If the product has an unexpected power failure that does not affect the RTC power source and the RTC was previously scheduled with a turn-on event that occurs after power is restored, the RTC would retain its configuration and turn-on at the previously scheduled turn-on time.

  • 0 in reply to Biser Gatchev-XID
    Intellectual 560 points

    Hi Biser,

    i m trying to understand the difference of wakeup between "RTC timer functionality but no RTC-only mode "  and " RTC-only mode:" on the wiki "http://processors.wiki.ti.com/index.php/AM335x_Schematic_Checklist.

    1- power consumption : whith "RTC timer functionality", the power consumption of VRTC (AM335X) should be less than "RTC-only mode" ? can you confirm that ?

    2- in this case, when we get a power failure on VCC7, can the PMIC switch directly to Backup (from coin cell) and provide the VRTC to the processeor during main power failure ?

    3- when we have the main power again, what is the scenario for wakeup for both "RTC timer functionality"  and " RTC-only mode:" ?

    regards, 

  • 0 in reply to AFM
    TI__Guru**** 393215 points
    RTC timer functionality means only that the RTC timer is fully functional. RTC-only mode is a low-power mode, basically the processor completely switched off except for the RTC, and it can return from this mode by an external wakeup signal.
     
    1. VRTC consumption will depend on silicon revision. See the updated wiki page for details: http://processors.wiki.ti.com/index.php/AM335x_Power_Consumption_Summary#RTC-Only
    2. Yes
    3. See above for the differences. The Schematic checklist also shows which signals are necessary to be connected for inplementation of RTC-only mode. See also AM335X TRM, section 8.1.4.3.5.
  • 0 in reply to Biser Gatchev-XID
    Prodigy 160 points

    Hi Biser

    1. Can i know where the supply input will come for LDO output in case of "RTC mode only". 

    2. As in below  it seems to be "RTC timer functionality" we are using external supply (VDD_CORE) for RTC core. So it means that the current consumption will be more than "RTC mode only". 

    3. What is functionality difference between "RTC mode only" and "RTC timer functionality"

  • 0 in reply to Karthik Puliyadi
    TI__Guru**** 393215 points

    Karthik Puliyadi said:
    1. Can i know where the supply input will come for LDO output in case of "RTC mode only". 

    The CAP_VDD_RTC terminal operates as an input to the RTC core voltage domain when the internal RTC LDO is disabled by connecting the RTC_KALDO_ENn terminal to VDDS_RTC. If the internal RTC LDO is disabled, CAP_VDD_RTC should be sourced from an external 1.1-V power supply.

    The internal RTC LDO is enabled when RTC_KALDO_ENn is connected to GND. In this case VDDS_RTC should be provided from the PMIC dedicated VRTC supply. CAP_VDD_RTC should have only a 1uF bypass capacitor to GND.

    Karthik Puliyadi said:
    2. As in below  it seems to be "RTC timer functionality" we are using external supply (VDD_CORE) for RTC core. So it means that the current consumption will be more than "RTC mode only". 

    Obviously with this configuration you cannot achieve RTC-only mode, because you will need an external 1.1V supply for the RTC.

    Karthik Puliyadi said:
    3. What is functionality difference between "RTC mode only" and "RTC timer functionality"

    RTC-only mode is the lowest power saving mode the processor can achieve. In this mode only the RTC is functional, all power supplies except VDDS_RTC are switched off. RTC timer functionality is the capability to use the RTC timer when the processor is active.