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AM3358 RTC-only backup battery issues

Jason Z
Intellectual 560 points
Other Parts Discussed in Thread: TPS65910A, TPS65910

Hi ,

I have two questions regarding the RTC battery:

1. I have Am3358evm Rev 1.1A, I found the backup battery isn't charged ,currently it is down to 2.0V, how to enable the charge function via software of uboot and linux? 

2. I have customized a board using Am3352BZCZ80 and as rtc-only mode referring to the Am3358evm. I want the backup batter to power the RTC only   when the main power is off, I don't need sleep and wakeup features,so I don't connect the EXT_WAKEUP pin to any source except for having a 10k pull-up resistor, can you advice if  it will work as my expected?

Thanks,

Jason

  • 0
    TI__Guru**** 393215 points
    Hi Jason,
     
    1. You have to program the BBCH_REG in the TPS65910A. You can read/write this register through I2C0. Please refer to the TPS65910A datasheet for details.
     
    2. You can refer to the Starter Kit schematic. EXT_WAKEUP is tied to GND there and PMIC_PWR_EN is not connected. This way VRTC will be provided as long as the backup battery holds. Power on will be achieved by either applying main power to the board (PWRHOLD signal pulled up to VBAT, max. allowed voltage on this pin is 5.5V)  or by starting the PMIC with a pushbutton (PWRHOLD signal pulled up to VAUX33 as on Starter Kit).
  • 0 in reply to Biser Gatchev-XID
    Intellectual 560 points

    Hi Biser,

    Thank you for reply!

    1. if I always enable this bit after power on, the charger will function automatically? and also what is the better configuration  using boot pins?

    2. unfortunately, we have made 200 PCBs based on my previous design with EXT_WAKEUP pin is pulled up rather than pull down and also all the other rtc related pins including PMIC_PWR_EN are referred to design as AM335xEVM Rev 1.1A, what is the problem for my design? can you advice ASAP?

    Thanks!

    Jason

     

  • 0 in reply to Jason Z
    TI__Guru**** 393215 points
    1. Yes, the charger will function properly if enabled. I suppose you mean the PMIC BOOT[1:0] pins. For AM335X the ymust always be configured BOOT1=VRTC, BOOT0=GND. There is no other possible configuration that will work.
     
    2. No problem, PCBs should function normally. If you observe any unexpected behaviour you can always reconfigure the AM335X RTC_PMIC Register as required by your application.
  • 0 in reply to Biser Gatchev-XID
    Intellectual 560 points

    Hi Biser,

    That is great! thanks.

    I still have some unclear .please advice how to easily and properly connecting pin

    GPIO_CKSYNC,

    INT1

    SLEEP for my application?

    Can I leave them open?

    BTW, the battery being used in AM335xevm is Ms920SE which has 100 life cycle , is it good and reliably enough for a product which is supposed to last at least 7 years? how do you recommend?

     

    Appreciate your reply?

    Jason

     

  • 0 in reply to Jason Z
    TI__Guru**** 393215 points
    Yes, you can leave them open. As for the battery, I suppose you need to look for something more reliable for a 7-year product life.
  • 0 in reply to Biser Gatchev-XID
    Intellectual 560 points

    Hi Biser,

    Thank you so much for the valuable reply!

    I 'd like to ask a few more questions to make sure my system running well.

    1. regarding the battery, what is the current consumed by RTC circuit when main power is off.

    2. in my current design , I have left pin PWRON (external on/off control) open as well, is it ok? I have attach the schematic for PMIC circuit, can you help double check what should be improved for better design and EMC as well?

    Cheers,

    Jason

  • 0 in reply to Jason Z
    TI__Guru**** 393215 points
    Hi Jason,
     
    1. Take a look at the http://processors.wiki.ti.com/index.php/AM335x_Power_Consumption_Summary. It has been updated with a lot of information earlier this year.
     
    2. Seems OK to me. I suppose you have pullups on I2C0 somewhere else on the schematic.
  • 0 in reply to Biser Gatchev-XID
    Intellectual 560 points

    Hi Biser,

    Thanks!

    I have pull-up for I2C0.

    Jason

     

     

  • 0 in reply to Jason Z
    Intellectual 560 points

    Hi Biser,

    I find a new issue regarding the charging . When I enable the charging by set up the register bit ,actually always enabled after power on,  the RTC running ok if power keep running , but when I power off and power on again, I found the RTC seems losing power, its time has been reset to 2000 Jan 1. if I diable the the charging function after power on , then power off and power on again, the RTC  works ok.  Can you advice how to fix the issue?

    BTW ,I have attached my schametic before and the MCU is AM3352BZCZD80.

    Appreciate your reply!

    Jason

     

  • 0 in reply to Jason Z
    TI__Guru**** 393215 points
    Hi Jason,
     
    I guess you should direct this question to the PMIC forum. There is a dedicated forum for the TPS65910: http://e2e.ti.com/support/power_management/pmu/f/43.aspx.
  • 0 in reply to Biser Gatchev-XID
    Intellectual 560 points

    Hi Bisel,

    Thanks for your advice, i have post to the forum you adviced, but I am still wondering if you have some idea about this issue, do you think the RTC-only mode not working well or ....?

    Thanks,

    Jason

     

  • 0 in reply to Jason Z
    TI__Guru**** 393215 points
    This seems to me like something related to the PMIC. Have you measured the VDDS_RTC voltage, 32.768kHz oscillator and RTC_PORZ level in power-off state, when RTC failure occurs? This can guide you to the possible source of the problem.