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32KIN Input Buffer Supply

Eric Zuber
Prodigy 60 points

Other Parts Discussed in Thread: TPS65930

Hoping to validate my understanding of this circuit based on the TRM....in TPS65930, it looks like the 32KIN and related RTC circuitry are powered as long as there is a valid voltage on Vbat....so driving 32KIN with an external 1.8V oscillator is no problem as long as VBAT > 3.2V. I see no notes about this pin supporting hot-socketing, so believe that driving 32KIN prior to this point (Vbat > 3.2V) would load down the 32k clk driver due to excessive leakage into the TPS's internal power rail for this buffer. Is this all correct or did I miss something in the TRM?
  • 0
    TI__Genius 15100 points

    Hi Eric,

    I dont think I completely understand what you are trying to ask. Let me explain what I think have gathered from your email.

    32KIN can be driven by an external oscillator, that is ok. Why are you not using a crystal, it is much cheaper option?

    If you are driving it with 1.8V then you can get this supply from the battery. During power up the device will need 32K clk. device will power up when the clk is stable. RTC is maintained till the battery level drops to 2.7V. Below this level the device will enter backup or switch off in case backup supply is not present.

    With the 32clk you shouldnt really try hot socketing. The device needs a clk for power-up. So, the clk must be provided. I dont know under waht circumstances you will use the clk for hot-swap.

    In this case your threshold for loading will be 2.7V. I havent seen any application using an oscillator, so I am not sure how it affects the system. I will try to get more info on this.

     

    Regards,

    Gandhar.

     

     

     

  • 0 in reply to Gandhar Dighe
    Prodigy 60 points

    Sorry - will clarify....

    The design has multiple OMAP/TPS65930 instances, which can be independently turned on or off depending on the processing needs.  We currently have all the TPS Vbat inputs connected to the same power source and are using the PWRON input of each to independently turn them on and off.  The 32k oscillator is being provided to each TPS 32KIN pin.  Want to make sure that simply connecting all the 32KIN pins together and driving from the 32K oscillator will work when not all PWRON signals are set to ON....if PWRON actually controls power to the 32KIN input buffer, the design wouldn't work (unless 32KIN supports hot-socketing).  But I believe the TRM indicates that the 32KIN input buffer is powered from a 1.5V regulator that is connected directly to the Vbat input power which would allow this implementation to work fine.   I just wanted to verify that I am interpreting the TRM correctly as it isn't absolutely clear on this.

    I also believe the TPS65930 will not generate any output voltages - or at least not the SMPS outputs - without the 32KIN providing a valid 32k clock....is this true?

    Thanks - Eric

  • 0 in reply to Eric Zuber
    TI__Genius 15100 points

    Hi Eric,

    We need some confirmation about the 32K clock - is it an external oscillator that supplies to all TPS parts? I guess it is and wanted to confirm it is not a crystal connected to one of the TPS parts.

    Also, can you please tell if TPS65930 is configured as master or slave?

     

    Regards,

    Gandhar.

     

  • 0 in reply to Gandhar Dighe
    Prodigy 60 points

    Hi - to answer the questions...

    Yes - it is an external 32k oscillator that drives all of the TPS parts. 

    All TPS65930's are configured as slaves with separate PWR_ON enables.

    Just to summarize - All TPS65930's have the same Vbat input....want to know that if one TPS is off (Vbat > 3.2, PWR_ON = 0) whether the 32k_IN buffer is powered on or if it will be loading down the 32k oscillator output which is connected to all of the TPS65930 devices?

     

    Thanks

  • 0 in reply to Eric Zuber
    TI__Genius 15100 points

    Hi Eric,

    Since PWRON will be at zero, the device is not ON, it is in WaitOn which essentially is an OFF state of the device. 32K buffer will not be ON. There will not be any loading on 32K oscillator.

     

    Regards,

    Gandhar.