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TPS65950 BACKUP domain & backup battery

Pev
Prodigy 245 points
Other Parts Discussed in Thread: TPS65950

Hi all,

In our TPS65950 based design we're currently using an XH414H super capacitor connected to BKBAT (and nothing else is obviously!) The software configuration used is :

  BB_CFG  =  0;
  BB_CFG |=  (3 << 2);    // BBSEL=11  (3.2v)
  BB_CFG |=  (2 << 0);    // BBISEL=10 (500uA)
   BB_CFG |=  (1 << 4);    // BBCHEN=1  (enable charging)

So we have a few queries :

  • Our charge cycle ultimately ends at 3.3v. Is this right given that we've programmed BBSEL = 3.2v?
  • The discharge seems overly fast. Measuring current flow at the backup battery we measure 6.8 - 7.0 uA rather than the 2.25 uA indicated in the TPS65950 data manual. This seems quite wrong to me.
  • I don't think I've got the configuration correct as I'd expected automatic charging of the backup battery to work in "WAIT-ON" mode. Is this the case? Or does goihng through the "BACKUP" state on the way to "WAIT-ON" cause the BB_CFG register to be reset?

~Pev

  • 0
    TI__Genius 15100 points

    Hi,

    1. Charging should ideally stop at 3.2V if that is what you select. I dont have a backup battery or super cap that I can test with. I will check into this and update you.

    2. How do you go to backup mode. I am assuming you set main battery voltage between 2.1V and 2.7V. With this all internal power resources should be off. Before you go to backup mode can you set CFG_BOOT[7]. This will put 32K in low power mode. I would expect this to take down your current by ~5uA.

    3. Only those registers retain value which are mentioned as (backup domain). BB_CFG is not part of this.

    Can you please check the charging voltage after the low power setting as mentioned in 2.

     

    Regards,

    Gandhar.