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TPS65910: RTC current consumption during OFF state too high (TPS65910A31)

Robert Finger
Genius 17647 points
Part Number: TPS65910


Team,

One of my customers is using TPS65910A31A1RSL to power AM335x. A CR2032 battery is connected to VBACKUP. During OFF state they measure ~40 uA current drawn from the battery. The datasheet (chapter 5.8) is not clear about which current to expect. The values there are only for BOOT[1:0] = 00 or 01. But as this is for AM335x, BOOT[1:0] is set to 10 (EEPROM sequence).

Do these values also apply for BOOT[1:0] = 10 ?

They verified that all voltages are off during OFF state. And BBCHEN in BBCH_REG is set to 0, so Backup Battery Charger should be off. 

Shouldn't current consumption be more in the ~20 uA range?

Thanks,
  Robert

  • +1
    TI__Mastermind 49891 points

    Hi Robert,

      Yes; these values also apply for BOOT[1:0] = 10; the ~40uA current drawn should be normal if CK32K clock is running.

    Thanks!

    Phil

  • 0 in reply to Phil Yi
    TI__Genius 17647 points

    Hi Phil, 

    But how does this aling with the datasheet? The only case where the max current consumption goes to 42 uA is "Backup Battery Charger on" (see chapter 5.8). It is confirmed that the charger is off. So I would expect 23 or 20 uA als maximum current!?

    Thanks, 
      Robert

  • +1 in reply to Robert Finger
    TI__Mastermind 49891 points

    Hi Robert,

       Is the 40uA current drawn from the CR2032 battery? What's the main VBAT level during OFF state? 

      Please see section below:

    6.6 Backup Battery Management
    The device includes a back-up battery switch connecting the VRTC regulator input to a main battery
    (VCC7) or to a back-up battery (VBACKUP), depending on the batteries voltage value.
    The VRTC supply can then be maintained during a BACKUP state as far as the input voltage is high
    enough (>VBNPR threshold). Below the VBNPR voltage threshold the digital core of the device is set
    under reset by internal signal POR (Power-on Reset).
    The back-up domain functions which are always supplied from VRTC comprehend:
    • The internal 32-kHz oscillator
    • Backup registers
    The back-up battery can be charged from the main battery through an embedded charger. The back-up
    battery charge voltage and enable is controlled through BBCH_REG register programming. This register
    content is maintained during the device Backup state.
    Hence enabled the back-up battery charge is maintained as far as the main battery voltage is higher than
    the VMBLO threshold and the back-up battery voltage.

    Thanks!

    Phil