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A unexpected current of Ivbak on msp430f5336

When the primary supply is on, the current of Ivbak is up to 20uA,, even if BAKDIS bit is set in the BAKCTL register, what is wrong ?

  • Looking at the schematics in the users guide, BAKDIS will disable VBAT but not VBAK. VBak is still powering the Back-up subsystem.
    Also, depending on BAKSW and BAKDIS, it is connected to DVCC. It's possible that some current flows if VBAK is above DVCC.

    Also, it's possible that the RTC and the 32kHz oscillator are driven by VBAK if RTC is active. But I'm not sure of this. The users guide isn't very detailed here and I don't have own experience with the backup module.-

  • Thank you  Jens-Michael Gross!
    Here is a part of my schematic.When the primary supply is off, there is about 0.7uA ( Ivbat )from the battery,such as the user's guide discribe.When the primary supply is on,the Ivbat dose't turn down to 0, but up to about 22uA. And then I set the BAKDIS bit in the BAKCTL register to disable the battery backup system, the current ( about 22uA ) is still existsing.22uA it is to large for a backup battery.How can i fix it ?

  • Hmmm, in this circuit, there shouldn't be any current when the device runs from primary supply. The only situation where I could imagine some current is when the battery voltage exceeds the supply voltage while the device is active. In this case, it could be that some cross current flows from battery to supply. I agree, it shouldn't, but that's the only idea I have.