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BQ32000 RTC battery draining issue

swapna bramandlapally1
Prodigy 170 points
Other Parts Discussed in Thread: BQ32000

Hi folks,

I am using BQ32000 RTC in my design.battery is fully discharged after came from assembly house.3V battery is discharged to 0.6V within 4 days or less.I observed same this condition in all the boards.
We observed below strange behavior i.e; I connected current meter in series to battery to monitor the current.
That time my board is in turnoff and only monitoring the battery discharging current.

As per datasheet(page no. 4 I backup supply current) ,it should not take discharge current more than 1.5uA.But sometimes it is taking 60uA of discharging current(whenever i am trying connect the multimeter operating in current mode) and sometimes 1.9uA of current.
If issue will be the probing, then it should give 21 days battery backup  .I am not able to conclude that what might be the issue.I opened ground pin of RTC(suspected leakage current) and connected battery directly on RTC 3rd and 4th pin.I observed the still same behavior.


We assembled only RTC IC and battery(MS412FE-FL26E) on the bare PCB board and observed battery discharging current, the behavior is same as above mentioned.
I did one more experiment , i added schottky diode from battery to IC 3rd pin.Still I observed the same problem as above.

I have added series 10K resistor instead of diode from battery to RTC 3rd pin.Constant voltage drop 19.3mV observed across resistor.

I have attached my RTC circuit for reference.Initially C90 and C94 are mounted on the board,while testing we removed the capacitors.


The above mentioned details are the our observations.We used rechargeable battery instead of non-rechargeable battery.

Please some body suggest me regarding this issue.

Thanks in advance.

Regards
Swapna.B

  • 0
    Prodigy 170 points

    Hi  folks,

    Below are the few more observations.

    1.  On the bare PCB battery is connected directly to RTC , battery is discharged almost 1.9uA of current(Note : I didn't power up the IC 3.3V)
    2. Whenever i  mounted crystal on the board and observed battery discharging current is almost 60uA (Note : i didn't power up the IC 3.3V)
    3. Whenever i powered up the RTC IC with  3.3V and monitored the battery current.It is taking almost nill current. when i turnoff the power supply and monitored the battery discharging 1.9uA of current(crystal is present on the board) .
    4. If i remove battery connection from IC and tried to connect it again, it was again start discharging 60uA current.
    We are suspecting below points,please let us know we are correct or not.
            1.  Whenever we powered up the IC with 3.3V , IC is initialized and loaded default configurations and giving                  proper discharging current of 1.9uA
            2. whenever power 3.3V turnoff and maintain default configurations with battery backup.
            3. Whenever we disconnect the battery from IC , it has lost default configurations and discharging higher                     current.
    Actually this should not be the case.The above conditions are observed after mount the crystal on the board.
    Can somebody suggest quick resolution for this issue.This is very critical for us.
    Thank You,
    Regards
    Swapna.B
  • 0 in reply to swapna bramandlapally1
    TI__Genius 13700 points

    Hello Swapna,

     

    I am working on a similar issue. Have you been able to figure out a solution?

    I wanted to check to see where you are meassureing this current that goes up to 60uA. Is this coming off of the Vbat pin or the Vcc pin?

     

  • 0 in reply to Ryan May
    Prodigy 170 points

    Hi Ryan,

    Thanks for your reply..

    We are working on that issue.

    I am measuring the current 60uA on Vbat pin.

    Thank You,

    Regards

    Swapna.B

  • 0 in reply to swapna bramandlapally1
    TI__Guru 54665 points

    All,

    Upon further investigation into this issue, there appears to be an issue in the device that requires Vcc to be initially applied as observed.  I am able to recreate this in the lab. 

    If the device is NOT powered externally on the Vcc pin at least once (even for a very brief moment) after initial startup (or battery replacement) then it is stuck in an excessive current draw state. 

    This appears to be exactly what Swapna is observing.  Unfortunately, the only work around is to power Vcc even for a brief moment. 

  • 0 in reply to Ryan Kehr
    Prodigy 10 points

    Hi Ryan;

    was there an App note that explain your findings?

    will the spec sheet for RTC BQ3200 be updated with design recommendations you provided?

    how TI expected the customers to be aware of the issue and avoid it?

    is there any plan(s) to fix this issue?

    thanks

    maisa

  • 0 in reply to Maisa Elganayni
    TI__Guru 54665 points

    Maisa,

    No application note, but I just submitted for a datasheet update.  This has to go through an extensive approval process, so it may be several weeks before you see an update. 

  • 0 in reply to Ryan Kehr
    Prodigy 140 points

    Hi Ryan:

    My customer meet the same issue, but they follow the suggestion to initial by Vcc start up and then switch to Vbat. But the current is not reduce, and could you description more detail about it?  

  • 0 in reply to Simon Lin
    TI__Guru 54665 points

    Simon,

    I am sorry your customer is having trouble, but maybe it is a different issue. 

    The description at the top of the forum is accurate.  The device needs to be powered initially with a voltage between 3-3.6V on VCC.  You can then switch to Vbat and the current specified in the datasheet is valid. 

    How long are they applying power to VCC before switching to Vback?

  • 0 in reply to Ryan Kehr
    Prodigy 140 points

    Hi Ryan:

    The customer normal using is not apply Vcc first and directly apply Vback with battery, but they have tested the apply Vcc about 5 sec before switching Vback, and they measure the current is about 70uA of Iback.

     

    Best regards.

    Simon Lin

  • 0 in reply to Simon Lin
    TI__Expert 6085 points

    Hi Simon:

    The roboust workaround for this issue, is to pulse the VCC.

    The I back current reflected in the datasheet is obtained after issuing a pulse  on VCC.The amplitude of the pulse can

    be 0-VCC with 1ms (min ) pulse width.

    thanks

    vish nadarajah

  • 0 in reply to Vish Nadarajah
    Prodigy 165 points
    Hi Vish,Does TI has a plan to fix this issue ?
    This has been go around for more than one year.
    most of cases, customer just attach battery into board, they will not power on the RTC.
    Thanks.Tom