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Original question:

BQ32000 RTC after power off clock time is stop counting

BQ32000: BQ32000 current is bigger from 1.2ua to about 100ua , when taking off the Backup device power

Eggsy Pang
Expert 4985 points
Part Number: BQ32000

Hi Team,

       My customers met some problem when using BQ32000 on their system, Below is their SCH for BQ32000. Let me introduce the problem.

1. when the system power up and run, we test the Backup device power (VBACK) current and it is about 1,2ua, which is normal.

2. We take off the Backup device power, meaning we disconnect the system and Backup device power. After 3 second, we connect system and Backup device power agabin. And now we test the Backup device power (VBACK) current, and it is about 100ua. It is so big current. Next, We power off the system, the Backup device power current keep 100ua. Lastly, we power up the system again, the Backup device power current is about 1.2ua.

So do you know what happen? Why the Backup device power current is 100ua when taking off the Backup device power? It confused the Customer. We need your help！Thanks！

  • 0
    TI__Genius 16845 points
    After any total power loss scenario, you must properly initialize the VCC pin to obtain the low 1.2uA backup supply current. See section 8.2.2.3 of the datasheet for more information. The relevant datasheet section is pasted below for reference:

    "In order for the bq32000 to achieve a low backup supply current as specified in the Electrical Characteristics, the VCC pin must be initialized after every total power loss situation. Initialization Is achieved by powering on VCC with a voltage between 3 to 3.6 V for at least 1 ms immediately after the backup supply is connected. If the VCC is not powered on while connecting the backup supply, then the expected leakage current from VBACK will be much greater than specified."

    Kind regards,
    Lane
  • 0 in reply to Lane Boyd
    TI__Expert 4985 points

    Hi Lane,

           Clearly. Thanks for your help! Could you have any idea to deal with it? Customers also accept to use other TI device.

    May I know why VCC pin must be initialized after every total power loss situation? Is it for safety or logic or other?

    Thanks!  

  • 0 in reply to Eggsy Pang
    TI__Genius 16845 points
    Hi Eggsy,

    My best recommendation is for the customer to initialize VCC with a pulse to achieve the low backup supply current.

    You can read this post for more history on the VCC initialization requirement: e2e.ti.com/.../295753

    Kind regards,
    Lane
  • 0 in reply to Lane Boyd
    TI__Expert 4985 points

    Hi Lane,

         I can't find the solution on link you gave! 

    I have a question, you said , "initialize VCC with a pulse", just need to give a pulse on VCC pin , it can achieve the low backup supply current, right?

    Do you have any simple SCH to show how to give a pulse on VCC pin?

    Thanks!

  • 0 in reply to Eggsy Pang
    TI__Genius 16845 points
    Hi Eggsy,

    Can the customer use the +3.3V to pulse VCC after VBACK is connected? Then no schematic change is necessary.

    Kind regards,
    Lane
  • 0 in reply to Lane Boyd
    TI__Expert 4985 points
    Hi Lane,

    After VBACK is connected, there are no +3.3V to pulse VCC in customers board. Because the system is power off at that time.
    Do you have any suggestions?
    Thanks!
  • 0 in reply to Eggsy Pang
    TI__Genius 16845 points
    Hi Eggsy,

    If the system power is turned off after VBACK is connected, one way to achieve low backup supply current is by using some external power source to initialize BQ32000.

    Kind regards,
    Lane