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How to turn TPS65070 on when battery is discharged?

Vsevolod Anisimov
Prodigy 240 points
Other Parts Discussed in Thread: TPS65070

Greetings,

In my scheme pin PB_IN is connected directly to GND, I don`t use a possibility of turning TPS65070 on and off using a button.

 

While discharging a battery DC/DC and LDO turns off  when VBT become less than 3.0V, and VSYS still is on. When I plug USB, the battery charging begins. But DC/DC and LDO doesn`t turn on and my device doesn`t start.

 

In that case I am used to make some actions to turn device on:

  1. Charge a battery for more than 3.0V (VBT > 3 V)
  2. Unplug USB from a device
  3. Disconnect and then connect battery (disconnect VBT from TPS65070 and then connect again)

 

Is it possible to turn my device on right after plugging USB even if battery is discharged?

Best regards.

 

  • 0
    TI__Mastermind 23810 points

    I've been working on an application report that covers this very topic.  It isn't released yet, but I can let you see a draft.  It sounds like what you need to do is tie both PB_IN and POWER_ON to logic high.  This will turn the LDO on when you plug in the USB.

    0714.How to Power the TPS6507x On and Off_unreleased.docx

  • 0 in reply to Clancy Soehren
    Prodigy 240 points

    Greetings!

     

    The state diagram  of TPS65070 is not fully described in datasheet and in document you sent to me in my opinion.  Possible mistake is in mode when PB_IN is always connected to GND, so there is no ON/OFF button in the project.

     

    The transition from “Stand-By SYS = OFF” state to “Decision SYS = ON” will not be done when PB_IN = 0, because there will be no action PB_IN = 0 (falling edge detect). The state machine is waiting for falling edge on PB_IN and during this state it does not reacting for plugging AC or USB.

     

    I think that checking of condition “voltage at AC applied OR voltage at USB applied OR PB_IN=0 (falling edge detect)” in that state could be done correctly only if PB_IN = 1.

     

    If  PB_IN = GND and USB will be plugged in the state “Stand-By SYS = OFF” – it will start only the battery charging but the transition to  “Decision SYS=ON” state will be not allowed. TPS65070 could go to “Decision SYS = ON” state only by unplugging and then plugging battery back to VBT (reset of state machine). In that case the state machine will start working from “Decision SYS = ON” state and will turn the device ON.

     

    It is very unconvenient for my device.

     

    In the case when there is ON/OFF button in the project the PB_IN signal will be high level in “Stand-By SYS=OFF” state. So the condition from the state machine diagram for transition between “Stand_By SYS=OFF” state and “Decision SYS = ON” state will work correct.

     

    If that is so, it would be great if all 3 mentioned actions could be checked in “Stand-By SYS=OFF” state independently of PB_IN voltage level.

    Best regards,

    Vsevolod Anisimov

  • 0 in reply to Vsevolod Anisimov
    TI__Mastermind 23810 points

    Can you explain exactly what your desired behavior is?  When do you want the LDO and DC/DC converter outputs turned on?  When do you want them turned off?  What power inputs will be active for each of these cases?  What do you want the trigger to be for turning the outputs on and off?  Are you using an application processor?

    If you can clearly explain what it is you want, I might be able to suggest a solution.

  • 0 in reply to Clancy Soehren
    Prodigy 240 points

    My device does not have ON/OFF button.

     

    Device must do following things:

    1. Turn ON when Li-Ion battery is plugged OR when usb cable is plugged
    2. Work until battery will be discharged (VBAT < VUVLO).

     

    There is the way I tried to do this:

    1. POWER_ON pin is connected to VSYS.
    2. PB_IN input is connected to TPS3823-25DBVT supervisor RESET_N output. VDD, MR_N, WDI outputs of supervisor are connected to AVDD6 output of TPS65070

     

    So supervisor generates pulses at PB_IN.

     

    I still can not turn device ON (as it was earlier, when PB_IN pin was connected to GND) using usb cable when the battery is discharged.

     

    So when VBAT < 3.0V, VSYS = VBAT, POWER_ON = SYS, pulses at PB_IN – TPS65070 does not start. Battery is charging, VBAT > VUVLO, but DC/DC does not start.

     

    I can turn the device on doing following things:

    1. unplug the battery and plug it again

    2. unplug the battery and connect usb cable.

     

    I expected that the device will turn ON while charging the battery when VBAT will be higher than 3,5V.

     

    Questions:

     

    1. What exactly in my scheme conflicts with figure 33 of TPS65070 datasheet? In what state does it`s state machine stuck?
    2. Can I however achieve turning my device ON when battery is discharged without unplugging it?  
  • 0 in reply to Clancy Soehren
    Expert 1380 points

    Clancy,

    we have posted a new question to the thread How to turn TPS65070 on when battery is discharged?

    Please review it.

  • 0 in reply to Vsevolod Anisimov
    TI__Mastermind 23810 points

    Vsevolod,

    My apologies for the delayed resopnse.  It sounds like maybe you are getting stuck in the "POWER_ON 2" state when UVLO is reached, but with the outputs turned off.  I'm not sure about this, but one of my colleagues might be able to elaborate more. 

    My suggestion would be to connect the RESET output of the TPS3823-25 to /PBIN (instead of connecting /RESET to /PBIN).  Then you could connect POWER_ON to PGOOD.  This way, when UVLO is reached, POWER_ON would turn off, causing the device to properly enter the "Stand-By" state.  Let me know how this works.

    -Clancy