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Problem with re-charge circuitry..

chethan kp
Expert 1150 points
Other Parts Discussed in Thread: BQ24070, TPS63031

I'm facing some problem with power managing part of my design. I'm using BQ24070 for recharging the 4.2 v li-ion battery(instead of waiting for battery to get recharged, here I wanted to check whether my system will work or not with BQ24070). The ckt is attached in this issue ( I have designed according to the suggestion given in this forum).

I have connected the fully charged li-ion battery to the charger (i.e. BAT1 and BAT2 pins) and tagged mode pin to the 3.3Vref, and I have used TPS63031 to regulate the output to 3.3V because my system works from 2 - 3.6V.

I was getting 3.12V at the regulator output but my system is not triggering with this voltage (common ground b/w sys and power part). If I remove this and connect external 3V battery to system then my system triggers.

What might be the problem with the above ckt..?

Regards,

 

 

  • 0
    TI__Expert 5640 points

    My first guess would be the TPS63031 is stuck in softstart.  This can be due to high source impedance (battery + bq24070) or some other current limit.  First check is to looks at the voltages of the BAT and OUT pins of the bq24070 to make sure the voltage is stable and maintained during start-up from the battery.  Also, there should be switching on either L1 or L2 pins of the TPS63031.  You should also see if it bq24070 & TPS63031 combination will start-up without a load.

  • 0 in reply to Scot Lester
    Expert 1150 points

    Still the problem is existing ..

    I checked the voltages of the BAT and OUT pins , There i'm getting stable output (4.2v).. I did not get the Inductor

    LPS3015 which is specified in the datasheet (b/w L1 and L2) so I used the following inductor 1.5uH, size 0402, type ceramic, res freq 8GHz, current 1A, Tolerance ±0.3nH,

    Will the above inductor work fine..?

    If above inductor wont work pls suggest some inductor which suits here..

    Since I have already fabricated the PCB I have to go with size 0402 if I need any changes in the inductor part.

    What are the other problems..?

    regards

    chethan

  • 0 in reply to Scot Lester
    Expert 1150 points

    Hi,

    In continuation with previous post.

    I checked in other way also..

    I just used voltage divider at the output of the BQ24070 to get 3V and given this to the system ,With this  setup my system triggers fine..

    from this its very sure that there is no problem at the BQ24070 only there is problem at the regulator TPS63031.

    I'm not getting stabilized  3.3 voltage at the regulator out put .

     I used the same ckt  given in the first page of the data sheet TPS63031. I did no get inductor specified in the data sheet so i used normal inductor of value 1.5uH ,1A,8GHz. ..

    what may be the problem at the regulator ..?

    thanks & regards

    chethan

  • 0 in reply to chethan kp
    TI__Expert 5640 points

    The problem is most likly the inductor.  The small ceramic inductors tend to lose inductance very quickly with current.  For example, at 1A the inductance may only be 0.5uH.  This effect will vary by inductor so check the specification of your inductor to make sure it still has 1.5uH of inductance with 1A of current flowing through it.  The wire wound inductors such as the LPS3015 tend to hold their inductance better with current.

    The TPS63031 could also be stuck in soft-start.  The current limit of the internal switches varies with the output voltage during power up.  Try to start it up with a lighter load and see if it comes up. 

    Both of these problems (soft-start and low inductance) will look the same from an output voltage standpoint.  You will need to look at the inductor current to isolate the problem further.  Loss of inductance will lead to non-linear current waveforms in the inductor.  Softstart will have a sawtooth current waveform that won't increase above some value.