• State
  • Locked Locked
  • Replies 8 replies
  • Subscribers 63 subscribers
  • Views 1638 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

BQ51050B current from battery

Fulvio Guidetti1
Prodigy 60 points
Other Parts Discussed in Thread: BQ500410A, BQ51050B

Hello,
I'm designing a battery charger complete with TX and RX using BQ500410A and BQ51050B for a lithium battery 2000mAh  stylus.
I made the coil transmit and receive because they have to be small.

The charge cycle works this correctly, and it is of 800mA and interuptiona at 40mA .
What they do not understand is that when the charge current is between 140 and 400mA, during transmission from RX to TX, the charging current reverses the direction for some tens of mcroseconds.

As seen from the figure is the signal C1 is COMM1 and C2 is the  current to the battery.

At the bottom you see the zoom and you can see the pulse of C2 at the beginning of COMM1 to 0 volts that go into the negative (current supplied by the battery)

I made 3 different layouts with capacitors as close as possible to the integrated circuit .On the  RECT signal there are 2 10uF X7R and  0.1uF X7R 1, on BATT 1uF X7R, and 0.1uF X /7R.

When the current exceeds 400mA, there are no negative current pulses.
When the current drops below 140mA, in an instant, negative pulses of current disappear.

What do you think?
 
Thanks.
 
Fulvio Guidetti
 

 

  • 0
    TI__Genius 14890 points

    Fulvio,

    I want to look at this a bit in my lab.  Can you tell me the capacitance you have on COMM1 and COMM2?  What is the current scale for this plot?  I'd like to understand the magnitude of the negative current you are seeing. is there any other loading on the BAT pin?

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 60 points

    Dick,

    COMM1-2 have 22nF,

    BOOT1-2 hane 10nF,

    CLMP1-2 have 47nF.

    The current scale is 1A/100mV.

    The magnitude of negative current is about 80mA.

    The bat pin is connected to two capacitors 1 and 0.1 microfarad and the battery.
    The LED indicator is on VREC    T.

    Rfod is 200ohms and RILIM is 174ohms (0.8A)

    RTERM is 1200ohms.

    thanks and best regards
     
    Fulvio

  • 0 in reply to Fulvio Guidetti1
    TI__Genius 14890 points

    Fulvio,

    Thank you for the information.  I think you have noted the CLAMP1-2 values as 47nF when they are 0.47uF.

    You mention in the original post that you have new coils for TX and RX.  Did you do the tuning for the Cs / Cd?  Have you tried running the RX on a known good TX?  If both coils have changed, there could be some issues with that.

    Where are you measuring the BAT current?  Is is between the battery and the board?  I am interested to determine if the current is going to the IC or to the BAT capacitors.

    Can you run the plot from above but add the RECT and BAT pins to the scope?  This can show us if the BAT is collapsing and if it is, then the RECT pin can indicate if the coil is collapsing or if it is internal to the bq51050B

    I have seen current dip when the ICOMM-CL comes into play, but this would be above 400mA and you see proper operation there. 

    You mentioned you made 3 layouts.  Depending on the information above, it may be worthwhile to evaluate that as well.  The placement of capacitors is critical (as your note indicates you took into account).

    I did look at this in the lab today (using EVM boards) and did not see any indication of negative current.  I was using a source meter to emulate the battery.

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 60 points

    Dick,

    Thanks for the collaboration.

    I measured the inductance of the TX and RX with an impedance analizer.And also the resonant frequency at 100KHz and 1MHz groups LC using the same tool. ( Z and phi in the frequency domain )
    The current probe is placed between the battery and the group of BQ51050B and its two capacitors. I measure only what circulates in the battery.
     
    This is an image of VRECT and IBATT(140mA < IBATT <400mA)
    This is an image of VBATT and IBATT (140mA <IBATT <400mA)
     
    This is an image of VRECT and IBATT(IBATT <140mA)
    In this case the battery voltage is perfectly continuous (there are no spikes)
     
    However, if you use a real battery or simullator battery, current and voltage signals do not change.
     
    If I place the capacitors a little more distant from the chip, the circuit loses control and turns on and off multiple times. (Why I'm worried)

     
    P.S. Unlike the EVM board I use the case QFN20
     
    Regards ,
     
    Fulvio
  • 0 in reply to Fulvio Guidetti1
    TI__Mastermind 18120 points

    Hi Fulvio,

    It has been a long time since we communicated on this project.  We would like to check the status.  Is there any assistance we can provide? Thanks!

  • 0 in reply to Xun
    Prodigy 60 points

    I did realize the circuit defined (a circle with a diameter of 18mm) to 4 layers.
    I have not seen the problem of  current oscillation.
    I hope it's a good signal to move forward.

    What do you think?

    Thanks for your interest.

    Best regards

    Fulvio

     

  • 0 in reply to Fulvio Guidetti1
    TI__Genius 14890 points

    Fluvio,

    Yes, it seems you've made good progress.  Congratulations!

    You are able to charge at 800mA without any oscillation?  The compact solution was a good resolution to your issues.

    Have you taken multiple batteries through the full charge cycles?

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 60 points

    I watched 5 circuits and two batteries.

    I will extend the test to make better statistics, but I'm already so happy.

     

    Reagards,

     

    Fulvio