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Weird battery boot up effect from wireless charging from a drained battery

Sean H
Prodigy 60 points
Other Parts Discussed in Thread: BQ500212A, BQ51050B, BQ500212AEVM-550

Hi, 

We are working on a device that will incorporate wireless charging. We are using BQ500212A for the transmitter and BQ51050B for the receiver. Our schematics are all based on the evaluation modules. The charging receive is incorporated into our device that also contains microcontroller, wireless module, and other components. The battery we are using is an 1850mAh lithium-ion rechargeable battery, and our device draws about 180mA current. 

A problem we are seeing happens after the battery drains to the point where device shuts off. After this occurs, when we put the device with charging receiver onto the charging transmitter, the device does not boot up properly. The battery appears to be charging, but the microcontroller and wireless module are not functioning properly. We would then have to unplug and plug in the battery again (while the device is on the charging transmitter) for everything else to boot up.

I probed the battery input pins, and I’ve attached the oscilloscope shot of the battery boot up effect:

  

When I placed the device to charging, this is when the battery ramps up, as shown in the attached picture. But there is a saw-toothed ripple happening for 10ms before the voltage reaches the full 3.3V. I am thinking this is what is causing the other components to not turn on correctly. 

I tried increasing the current limit, Ilim, to 1.4A (originally at 1A), but this still does not fix the drained battery boot up problem. The battery and the charging receiver chip got really hot instead.

What could be causing this? Are there settings on the BQ51050B chip that deals with this?

Thanks for the help!

  • 0
    TI__Genius 14890 points

    Sean,

    Have you tried with a standard Transmitter and not the one you designed?  This is just to confirm that it's not some sort of interaction problem with the new TX and new RX.

    The included plots are at the battery input.  Is there anything between the bq51050B BAT pin and the battery input?

    I'd like to see the schematic around the bq51050B and battery.  Also, how the system is receiving its power.  If the system is powering up and the battery is charging but both are getting power from the bq51050B then both systems will be fighting for the limited (1A) power from the bq51050B.

    Is there a way to monitor the current coming from the bq51050B to the battery and system? 

    Can you get plots of the RECT pin and BAT pin from the bq51050B?

    Regards,

    Dick

  • 0 in reply to Dick Stacey
    Prodigy 60 points

    Hi Mr. Stacey,

    Thanks for the response.

    1. We have three TI transmitter evaluation boards (two BQ500212AEVM-550, one BQ500210EVM-689). I did try it on all the eval boards, and saw the same results.

    2. Between the BAT pin and battery input, we hooked up the connection to one 3.3Vout regulator (ADP2504ACPZ-3.3), one 5Vout regulator (ADP2504ACPZ-5.0), and various capacitors. The caps are tied to ground, and the regulator inputs share the same node as the BAT pin. So the BAT pin should have the same result as the battery input pin.

    3. I’ve attached the schematic for bq51050B and battery input, and the two regulators that will deliver the 3.3V and 5V power to the rest of the components.

    5618.US Transmitter Rev 1-b.PDF

    4. The current coming from bq51050B to the battery and system (when battery is drained) goes up to around 1.2A, and drops slowly. Current draw from the battery to system is about 0.18A.

    5. I can get the RECT pin plot, but currently the PCBs with this charging problem were sent offsite for some testing and demo. So when I get them back next week, I will upload the plot. The BAT pin plot should be the same as the battery input pin plot.

    As a fix for this problem, can we somehow isolate the system from the battery? Does a current limiter work here? Do you have a device that does this?

  • 0 in reply to Sean H
    Prodigy 60 points

    I just want to add new plots of the battery input pin and RECT pin.

    The battery input pin is shown below:

    This is when I put the device onto our charging transmitter. The battery on the device is of course drained at this point. This causes a screeching noise in our 5V regulator, and the ringing waveform shown here. The noise goes on for about 5 seconds, stops for 1 second and resumes for another 5 seconds. Sometimes this effect goes away completely, and a clear voltage level will be shown. But it is not consistent on when and how this ringing will go away. And even if it does go away, our other components would not work because of this improper boot up.

    The below pictures show the RECT pin (when the drained battery is charging and having the sawtooth ringing):

    And the below shows the RECT pin when the battery charging is normal (stable battery voltage):

    Our battery is a Lithium-ion battery, EXPOCELL PL-103450, with an automatic cut-off voltage of 2.75V. It also has a protection circuit built-in. The protection circuit is just to prevent over charge/discharge.