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BQ51050B: Active load attached during charging

Wilco van den Brink
Prodigy 30 points
Part Number: BQ51050B
Other Parts Discussed in Thread: BQ24073, BQ51013B

I'm currently working on a wireless charging module that will be used in a mobile device. The schematic is almost finished (see below), only the calibration of some components still needs to be done.

The only subject I'm missing in the documentation is information about the load attached to the battery (and thus the IC) during charging. In my case I will have the battery and the load/device in parallel connected to the IC, as seen in the image below. The device will be active during charging, with a peak current of 2A. I do understand that the current draw from the device will affect the charge termination, but are there any other issues I need to keep in mind?

  • 0
    TI__Guru* 75676 points
    Hi Wilco
    A couple of the problem you will see with a load connected to the battery.
    1.) Battery charge does not complete, 10 hr times trips. With a load in parallel with the battery the current may not drop low enough for charge complete.
    2.) Deep discharge battery, the bq51050 will supply less current with battery below 3.0V, 20% of charge current. The battery short will only supply 20mA, when voltage is 0.8V. Additional load during this time will make it difficult to increase battery voltage to normal operation.
  • 0 in reply to Bill Johns
    Prodigy 30 points
    Issue 1 was expected, but thanks for reminding me of the second issue. If I make sure that the device is 'off' (drawing a relatively small amount of current) during charging, would that solve these issues? Or is there a better solution for implementing wireless charging in this situation? Now I'm curious how this problem is solved with devices like smartphones.
  • 0 in reply to Wilco van den Brink
    TI__Guru* 75676 points
    For a deep discharge battery condition a couple of things will help. UVLO of the load device, many of the switchers have this and you would want to pick a device with start up voltage near 3.0V. If you have some device that could disconnect the load when battery voltage is low, control enable of the LDO or Switchers. Best to inhibit operation until battery is above 3.0V.

    The cell phones will use this approach, inhibit load until battery voltage is above 3.0V.
  • 0 in reply to Bill Johns
    Prodigy 30 points
    I've been researching some other solutions for wireless charging with an active load. The one that to me seems to be the best option is a combination of BQ51013B and BQ24073. The BQ51013B will be used to create a stable 5V power supply. The built-in battery charging of my previous solutions is replaced with the BQ24073 which supports Power-Path Management, basically solving the issue I had.

    This solutions looks like it will work, but if I missed anything, I would appreciate any tips. Also, are there any plans for a WPC Compatible Receiver IC that supports both Li-Ion charging and Power-Path Management?