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BQ51050B: Issue uisng wireless charging and boost converter

Michael Bajema27
Prodigy 100 points
Part Number: BQ51050B
Other Parts Discussed in Thread: BQ500212AEVM-550, TIDA-00669, TPS63050

I have a design based on TIDA-00329 using the BQ51050B.  I have a boost converter (MCP1624) and an LDO coming off the Battery line in addition to the BQ1050B. I have attached a picture of the schematic for the LDO and boost converter.

I am unable to get the battery to charge while the boost converter is attached if the battery voltage is very low and engages the Li-poly's low voltage cutoff protection circuit. It does not matter what voltage is on the enable pin of the boost converter. If I take off the boost converter, I can charge the battery even when the low voltage cut-off has engaged. If the battery low voltage cut-off does not engage, I can charge the battery with the boost converter attached. I can charge the battery from any state when it is directly connected to the TIDA-00329 design or BQ41040BEVM-764  I have normal operation if the battery has been charged elsewhere and attached to this circuit.

I am using a BQ500212AEVM-550 as a transmitter. In all the above cases, the green LED on the transmitter blinks indicating power transfer. In the case of the boost converter is attached and the battery's low voltage cut-off is engaged, the transmitter still thinks it is transmitting but the voltage on the battery only goes up to 0.5V to 0.6V and very small current (about 5 uA) is found going between the BQ51050B and the battery.

I have tried using the BQ41040BEVM-764 to adjust current limiting and termination settings but have had the same results. I am baffled by this as there is a boost converter attached similarly in TIDA-00669 500mA wireless charger Booster Pack with Gauge Reference Design. Do I need the Gauge to better isolate the battery for this to work? It seems like the charger isn’t really trying to get to the charge voltage.

  • 0
    Prodigy 100 points
    I was wrong about the current measurements. I get 18mA out of the BQ500212AEVM-550 when the boost converter and battery are connected. This happens when Ibulk is set to 200mA as well as when Ibulk is set as 79mA.
  • 0 in reply to Michael Bajema27
    Prodigy 100 points

    It has been a while and I still have not had any response. Why would my Qi charger get stuck at ~0.6V and ~18mA even though the Ilim is set much higher when the battery is attached to a boost converter?

  • 0 in reply to Michael Bajema27
    TI__Guru 65796 points
    Hi Michael
    The problem is possible caused by the bq51050 Battery Short Protection feature or Precharge feature, See Section 9.3.4.1, Precharge Mode.
    Both will limit the available current at start up.
    The boost converter load on a low battery can possibly reduce the voltage and trigger the above condition.

    MCP1624 boost convert is designed to start with very low input voltage, typically 0.65V. This feature is probably placing a load on the battery charger and pulling the voltage below Battery Short Protection, 0.8V.
    The tps63050 has and under voltage lock out of about 2.7V, avoiding the Battery Short Protection.

    A possible option is to inhibit the MCP1624 until battery voltage is higher.
  • 0 in reply to Bill Johns
    Prodigy 100 points
    This makes sense to me. I found that I was using a uP that was pulling the enable line high during startup so even though I thought I was disabling it, I wasn't. I'll try this out and then verify your answer.