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BQ25890 Max Charge Adapter

Ganesan Manikandan7
Intellectual 285 points
Other Parts Discussed in Thread: BQ25890, BQ25890H

Hello Sir/Madam,

I am using the BQ25890 charger to fast charge a 1S 2P Li Polymer battery that is 7.2Ah in capacity. I have two questions:

1. I would like to understand if there are any special USB power adapters (wall warts) that incorporate the TI Maxcharge algorithm so the handshake can be completed without hiccup. Currently I am using a QC 3.0 Qualcomm quick charge adapter and the charger reads it as a "HVDCP" and sets input current limit at 1.5A (REG00[0:5]). I want to set the input current limit at 3.25A (USB DCP) so that I can perform autonomous charging cycles.

2. I would like to know if the charge time is adjusted based on the battery capacity because I see that charging cycle takes forever to complete. Theoretically, a 7.2Ah at 3.5A charge rate should be completely charged within 3 hours time, but I see the charge time is around 4 hours. Even if I plug in a 3.8V battery (about 50% charged, I see that the charge time is still more than 3 hours) The current seems to drop ever so slowly. Is it possible that the software driver is programmed to do such a thing? Or the resistance of my design is so much? The CC-CV transition seems to occur quicker than expected.

Please enlighten me! Thanks,

Ganesan. M 

  • 0
    TI__Expert 8230 points

    Hello Ganesan,

    Most HVDCP adapters that use the QC3.0 protocol are rated to 1.5A instead of the 3.25A of a DCP. This allows them to have a smaller transformer and when the application requires higher currents, the protocol allows the output to be adjusted to a higher voltage to meet the power demand. Depending on which type of QC3.0 adapter you have (Class A or B) the adapter can step up to 12V or 20V accordingly. This is why the bq25890 sets the input current limit to 1.5A instead of 3.25A. At the present time, there are no adapters that include the MaxCharge algorithm.

    Charge time is not adjusted autonomously based on charge capacity. We allow the user to set the charge current based on their criteria and this way the charge time can be estimated accordingly. Like you mentioned, high impedance along the charge path can affect the transition between the CC and CV portion affecting charge time if the CC portion is too short. Have you experimented using the IR compensation feature on the charger? This feature is meant to help mitigate the effect of the impedance along the charge path to help stay in CC longer and regulate the charge voltage closer to the target.

    Also, if you are working with QC3.0 I recommend reviewing as well the bq25890H, which has an integrated programmable D+/D- driver that helps you emulate the handshaking protocol with a HVDCP adapter to allow you to get the most out of the adapter while optimizing efficiency as well. We have an app note that discusses this in more detail.

    Hope this helps.

  • 0 in reply to Fernando Lopez
    Intellectual 285 points

    Fernando, Thanks a lot for the quick response. Yes it helps.

    I was able to play around with Reg 08 and increase the CC time and charging is fine now.

    I have a concern. I understand the BQ2589x is tested and verified to work with QC 2.0 certified chargers. If this is right, then I am seeing contradictory results. Every time I plug in a QC 2.0 based charger, I see only a 5V at VBUS input. However when I use any QC 3.0 based charger, I am seeing either 9V/12V at VBUS. Does this make sense to you?

    Thanks!

    Ganesan

  • 0 in reply to Ganesan Manikandan7
    TI__Expert 8230 points

    Hello Ganesan,

    Ganesan Manikandan7 said:
    I was able to play around with Reg 08 and increase the CC time and charging is fine now.

    Glad to hear this.

    Regarding the QC 2.0 vs 3.0, this makes sense. It is to my understanding that QC2.0 adapters default to 5V output initially and then step up when needed. QC3.0 in the other hand, defaults to 9V and if high voltage is enabled, it should default to 12V.