• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 62 subscribers
  • Views 959 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.

BQ25886: Charging current lower then the set value

Angelo Panev
Prodigy 40 points
Part Number: BQ25886

Hello everyone,

This is my problem. I am using BQ25886 for building a USB powered charging circuit on my device. I have a 2 cell Li-ion battery with 7.4 V nominal voltage. The measured charging current is 750 mA instead of the set value of 1.2 A. I am using several different wall adapters with maximum output current of 2.4A.

I am attaching the schematics of my charging block.

The input current is set to the maximum value of 3A via shorting ILIM pin to GND (R15 = 0 Ohm).

The charging voltage is set to 8.2 V via shorting VSET pin to GND (R16 = 0 Ohm).

The charging current is set to 1.2A (R17 =4k7)

Since I am not using a thermistor, I connected the TS pin to a voltage divider, that sets the TS voltage to 50% of the REGN voltage. According to page 9 from the datasheet, this voltage should be between 45 and 68 % of VREGN in order to have a full charging current. I tried also the divider configuration from page 21 (R24 =4.7k, R25 =27k in parallel with 10k, resulting in TS voltage =60% of VREGN) and the charging current was still 750 mA.

Additional information is that I have the data lines of the USB connected to an FTDI USB to UART translator chip. However, disconnecting the FTDI didn’t fix the charging current.

I have tried also to bypass transistor T3 from my false polarity protection circuit but it had no effect neither. Instead of the fuse R14 I have a 0 Ohm resistor.

I hope my description of the schematics and the issue is detailed and clear enough. I am looking forward for any ideas and suggestions. Thank you in advance.

 

Best Regards

Angelo

  • 0
    TI__Mastermind 32525 points

    Dear Angelo,

    Could you please measure and confirm the input current when you are only charging at 750 mA? How much of a system load do you have when the battery is charging? This could lower the charging current.

    Thanks,

    Mike Emanuel

    Please click "This resolved my issue" button if this post answers your question.

  • 0 in reply to Michael Emanuel35
    Prodigy 40 points

    Hi Mark,

    Thanks for your suggestion. The input current is around 1.4A, which makes sense. Do you see anything wrong with my schematics?

    Angelo

  • 0 in reply to Angelo Panev
    TI__Mastermind 32525 points

    Angelo,

    I need to confirm a few things.

    First, what is the voltage at the VBUS pin when you are pulling the 1.4 A? If it is around the VINDPM of 4.3 V, your cable may be dropping more voltage than expected or the adapter may not be functioning to the performance advertised.

    Second, it doesn't look like this in the schematic, but do you short D+/D-? If so you may be triggering ICO because a DCP is detected. This could again limit your performance.

    Thanks,

    Mike Emanuel

    Please click "This resolved my issue" button if this post answers your question.

  • 0 in reply to Michael Emanuel35
    Prodigy 40 points

    Hi Mike,

    Thanks for the reply. Some minutes ago we found out that the problem is exactly the cable. With another cable (rated for 2 A) I got 1.1 A charging current.

    The issue is now solved. Once again thanks for the help!

    Angelo