• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 63 subscribers
  • Views 186 views
  • Users 0 members are here
Support feedback
Options
Options
Related

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.

BQ24075: CHG pin stays high impedance even when charging battery

Zhiyong Li (FT)
Expert 2910 points
Part Number: BQ24075
Other Parts Discussed in Thread: BQ24079

Tool/software:

Hi,

In one of our designs, the CHG pin on BQ24075 is connected to an INPUT pin (with internal pullup to VCC, 3.3V) on MSP430. If everything works as intended, the INPUT pin on MSP430 shall read low when BQ24075 is charging li-ion battery. But when we test the first batch of PCB, the INPUT pin on MSP430 always reads high, even we know for sure battery is being charged.

What did I miss here? Please advise.

Thanks,

ZL

  • 0
    TI__Mastermind 31550 points

    Hi ZL, 

    Please see my comments below. 

    Firstly, in your design is the /CHG pin being connected to MSP430 pin with internal pullup via a resistor in range of 1Kohm to 100kohm? It is not recommended to connect /CHG pin to a pullup rail directly. 

    I would also like to point out that /CHG pin will remain high for any recharge after termination. This is stated in table 9-2 in the datasheet. Is it possible you see /CHG pin read high due to battery charging again after an initial termination? 

    Are you able to take a waveform showing input source plug in voltage at IN pin, /CHG pin voltage, and charge (or input) current? Expectation is /CHG will drive low once charge starts following an adapter plug in. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Expert 2910 points

    Hi Mr. Kreger,

    Thanks for your reply.

    1) Unfortunately, the CHG pin on BQ24075 is connected to MSP430 INPUT pin directly without a resistor in between. We will add it in next iteration. But I doubt this causes CHG pin to remain in high impedance when charging.

    2) I did notice table 9-2. We tried to deplete the battery to under 3.5V then unplug the adapter and plug it back. CHG pin stays high impedance after such procedures. In our design, the li-ion battery is soldered onto PCB therefore always connected to BQ24075 circuit. In such a setup, will later on charging always be considered "after initial termination"? That's my primary suspicion.

    3) On a side note, what is the benefit of terminating at 4.1V as in BQ24079? In our previous design, if our devices have adapters always plugged in, some of the li-ion batteries will severely degrade after several years. Will BQ24079 help alleviate the battery degradation with constant full-charge?

    Best,

    ZL

  • 0 in reply to Zhiyong Li (FT)
    TI__Mastermind 31550 points

    Hi ZL, 

    Please see my comments below. 

    1)Are you able to perform any testing with a modified board where /CHG is connected to pullup rail via resistor? The BQ24075 does not have a known issue with /CHG pin function and has been released to market for over 10 years. 

    2)There is no issue with having battery connected at all times. When adapter is unplugged then plugged back in that is considered a new charge cycle. 

    3)In general reducing the full charge voltage can help with battery degradation, but I recommend you check with your battery manufacturer to determine if changing from 4.2V full charge voltage to 4.1V will benefit the specific battery you use in your system. 

    Best Regards,

    Garrett

  • 0 in reply to Garrett Kreger
    Expert 2910 points

    Hi Mr. Kreger,

    I will order a revised board to test CHG with resistor in between, and get back to you if I find anything.

    Thanks for your response again.

    Best,

    ZL