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BQ24650 / Does device have a threshold to battery voltage?

ACGUY
Guru 11170 points
Other Parts Discussed in Thread: BQ24650

Hi all,

Please let me know about BQ24650.
Our Customer evaluating this device now.

When Vfb is lower than 2.1V, this device doesn't fast-charge.
However, when Vbat is 0.1V higher, it will be fast-charge.

To voltage low, why doesn't it a fast-charging?
Trigger of mode changing is Vfb or Vbat?

Best Regards,
Yoshitaka Nagai,



6011.BQ24650.pdf

  • 0
    Intellectual 265 points

    Hi Yoshitaka ,

    The BQ24650 will adjust the output current as he reaches the battery programmed voltage ( With the VFB resistors). So its a relation between the two signals (The sensed battery voltage and the current delivered) The current delivered is controlled by the control system of the BQ24650

    Take a look at this plot that I take

    (Left axis in mA and right axis in Volts)

    In this charging profile, as you can see in point #1, the voltage is reaching 2.1 V, but is not there yet (Take ~1.95V as referece).  It is until the point #2 that the system reaches 2.1. Also note how the current behaves.

    The transition from ~1.95Volts to 2.1 volts (final voltage) can take as long as 2-3 hours in small batteries (5Amp hour to 20 Amp hour 12 volt) to up to 10 hours in bigger batteries. 

    To continue to charge maybe you can change the configuration in the Term Enable pin but Im not quite sure if it will work 

  • 0 in reply to Victor Vargas
    Guru 11170 points

    Hi Alb,

    Thank you for reply.
    Sorry, my attached file has old information, so I'll update it.

    1st,
    Our customers had tried fast charge to battery got low voltage (Vbat=2.05V).
    Vfb didn't reach to 2.1V, but BQ24650 didn't start fast charge.
    When they raised Vbat to 2.15V, BQ24650 did start fast charge.

    2nd,
    They thought that, Vfb voltage as be higher started fast charge.
    They added 27k resister.
    However, result was the same as the [1st].

    Please let me know about reason for BQ24650 didn't start fast charge at Vbat=2.05V.

    Best Regards,

    Yoshitaka Nagai

     0523.BQ24650.pdf

  • 0 in reply to ACGUY
    Intellectual 265 points
    Mr Nagai,

    Is it possible to describe a little bit more the problem? Also if you are using the Eval board or your own design ?

    Thanks
  • 0 in reply to Victor Vargas
    Guru 11170 points

    Hello Cosvar-san,

    I can't make a more detailed description.
    I haven't EVM.
    However, I can not understand about this device does not to fast-charge though it is less than VFB <2.1V.

    Regard

  • 0 in reply to ACGUY
    TI__Expert 5565 points

    Yoshitaka-san,

    VFB is not equivalent to VBAT. VFB is a resistor divided voltage of VBAT. Therefore, if your VBAT = 2.05V, that means the bq24650 is sensing on the SRP pin that as a battery short and will stop charging. You will have to raise the battery voltage to ~2.2V to come out of battery short fault to charge. See the following section from the datasheet:

  • 0 in reply to Smriti B
    Guru 11170 points

    Smriti-san

    Thank you for your reply.
    Our customer was confirmed by actual equipment that your comment is correct.

    Thanks,
    Yoshitaka Nagai.