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BQ25570EVM-206: Li-ion battery not charging

Evan Risley
Prodigy 40 points
Part Number: BQ25570EVM-206
Other Parts Discussed in Thread: BQ25570

Current setup:

BQ25570EVM-206 board as received, with jumpers in original default positions

datasheet: http://www.ti.com/lit/ug/sluuaa7a/sluuaa7a.pdf 

Indoor low-light solar cell: https://www.digikey.com/product-detail/en/panasonic-bsg/AM-1454CA/869-1001-ND/2165186 

at 240 Lux: OCV = 2.5V  Short-circuit current: 46uA.

Battery:  6SP 585460 2000mAh 3.7V 7.4Wh rechargeable Li-ion

With only the solar cell attached to J2 on the EVM board, I get the following readings:

Vin:

VSTOR and VBAT are the same:

Now with the Battery attached to VBAT (has 3.3V charge on it prior)

Vin:

VSTOR and VBAT are the same:

There is no load on VSTOR or VOUT.  The battery is staying the same voltage as VSTOR.  

JP4 is at 80%.  I have tried 50% and battery still does not charge.

Any ideas?

  • 0
    TI__Intellectual 2050 points
    Hi Evan,

    Without the battery attached:

    How long did you leave the light on the solar cell and let the IC charge? Are you providing the panel with 240 Lux?

    The VSTOR voltage hasn't reached the VSTOR_CHEN threshold so the main boost charger hasn't turned on yet. I suggest let it sit for a long time. The panel you are using is very low power.

    With the battery attached:

    It looks like the MPPT is being measured every 16s as expected and setting the voltage to the right 80% default value. 0.8 * 2.5 V= 2V

    The Vmpp for this panel is 1.5V, so you need to adjust the MPPT resistors so that the MPPT point is set to 60% of VOC. 1.5/2.5=0.6.

    Even then, it will take a long time to charge a 2000mAh battery with 31uA of charge current.

    You may want to consider a larger panel.

    Regards,

    Joe
  • 0 in reply to Joe Stephan
    Prodigy 40 points

    Hi Joe,

    Thanks for the response -- It is what I figured was happening.  

    I have a larger low-light solar panel that has OCV of 5V, but I think I will need to change the resistors on the EVM for it to work, since VIN only allows 4V OCV with the current setup.  The power output of this solar cell is about 5x higher than the small one.

    Solar cell here: https://www.digikey.com/product-detail/en/panasonic-bsg/AM-1816CA/869-1005-ND/2165190 

    I have downloaded and input my values in the bq25570 Design help excel sheet.  Can you take a look and confirm my inputs before I replace these resistors?

    5344.bq25505(70_Design_Help_V1_3.xlsx

  • 0 in reply to Evan Risley
    TI__Intellectual 2050 points
    Evan,

    You're going to want to have the OVP threshold set to the charge cut-off voltage, which is 4.2V. This is actually what the default setting is for the EVM.

    The reason the EVM schematic says 0.1V to 4V for the input is because the OVP is set to 4.2V. If the input goes above 4V with 4.2V OVP, then IC will be forced to sink current to keep the input low enough for normal boost operation. The IC can still handle input voltage up to 5.1V, so no need for concern about the 5V open circuit voltage. Also, the absolute max for the input is 5.5V so you have headroom.

    Vmpp for this panel is 3V, but it looks like you are choosing resistors for Vmpp of 4V. I suggest choosing resistors for 3V instead.

    Let me know if you have any more questions!

    Cheers,

    Joe
  • 0 in reply to Joe Stephan
    TI__Intellectual 2050 points
    Evan,

    Any update on this? I will be closing this thread due to inactivity. Feel free to still post here.

    -Joe