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Original question:

BQ25120A: LS/LDO output voltage

BQ25120A: How to set the charging current of BQ25120A

Lumina Gui
Genius 3055 points
Part Number: BQ25120A
Other Parts Discussed in Thread: TPS7A02

Hi Sir,

We konw that bq25120A is a low IQ highly integrated battery charge management solution for wearables and IoT, and one of our project have used it for design.

But we have some question about it, as follows:

  1. Our battery is 30mAh, are ISET resistor is suitable to set 7320ohm so that charging current is set to 27mA? (instead of 3920ohm for 50mA).
  2. During the CE safety test, there are "single component fault test" applied. (Test will short & open for every component.)

Case 1.    While they test for the BQ25120A, They short A2 to B1. (They suppose BQ25120A damaged.)

                Then it draw a very large current to the battery.

                How can we do to solve such safety test?

Case 2.    While I short C17 capacitor, current draw around 310mA. under the attached setting, why the BQ25120A do not cut the circuit?

                Why the over discharge protection haven't cut the large current draw?

                Are our setting have problem?

I added the circuit schematic to the below, and hope it can do some help for you to analyze the problem.

Thanks,

Best Regards

  • 0
    TI__Mastermind 19195 points

    Hello,

    1. Our battery is 30mAh, are ISET resistor is suitable to set 7320ohm so that charging current is set to 27mA? (instead of 3920ohm for 50mA).   - This is the correct setting, yes. 
    2. Case 1 is shorting the input directly to battery, you could add back-to-back diodes between the pins to prevent this. One diode would not be enough as there would be a short in the Vin < Vbat condition.  For case 2 was this with the adapter present or running off battery? The max current off the SYS rail is limited by I(LIMF) 

    Best regards,

    Nick

  • 0 in reply to Nick Brylski
    Genius 3055 points

    Hi Nick,

    Thanks a lot.

    But I still have some questions about the case1 in your answer, as follows:

    Can you give more information for the solution? What is back-to-back diode and how does back-to-back diode works in our case? Any suggestion part can be provide for reference?

    Thanks,

    Best Regards

  • 0 in reply to Lumina Gui
    TI__Mastermind 19195 points

    Hi Lumina,

    Placing a diode like this one between In and battery may work: https://www.ti.com/product/TPD1E6B06

    May I know what CE safety test you are looking to pass? We have passed IEC 62368 G.9 with this device and did not need this diode in place to pass the test.

    Best regards,

    Nick

  • 0 in reply to Nick Brylski
    Genius 3055 points

    Hi Nick,

    Thanks for your reply. Actually, we are looking for pass the single fault condition test. 

    As previous said, They short A2 to B1, How can TI pass the test if it's short A2 to B1 the without diode? Are there any condition?

    Regarding your previous reply mentioned that BQ25120A have passed IEC 62368 G.9 with this device and did not need this diode in place to pass the test, did it relater to this part as follows:

    If then, do you have any valid cert. and test report of IC about the "IC current limiters" for evaluation?

    Thanks,

    Kind Regards

  • 0 in reply to Lumina Gui
    TI__Mastermind 19195 points

    Hi Lumina,

    I will contact you offline to share the report.

    Thanks,

    Nick

  • 0 in reply to Nick Brylski
    Genius 3055 points

    Hi Nick,

    Thanks a lot. While I still have two question for my project as follows:

    1. Can you also provide the CB Cert  together? (For the CB report, Cert vendor checked is OK, they will stop to short the Input to output.)

    2.  For C11 issue, we will replace 1cap with 2cap in series to against the single fault test, as shown below:

    As Cert vendor point out that IEC62368 test will short every port of IC. For BQ25120A, vendor will also short Bat1/Bat2 to A1, D5, A5.

    In our circuit, we also had a TI - LDO TPS7A02. It also have a port to connect the Battery. Thus it also needed to test for the single fault test and vendor will also short the port Pin3/4 to Pin2/5(GND).

    For such single fault testing, how can we solve & get safety test pass?

    Thanks,

    Best Regards