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Original question:

bq25505 VBAT_OK, VB_PRI_ON and VB_SEC_ON signal delay

BQ25505: BQ25505 VBAT_OK keep low

Star Xu
Genius 9645 points
Part Number: BQ25505

Hi

The customer design with BQ25505, they set Vbat_ OV is 4.5V, Vbat_ OK_ HYST is 4.2V, but it is found that the super capacitor can be charged to 4.5V, while Vbat_ OK is always low.

Attached the schematic for your reference.

They use the DC input to charge the super capacitor, and disable MMPT and sampling.  

The super capacitor can be charged but VBAT_OK keep low.

Please give some suggestions about this query.

Thanks

Star

  • 0
    TI__Guru**** 150055 points

    Hi Star,

    I get OK_HYST=4.3V from one set of the resistors in the schematic. 

    The issue could be the parallel, parasitic ~ 1M resistor from solder flux as explained in datasheet section 10.  There are 2 ways to test:

    1. remove the resistors, clean off the flux and replace there resistors on their edge to minimize surface area for new parasitic resistor

    2. replace resistors with 1/3 - 1/10 the value 

    Regards,
    Jeff