• State TI Thinks Resolved
  • Locked Locked
  • Replies 1 reply
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 203 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.

BQ25570: Overshoots to 8V

cy drollinger
Prodigy 170 points
Part Number: BQ25570

I am inquiring about the BQ25570 wired up as a typical application with a solar cell input. The circuit is very near figure 24 in the datasheet. I have three prototypes and one seems to work, as the battery output rails at 4.17V when enough lite shines on the cells. The other two boards will continue to bang bang at a rate of 3-4Hz with a peak voltage at the battery, not present, of 8V. Once the peak is reached the signal looks like a capacitive disharge. I haveloked over the voltage dividers and their voltage and compared them across all three units, with very near the same results. 

Any suggestion to these two non working units would be appreciated, thank you!

  • 0
    TI__Guru**** 165886 points

    Hi Cy,

    Do you have a minimum capacitance of 47uF ceramic on VBAT even when the battery is removed?  All boost converters need some capacitance at their output to prevent over-voltage.

    If so, do you have the CBYP on VSTOR as close to the IC VSTOR and VSS/GND pins as possible as shown in the layout figure of page 35?  Switching noise has been known to cause problems with regulation (but usually only up to 6V).

    If so, as explained in section 10.1 Layout Guidelines, any solder flux residue that remains after assembly of a high megaohm resistor presents as a parasitic resistor in the megaohm range.  Can you remove the VBAT_OV resistors, clean the board then replace the resistors but stand them on their edge?  Alternatively, you can lower all the resistors by at least 10x.  If either fixes the issue, then it is solder flux problem.

    Regards,

    Jeff