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BQ24166: Switcher output bad if USB voltage is higher than 5V

Jarrod Cook
Expert 1100 points
Part Number: BQ24166
Other Parts Discussed in Thread: BQ25606

Hello,

I am having some strange issue with BQ24166 in that if the USB input voltage is any higher than 5V (this threshold varies slightly board to board but it is right around 5V) the output becomes very unstable.  Here is what i mean:

Switcher Voltage output (VBAT from circuit below) when USB < 5V:

Switcher Voltage output (VBAT from circuit below) when USB > 5V:

Both scope plots above you are looking at a time when i power on the board at the trigger point, you can see the < 5V image there is basically no droop on the output and it just stays pretty consistent, if i zoom in i can see a miniscule droop during the inrush current.  For the USB > 5V you can see the output is already lower and highly unstable then when i power on the board the inrush current pulls the voltage low enough to cause the board to brown out and turn off allowing the voltage to rise again.

I am not sure what the issue is, it is fine at 5V and lower but the problem is i can't control the voltage supplied by a given USB port and often times they are slightly above 5V, so when that happens the board just won't run without a battery.

Here is my circuit:

Any ideas what i have done wrong or what the problem could be?  Note i have tried swapping C99 to a 47uF capacitor to no avail.

Thanks,

Jarrod

  • 0
    TI__Guru**** 158501 points

    Hi Jarrod,

    DRV pin requires at least a 1.0uF capacitor.  Since DRV provides power to all of the logic circuits, if it isn't stable, I can't predict IC operation.  Also, R208 is too small.  ICHARGE = KISET/RISET where KISET=490Aohm.

    Also, since it appears that you are using only 1 of the 2 inputs, just curious why you chose the BQ24166?  The BQ25606 might be a better choice.

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 1100 points

    Jeff,

    Thank you so much for the quick response!  The DRV capacitor definitely fixed the issue I must have missed that!  Also i fixed RISET I think I misread KISET as 490mAohm so my bad there. 

    We originally had a design with both USB and AC powered input but the plans changed, and also because we 24166 allowed us to change the current limit using pins from the CPU.

    I may take a look at BQ25606 for the next rev; however, it appears that this part handles the USB negotiation which is good BUT i also need to be able to have my CPU (am335x) act as USB Host and communicate over these lines as well, so it looks like maybe this is a no-go?  Unless there is someway to still use the D+/D- lines for communication with my CPU as host as well?

    Thanks,
    Jarrod

  • 0 in reply to Jarrod Cook
    TI__Guru**** 158501 points

    Jarrod,

    For all of our chargers with D+/D-, the input detection only runs for the first 1-2s following input voltage power up.  After that, the lines go HiZ so you can use them for other comms. 

    Regards,

    Jeff

  • 0 in reply to Jeff F
    Expert 1100 points

    Jeff,

    Oh nice, i didn't realize that!  In that case it sounds like switching to that part is probably my best choice for the next rev of this board!  Thanks for the information and thanks again for all the help on the quick fix, i greatly appreciate it!!!

    Have a great night!

    Thanks,

    Jarrod