• State
  • Locked Locked
  • Replies 4 replies
  • Subscribers 64 subscribers
  • Views 197 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

BQ25890H: Charge disabled by ferrite bead on VBUS?

HYEONTAEK KOH
Prodigy 40 points
Part Number: BQ25890H
Other Parts Discussed in Thread: BQ27220

Tool/software:

Hi Team, 

recently we added a ferrite bead which has 220 ohm impedance @ 100Mhz band. 

we placed it right before the VBUS trace, but there is a symptom that bead added board (charger IC) is not charging the battery and unable to I2C communication with uC. 

this happens some time passed after charger plugged to board. and those boards have newly added a bead. 

when this happened, voltage on VBUS is same as before, but I2C is just high all the time (previously it was moving). 

again, like I said, only difference is bead in serial of VUSB. 

is there any reported issue which is similar with this? 

Thanks, 

  • 0
    TI__Mastermind 26110 points

    Hello, 

    We have had other customers use ferrite beads in their design without issue. I specifically would not expect a ferrite bead to have any impact on BQ25890H I2C communication.

    To verify there is a battery connected when you are unable to perform I2C communications correct? Can you also help to share a schematic of the BQ25890H portion of your design? 

    Best Regards,

    Garrett

  • 0
    Prodigy 40 points

    Hello Garrett, 

    Yes, the battery connected and there is I2C bus for fuel gauge BQ27220, MCU Attiny3226 and charger IC BQ25890H.

    Here's a part of schematic of charger 

    right now there is bead right before VBUS. and the other things are same with problematic boards.

    Thanks,

  • 0 in reply to HYEONTAEK KOH
    Prodigy 40 points

    Hi Garrett, about the pin STAT of charger, what if we connect that pin to our uC directly? 

    as you can see there is no pull up and no LED. what if we just put that pin like that way, charger will do something weird working?(such as I2C malfunction)

    is this pin originally designed for indicating LED only? or can we use this pin as a input to the uC?

    I checked the signal on that pin with scope and it shows some periodic noise when the battery is charging. if the battery is charged, that pin goes low(0v).

    where these periodic signals come from?

    Regards, 

    Hyeontaek

  • 0 in reply to HYEONTAEK KOH
    TI__Mastermind 26110 points

    Hi Hyeontaek, 

    Thank you for your response. What is the pullup rail for I2C lines? It does not appear to be shown in schematic. 

    Even if ferrite bead caused an issue with input voltage at VBUS the BQ25890H is still able to perform I2C communication when powered by battery only. 

    Regarding STAT pin it is not designed for LED only and can be connected to an MCU. Please keep in mind STAT pin is an open drain output (i.e. it only has the ability to pull pin low to GND). Whether an LED is used or not this pin requires pull up to a logic rail via a 2.2kohm to 10kohm resistor to function as designed. 

    Additionally, STAT pin is an optional connection. Your current connection with no pull up and no LED should have no impact on charger IC's ability to work normally.

    Periodic noise when STAT is being driven low is expected and is not an issue. If you refer to Figures 50 and 51 in the datasheet you will see same noise on STAT in application curves. 

    Best Regards,

    Garrett