• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 390 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.

Original question:

BQ24618: What is minimum difference between Vin and Vout?

BQ24618: Pin 3 of this device was oscillating

Yunfa Yang
Intellectual 515 points
Part Number: BQ24618

BQ24618 is being brought up, after adapter was on, ACDRV pin (pin3, FET gate drive) started oscillating at about 20hz, what could be the root cause?

Thanks,

Yunfa

  • 0
    TI__Mastermind 24075 points

    Hi Yunfa,

       Can you show ACDRV on a scope capture? Also are you using powerpath function, i.e do you have a FET being driven by BATFET? If so can you overlay ACDRV, BATDRV, VCC and SRN on the same scope capture?

  • 0 in reply to Kedar Manishankar
    Intellectual 515 points

    1. ACDRV

    2.BATDRV

    3.SRN

    4. All together (Ch1-ACDRV-Ch2-BATDRV-Ch3-VCC)

    Hi Kedar,

    Please see above captures. thanks for help.

    Yunfa

  • 0 in reply to Yunfa Yang
    TI__Mastermind 24075 points

    Hi Yunfa,

       There seems to be a lot of fluctuation on the SRN node which is not ideal. The ACDRV oscillation is because your VCC is too close to SRN, causing the charger to cyclically enter and exit SLEEP mode. ACDRV and BATDRV are asymmetrical and only one will be on at a time, so when the SLEEP condition is hit ACDRV will turn off, BATDRV will turn on. As ADCRV off causes input power supply to be disconnected, looks like the VCC voltage is enough to satisfy leaving SLEEP mode, and BATDRV will turn off and ACDRV will turn on. I would refer you to section 10 Power Supply Recommendations of the datasheet for recommended voltages of VCC w.r.t SRN. You can add C17 and C19 from the EVM user guide schematic to help filter noise on SRN but I am not sure why you are seeing such a high fluctuation.

  • 0 in reply to Kedar Manishankar
    Intellectual 515 points

    Hi Kedar,

    Thanks for quick answer.

    Actually when the high fluctuation was seen, battery was not connected yet, my understanding the charging was supposed to be idle with battery's absence, or something like always in sleep mode.  in such condition, the fluctuation seems more strange, might the noise be the cause?

    Regards,

    Yunfa

  • 0 in reply to Yunfa Yang
    TI__Mastermind 24075 points

    Hi Yunfa,

       Ah I didn't realize battery was disconnected from test condition. This explains the oscillation frequency. IC is undergoing battery absent detection, and SRN will oscillate between VREG (max charge voltage set by resistors) and VLOWV (precharge to fast charge threshold). As SRN reaches VREG, the voltage difference between VCC and SRN satisfies SLEEP mode condition, causing ACDRV to turn off, and as battery is not detected, SRN will then fall down to the precharge-fast charge transition voltage, satisfying the SLEEP exit condition, which further caused BATDRV to turn off and ACDRV to turn on. You can see battery absent detection in figure 17. of the datasheet. Root cause is input adapter voltage is too low to fully charge battery without entering SLEEP mode.

  • 0 in reply to Kedar Manishankar
    Intellectual 515 points

    Thanks Kedar, you were correct, the root cause was that full charge voltage set point was higher than adapter.