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BQ25790: 2Khz switching frequency noise in SW

Yishan Chen
Intellectual 1670 points
Part Number: BQ25790

Tool/software:

Hi Jeff,

When BQ25790 is negotiated to 12V in and when customer pull down CE, they found there is a 2Khz switching noise add into the SW point, this cause the audio noise, Do you have any insight on that?

Please check the waveform:

The noise is occurred after second time the CE goes low.

Yellow: Vsys, Blue: CE, purple: SW1

Thank you,

Yishan Chen

  • 0
    TI__Guru**** 165986 points

    Hi Yishan,

    Is PFM OOA enabled or disabled?  If PFM is disabled so the noise go away?  If not, what is the battery voltage, charge current and system load?

    Regards,
    Jeff

  • 0 in reply to Jeff F
    TI__Intellectual 1670 points

    Hi Jeff,

    I already told them to disable OOA and PFM mode, but the noise still here.

    The battery voltage is 7.8V, system voltage is 8.6V, charging current is 2A, system current is about 150mA

    Thank you

    Yishan Chen

  • 0 in reply to Yishan Chen
    TI__Guru**** 165986 points

    Hi Yishan,

    The noise is from the small footprint ceramic capacitor's on PMID and/or SYS piezo-electric effect.   Is 2A charge current flowing?  I do not expect to see PFM pulses at such high current.  There is a known issue where at ISYS+IBAT=150mA-300mA where the charger repeatedly moves between PFM and PWM.  But if PFM is disabled and you still hear the noise, this is not the issue.  Is the second plot above (excerpt below) with PFM disabled?  Can you ask customer to repeat but zoom in so I can see at least one pulse in each mode from the circled area?

    Regards,

    Jeff