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BQ25611D: there is audible noise come out from BQ25611D when battery connect to a PFM boost

Part Number: BQ25611D

Hi Experts,

In customer's system they use a BQ25611D as a charger for battery, and also the battery connect to a PFM boost SY7901 for Audio amplifier power supply.

when the PFM boost SY7901 work at light load, the switching frequency will drop to audible frequency range, in this case there is audible noise come from BQ25611D chip (not from the PFM boost).

this issue can be repeated on BQ25611D EVM using electronic load drawing transient current load at audible frequency , fox example 0A~2A transient load @1Khz-3Khz.

another issue is the charger BQ25611D can't terminate due to peak current draw by PFM boost is higher than termination current.

can you help to provide solution to fix this two issues?

  • Hi,

    1. To avoid audible noise, please disable PFM operation by PFM_DIS (REG01[7]).

    2. Where is the PFM boost SY7901 connected?

    Thanks,

    Ning.

  • HI Ning,

    1. the BQ25611D is working in the buck mode, switching frequency is 1.4Mhz at issue occurs.

    2. the boost SY7901 connect to battery, battery connect with BQ25611D's output. so the boost SY7901 will draw pulse current from battery and BQ25611D on the audible frequency when it work in light load. in this case , the audible noise come out from BQ25611D.

  • Hi,

    1. What are the charger operating conditions such as VBUS (voltage at VBUS pin), IVBUS, VBAT (voltage at BAT pin), IBAT, VSYS, ISYS. VBATSNS (voltage at BATSNS pin) when audible noise occur?

    2. Charge termination current is based on the current flowing through BATFET Q4. Referring to Figure 10-1. BQ25611D Application Diagram on the d/s, load should be connected to SYS pin not BAT pin in order to control the charge current accurately.

    Thanks,

    Ning.

  • Hi,

    We have not heard back from you for a while. The thread is considered solved and closed.

    Thanks,

    Ning.