BQ25798: Audible Noise/Disabling PFM Mode

Michael Balourdas

Part Number: BQ25798

Hello,

My customer is encountering audible noise in PFM mode while using BQ25798. I see that PFM mode can be disabled or the PFM frequency can be limited to 25kHz max. However, they want to know if there are any other methods that don't require a command to be sent to the charger every time it is powered on. Is there any other way to disable pfm mode or otherwise limit audible noise?

Thanks,

Michael

over 3 years ago

0 Jeff F over 3 years ago

TI__Guru**** 169636 points

HI Michael,

Unfortunately, no. The default state is PFM enabled for high efficiency at light load.

Regards,

Jeff

0 Michael Balourdas over 3 years ago in reply to Jeff F

TI__Expert 5545 points

Hi Jeff,

Do you know the rough load range where PFM mode kicks in? My customer seems to be in a transition region where it switches between PFM and PWM.

Thanks,

Michael

0 Jeff F over 3 years ago in reply to Michael Balourdas

TI__Guru**** 169636 points

Hi Michael,

PFM transition point is about 300mA of average inductor current.

Regards,

Jeff

0 Michael Balourdas over 3 years ago in reply to Jeff F

TI__Expert 5545 points

Thanks Jeff. Is there any kind of hysteresis?

0 Jeff F over 3 years ago in reply to Michael Balourdas

TI__Guru**** 169636 points

Hi Michael,

Per the designer, not traditional hysteresis. Once in PFM, if any of the regulation loops (input current, input voltage, charge current, charge voltage, etc) fall out of regulation or if there are continuous, back-to-back PFM pulses for 11us, the converter exits PFM and returns to PWM.

Regards,

Jeff

Power management

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BQ25798: Audible Noise/Disabling PFM Mode