we have a combination of bq24297 used as power manager + charger for a battery operated handheld.
VSYS drives (in parallel to our microcontroller) a tps2505 to provide two external USB host ports with 5V. We do not see any malfunction of the bq24297 or tps2505 so we assume that the circuits are basically ok.
But this setup makes audible noise. Noise sounds like a mosquito and is audible up to a distance of 1 - 5cm (depending on scenario and environment noise).
It depends on the USB host device plugged it. It also depends on battery installed or charger only. Or no charger and battery. It changes pitch and tone color after plugging in some USB device on the tps2505 side (as if we can "hear" the USB negotiation/enumeration).
But there is also noise if nothing is plugged into the USB ports.
We even have a barely audible noise when no battery is installed and only VBUS voltage is provided to the bq24297 and everything else is off. The sound has the same rhythm as the LED is blinking we have connected to the STAT output.
We have chosen the inductors as recommended by the data sheets (LPS4018-222MRB for the tps2505 and MDMK2020T1R0MM for the bq24297). Output capacity of the bq24297 is ca. 208µF and 120µF for each output of the tps2505.
Anyone else who can share similar experiences? Any suggestions how to trace down and solve the real issue (inductors? PCB layout?)
