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Original question:
Good Morning,
in a previous version of an electronic board that my company is developing, we experienced some issues concerning the input line impedance of VBUS; in the event of a deeply discharged battery, the system turned off, and when external power was applied to the battery charger via USB in order to recharge the battery, it might occur that the input voltage on VBUS would drop and consequently the battery charger would reset, thus not providing a stable output voltage to the system and to the battery; due to these voltage ripples on VBUS, the system would not ever be able to recover and turn back again.
The problem was mainly due to a bad USB cable; additional suggestions on optimal design and layout were also provided by TI's design support team, the last one being the one contained inside the related question linked to this current one.
I understood that the input line impedance is a delicate matter. For this reason, I wanted to ask what is your opinion about adding a ferrite bead on USB VBUS line and/or USB GND pin. The next version of the electronic board will be used for EMC/EMI precompliance testing. The input power for recharging the battery will be provided by an AC-DC wall-plug adapter + USB cable (male type-A to male type-C, 2.0 standard). The main functioning of the device will occur when only the battery supplies the system, however some additional functions may also be performed when the adapter is connected and the battery is being recharged. I'm concerned about possible noise coming from the wall-plug adapter that may enter the electronic board through both VBUS and GND and also through the cable shield. However, ferrite beads would also add additional impedance to the input line and may cause the abovementioned unwanted behaviour.
Thank you. Kind regards.
