[STUSB4500] Can I remove the typical circuit on STUSB4500's VBUS_VS_Disch pin?

[AEber.3]

Hello,

In the STUSB4500 datasheet, there are 2 typical circuits. Both of them include a circuit for the VBUS_VS_Disch pin. Components are D4, C4, R1 and R4. Based on the information in the datasheet, this circuit should be here to limit the discharge current to 50mA. Moreover, this pin is used by the chip to sense vbus voltage.

What's the purpose of the diode D4?

Discharge feature is optional and can be disabled in NVM. I want to disable it in my application, do I still need to link VBUS_VS_Disch to VBUS to sense VBUS? If so, what is the minimal circuit, do I need some resistors?

Thanks,

Arthur

[Winfred LU]

When VBUS is charging up, D4 switches ON and charges the capacitor.

The minimal circuit for VBUS_VS_Disch would be:

[AEber.3]

Thanks for sharing the minimal circuit.

Just for my understanding, in the initial typical circuit, what's the purpose of the circuit with C4, D4 and R1? Is it some sort of protection because VBUS will sense the capacitor voltage instead of VBUS directly?

Are R1 and R4 a voltage divider? Or R1 is here to "finish" C4 charging when diode is switching off?

Thank you,

Arthur

[Winfred LU]

They are the VBUS discharge circuit.

When VBUS is charging up, D4 switches ON and charges the capacitor in a very short time.

The fluctuations in VBUS will be filtered by the C4 and R1.

The voltage is monitored with R4.

During there is a significant drop in the VBUS (cable disconnection, power down transitions, hard reset and error recovery state), the VBUS discharge path is activated on the VBUS_VS_Disch pin.

[AEber.3]

Oh ok, R1 and C4 act as a filter. Without D4, the capacitor C4 will take too much time to charge up that's why we need the diode right?

[Winfred LU]

Yes. We need it charged rapidly ; as well as discharged at a controlled speed. A diode fits the need perfectly.