nRF5340 - VBUS pin issues

[Gabriele]

Hello guys,
the USB controller of nRF5340 requires a voltage on VBUS pin.

1. Can nRF5340 be damaged if VBUS voltage rises into its valid range while the device OFF (VDD = VDDH = 0V) ?

2. What’s the state of D+\D- when VBUS = 0V ? Are they in high impedance?

Thank you

[Stian Røed Hafskjold]

When you say VDD = VDDH = 0V, does that mean grounded or open?

[Gabriele]

Hello Stian,

any news on this ?

[Stian Røed Hafskjold]

Hi,

The nRF5340 cannot be damaged if VBUS is powered while VDD and VDDH are forced to 0V. However, the D+/D- are not floating, they are pulled towards VSS by a diode and a series resistor. The resistance is ~100kohm if VDD=0V, and in the 1kohm range if VDD is present.

[Gabriele]

Thank you Stian.
Now, suppose to have a situation where nRF5340's pin VBUS = 0V, and another IC with its own USB Device interface attached on the same D+/D- bus.
Will the nRF5340's internal diodes plus resistors disrupt the bus communication between the host and the IC?
I know this is a difficult question, but I'm pretty sure you have an answer also for this.

[Stian Røed Hafskjold]

Do you mean VDD = 0V and VBUS=5V? nRF53 VDD is forced to 0V and the VBUS and D+/D- lines are shared with another USB device, leaving VBUS at 5V?

If VBUS is forced to GND there will be a short circuit between GND and D+/D-

[Gabriele]

This is the circuit.
The question is can IC communicate with PC when nRF5340's VBUS is 0V ?
I want to avoid a USB switch.
Consider that a pull down to GND is not a short to GND.

[Stian Røed Hafskjold]

When VBUS is not powered on the nRF52, there will be flowing current through the internal ESD diodes from D+/D- to VBUS. The current will then only be limited by the pull down resistor on VBUS to GND. So that's not a solution. You will at least have to power VBUS, but again, there will flow current to ground in the milliamp range.

[Gabriele]

Ok, I see using a switch is unavoidable.
Thanks.