USB Interface protection reference

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In my design, I aimed to isolate the USB interface. To achieve this, I used the Analog Devices USB isolation chip, ADUM3160BRWZ, to isolate the connection between the PC and the nRF52840. However, during our real-world testing, the USB virtual COM port loses connection after approximately 6 hours of continuous operation.

We hope locating the problem source, here are some design details.

1.  VBUS power supply is derived from a 5V LDO.

2.  DECUSB pin is connected to a 4.7µF capacitor.

3. SYS_LFXO bypass capacitor used is 9pF (Ccap = 2*CL – C_pcb – C_pin), and we have confirmed that the LFXO is functioning properly.

nRF52840 core sch: 

ADUM3160 Isolation sch: 

I would appreciate any troubleshooting methods you could suggest.

[Priyanka]

Hi,

Do you have any logs that you capture so that we can try to find what happens just before the disconnection?

Also, maybe you could try to temporarily bypass the isolation chip and connect the nRF52840 directly to the PC. If the issue persists, then it might be firmware or hardware related on the nRF52840 side. If it disappears, then the isolator is causing the issue.

Regards,

Priyanka

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Hi,

We currently don’t have any logs available. However, I will coordinate with our software engineers to start recording logs.

In our previous version, the USB DP and DN lines were directly connected to the PC. This setup exhibited performance issues, as the connection would drop after a certain period. We initially suspected that the issue was related to the computer’s power-saving strategy or the stability of the VBUS power supply. To address this in the current version, we changed the VBUS supply from a direct connection to an LDO supply.

I also have a question: USB isolators are common application circuits. Does Nordic have any mature or verified application solutions for this?

Regards，

[Priyanka]

Hi,

I don't think we have such solutions or applications for USB isolators.

-Priyanka