Problem
A USB-C hub's power-delivery rail sags when a bus-powered SSD and card reader start simultaneously, resetting the connected storage devices.
Solution
Root Cause / Diagnostic:
Unpowered or pass-through USB-C hubs divide host 5V/900mA (or negotiated PD pass-through) across internal buck converters without per-port current regulation. Simultaneous peak inrush current from the NVMe SSD controller initializing and the UHS-II card reader spinning up pulls the shared 5V power plane below the 4.75V USB minimum threshold, triggering an undervoltage lockout (UVLO) bus reset.
Actionable Fix:
1. Dedicated External Power Supply: Connect a dedicated 60W–100W USB-PD power adapter directly to the hub's pass-through power delivery port to decouple peripheral power from host rail limits.
2. Ingest Workflow Separation: Stagger peripheral connections by mounting the external SSD first, waiting for filesystem enumeration, and then inserting the media card reader.
3. Voltage Stability Verification: Monitor OS hardware logs (dmesg on Linux/macOS or Windows USB Event ID 1001) during simultaneous load to verify no OverCurrent or Device Reset events occur.
Pro Tip:
Never run simultaneous multi-device ingest off bus power alone; always supply dedicated wall power to your hub or dock so high inrush currents don't reset your editing drives mid-transfer.
Unpowered or pass-through USB-C hubs divide host 5V/900mA (or negotiated PD pass-through) across internal buck converters without per-port current regulation. Simultaneous peak inrush current from the NVMe SSD controller initializing and the UHS-II card reader spinning up pulls the shared 5V power plane below the 4.75V USB minimum threshold, triggering an undervoltage lockout (UVLO) bus reset.
Actionable Fix:
1. Dedicated External Power Supply: Connect a dedicated 60W–100W USB-PD power adapter directly to the hub's pass-through power delivery port to decouple peripheral power from host rail limits.
2. Ingest Workflow Separation: Stagger peripheral connections by mounting the external SSD first, waiting for filesystem enumeration, and then inserting the media card reader.
3. Voltage Stability Verification: Monitor OS hardware logs (dmesg on Linux/macOS or Windows USB Event ID 1001) during simultaneous load to verify no OverCurrent or Device Reset events occur.
Pro Tip:
Never run simultaneous multi-device ingest off bus power alone; always supply dedicated wall power to your hub or dock so high inrush currents don't reset your editing drives mid-transfer.