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USB ESD protection (USBLC6-2SC6)

A small chip of clamp diodes that absorbs static discharges on the USB data lines and VBUS before they reach your microcontroller.

What it does#

Touching a USB connector can inject kilovolts for a few nanoseconds. The USBLC6-2SC6 holds two data lines and VBUS with low-capacitance diodes, so the pulse goes to ground instead of into the microcontroller’s USB pins.

Pins (SOT-23-6): 1 and 6 = I/O1, 3 and 4 = I/O2, 2 = GND, 5 = VBUS. Each pair is internally connected (“flow-through”): route the line through pin 1 → 6 and pin 3 → 4.

Example circuit: The USB-C device block used in every ESP32 example: CC pull-downs, D+/D− of both orientations joined, U1 on D+ (I/O1), D− (I/O2) and VBUS. C2 is the 100 nF from ST's layout example, C1 the 10 µF bulk.
The USB-C device block used in every ESP32 example: CC pull-downs, D+/D− of both orientations joined, U1 on D+ (I/O1), D− (I/O2) and VBUS. C2 is the 100 nF from ST's layout example, C1 the 10 µF bulk. Open the usb_esd example from this page in PCB Canvas: “Insert into my schematic”.

Layout#

  • Place it right behind the connector, before anything else on the lines.
  • Keep every track to it short: the data lines into pins 1/3, the VBUS track to pin 5 and the ground (a via to the pour next to pin 2). A few nanohenries of track add more clamping voltage than the chip itself.
  • ST’s layout example puts 100 nF from the VBUS pin to GND, close to the chip.
  • Keep D+/D− as a pair through it.

Pitfalls#

  • VBUS pin is the clamp reference, not a power path; connect it to VBUS.
  • Not a fuse: it does not limit overcurrent. Combine with a polyfuse for a robust input.

Footprint#

SOT-23-6, hand-solderable. JLCPCB C7519 (extended).