Lesson · Problem 13
Add USB 2.0
USB-C is not one pair of pads
You should be able to
- Join both USB-C data contacts of each polarity and terminate both CC pins.
- Put ESD on the connector side of the data pair, to ground.
High-Speed Fundamentals · Datasheets & Components · Schematic Reasoning
What it is
The two D+ pads must be the same net, and the two D− pads must be the same net. Each CC pin gets the resistor the card specifies. The data pair is still a differential pair over ground, with ESD parts on the connector side of the pair. Series resistors, if required, sit in each polarity.
Why this matters
A USB-C receptacle repeats the USB 2.0 data pins. The CC pins let the source see that a sink is attached. Each CC pin on this board gets a 5.1 kΩ pull-down.
What you are building
A USB-C connector with both data pads joined, CC resistors, ESD, and the pair over ground.
Prerequisites
This lesson uses differential pair, skew, pair gap, reference plane, shunt, net, device card. It introduces D+, D−, USB-C duplicate pads, CC pin, ESD, series resistor.
Component guide
What the parts are. The requirements panel is still the list that is graded.
USB-C receptacle
- What it does
- The connector repeats the USB 2.0 data pins and adds CC pins.
- Why it is here
- Both D+ pads are one net. Both D− pads are the other. One side left open still fails.
- Symbol
- A connector with D+, D−, CC1, CC2, and ground.
- Pins
- D+ pair, D− pair, CC1, CC2, GND.
- Beginner mistake
- Routing only one D+ pad and treating the duplicate as spare.
- What an engineer checks
- Which pads are the duplicates, and the CC resistor the card names.
CC pin
- What it does
- Configuration Channel. A pull-down tells a USB-C source that a sink is attached.
- Why it is here
- Each CC pin on this board gets its own 5.1 kΩ resistor to ground.
- Symbol
- A resistor from CC to ground.
- Values
- 5.1 kΩ, one per CC pin.
- Beginner mistake
- One resistor shared between CC1 and CC2.
- What an engineer checks
- The resistor value and that the two pins are separate.
ESD diode
- What it does
- A clamp from a data net to ground at the connector.
- Why it is here
- It has to be on the data net, and its ground pin has to reach ground.
- Symbol
- A shunt at the connector side of the pair.
- Beginner mistake
- An ESD part that is not on D+ or D−, or not grounded.
- What an engineer checks
- Which net each channel protects, and the ground pin.
Interview lens
Name CC, the 5.1 kΩ pull-down, and why the connector has two D+ pads.
What PCBGrade measures
Net joins, the CC resistors, ESD on the data nets, and the pair geometry. It is not USB-IF compliance.
Where this shows up
A USB-C device that is invisible to the host is often a missing CC resistor or one D+ pad left open.
Terms
- CC
- Configuration-channel pins on USB-C. Each needs the resistor the card names.
- ESD
- A protection part from a data line to ground, placed where the connector energy arrives.
What is happening electrically
USB 2.0 full speed uses D+ and D− as one differential pair. The host watches the difference, and it also watches how the pair sits at idle to decide what was attached. A USB-C receptacle repeats those data contacts so a cable can be flipped. Both D+ pads are the same net. Both D− pads are the same net. Leaving one pad off means one orientation is an open circuit.
CC1 and CC2 are how a Type-C source notices a sink. On this board each CC pin gets the pull-down the card names. They are not the data pair. ESD devices shunt a strike from a data line into ground, and they belong where the strike arrives: the connector side. Series resistors, when the card asks for them, sit in each polarity and limit what a short or a reflection can do. They do not replace the pair geometry.
Why the geometry matters
Join both contacts of each polarity. Place ESD from each data net to ground on the connector side of the series parts. Route D+ and D− as the pair you already learned: together, length-matched, over the ground reference, inside the via and gap limits. The return for the pair is that reference, not a hope that the connector shell is enough.
How an engineer reasons
Separate three jobs. Data is the pair. CC is the attach detection. Protection is the shunt at the connector. A board that enumerates on one cable orientation and fails on the other usually missed a duplicate pad. A board whose ESD part is on the wrong net, or has no ground, does not clamp the pin the strike hits. Continuity and geometry are both required: a connected pair with a huge skew is still wrong, and a pretty pair that leaves one D+ pad open is still wrong.
Worked example
Join both D+ contacts, join both D− contacts, fit the CC resistors, place ESD from each data net to ground, and route the pair over the ground reference with the via and gap limits in the requirements.
Good and bad
Both D+ pads tied, both D− pads tied, a resistor on each CC pin, ESD to ground at the connector, and the pair over L2: the connector is actually a USB-C port. Routing only the pad you can see, and treating the second pad as spare, fails the net even if one cable happens to work on the bench.
Common mistake
Routing only one D+ pad and treating the second footprint pad as spare.
Where this rule stops
This challenge does not claim the link enumerates, does not run a USB electrical compliance test, and does not solve 90 Ω. Continuity of the duplicate pads and the geometry of the pair are both graded because either one can make the port wrong. A real Type-C design also has to get VBUS current, dead battery, and connector mechanics from the specification. Those are outside this board.
Series resistors, when the card includes them, sit in each polarity. They do not set the pair’s impedance, and they do not replace ESD at the connector.
Before the challenge
The challenge uses a USB-C footprint with duplicated data contacts and two CC pins. Join each polarity, fit the resistors the card names, and keep the pair over ground.
Ready for the challenge
You can join both D+ pads, both D− pads, and give each CC pin its own resistor.
Question 1 of 2