AN-002 · APPLICATION NOTE

The 100 W cable myth

Two myths, mirror images of each other. First: a high-wattage cable must be a fast cable. Second: any USB-C cable will deliver whatever the charger can supply. Both wrong, both expensive.

The rules the cable enforces

• Up to 60 W: any USB-C cable. 20 V at 3 A is the baseline every compliant cable must carry.
• Above 60 W: the cable needs an e-marker chip declaring 5 A. Without it, charger and laptop quietly negotiate down to 60 W. Charging works; it is just slower than the hardware you paid for.
• Above 100 W: the cable must be EPR rated (the 240 W class, USB PD 3.1). A 100 W cable into a 140 W charger gives you 100 W at best.

None of this says anything about data. The majority of 240 W cables on the market are USB 2.0 charging cables: superb at power, incapable of video, and 480 Mbps at data. The reverse is also true; plenty of 40 Gbps cables are only rated 100 W. Check both axes on the matrix before buying.