The USB2.0 standards specify TX and RX eye-diagram templates that must be met at the connector. The horizontal eye-opening achieved at the connector is a combination of the performance at the microcontroller, the additive jitter of the ISOUSB211-Q1, and the inter-symbol interference resulting from the insertion loss of D+/D- board traces. For best performance, minimize the length of D+/D- board traces from the MCU to ISOUSB211-Q1, and from ISOUSB211-Q1 to the connector. Vias and stubs on D+/D- lines must be avoided.

The ISOUSB211-Q1 has inbuilt programmable receive equalization and transmit pre-emphasis to cancel signal loss caused by board traces, which helps in meeting USB2.0 high-speed TX and RX eye-diagrams. EQ11 and EQ10 can be chosen based on the length of D+/D- board traces and corresponding channel loss estimated on side 1, and similarly EQ21 and EQ20 for side 2. The EQxx pins can be connected to ground, connected to 3.3V supply or left floating, together creating 9 different equalization levels.

Typical 45Ω traces in FR4 have an insertion loss of approximately 0.15dB/inch for 480Mbps signaling. This number can be used to arrive at an estimate for the amount of Equalization/Pre-emphasis needed and the corresponding EQ settings. Further adjustments to the EQxx settings can be made by observing the transmit eye-diagram at the connector, and choosing the setting that gives the best eye opening. Choosing the right setting for the transmit path also results in an optimum performance for the receive path. Refer to Compensate for Channel Loss with Equalizer Settings on High-Speed USB Isolators application note for details. If the trace lengths are very small, no equalization is needed, and the EQxx pins can be connected to ground.