The USB2.0 standadards specifies 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, it is recommended to 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 3.3-V supply or left floating, together creating 9 different equalization levels.

Typical 45-Ohm traces in FR4 have an insertion loss of about 0.15 dB/inch for 480 Mbps 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 chossing the setting that gives the best eye-opening. Chosing the right setting for the transmit path will also result 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 may be needed, and the EQxx pins can be connected to ground.