The OPT3004 operates as a target device on both the I²C bus and SMBus. Connections to the bus are made via the SCL clock input line and the SDA open-drain I/O line. The OPT3004 supports the transmission protocol for standard mode (up to 100 kHz), fast mode (up to 400 kHz), and high-speed mode (up to 2.6 MHz). All data bytes are transmitted most-significant bits first.

The SDA and SCL pins feature integrated spike-suppression filters and Schmitt triggers to minimize the effects of input spikes and bus noise. See the Electrical Interface section for further details of the I²C bus noise immunity.