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The MMA2L20 converts 25 Gbit/s serial PECL or CML electrical data into serial optical data compliant with the 25GBASE-LR standard. An open collector compatible Transmit Disable (Tx_Dis) is provided. Logic “1” or no connection on this pin will disable the laser from transmitting. Logic “0” on this pin provides normal operation. The transceiver has selectable retiming, which is default on for 25G operation. It can be disabled by firmware or hardware control for operation at other data rates, e.g. 10G. The retiming control is described in ‎Appendix A:

The transmitter has an internal automatic power control loop (APC) to ensure constant optical power output across supply voltage and temperature variations. An open collector compatible Transmit Fault (Tx_Fault) is provided.

TX_Fault is a module output signal which when high, indicates that the module transmitter has detected a fault condition related to laser operation or safety. The TX_Fault output contact is an open drain/collector and shall be pulled up to the Vcc_Host in the host with a resistor in the range 4.7-10 kΩ.

TX_Disable is a module input signal. When TX_Disable is asserted high or left open, the SFP28 module transmitter output shall be turned off. This contact shall be pulled up to VccT with a 4.7 kΩ to 10 kΩ resistor.

The receiver converts 25 Gbit/s serial optical data into serial PECL/CML electrical data.

Loss of Signal, Rx_LOS: a logic high level indicates that the optical signal level is below the level specified in the standard. The Rx_LOS signal is an open drain/collector output and shall be pulled up to Vcc_Host in the host with a resistor in the range 4.7-10 kΩ, or with an active termination.

Power supply filtering is recommended for both the transmitter and receiver.

Handling and Cleaning

The transceiver can be damaged by exposure to current surges and over voltage events. Take care to restrict exposure to the conditions defined in Absolute Maximum Ratings. Observe normal handling precautions for electrostatic discharge-sensitive devices. The transceiver is shipped with dust caps on both the electrical and the optical port. The cap on the optical port should always be in place when there is no fiber cable connected. The optical connector has a recessed connector surface which is exposed whenever it has no cable nor cap.

Prior to insertion of the fiber cable, clean the cable connector to prevent contamination from it. The dust cap ensures that the optics remain clean and no additional cleaning should be needed. In the event of contamination, standard cleaning tools and methods should be used. Liquids must not be applied.