The Tigo products TS4-O, TS4-L, TS4-B Smart Module junction boxes have a continuous output current rating of 12A, when used in a string application.
The TS4-A has a continuous current rating of 15A.
Being electronically-controlled devices, according to the National Electrical Code, the proper fusing for a single string is 15A (refer to the Smart Module's datasheet.)
The diagram below shows the optimizer's output curve during continuous operation in a string application. Maximum current depends on panel type, operating and environmental conditions.
IV and power curves of optimizers in a continuous string configuration.
Current can go up to anywhere between Isc and 12.5A