LM2576XX Output Current
"Specified 3-A Output Current" means it can drive max 3A load. In other words, you can power up load upto 3A current rating. If you are finding suitability of IC, find out your load requirement and if it is less than 3A, it is safe to be used (considering all other parameters are within range as per datasheet such as input voltage, VIH-VIL for logic inputs etc )