The admission is based on two ways:
Stream 1: JEE main marks + board exam marks (70% seats)
Stream 2: only board exam marks (30% seats)
There is no specific cut off to get a seat in SASTRA University. It depends on the student who scores the highest marks. If you have appeared for JEE Mains then apply under stream 1. If your board exam marks is 90-95% and JEE main marks is between 50-120 then you can get admission under stream 1. 
For stream 2, your board exam marks should be at least above 85-90% to get a seat and if it is more than 95% you can get a good course. 

Yes, you will get EEE but  ECE is bit doubtful. For further clarification refer - 

https://university.careers360.com/colleges/sastra-university-thanjavur

All the best!