Hello, 

As of the eligibility criteria for various psus

Anything above 6.84 CGPA, would make you eligible into 99% of after graduation(after BTech) jobs/studies including PSU's in India.

6.84 was the cutoff provided by ISRO for there exams and thats the highest CGPA being demanded in 2017.

Different psus have different pointer cutoffs but the highest of all the psus and isro is 6.84. So, CGPA >6.84 will do the job. 

Regarding the recruitment, once your are eligible corresponding to your cgpa, your gate score and your interview skills are the major part that get you to be hired. 

Hope this helps .....