It is set by agreement between you and the landlord, and nothing in Karnataka law fixes the number today. You usually have more room to negotiate when no broker is involved, when the flat has sat empty for a while, or when you can commit to a longer stay. Ask for a lower deposit in exchange for a longer lock-in or a clean payment record, and get whatever you agree written into the agreement.
Sources
No outside source: this is how the practice works, in words, with nothing to cite.