My automotive application uses a generic 7805 regulator to provide a 5V reference. The design has worked well. Recently I decided to substitute a LM2940T-5 regulator for the 7805 (making no other design changes) and found that the circuit no longer works properly. The LM2940T is not regulating output. I am getting a variable output depending on Vin.
I have the same issue with a batch of LM2940T-8 regulators. On the bench I have a LM2940T-8 alongside a 7808. I have no other connections to the regulators other than power and ground. With any voltage above about 10V. the Vout of the 7808 measured directly on the part locks in at 7.98V while the voltage on the LM2940T-8 continues to rise as voltage increases.
Every one of the 25 LM2940T-8 regulators I have tests the same way.
Am I misunderstanding something about this part?
Thanks,
Peter
