Hello Anthony,
Previously we discussed a circuit that will control the TPS40200 through an SS pin connection.
This circuit will turn have an output that goes high when the input voltage to the TPS40200 reaches approximately 30 VDC.
The high transition on the SS pin will cause the output of the TPS40200 to begin the switching necessary to create +3.3VDC.
I implemented this circuit and I am having a problem that crops up when the input voltage is intermittently interrupted.
For example if the input is 50 VDC (then SS pin will be high) and I break and make the connection to this 50 VDC I can pretty easily get into a situation where the output is at ~1.5 VDC and I believe this is because the signal at the SS pin is not high and is oscillating. Please see the scope shot of this.
I have tried disconnecting the transistor circuit to see if its output oscillates when disconnected from the SS pin and found that it does not oscillate.
On the same token I have checked the SS pin for the oscillation once disconnected and found it ok as well.
In fact the TPS40200 does not have a problem with the break and make situation if the transistor circuit is disconnected.
Any ideas?
David Robinson