Other Parts Discussed in Thread: LMR14050
I have an arcane question.relating to what happens to a LMR14050 switching regulator under a certain circuit fault situation. I am building (actually for the 3rd time!) a multivolt power supply that effectuates the four different output voltages by switching in and out four different R_FBT resistors with a rotary switch. The 5th throw of the switch eliminates all R_FBT resistors making R_FBT infinite, leaving the FB pin connected to ground through a 22K R_FBB resistor. The 5th throw also puts 0.2 volts on the EN pin shutting the regulator off. However, if the latter faults somehow the FB pin will still see 0 volts through the resistor but the regulator will remain operational. The datasheet says DO NOT short the FB pin to ground, but the Max Rating of FB voltage is listed as ─0.3V, and the Recommended Minimum is listed as 0.0V. Is connecting the FB pin to ground through a resistor the same as shorting the pin to ground? If it is, don't the Max Rating and Recommended Minimum violate the admonition to not short the pin to ground? Or, what would actually happen? My best guess is that 0 volts on FB would tell the regulator to raise the output which it would do continuously driving the output voltage to the input voltage with a 97% duty cycle though with zero current flow. The overvoltage protection seems no help in this situation. Am I correct? What is the risk to the regulator or any other part of the circuit in this scenario?
