In general, will a buck converter allow current to pass through if Vin is less than the configured output voltage?
Specifically, I'm reading the TPS54308 datasheet and I'm not seeing an answer to my question.
Electronic – Will a buck converter allow current to pass through if Vin is less than the configured output voltage
buckstep-downswitching-regulatortexas instruments
Related Solutions
Yes the potentiometers act as a variable voltage divider, so you can change the output voltage of the converter whenever you like. This voltage divider is connected to the Feedback (usually this pin is named as "Feedback") pin of converter IC, providing feedback for the regulation loop.
The datasheet usually contains information about this pin's bias current. In case of the LM2596, it is typically 10nA.
The feedback resistors are also recommended in the \$ k\Omega \$ range, reducing current flow.
Since the Buck converter will be running, the battery will get drained, if the switch is placed after the DC-DC output. you had mentioned placing the switch at the output is convenient, you can use the switch to shut down the buck converter also.
Most of DC-DC converter IC will have shutdown pins, which will put the device to low power mode in which it consume very low power, so you can combine this shutdown pin and the switch to reduce the power drain of the battery significantly
Best Answer
Yes, many Buck regulators (including the TPS54308) will do this. As long as the input voltage doesn't trip a UVLO protection (either internal to the chip or part of your circuit), it will pass through at 100% duty cycle trying to reach the desired output voltage. If you want a higher cutoff voltage than the chip provides, you'll need an external circuit to measure the input and drive the EN pin accordingly.
From your datasheet: