I need to develop a device that requires 5V power. The device must be powered from 5V (USB) or 12V. I need such a system that will bypass the DC-DC converter when it works from USB and enable the DC-DC converter when it works from 12V.
Will my solution work?
I want to use a voltage comparator with some voltage dividers and voltage reference, so it can short the input and output of a DC-DC converter when the VIN is (let's say) <6V with a P-MOSFET, thus disabling the DC-DC converter and providing the power to the device.
I want to use TPS54331. What will happen if I feed 5V to the DC-DC converter when it configured to output 5V? Will there be a drop? I haven't found this info in the datasheet.
Answer
You could save yourself a lot of messing around by using a buck-boost converter like this: -
The USB supply can be fed via a low-volt-drop schottky diode to the input (Vin) and if you have 12 volts also present at the input it will take over and power the converter.
Another option: -
You can get these types of devices from TI too like this: -
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