Teacher gave me a schematic,and it includes a DC/DC buck converter with "LB" input and output,but i have no idea what the "LB" is,so i want to ask that does someone know what may the "LB" be?
"LB" stands for "low battery". They are the input and output pins for a comparator and voltage reference (internal to the device) which can be wired to detect a low battery voltage and provide a shutdown signal.
For example, see this Linear Technology datasheet, page 4: http://cds.linear.com/docs/en/datasheet/126535fb.pdf
"LBOUT (Pin 3): Open-Drain Output of the Low-Battery Comparator. This pin will sink current when Pin 4 (LBIN) goes below 1.25V. During shutdown, this pin is high impedance.
LBIN (Pin 4): The (–) Input of the Low-Battery Comparator. The (+) input is connected to a reference voltage of 1.25V."