1V to 5V dc-dc step-up circuit @ Iout = 1A
If you are trying to use the MAX757 for this application, you are unfortunately going to be disappointed - a quick read of the datasheet tells you this quite explicitly.

From the top-right of page 3 of the datasheet:



We see clearly here that the maximum output current for an input of 1V and an output of 5V is only about 50mA. If you try and draw 1A from it, it's going to shut down completely or the output voltage will drop significantly (probably down to below the input voltage).

Why is this the case? Well a switching regulator effectively acts like a transformer - it converts current to voltage or vice versa. You require an output of 5V@1A=5W. That means the input power must be at least 6W allowing for inefficiencies. For a 1V input, that means you would have 6A (!) being drawn from the supply. The integrated switch in the MAX757 is rated for only 1A, so trying to switch 6 times the rated current is not going to happen.



There is a potential work around - you could use an external transistor to increase the switching current capacity. You would have to find a MOSFET with low enough Rds(on) and high enough current handling capacity at 1V and connect its gate to the MAX757s LX pin (with pull up resistor to the input voltage), the source to GND, and the drain to the inductor/diode. You would also need an inductor that is rated for 6A at the correct inductance.

However in all likelihood the above won't work. Firstly inductors generally derate at high currents (the inductance reduces), so you would need probably a very large inductor. Secondly, and perhaps more fatally, it will be next to impossible to find a MOSFET with that low of a threshold voltage (typically high power MOSFETs require at least 5V on the gate to be fully on). You could use a BJT, however the MAX757 is designed to sink current not source it meaning you would need additional circuitry to drive the base of a BJT.



To summarise, I doubt you will be able to convert from 1V to 5V@1A. The input and switching current requirements are too high.