The MAX756 is CMOS step-up DC-DC switching regulators for small, low input voltage or battery-powered systems. The MAX756 accepts a positive input
voltage down to 0.7V and converts it to a higher pinselectable output voltage of 3.3V or 5V. Typical full-load efficiencies
for the MAX756 is greater than 87%.
The MAX756 provide three improvements over
previous devices. Physical size is reduced—the high
switching frequencies (up to 0.5MHz) made possible by
MOSFET power transistors allow for tiny (<5mm diameter)
surface-mount magnetics. Efficiency is improved to 87%
(10% better than with low-voltage regulators fabricated in
bipolar technology). Supply current is reduced to 60µA
by CMOS construction and a unique constant-off-time
pulse-frequency modulation control scheme.

Documents:

http://datasheets.maximintegrated.com/en/ds/MAX756-MAX757.pdf