MAX668/MAX669 1.8V to 28V Input, PWM Step-Up
Controllers in ОјMAX General Description The MAX668/MAX669 constant-frequency, pulse-widthmodulating (PWM), current-mode DC-DC controllers are
designed for a wide range of DC-DC conversion applications
including step-up, SEPIC, flyback, and isolated-output
configurations. Power levels of 20W or more can be
controlled with conversion efficiencies of over 90%. The
1.8V to 28V input voltage range supports a wide range of
battery and AC-powered inputs. An advanced BiCMOS
design features low operating current (220ОјA), adjustable
operating frequency (100kHz to 500kHz), soft-start, and
a SYNC input allowing the MAX668/MAX669 oscillator to
be locked to an external clock.
DC-DC conversion efficiency is optimized with a low
100mV current-sense voltage as well as with Maxim’s
proprietary Idle Modeв„ў control scheme. The controller
operates in PWM mode at medium and heavy loads for
lowest noise and optimum efficiency, then pulses only as
needed (with reduced inductor current) to reduce operating
current and maximize efficiency under light loads. A logiclevel shutdown input is also included, reducing supply
current to 3.5ОјA.
The MAX669, optimized for low input voltages with a
guaranteed start-up voltage of 1.8V, requires bootstrapped
operation (IC powered from boosted output). It supports …