19-4778; Rev 0a; 8/98
1.8V to 28V Input, PWM Step-Up
Controllers in µMAX
1.8V Minimum Start-Up Voltage (MAX669)
Wide Input Voltage Range (1.8V to 28V)
Tiny 10-Pin µMAX Package
Current-Mode PWM and Idle Mode™ Operation
Efficiency over 90%
Adjustable 100kHz to 500kHz Oscillator or
220µA Quiescent Current
The MAX668/MAX669 constant-frequency, pulse-width-
modulating (PWM), current-mode DC-DC controllers are
designed for a wide range of DC-DC conversion applica-
tions 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 (220µA),
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 Mode™ 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 oper-
ating current and maximize efficiency under light loads.
A logic-level shutdown input is also included, reducing
supply current to 3.5µA.
The MAX669, optimized for low input voltages with a
guaranteed start-up voltage of 1.8V, requires boot-
strapped operation (IC powered from boosted output). It
supports output voltages up to 28V. The MAX668 oper-
ates with inputs as low as 3V and can be connected in
either a bootstrapped or non-bootstrapped (IC powered
from input supply or other source) configuration. When
not bootstrapped, it has no restriction on output voltage.
Both ICs are available in an extremely compact 10-pin
LANs and Network Systems
-40°C to +85°C
-40°C to +85°C
Idle Mode is a trademark of Maxim Integrated Products.
Typical Operating Circuit
= 1.8V to 28V
Maxim Integrated Products
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800.
For small orders, phone 1-800-835-8769.