LM3489_08 Datasheet, PDF (1/16 Pages) National Semiconductor (TI) – Hysteretic PFET Buck Controller with Enable Pin

June 23, 2008
LM3489/LM3489Q
Hysteretic PFET Buck Controller with Enable Pin
General Description
The LM3489 is a high efficiency PFET switching regulator
controller that can be used to quickly and easily develop a
small, cost effective, switching buck regulator for a wide range
of applications. The hysteretic control architecture provides
for simple design without any control loop stability concerns
using a wide variety of external components. The PFET ar-
chitecture also allows for low component count as well as
ultra-low dropout, 100% duty cycle operation. Another benefit
is high efficiency operation at light loads without an increase
in output ripple. A dedicated Enable Pin provides a shutdown
mode drawing only 7µA. Leaving the Enable Pin unconnected
defaults to on.
Current limit protection can be implemented by measuring the
voltage across the PFET’s R_DS(ON), thus eliminating the need
for a sense resistor. A sense resistor may be used to improve
current limit accuracy if desired. The cycle-by-cycle current
limit can be adjusted with a single resistor, ensuring safe op-
eration over a range of output currents.
Features
■ ^{Easy to use control methodology}
■ ^{No control loop compensation required}
■ ^{Wide 4.5V to 35V input range}
■ ^{1.239V to V}_IN ^{adjustable output range}
■ ^{High efficiency 93%}
■ ^{±1.3% (±2% over temp) internal reference}
■ ^{100% duty cycle operation}
■ ^{Maximum operation frequency > 1MHz}
■ ^{Current limit protection}
■ ^{Dedicated enable pin (on if unconnected)}
■ ^{Shutdown mode draws only 7µA supply current}
■ ^MSOP-8
■ ^{LM3489 is AEC-Q100 Grade 1 qualified}
Applications
■ ^{Set-Top Box}
■ ^{DSL/Cable Modem}
■ ^PC/IA
■ ^{Auto PC}
■ ^{TFT Monitor}
■ ^{Battery Powered Portable Applications}
■ ^{Distributed Power Systems}
■ ^{Always On Power}
■ ^{High Power LED Driver}
■ ^Automotive
Typical Application Circuit
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