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
www.DinatoauSthpeuterti4pUp.lec.oAmdedicated 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 RDS(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 VIN 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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