LM3489 Datasheet, PDF (1/15 Pages) National Semiconductor (TI) – Hysteretic PFET Buck Controller with Enable Pin

May 2006
LM3489
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 architecture also allows for low component count as
well as ultra-low dropout, 100% duty cycle operation. An-
other 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 operation over a range of output currents.
Features
n Easy to use control methodology
n No control loop compensation required
n Wide 4.5V to 35V input range
n 1.239V to V_IN adjustable output range
n High efficiency 93%
n ±1.3% (±2% over temp) internal reference
n 100% duty cycle operation
n Maximum operation frequency > 1MHz
n Current limit protection
n Dedicated enable pin (on if unconnected)
n Shutdown mode draws only 7µA supply current
n MSOP-8
Applications
n Set-Top Box
n DSL/Cable Modem
n PC/IA
n Auto PC
n TFT Monitor
n Battery Powered Portable Applications
n Distributed Power Systems
n Always On Power
n High Power LED Driver
Typical Application Circuit
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