LM3485 Datasheet, PDF (1/15 Pages) National Semiconductor (TI) – Hysteretic PFET Buck Controller

May 2002
LM3485
Hysteretic PFET Buck Controller
General Description
The LM3485 is a high efficiency PFET switching regulator
controller that a system designer can use to quickly and
easily develop a small, low cost, switching buck regulator for
a wide range of applications. The use of a hysteretic control
scheme provides for simple design without any control loop
stability concerns using a wide variety of external compo-
nents. The PFET architecture also allows for low component
count as well as ultra-low dropout operation. Another benefit
is high efficiency operation at light loads without an increase
in output ripple. Current limit protection circuit is provided by
measuring the voltage across the PFET’s R_DSON thus elimi-
nating a costly sense resistor. The current limit can be ad-
justed allowing for designs at various output currents and
costs.
Features
n Easy to use control methodology
n No control loop compensation required
n 4.5V to 35V wide input range
n 1.242V to V_IN adjustable output range
n High Efficiency 93%
n ±1.3% (±2% over temp) internal reference
n 100% duty cycle
n Maximum operating frequency > 1MHz
n Current limit protection
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
Typical Application Circuit
20034608
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