LM3485 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.
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4.5V to 35V wide input range
1.242V to V
IN
adjustable output range
High Efficiency 93%
±
1.3% (
±
2% over temp) internal reference
100% duty cycle
Maximum operating frequency
>
1MHz
Current limit protection
MSOP-8
Applications
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Set-Top Box
DSL/Cable Modem
PC/IA
Auto PC
TFT Monitor
Battery Powered Portable Applications
Distributed Power Systems
Always On Power
Features
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Easy to use control methodology
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No control loop compensation required
Typical Application Circuit
20034608
© 2002 National Semiconductor Corporation
DS200346
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
