LM3478 High Efficiency Low-Side N-Channel Controller for Switching Regulator
May 2003
LM3478
High Efficiency Low-Side N-Channel Controller for
Switching Regulator
General Description
The LM3478 is a versatile Low-Side N-FET switching regu-
lator controller. It is suitable for use in topologies requiring
low side FET, such as boost, flyback, SEPIC, etc. Moreover,
the LM3478 can be operated at extremely high switching
frequency in order to reduce the overall solution size. The
switching frequency of LM3478 can be adjusted to any value
between 100kHz and 1MHz by using a single external resis-
tor. Current mode control provides superior bandwidth and
transient response, besides cycle-by-cycle current limiting.
Output current can be programmed with a single external
resistor.
The LM3478 has built in features such as thermal shutdown,
short-circuit protection, over voltage protection, etc. Power
saving shutdown mode reduces the total supply current to
5µA and allows power supply sequencing. Internal soft-start
limits the inrush current at start-up.
n
10µA shutdown current (over temperature)
Features
8-lead Mini-SO8 (MSOP-8) package
Internal push-pull driver with 1A peak current capability
Current limit and thermal shutdown
Frequency compensation optimized with a capacitor and
a resistor
n
Internal softstart
n
Current Mode Operation
n
Undervoltage Lockout with hysteresis
n
n
n
n
Applications
n
n
n
n
n
Distributed Power Systems
Battery Chargers
Offline Power Supplies
Telecom Power Supplies
Automotive Power Systems
Key Specifications
n
Wide supply voltage range of 2.97V to 40V
n
100kHz to 1MHz Adjustable clock frequency
n
±
2.5% (over temperature) internal reference
Typical Application Circuit
10135501
Typical High Efficiency Step-Up (Boost) Converter
© 2003 National Semiconductor Corporation
DS101355
www.national.com
NSC [ NATIONAL SEMICONDUCTOR ]
