National Semiconductor LM3478 Data Sheet
Summary
The LM3478 is a high-efficiency, versatile low-side N-FET controller designed for miniature switching regulator applications. It supports various topologies—including boost and flyback converters—and operates at highly adjustable frequencies between 100kHz and 1MHz. Featuring internal soft-start, cycle-by-cycle current limiting, and robust protections (such as thermal shutdown), this controller is ideal for sophisticated power systems ranging from battery chargers and offline supplies to demanding telecom and automotive environments. The accompanying manual provides comprehensive electrical specifications, application diagrams, and integration details necessary for reliable circuit design.
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LM igh fficiency Low -S ide -C hannel C ontroller for itching egulator
LM3478 High Efficiency Low-Side N-Channel Controller for Switching Regulator
±2.5% (over temperature) internal reference
General Description
10µA shutdown current (over temperature)
The LM3478 is versatile Low-Side N-FET switching regu- lator controller. It is suitable for use in topologies requiring
Features
low side FET, such as boost, flyback, SEPIC, etc. Moreover,
the LM3478 can be operated at extremely high switching 8-lead Mini-SO8 (MSOP-8) package
frequency in order to reduce the overall solution size. The Internal push-pull driver with 1A peak current capability switching frequency of LM3478 can be adjusted to any value Current limit and thermal shutdown between 100k Hz and 1MHz by using single external resis-
Frequency compensation optimized with capacitor and
tor. Current mode control provides superior bandwidth and
resistor
transient response, besides cycle-by-cycle current limiting.
Internal softstart
Output current can be programmed with single external
Current Mode Operation
resistor.
Undervoltage Lockout with hysteresis
The LM3478 has built in features such as thermal shutdown, short-circuit protection, over voltage protection, etc. Power
Applications
saving shutdown mode reduces the total supply current to
5µA and allows power supply sequencing. Internal soft-start Distributed Power Systems
limits the inrush current at start-up. Battery Chargers
Offline Power Supplies Key Specifications Telecom Power Supplies Wide supply voltage range of 2.95V to 40V Automotive Power Systems
100k Hz to 1MHz Adjustable clock frequency
Typical Application Circuit
Typical High Efficiency Step-Up (Boost) Converter
National Semiconductor Corporation DS101355 www.national.com
Page Summary Contents For National Semiconductor LM3478 Data Sheet
Manual Details
| Brand | National |
|---|---|
| Pages | 21 |
| File Size | 565.49 KB |
| Published | June 01, 2026 |
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Frequently Asked Questions
What is the operating voltage range for this controller?
The supply voltage can operate within a wide range of 2.95V to 40V.
How do I adjust the switching frequency?
A resistor connected to the FA/SD pin controls and sets the oscillator frequency between 100kHz and 1MHz.
What protection features are built into the LM3478?
It includes thermal shutdown, short-circuit protection, over voltage protection, and Undervoltage Lockout (UVLO).
How can I program the output voltage?
The output voltage must be adjusted using a resistor divider connected to the Feedback pin (FB).