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National Semiconductor Electronic Components Datasheet

LM3481 Datasheet

High Efficiency Low-Side N-Channel Controller

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LM3481 pdf
November 16, 2007
LM3481
High Efficiency Low-Side N-Channel Controller for
Switching Regulators
General Description
The LM3481 is a versatile Low-Side N-FET high performance
controller for switching regulators. It is suitable for use in
topologies requiring a low-side FET, such as boost, flyback,
SEPIC, etc. The LM3481 can be operated at extremely high
switching frequencies in order to reduce the overall solution
www.DataSheest4izUe..cTohme switching frequency of the LM3481 can be adjusted
to any value between 100 kHz and 1 MHz by using a single
external resistor or by synchronizing it to an external clock.
Current mode control provides superior bandwidth and tran-
sient response in addition to cycle-by-cycle current limiting.
Current limit can be programmed with a single external resis-
tor.
The LM3481 has built in protection features such as thermal
shutdown, short-circuit protection and over voltage protec-
tion. 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.
Key Specifications
Wide supply voltage range of 2.97V to 48V
100 kHz to 1 MHz Adjustable and Synchronizable clock
frequency
±1.5% (over temperature) internal reference
10 µA shutdown current (over temperature)
Features
10-lead MSOP package
Internal push-pull driver with 1A peak current capability
Current limit and thermal shutdown
Frequency compensation optimized with a capacitor and
a resistor
Internal softstart
Current Mode Operation
Adjustable Undervoltage Lockout with Hysteresis
Pulse Skipping at Light Loads
Applications
Distributed Power Systems
Notebook, PDA, Digital Camera, and other Portable
Applications
Offline Power Supplies
Set-Top Boxes
Typical Application Circuit
Typical SEPIC Converter
© 2007 National Semiconductor Corporation 201365
201365a5
www.national.com


National Semiconductor Electronic Components Datasheet

LM3481 Datasheet

High Efficiency Low-Side N-Channel Controller

No Preview Available !

LM3481 pdf
Connection Diagram
20136502
10-Lead Mini SOIC Package (MSOP-10 Package)
Package Marking and Ordering Information
www.DataSheet4U.com
Order Number
LM3481MM
LM3481MMX
Package Type
MSOP-10
MSOP-10
Package Marking
SJPB
SJPB
Supplied As:
1000 units on Tape and Reel
3500 units on Tape and Reel
Pin Description
Pin Name
ISEN
UVLO
COMP
FB
AGND
FA/SYNC/SD
PGND
DR
VCC
VIN
Pin Number
1
2
3
4
5
6
7
8
9
10
Description
Current sense input pin. Voltage generated across an external sense
resistor is fed into this pin.
Under voltage lockout pin. A resistor divider from VIN to ground is
connected to the UVLO pin. The ratio of these resistances determine
the input voltage which allows switching and the hysteresis to disable
switching.
Compensation pin. A resistor and capacitor combination connected to
this pin provides compensation for the control loop.
Feedback pin. Inverting input of the error amplifier.
Analog ground pin. Internal bias circuitry reference. Should be
connected to PGND at a single point.
Frequency adjust, synchronization, and shutdown pin. A resistor
connected from this pin to ground sets the oscillator frequency. An
external clock signal at this pin will synchronize the controller to the
frequency of the clock. A high level on this pin for 30 µs will turn the
device off and the device will then draw 5 µA from the supply typically.
Power ground pin. External power circuitry reference. Should be
connected to AGND at a single point.
Drive pin of the IC. The gate of the external MOSFET should be
connected to this pin.
Driver supply voltage pin. Typically a capacitor is tied from the VCC pin
to ground.
Power supply input pin.
www.national.com
2


Part Number LM3481
Description High Efficiency Low-Side N-Channel Controller
Maker National Semiconductor
Total Page 22 Pages
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