LM3487
High Efficiency High-Side N-Channel Controller for
Switching Regulator
General Description
Features
The LM3487 is a high-side N-channel MOSFET switching
regulator controller. It can be used in topologies requiring a
high side MOSFET such as buck, inverting (buck-boost) and
zeta regulators. The LM3487's internal push pull driver allows
compatibility with a wide range of MOSFETs. A wide input
voltage range and an adjustable current limit allow the
LM3487 to be optimized for a wide variety of applications.
The LM3487 has an adjustable switching frequency which
can also be synchronized to an external clock. Current-mode
control requires only a single resistor and capacitor for frequency compensation. The current mode architecture also
yields superior line and load regulation and cycle-by-cycle
current limiting. A 7µA shutdown state can be used for power
savings and for power supply sequencing. Other features include external soft-start to reduce inrush current and output
over voltage protection.
■ Adjustable/synchronizable switching frequency from
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100kHz to 1.4MHz
Adjustable cycle by cycle current limit
Wide 3V-35V input voltage range
Thermal shutdown
Frequency compensation optimized with a single
capacitor and resistor
External softstart
Current mode operation
Undervoltage lockout with hysteresis
10-lead Mini-SO10 (MSOP-10) package
Automotive grade including AEC-Q100 is available
Applications
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ADSL Modems
Local Voltage Regulation
Distributed Power
Notebook and Palmtop Computers
Internet Appliances
Printers and Office Automation
Battery operated Devices
Cable Modems
Battery Chargers
Typical Application Circuit
20049233
Typical High Efficiency Step-Down (Buck) Converter
© 2008 National Semiconductor Corporation
200492
www.national.com
LM3487 High Efficiency High-Side N-Channel Controller for Switching Regulator
February 19, 2008
LM3487
Connection Diagram
20049202
10-Lead Mini SO10 Package (MSOP-10 Package)
Package Marking and Ordering
Information
Order Number
Package Type
Package Marking
LM3487MM
Supplied As:
1000 units on Tape and Reel
LM3487MMX
MSOP-10
LM3487QMM
S38B
LM3487QMMX
3500 units on Tape and Reel
1000 units on Tape and Reel
3500 units on Tape and Reel
For automotive grade including AEC-Q100 use ‘Q’ versions.
Pin Descriptions
Pin Name
Pin Number
ISEN
1
Current sense input pin. Voltage generated across an external sense resistor is fed
into this pin.
Description
SS/SD
2
Soft-Start and Shutdown pin. Connect a capacitor from this pin to ground to achieve
soft-start. Pull this pin below 0.7V (typical) to shutdown the device.
COMP
3
Compensation pin. A resistor-capacitor combination connected to this pin provides
compensation for the control loop.
FB
4
Feedback pin. The output voltage should be adjusted using a resistor divider to provide
1.260V (typical) at this pin.
GND
5
Ground pin.
FA/SYNC
6
Frequency adjust and synchronization pin. Connect a resistor from this pin to ground
to set the switching frequency. Connect a high impedance clock signal to this pin to
synchronize the switching frequency with the rising edge of the clock.
SW
7
Switch Node. Source of the external MOSFET is connected to this node.
DR
8
Drive pin. The gate of the external MOSFET should be connected to this pin.
CB
9
Boot-strap pin. A capacitor must be connected between this pin and SW pin (pin 5) for
proper operation. The voltage developed across this capacitor provides the gate drive
for the external MOSFET.
VIN
10
Power Supply Input pin.
www.national.com
2
If Military/Aerospace specified devices are required,
please contact the National Semiconductor Sales Office/
Distributors for availability and specifications.
VIN (Note 2)
Peak Driver Output Current (
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