LM3477 Datasheet, PDF (1/23 Pages) National Semiconductor (TI) – High Efficiency High-Side N-Channel Controller for Switching Regulator

June 2002
LM3477/LM3477A
High Efficiency High-Side N-Channel Controller for
Switching Regulator
General Description
The LM3477/A 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 LM3477/A’s internal push pull driver
allows compatibility with a wide range of MOSFETs. This, the
wide input voltage range, use of discrete power components
and adjustable current limit allows the LM3477/A to be opti-
mized for a wide variety of applications.
The LM3477/A uses a high switching frequency of 500kHz to
reduce the overall solution size. Current-mode control re-
quires 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 5µA shutdown state can be used for power sav-
ings and for power supply sequencing. Other features in-
clude internal soft-start and output over voltage protection.
The internal soft-start reduces inrush current. Over voltage
protection is a safety feature to ensure that the output volt-
age stays within regulation.
The LM3477A is similar to the LM3477. The primary differ-
ence between the two is the point at which the device
transitions into hysteretic mode. The hysteretic threshold of
the LM3477A is one-third of the LM3477.
Features
n 500kHz switching frequency
n Adjustable current limit
n 1.5% reference
n Thermal shutdown
n Frequency compensation optimized with a single
capacitor and resistor
n Internal softstart
n Current mode operation
n Undervoltage lockout with hysteresis
n 8-lead Mini-SO8 (MSOP-8) package
Applications
n Local Voltage Regulation
n Distributed Power
n Notebook and Palmtop Computers
n Internet Appliances
n Printers and Office Automation
n Battery operated Devices
n Cable Modems
n Battery Chargers
LM3477
LM3477A
Hysteretic
Threshold
) 36% of
programmed current
limit
) 12% of
programmed current
limit
*See Hysteretic Threshold and section for more information.
Typical Application Circuit
20003333
Typical High Efficiency Step-Down (Buck) Converter
© 2002 National Semiconductor Corporation DS200033
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