LM34914 Datasheet, PDF (1/14 Pages) National Semiconductor (TI) – Ultra Small 1.25A Step-Down Switching Regulator with Intelligent Current Limit

December 20, 2007
LM34914
Ultra Small 1.25A Step-Down Switching Regulator with
Intelligent Current Limit
General Description
The LM34914 Step-Down Switching Regulator features all
the functions needed to implement a low cost, efficient, buck
bias regulator capable of supplying at least 1.25A to the load.
To reduce excessive switch current due to the possibility of a
saturating inductor the valley current limit threshold changes
with input and output voltages, and the on-time is reduced
when current limit is detected. This buck regulator contains a
44V N-Channel Buck Switch, and is available in the thermally
enhanced 3 mm x 3 mm LLP-10 package. The feedback reg-
ulation scheme requires no loop compensation, results in fast
load transient response, and simplifies circuit implementation.
The operating frequency remains constant with line and load
variations due to the inverse relationship between the input
voltage and the on-time. The valley current limit results in a
smooth transition from constant voltage to constant current
mode when current limit is detected, reducing the frequency
and output voltage, without the use of foldback. Additional
features include: VCC under-voltage lock-out, thermal shut-
down, gate drive under-voltage lock-out, and maximum duty
cycle limit.
Features
■ ^{Input Voltage Range: 8V to 40V}
■ ^{Integrated N-Channel buck switch}
■ ^{Valley current limit varies with V}_IN ^{and V}_OUT ^{to reduce}
excessive inductor current
■ ^{On-time is reduced when in current limit}
■ ^{Integrated start-up regulator}
■ ^{No loop compensation required}
■ ^{Ultra-Fast transient response}
■ ^{Maximum switching frequency: 1.3 MHz}
■ ^{Operating frequency remains nearly constant with load}
current and input voltage variations
■ ^{Programmable soft-start}
■ ^{Precision internal reference}
■ ^{Adjustable output voltage}
■ ^{Thermal shutdown}
Typical Applications
■ ^{High Efficiency Point-Of-Load (POL) Regulator}
■ ^{Non-Isolated Buck Regulator}
■ ^{Secondary High Voltage Post Regulator}
Package
■ ^{LLP-10 (3 mm x 3mm)}
■ ^{Exposed Thermal Pad For Improved Heat Dissipation}
Basic Step Down Regulator
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