LM34917A Datasheet, PDF (1/16 Pages) National Semiconductor (TI) – Ultra Small 33V, 1.25A Constant On-Time Buck Switching Regulator with Intelligent Current Limit

May 8, 2008
LM34917A
Ultra Small 33V, 1.25A Constant On-Time Buck Switching
Regulator with Intelligent Current Limit
General Description
The LM34917A 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
an N-Channel Buck Switch, and is available in the 12 pin mi-
cro SMD package. The constant on-time feedback regulation
scheme requires no loop compensation, results in fast load
transient response, and simplifies circuit implementation. The
operating frequency remains constant with line and load vari-
ations due to the inverse relationship between the input volt-
age 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: V_CC under-voltage lock-out, input over-volt-
age shutdown, thermal shutdown, gate drive under-voltage
lock-out, and maximum duty cycle limit.
Features
■ ^{Transient Capability to 50V}
■ ^{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: 2 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}
■ ^{Functional Input Voltage Range: 8V to 33V}
■ ^{Micro SMD package}
■ ^{Input Over-Voltage Shutdown at ≊35V}
Package
■ ^{micro SMD Package}
Basic Step Down Regulator
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