LM34917A

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SNOSAX7C – DECEMBER 2007 – REVISED MAY 2008

LM34917A Ultra Small 33V, 1.25A Constant On-Time Buck Switching Regulator with

Intelligent Current Limit

Check for Samples: LM34917A

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FEATURES

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Maximum switching frequency: 2 MHz

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Operating frequency remains nearly constant

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Functional Input Voltage Range: 8V to 33V

with load current and input voltage variations

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Micro SMD package

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Programmable soft-start

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Input Over-Voltage Shutdown at

≊

≊35V

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Precision internal reference

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Transient Capability to 50V

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Adjustable output voltage

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Integrated N-Channel buck switch

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Thermal shutdown

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reduce excessive inductor current

TYPICAL APPLICATIONS

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On-time is reduced when in current limit

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High Efficiency Point-Of-Load (POL) Regulator

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Integrated start-up regulator

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Non-Isolated Buck Regulator

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No loop compensation required

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Secondary High Voltage Post Regulator

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Ultra-Fast transient response

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 micro 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 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

shutdown, thermal shutdown, gate drive under-voltage lock-out, and maximum duty cycle limit.

Package

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micro SMD Package

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PRODUCTION DATA information is current as of publication date.

Copyright © 2007–2008, Texas Instruments Incorporated

Products conform to specifications per the terms of the Texas

Instruments standard warranty. Production processing does not

necessarily include testing of all parameters.