Features Functional Input Voltage Range: 8V to 33V Micro SMD package Input Over-Voltage Shutdown at ≊35V Transient Capability to 50V Integrated N-Channel buck switch Valley current limit varies with VIN and VOUT 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 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 voltage, without the use of foldback. Additional features include: VCC under-voltage lock-out, input over-voltage shutdown, thermal shutdown, gate drive under-voltage lock-out, and maximum duty cycle limit.

WEBENCH® LM34917A     Min   Max   Range     VIN – V    8.00 – 33.00V     VOUT V    2.51 – 30.00V     IOUT A    ≤ 1.20A     Ambient Temp °C    ≤ 100°C   Footprint BOM Cost Efficiency What are WEBENCH® tools? LM34917A Basic Step Down Regulator

Typical Application *click for larger image LM34917A Basic Step Down Regulator	Block Diagram *click for larger image LM34917A Typical Application and Block Diagram
Typical Performance *click for larger image Typical Performance at 1.5 MHz

Parameters Values Output Current 1250 mA Input Min Voltage 8 Volt Input Max Voltage 33 Volt Output Min 2.5 Volt Output Max 30 Volt Frequency Min Undefined kHz Frequency Max 2000 kHz Efficiency (peak) 92 % On/Off Pin Yes PowerGood / Error Flag No SoftStart Yes Sync Pin No Inverting Yes Flyback No RegType Switching Regulator Temperature Min -40 deg C Temperature Max 125 deg C Adjustable Output Yes Adj Switch Frequency Yes PWM Mode Constant on-time Topology Buck Special Features Intellegent Current Limit, No Loop Compensation Required Step-Down Yes Multiple Output Capability No Output Power Undefined Watt Output Voltage Undefined Volt Output Range Undefined Feedback Voltage 2.5 Volt Regulator Family Undefined Automotive No PowerWise Yes Synchronous Rectification No

Datasheets

Title		Size	Date	Other Language
	LM34917A Ultra Small 33V, 1.25A Constant On-Time Buck Switching Regulator with Intelligent Current Limit	555 Kbytes	8-May-08

Part Number(s) (NSID)	Top View	Availability	Current Reported Stock	Budgetary Pricing	Pack Size
LM34917ATL/NOPB RoHS Status	MICRO SMD	Full production Lead Time: 6 weeks	Distributor Region Qty DIGI-KEY Worldwide 692 MOUSER Worldwide 500	$1.35 each at 1K+ pcs	reel of 250
LM34917ATLX/NOPB RoHS Status	MICRO SMD	Full production Lead Time: 6 weeks	Distributor Region Qty DIGI-KEY Worldwide 0	$1.35 each at 1K+ pcs	reel of 3000

All information pertaining to the RoHS Compliance Standard can be found at http://www.national.com/en/packaging/leadfree.html.

Moisture Sensitivity Level Data for LM34917A.

A RoHS compliance or an IPC 1752 report can be acquired at http://www.national.com/en/packaging/greennopb.html.

National's certificate of product compliance for LM34917A is located at RoHS Status.

Part Number(s) (NSID)	Description	Availability	Current Reported Stock	Budgetary Pricing	Pack Size
LM34917AEVAL	Evaluation Board for the LM34917AEVAL 33V, 1.3A Step-Down Switching Regulator with Over-Voltage Shutdown	Full production	Distributor Region Qty DIGI-KEY Worldwide 0 MOUSER Worldwide 1	$45.00 each	1
Description: The LM34917AEVAL evaluation board provides the design engineer with a fully functional buck regulator, employing the constant on-time (COT) operating principle. This evaluation board provides a 5V output over an input range of 8V to 33V. The circuit delivers load currents to 1A, with current limit set at approximately 1.3A. Over-Voltage shutdown occurs at 35V. Contents: LM34917A Assembled Evaluation Board LM34917A Datasheet Application Note 1601 LM34917A Evaluation Board

National Semiconductor follows the provisions of the Product Stewardship Guide for Customers (CSP-9-111C1) and Banned Substances and Materials of Interest Specification (CSP-9-111S2) for regulatory environmental compliance. Details may be found at: www.national.com/en/packaging/greennopb.html. Lead free products are RoHS compliant.

Lead Free product status is available through the search tool located here

Part Number(s) (NSID)	Weight (milligrams)	Type	Pins	MSL Rating	Peak Reflow	RoHS Status	CAD Symbols	Models	Package Marking Format
LM34917ATL/NOPB	4.918	MICRO SMD	12	1	260	Detail	Download	N/A	XYTT I SRHA
LM34917ATLX/NOPB	4.918	MICRO SMD	12	1	260	Detail	Download	N/A	XYTT I SRHA

All information pertaining to the RoHS Compliance Standard can be found at http://www.national.com/en/packaging/leadfree.html.

Moisture Sensitivity Level Data for LM34917A.

A RoHS compliance or an IPC 1752 report can be acquired at http://www.national.com/en/packaging/greennopb.html.

National's certificate of product compliance for LM34917A is located at RoHS Status.

Design Tools

Title	Size	Date
LM34917A Quick Start Calculator

CAD Symbols and Models Download LM34917A CAD Symbols

Models N/A

Reliability Metrics

Part Number	Process	EFR Reject	EFR Sample Size	PPM	LTA Rejects	LTA Device Hours	FITS	MTTF (Hours)
LM34917ATL	ABCD150XV1	0	3868	0	0	2595000	2	736338335
LM34917ATLX	ABCD150XV1	0	3868	0	0	2595000	2	736338335

Note: The Early Failure Rates (EFR) were calculated as point estimate PPM based on rejects and sample size for EFR. The Long Term Failure Rates were calculated at 60% confidence using the Arrhenius equation at 0.7eV activation energy and derating the assumed stress temperature of 150°C to an application temperature of 55°C.

For more information on Reliability Metrics, please click here.

All information pertaining to the RoHS Compliance Standard can be found at http://www.national.com/en/packaging/leadfree.html.

Moisture Sensitivity Level Data for LM34917A.

A RoHS compliance or an IPC 1752 report can be acquired at http://www.national.com/en/packaging/greennopb.html.

National's certificate of product compliance for LM34917A is located at RoHS Status.