Features Input voltage from 3.0V to 5.5V Output voltage adjustable down to 0.8V Reference accuracy: ±1.75%, over full temperature and input voltage range High-side and Low-side N-Channel MOSFETs Switching frequency options of 1 MHz or 300 kHz Comprehensive Fault Protection Features:  High-side current limit  Low-side current limit  Output under-voltage protection Hiccup mode protection eliminates thermal runaway during fault conditions Externally programmable soft-start with tracking capability Pre-bias start-up capability MSOP-10 package Description The LM3743 is a DC-DC voltage mode PWM buck controller featuring synchronous rectification at 300 kHz or 1 MHz. It can deliver current as high as 20A and step down from an input voltage between 3V and 5.5V down to a minimum output voltage of 0.8V, with a ±1.75% internal reference accuracy. The LM3743 provides a set of comprehensive fault protection features such as high-side current limit, output under-voltage protection, and low-side current limit. When any of these fault protection features are engaged, it enters a hiccup protection mode which is suitable for high reliability systems such as rack mounted servers and telecom base station subsystems. The LM3743 also employs a proprietary monolithic glitch free pre-bias start-up method suited for FPGA and ASIC logic devices. An external programmable soft-start allows for tracking and timing flexibility. The driver features 1.6Ω of pull-up resistance and 1Ω of pull-down drive resistance for high power density and very efficient power processing. Applications Rack-mount servers Telecom base stations Routers Printers/Scanners Multi-media set-top boxes FPGAs, ASICs, and DSPs

Also Recommended LM1770▲ SOT23 Synchronous Buck Controller LM1771▲ Synchronous Buck Controller With Precision Enable LM2743▲ Synchronous Buck Controller With Vin Up To 16V

Typical Application click for larger image	Block Diagram click for larger image
Typical Performance *click for larger image 300 kHz, Vout = 2.5V

Parameters / Values	LM3743	LM1770	LM1771	LM2743
Output Current	10000 mA	4000 mA	6000 mA	20000 mA
Input Min Voltage	3 Volt	2.8 Volt	2.8 Volt	1 Volt
Input Max Voltage	5.5 Volt	5.5 Volt	5.5 Volt	16 Volt
Feedback Voltage	0.8 Volt	0.8 Volt	0.8 Volt	0.6 Volt
Feedback Tolerance	1.75 %	2 %	2 %
Frequency Min	300 kHz	300 kHz	300 kHz	50 kHz
Frequency Max	1000 kHz	1000 kHz	1000 kHz	2000 kHz
Efficiency (peak)	95 %	95 %	95 %	85 %
Output Range	0.8V to 4.6V	0.8V to 4.5V	0.8V to 4.5V	0.6V to 13.5V
Adj Switch Frequency	No	No	No	Yes
Adjustable Output	Yes	Yes	Yes	Yes
Synchronous Rectification	Yes	Yes	Yes
On/Off Pin	Yes	No	Yes	Yes
PowerGood / Error Flag	No	No	No	Yes
SoftStart	Yes	Yes	Yes	Yes
Sync Pin	No	No	No	No
Inverting	No	Yes	No	No
Flyback	No	No	No	No
Lossless Current Sense	Yes	No	No	Yes
RegType	Switching Regulator	Switching Controller	Switching Controller	Switching Controller
Temperature Min	-40 deg C	-40 deg C	-40 deg C	-40 deg C
Temperature Max	125 deg C	125 deg C	125 deg C	125 deg C
Channels	1 Channels	1 Channels	1 Channels	1 Channels
Special Features	Pre-bias start-up; Hiccup mode; External programmable soft-start and tracking	No compensation required	Precision enable for sequencing multiple rails	2.7V UVLO; Tri-State output during SD; Tracking; Precision SD threshold
Topology	Buck	Buck	Buck	Buck
PWM Mode	Voltage	Constant on-time	Constant on-time	Voltage
Step-Down	Yes	No	Yes	Yes
Step-Up	No	No	No	No
Output Power	Undefined Watt		Undefined Watt	Undefined Watt
Output Max	4.6 Volt	4.5 Volt	4.5 Volt	13.5 Volt
Output Min	0.8 Volt	0.8 Volt	0.8 Volt	0.6 Volt
PowerWise	Yes	Yes	Yes	Yes

Datasheets

Title		Size	Date	Other Language
	LM3743 High-Performance Synchronous Buck Controller with Comprehensive Fault Protection Features	590 Kbytes	7-Oct-08

Application Notes

Title		Size	Date	Other Language
	AN-1669: Application Note 1669 LM3743 High Performance Controller with Comprehensive Fault Protection Features Designed for High Reliability Systems	118 Kbytes	19-Jun-07	日本語 中文
	AN-1450: Application Note 1450 LM3743 Evaluation Board	694 Kbytes	12-Sep-06	中文
	AN-1997: Application Note 1997 Error Amplifier Limitations in High Performance Regulator Applications	274 Kbytes	13-Nov-09

Other Technical Documents

Title		Type	Date
	Error amplifier limitations in high-performance regulator applications	External Article	2009-06-24
	Voltage-Mode Control and Compensation: Intricacies for Buck Regulators	External Article	2008-06-30
	Power Supply Design Considerations for Modern FPGAs	Power Designer	2010-02-02

Part Number(s) (NSID)	Top View	Availability	Current Reported Stock	Budgetary Pricing	Pack Size
LM3743MM-1000/NOPB LM3743MM-1000 RoHS Status	MINI SOIC	Full production Lead Time: 6 weeks	Distributor Region Qty DIGI-KEY Worldwide 0	$1.10 each at 1K+ pcs	reel of 1000
LM3743MM-300/NOPB LM3743MM-300 RoHS Status	MINI SOIC	Full production Lead Time: 6 weeks	Distributor Region Qty DIGI-KEY Worldwide 1000 MOUSER Worldwide 890	$1.10 each at 1K+ pcs	reel of 1000
LM3743MMX-1000/NOPB LM3743MMX-1000 RoHS Status	MINI SOIC	Full production Lead Time: 8 weeks	Distributor Region Qty DIGI-KEY Worldwide 0	$1.10 each at 1K+ pcs	reel of 3500
LM3743MMX-300/NOPB LM3743MMX-300 RoHS Status	MINI SOIC	Full production Lead Time: 8 weeks	Distributor Region Qty DIGI-KEY Worldwide 0	$1.10 each at 1K+ pcs	reel of 3500

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 LM3743.

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 LM3743 is located at RoHS Status.

Part Number(s) (NSID)	Description	Availability	Current Reported Stock	Budgetary Pricing	Pack Size
LM3743-1000EVAL	N-Channel FET Synchronous Buck Regulator Controller for Low Output Voltages	Full production	Distributor Region Qty DIGI-KEY Worldwide 0 MOUSER Worldwide 1	$77.30 each	1
LM3743 N-Channel FET Synchronous Buck Controler for Low Output Voltages Features: Input voltage from 3.0V to 5.5V Output voltage adjustable down to 0.8V Reference accuracy ±1.75%, over full temperature and input voltage range Low-side sensing programmable current limit Fixed high-side sensing for supplemental short-circuit protection Undervoltage protection Hiccup mode protection eliminates thermal runaway during fault conditions Externally programmable soft-start with tracking capability Switching frequency options of 1 MHz or 300 kHz Pre-bias start-up capability MSOP-10 package Applications: ASIC/FPGA/DSP core power Broadband Communications Multi-Media Set Top Boxes Networking Equipment Printers/Scanners Servers Low-Voltage Distributed Power

Part Number(s) (NSID)	Description	Availability	Current Reported Stock	Budgetary Pricing	Pack Size
LM3743-300EVAL	N-Channel FET Synchronous Buck Regulator Controller for Low Output Voltages	Full production	Distributor Region Qty DIGI-KEY Worldwide 0	$77.30 each	1
Features: Input voltage from 3.0V to 5.5V Output voltage adjustable down to 0.8V Reference accuracy ±1.75%, over full temperature and input voltage range Low-side sensing programmable current limit Fixed high-side sensing for supplemental short-circuit protection Undervoltage protection Hiccup mode protection eliminates thermal runaway during fault conditions Externally programmable soft-start with tracking capability Switching frequency options of 1 MHz or 300 kHz Pre-bias start-up capability MSOP-10 package Applications: ASIC/FPGA/DSP core power Broadband Communications Multi-Media Set Top Boxes Networking Equipment Printers/Scanners Servers Low-Voltage Distributed Power

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
LM3743MM-1000/NOPB LM3743MM-1000	29.841 30.002	MINI SOIC	10	1 1	260 260	Detail	Download	N/A	ZXTT SKNB
LM3743MM-300/NOPB LM3743MM-300	29.841 30.002	MINI SOIC	10	1 1	260 260	Detail	Download	N/A	ZXTT SKPB
LM3743MMX-1000/NOPB LM3743MMX-1000	29.841 30.002	MINI SOIC	10	1 1	260 260	Detail	Download	N/A	ZXTT SKNB
LM3743MMX-300/NOPB LM3743MMX-300	29.841 30.002	MINI SOIC	10	1 1	260 260	Detail	Download	N/A	ZXTT SKPB

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 LM3743.

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 LM3743 is located at RoHS Status.

Design Tools

Title	Size	Date
Article - Voltage Mode Compensation of Buck Regulators

CAD Symbols and Models Download LM3743 CAD Symbols

Models N/A

Reliability Metrics

Part Number	Process	EFR Reject	EFR Sample Size	PPM	LTA Rejects	LTA Device Hours	FITS	MTTF (Hours)
LM3743MM-1000	PVIP050	0	14280	0	0	1755000	3	497986041
LM3743MM-300	PVIP050	0	14280	0	0	1755000	3	497986041
LM3743MMX-1000	PVIP050	0	14280	0	0	1755000	3	497986041
LM3743MMX-300	PVIP050	0	14280	0	0	1755000	3	497986041

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 LM3743.

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 LM3743 is located at RoHS Status.