Features • Input voltage range from 4.5V to 28V • Synchronous dual-channel interleaved switching • Forced-PWM or Pulse-skip modes • Lossless bottom-side FET current sensing • Adaptive duty cycle clamp • High current N-channel FET drivers • Low shutdown supply current • Reference voltage accurate to within ±1.5% • Output voltage adjustable down to 0.6V • Power Good flag and Chip Enable • Under-voltage lockout • Over-voltage/Under-voltage protection • Soft-start • Switching frequency adjustable 200kHz-500kHz • TSSOP-28 package Description The LM2657 is an adjustable 200kHz-500kHz dual channel voltage-mode controlled high-speed synchronous buck regulator controller ideally suited for high current applications. The LM2657 requires only N-channel FETs for both the upper and lower positions of each stage. It features line feedforward to improve the response to input transients. At very light loads, the user can choose between the high-efficiency Pulse-skip mode or the constant frequency Forced-PWM mode. Lossless current limiting without the use of external sense resistors is made possible by sensing the voltage drop across the bottom FET. A unique adaptive duty cycle clamping technique is incorporated to significantly reduce peak currents under abnormal load conditions. The two independently programmable outputs switch 180° out of phase (interleaved switching) reducing the input capacitor and filter requirements. The input voltage range is 4.5V to 28V while the output voltages are adjustable down to 0.6V. Standard supervisory and control features include Soft-start, Power Good, output Under-voltage and Over-voltage protection, Under-voltage Lockout, and chip Enable. Applications • Low Output Voltage High-Efficiency Buck Regulators

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Datasheets

Title		Size	Date	Other Language
	LM2657 Dual Synchronous Buck Regulator Controller	982 Kbytes	15-Mar-05

Part Number(s) (NSID)	Top View	Availability	Current Reported Stock	Budgetary Pricing	Standard Pack Size
LM2657MTC/NOPB LM2657MTC RoHS Status	TSSOP	Full production Lead Time: 8 weeks	Distributor Region Qty ARROW Worldwide 192 AVNET-EM Worldwide 5 DIGIKEY Worldwide 384 FARNELL Europe and Asia 230 FUTURE Worldwide 192 RS COMPONENTS Worldwide 45	$1.75 each at 1K+ pcs	rail of 48
LM2657MTCX/NOPB LM2657MTCX RoHS Status	TSSOP	Full production Lead Time: 6 weeks	Distributor Region Qty DIGIKEY Worldwide 0	$1.75 each at 1K+ pcs	reel of 2500

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

Part Number(s) (NSID)	Top View	Type	Pins	MSL Rating	Peak Reflow	RoHS Status	CAD Symbols	Models	Package Marking Format
LM2657MTC/NOPB LM2657MTC		TSSOP	28	3 3	260 235	Detail	Download	N/A	NSUZXYTTE# LM2657 MTC
LM2657MTCX/NOPB LM2657MTCX		TSSOP	28	3 3	260 235	Detail	Download	N/A	NSUZXYTTE# LM2657 MTC

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

A RoHS compliance or an IPC 1752 report can be acquired at http://www.national.com/quality/green.

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

Design Tools

Title	Size	Date
Article - Reducing Buck Converter Input Capacitance through Multi-Phasing and Clock Synchronization
Article - Robust Controller Design Using Multi-Objective Optimization

CAD Symbols and Models Download LM2657 CAD Symbols

Models N/A

Reliability Metrics

Part Number	Process	EFR Reject	EFR Sample Size	PPM	LTA Rejects	LTA Device Hours	FITS	MTTF (Hours)
LM2657MTC	ABCD150	0	34175	0	0	4234000	1	1201409060
LM2657MTCX	ABCD150	0	34175	0	0	4234000	1	1201409060

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.

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

A RoHS compliance or an IPC 1752 report can be acquired at http://www.national.com/quality/green.

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