NSC LM2733XMF, LM2733XEVAL, LM2733YMF, LM2733YEVAL, LM2733XMFX Datasheet

February 2003

LM2733

0.6/1.6 MHz Boost Converters With 40V Internal FET

Switch in SOT-23

General Description

The LM2733 switching regulators are current-mode boost converters operating fixed frequency of 1.6 MHz (“X” option) and 600 kHz (“Y” option).

The use of SOT-23 package, made possible by the minimal power loss of the internal 1A switch, and use of small inductors and capacitors result in the industry’s highest power density. The 40V internal switch makes these solutions perfect for boosting to voltages of 16V or greater.

These parts have a logic-level shutdown pin that can be used to reduce quiescent current and extend battery life.

Protection is provided through cycle-by-cycle current limiting and thermal shutdown. Internal compensation simplifies design and reduces component count.

Switch Frequency

X	Y
1.6 MHz	0.6 MHz

Features

n40V DMOS FET switch

n1.6 MHz (“X”), 0.6 MHz (“Y”) switching frequency

nLow RDS(ON) DMOS FET

nSwitch current up to 1A

nWide input voltage range (2.7V–14V)

nLow shutdown current (<1 µA)

n5-Lead SOT-23 package

nUses tiny capacitors and inductors

nCycle-by-cycle current limiting

nInternally compensated

Applications

nWhite LED Current Source

nPDA’s and Palm-Top Computers

nDigital Cameras

nPortable Phones and Games

nLocal Boost Regulator

Typical Application Circuit

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23-SOT in Switch FET Internal 40V With Converters Boost MHz 6.6/1.0 LM2733

© 2003 National Semiconductor Corporation

DS200554

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LM2733

Typical Application Circuit (Continued)

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Connection Diagram

Top View

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5-Lead SOT-23 Package

See NS Package Number MF05A

Ordering Information

	Order Number	Package Type	Package Drawing	Supplied As	Package ID
	LM2733XMF			1K Tape and Reel	S52A
	LM2733XMFX	SOT23-5	MF05A	3K Tape and Reel	S52A
	LM2733YMF			1K Tape and Reel	S52B
	LM2733YMFX			3K Tape and Reel	S52B

Pin Description

Pin		Name		Function
1		SW		Drain of the internal FET switch.
2		GND		Analog and power ground.
3		FB		Feedback point that connects to external resistive divider.
4				Shutdown control input. Connect to VIN if this feature is not used.
		SHDN
5		VIN		Analog and power input.

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Block Diagram

Theory of Operation

The LM2733 is a switching converter IC that operates at a fixed frequency (0.6 or 1.6 MHz) using current-mode control for fast transient response over a wide input voltage range and incorporate pulse-by-pulse current limiting protection. Because this is current mode control, a 50 mΩ sense resistor in series with the switch FET is used to provide a voltage (which is proportional to the FET current) to both the input of the pulse width modulation (PWM) comparator and the current limit amplifier.

At the beginning of each cycle, the S-R latch turns on the FET. As the current through the FET increases, a voltage (proportional to this current) is summed with the ramp coming from the ramp generator and then fed into the input of the PWM comparator. When this voltage exceeds the voltage on the other input (coming from the Gm amplifier), the latch resets and turns the FET off. Since the signal coming from

LM2733

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the Gm amplifier is derived from the feedback (which samples the voltage at the output), the action of the PWM comparator constantly sets the correct peak current through the FET to keep the output volatge in regulation.

Q1 and Q2 along with R3 - R6 form a bandgap voltage reference used by the IC to hold the output in regulation. The currents flowing through Q1 and Q2 will be equal, and the feedback loop will adjust the regulated output to maintain this. Because of this, the regulated output is always maintained at a voltage level equal to the voltage at the FB node "multiplied up" by the ratio of the output resistive divider.

The current limit comparator feeds directly into the flip-flop, that drives the switch FET. If the FET current reaches the limit threshold, the FET is turned off and the cycle terminated until the next clock pulse. The current limit input terminates the pulse regardless of the status of the output of the PWM comparator.

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LM2733

Absolute Maximum Ratings (Note 1)

If Military/Aerospace specified devices are required, please contact the National Semiconductor Sales Office/ Distributors for availability and specifications.

Storage Temperature Range	−65˚C to +150˚C
Operating Junction
Temperature Range	−40˚C to +125˚C
Lead Temp. (Soldering, 5 sec.)	300˚C
Power Dissipation (Note 2)	Internally Limited

FB Pin Voltage	−0.4V to +6V
SW Pin Voltage	−0.4V to +40V
Input Supply Voltage	−0.4V to +14.5V
Shutdown Input Voltage
(Survival)	−0.4V to +14.5V
θJ-A (SOT23-5)	265˚C/W
ESD Rating (Note 3)
Human Body Model	2 kV
Machine Model	200V

Electrical Characteristics

Limits in standard typeface are for TJ = 25˚C, and limits in boldface type apply over the full operating temperature range (−40˚C ≤ TJ ≤ +125˚C). Unless otherwise specified: VIN = 5V, VSHDN = 5V, IL = 0A.

	Symbol	Parameter	Conditions	Min	Typical	Max	Units
				(Note 4)	(Note 5)	(Note 4)
	VIN	Input Voltage		2.7		14	V
	ISW	Switch Current Limit	(Note 6)	1.0	1.5		A
	RDS(ON)	Switch ON Resistance	ISW = 100 mA		500	650	mΩ
	SHDNTH	Shutdown Threshold	Device ON	1.5			V
			Device OFF			0.50
	ISHDN	Shutdown Pin Bias Current	VSHDN = 0		0		µA
			VSHDN = 5V		0	2
	VFB	Feedback Pin Reference	VIN = 3V	1.205	1.230	1.255	V
		Voltage
	IFB	Feedback Pin Bias Current	VFB = 1.23V		60		nA
	IQ	Quiescent Current	VSHDN = 5V, Switching "X"		2.1	3.0	mA
			VSHDN = 5V, Switching "Y"		1.1	2
			VSHDN = 5V, Not Switching		400	500	µA
			VSHDN = 0		0.024	1
		FB Voltage Line Regulation	2.7V ≤ VIN ≤ 14V		0.02		%/V
	FSW	Switching Frequency	“X” Option	1.15	1.6	1.85	MHz
			“Y” Option	0.40	0.60	0.8
	DMAX	Maximum Duty Cycle	“X” Option	87	93		%
			“Y” Option	93	96
	IL	Switch Leakage	Not Switching VSW = 5V			1	µA

Note 1: Absolute Maximum Ratings indicate limits beyond which damage to the component may occur. Electrical specifications do not apply when operating the device outside of the limits set forth under the operating ratings which specify the intended range of operating conditions.

Note 2: The maximum power dissipation which can be safely dissipated for any application is a function of the maximum junction temperature, TJ(MAX) = 125˚C, the junction-to-ambient thermal resistance for the SOT-23 package, θJ-A = 265˚C/W, and the ambient temperature, TA. The maximum allowable power dissipation at any ambient temperature for designs using this device can be calculated using the formula:

If power dissipation exceeds the maximum specified above, the internal thermal protection circuitry will protect the device by reducing the output voltage as required to maintain a safe junction temperature.

Note 3: The human body model is a 100 pF capacitor discharged through a 1.5 kΩ resistor into each pin. The machine model is a 200 pF capacitor discharged directly into each pin.

Note 4: Limits are guaranteed by testing, statistical correlation, or design.

Note 5: Typical values are derived from the mean value of a large quantity of samples tested during characterization and represent the most likely expected value of the parameter at room temperature.

Note 6: Switch current limit is dependent on duty cycle (see Typical Performance Characteristics). Limits shown are for duty cycles ≤ 50%.

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