Linear Technology LT1767EMS8-1.8, LT1767EMS8, LT1767EMS8E-5, LT1767EMS8E-3.3, LT1767EMS8E-2.5 Datasheet

Monolithic 1.5A, 1.25MHz

Step-Down Switching Regulators

FEATURES

■1.5A Switch in a Small MSOP Package

■Constant 1.25MHz Switching Frequency

■High Power Exposed Pad (MS8E) Package

■Wide Operating Voltage Range: 3V to 25V

■High Efficiency 0.22Ω Switch

■1.2V Feedback Reference Voltage

■Fixed Output Voltages of 1.8V, 2.5V, 3.3V, 5V

■2% Overall Output Tolerance

■Uses Low Profile Surface Mount Components

■Low Shutdown Current: 6µA

■Synchronizable to 2MHz

■Current Mode Loop Control

■Constant Maximum Switch Current Rating at All Duty Cycles*

APPLICATIOUS

■DSL Modems

■Portable Computers

■Wall Adapters

■Battery-Powered Systems

■Distributed Power

DESCRIPTIOU

The LT®1767 is a 1.25MHz monolithic buck switching regulator. A high efficiency 1.5A, 0.22Ω switch is included on the die together with all the control circuitry required to complete a high frequency, current mode switching regulator. Current mode control provides fast transient response and excellent loop stability.

New design techniques achieve high efficiency at high switching frequencies over a wide operating range. A low dropout internal regulator maintains consistent performance over a wide range of inputs from 24V systems to LiIon batteries. An operating supply current of 1mA improves efficiency, especially at lower output currents. Shutdown reduces quiescent current to 6µA. Maximum switch current remains constant at all duty cycles. Synchronization allows an external logic level signal to increase the internal oscillator from 1.4MHz to 2MHz.

The LT1767 is available in an 8-pin MSOP fused leadframe package and a low thermal resistance exposed pad package. Full cycle-by-cycle short-circuit protection and thermal shutdown are provided. High frequency operation allows the reduction of input and output filtering components and permits the use of chip inductors.

, LTC and LT are registered trademarks of Linear Technology Corporation.

*Patent Pending

TYPICAL APPLICATIOU

			12V to 3.3V Step-Down Converter
						D2
						CMDSH-3
					C2
					0.1 F	L1
VIN				BOOST		5 H	OUTPUT
			VIN		VSW		3.3V
12V	C3
		OPEN		LT1767-3.3			1.2A*
	2.2 F
		OR
CERAMIC			SHDN		FB
		HIGH
			SYNC	GND	VC
		= ON					C1
					CC	D1	10 F
					1.5nF	UPS120	CERAMIC
					RC
					4.7k
*MAXIMUM OUTPUT CURRENT IS SUBJECT TO THERMAL DERATING.							1767 TA01

EFFICIENCY (%)

		Efficiency vs Load Current
95
										VIN = 10V
90										VOUT = 5V
85
										VIN = 5V
80										VOUT = 3.3V
75
70
		0.2		0.4		0.6		0.8		1		1.2			1.4
0

LOAD CURRENT (A)

1767 TA01a

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LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5

ABSOLUTE WMAXIWMUWM RATINGSU

(Note 1)

Input Voltage ..........................................................	25V
BOOST Pin Above SW ............................................	20V
Max BOOST Pin Voltage ..........................................	35V
SHDN Pin ...............................................................	25V
FB Pin Voltage ..........................................................	6V
FB Pin Current .......................................................	1mA

SYNC Pin Current ..................................................	1mA
Operating Junction Temperature Range (Note 2)
LT1767E ..........................................	– 40°C to 125°C
Storage Temperature Range ................	– 65°C to 150°C
Lead Temperature (Soldering, 10 sec).................	300°C

PACKAGE/ORDER IUNFORWMATIOUN

		TOP VIEW
BOOST	1	8	SYNC
VIN	2	7	VC
SW	3	6	FB
GND	4	5	SHDN
		MS8 PACKAGE

8-LEAD PLASTIC MSOP

TJMAX = 125°C, θJA = 110°C/W

GROUND PIN CONNECTED

TO LARGE COPPER AREA

ORDER PART NUMBER

LT1767EMS8

LT1767EMS8-1.8

LT1767EMS8-2.5

LT1767EMS8-3.3

LT1767EMS8-5

MS8 PART MARKING

LTLS

LTWG

LTWD

LTWE

LTWF

		TOP VIEW
BOOST	1	8	SYNC
VIN	2	7	VC
SW	3	6	FB
GND	4	5	SHDN

MS8E PACKAGE

8-LEAD PLASTIC MSOP

TJMAX = 125°C, θJA = 40°C/W

EXPOSED GND PAD

CONNECTED TO LARGE

COPPER AREA ON PCB

ORDER PART NUMBER

LT1767EMS8E LT1767EMS8E-1.8 LT1767EMS8E-2.5 LT1767EMS8E-3.3 LT1767EMS8E-5

MS8E PART MARKING

LTZG

LTZH

LTZJ

LTZK

LTZL

Consult LTC Marketing for parts specified with wider operating temperature ranges.

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.

VIN = 15V, VC = 0.8V, Boost = VIN + 5V, SHDN, SYNC and switch open unless otherwise noted.

PARAMETER	CONDITION					MIN	TYP	MAX	UNITS
Maximum Switch Current Limit	TA = 0°C to 125°C					1.5	2	3	A
	TA = < 0°C					1.3		3	A
Oscillator Frequency	3.3V < VIN < 25V					1.1	1.25	1.4	MHz
					●	1.1		1.5	MHz
Switch On Voltage Drop	ISW = –1.5A, 0°C ≤ TA ≤ 125°C and –1.3A, TA < 0°C						330	400	mV
					●			500	mV
VIN Undervoltage Lockout	(Note 3)				●	2.47	2.6	2.73	V
VIN Supply Current	VFB = VNOM + 17%				●		1	1.3	mA
Shutdown Supply Current	V		= 0V, VIN = 25V, VSW = 0V				6	20	A
		SHDN
					●			45	A
Feedback Voltage	3V < VIN < 25V, 0.4V < VC < 0.9V			LT1767 (Adj)		1.182	1.2	1.218	V
	(Note 3)				●	1.176		1.224	V
				LT1767-1.8	●	1.764	1.8	1.836	V
				LT1767-2.5	●	2.45	2.5	2.55	V
				LT1767-3.3	●	3.234	3.3	3.366	V
				LT1767-5	●	4.9	5	5.1	V
FB Input Current	LT1767 (Adj)				●		– 0.25	– 0.5	A

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LT1767/LT1767-1.8/

LT1767-2.5/LT1767-3.3/LT1767-5

ELECTRICAL CHARACTERISTICS

The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C.

VIN = 15V, VC = 0.8V, Boost = VIN + 5V, SHDN, SYNC and switch open unless otherwise noted.

PARAMETER		CONDITION				MIN	TYP	MAX	UNITS
FB Input Resistance		LT1767-1.8			●	10.5	15	21	kΩ
		LT1767-2.5			●	14.7	21	30	kΩ
		LT1767-3.3			●	19	27.5	39	kΩ
		LT1767-5			●	29	42	60	kΩ
Error Amp Voltage Gain		0.4V < VC < 0.9V				150	350
Error Amp Transconductance			IVC = ±10µA		●	500	850	1300	µMho
VC Pin Source Current		VFB = VNOM – 17%			●	80	120	160	µA
VC Pin Sink Current		VFB = VNOM + 17%			●	70	110	180	µA
VC Pin to Switch Current Transconductance							2.5		A/V
VC Pin Minimum Switching Threshold		Duty Cycle = 0%					0.35		V
VC Pin 1.5A ISW Threshold							0.9		V
Maximum Switch Duty Cycle		VC = 1.2V, ISW = 400mA				85	90		%
					●	80			%
Minimum Boost Voltage Above Switch		ISW = –1.5A, 0°C ≤ TA ≤ 125°C and –1.3A, TA < 0°C			●		1.8	2.7	V
Boost Current		ISW = – 0.5A (Note 4)			●		10	15	mA
		ISW = –1.5A, 0°C ≤ TA ≤ 125°C and –1.3A, TA < 0°C (Note 4)			●		30	45	mA
	Threshold Voltage					1.27	1.33	1.40	V
SHDN					●
	Input Current (Shutting Down)			= 60mV Above Threshold		– 7	–10	–13	µA
SHDN			SHDN		●
	Threshold Current Hysteresis			= 100mV Below Threshold		4	7	10	µA
SHDN			SHDN		●
SYNC Threshold Voltage							1.5	2.2	V
SYNC Input Frequency						1.5		2	MHz
SYNC Pin Resistance		ISYNC = 1mA					20		kΩ

Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired.

Note 2: The LT1767E is guaranteed to meet performance specifications from 0°C to 125°C. Specifications over the – 40°C to 125°C operating junction temperature range are assured by design, characterization and correlation with statistical process controls.

Note 3: Minimum input voltage is defined as the voltage where the internal regulator enters lockout. Actual minimum input voltage to maintain a regulated output will depend on output voltage and load current. See Applications Information.

Note 4: Current flows into the BOOST pin only during the on period of the switch cycle.

TYPICAL PERFORWMAUNCE CHARACTERISTICS

FB VOLTAGE (V)

FB vs Temperature (Adj)

1.22

1.21

1.20

1.19

1.18
		–25	0	25	50	75	100	125
–50
			TEMPERATURE (°C)					1767 G01

SWITCH VOLTAGE (mV)

Switch On Voltage Drop

400

125°C

350

300		25°C

250

–40°C

200

150

100

50

0

0	0.5	1	1.5
	SWITCH CURRENT (A)		1767 G02

FREQUENCY (MHz)

Oscillator Frequency

1.50

1.45

1.40

1.35

1.30

1.25

1.20

1.15

1.10 –50 –25 0 25 50 75 100 125

TEMPERATURE (°C)

1767 G03 sn1767 1767fas

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LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5

TYPICAL PERFORWAUCE CHARACTERISTICS

		SHDN Threshold vs Temperature								SHDN Supply Current vs VIN
	1.40									7
										6			SHDN		= 0V
THRESHOLD(V)	1.38
									CURRENT( A)	5
	1.34									3
SHDN	1.36								V	4
										2
									IN
	1.32									1
	1.30									0

–50	–25	0	25	50	75	100	125	0	5	10	15	20	25	30
		TEMPERATURE (°C)									VIN (V)
						1767 G04								1767 G05

SHDN IP Current vs Temperature

	–12
	–10
							SHUTTING DOWN
A)	–8
(
SHDNINPUT	–4
	–6
	–2							STARTING UP
	0
			–25		0		25			50		75			100		125
	–50

TEMPERATURE (°C)

1767 G06

INPUT VOLTAGE (V)

Minimum Input Voltage for 2.5V Out

3.5

3.3

3.1

2.9

2.7

2.5

0.001 0.01 0.1 1 LOAD CURRENT (A)

1767 G07

SHDN Supply Current

Input Supply Current

	300									1200
		VIN = 15V
	250									1000
( A)	200								( A)		800		MINIMUM
													INPUT
CURRENT									CURRENT				VOLTAGE
	150										600
IN	100								IN		400
V									V
	50										200
	0	0.2	0.4	0.6	0.8	1	1.2	1.4			0	5	10	15	20	25	30
	0										0
			SHUTDOWN VOLTAGE (V)										INPUT VOLTAGE (V)
							1767 G08										1767 G09

SWITCH PEAK CURRENT (A)

Current Limit Foldback

2.0														40	FB
1.5														30
															INPUT
					SWITCH CURRENT
1.0														20	A)(CURRENT
0.5														10
					FB CURRENT
0														0
		0.2		0.4		0.6		0.8			1
0													1.2

FEEDBACK VOLTAGE (V)

1767 G10

OUTPUT CURRENT (A)

	Maximum Load Current,
	VOUT = 5V
1.5
1.3
								L = 4.7 H
1.1
0.9
								L = 2.2 H
0.7
								L = 1.5 H
0.5
		5		10		15		20		25
0

INPUT VOLTAGE (V)

1767 G11

OUTPUT CURRENT (A)

Maximum Load Current,

VOUT = 2.5V

1.5

L = 4.7 H

1.3

L = 2.2 H

1.1

L = 1.5 H

0.9

0.7

0 5 10 15 20 25 INPUT VOLTAGE (V)

1767 G12

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LT1767/LT1767-1.8/ LT1767-2.5/LT1767-3.3/LT1767-5

PIUN FUUNCTIOUNS

FB: The feedback pin is used to set output voltage using an external voltage divider that generates 1.2V at the pin with the desired output voltage. The fixed voltage 1.8V, 2.5V, 3.3V and 5V versions have the divider network included internally and the FB pin is connected directly to the output. If required, the current limit can be reduced during start up or short-circuit when the FB pin is below 0.5V (see the Current Limit Foldback graph in the Typical Performance Characteristics section). An impedance of less than 5kΩ (adjustable part only) at the FB pin is needed for this feature to operate.

BOOST: The BOOST pin is used to provide a drive voltage, higher than the input voltage, to the internal bipolar NPN power switch. Without this added voltage, the typical switch voltage loss would be about 1.5V. The additional boost voltage allows the switch to saturate and voltage loss approximates that of a 0.22Ω FET structure.

VIN: This is the collector of the on-chip power NPN switch. This pin powers the internal circuitry and internal regulator. At NPN switch on and off, high dI/dt edges occur on this pin. Keep the external bypass capacitor and catch diode close to this pin. All trace inductance in this path will create a voltage spike at switch off, adding to the VCE voltage across the internal NPN.

GND: The GND pin acts as the reference for the regulated output, so load regulation will suffer if the “ground” end of the load is not at the same voltage as the GND pin of the IC. This condition will occur when load current or other currents flow through metal paths between the GND pin and the load ground point. Keep the ground path short between the GND pin and the load and use a ground plane

when possible. Keep the path between the input bypass and the GND pin short. The GND pin of the MS8 package is directly attached to the internal tab. This pin should be attached to a large copper area to improve thermal resistance. The exposed pad of the MS8E package is also connected to GND. This should be soldered to a large copper area to improve its thermal resistance.

VSW: The switch pin is the emitter of the on-chip power NPN switch. This pin is driven up to the input pin voltage during switch on time. Inductor current drives the switch pin negative during switch off time. Negative voltage must be clamped with an external catch diode with a VBR <0.8V.

SYNC: The sync pin is used to synchronize the internal oscillator to an external signal. It is directly logic compatible and can be driven with any signal between 20% and 80% duty cycle. The synchronizing range is equal to initial operating frequency, up to 2MHz. See Synchronization section in Applications Information for details. When not in use, this pin should be grounded.

SHDN: The shutdown pin is used to turn off the regulator and to reduce input drain current to a few microamperes. The 1.33V threshold can function as an accurate undervoltage lockout (UVLO), preventing the regulator from operating until the input voltage has reached a predetermined level. Float or pull high to put the regulator in the operating mode.

VC: The VC pin is the output of the error amplifier and the input of the peak switch current comparator. It is normally used for frequency compensation, but can do double duty as a current clamp or control loop override. This pin sits at about 0.35V for very light loads and 0.9V at maximum load. It can be driven to ground to shut off the output.

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