LT3991/LT3991-3.3/LT3991-5

55V, 1.2A Step-Down

Regulator with 2.8µA

Quiescent Current

FeaTures

n

DescripTion

The LT

®

3991 is an adjustable frequency monolithic buck

switching regulator that accepts a wide input voltage range

up to 55V. Low quiescent current design consumes only

2.8µA of supply current while regulating with no load. Low

ripple Burst Mode operation maintains high efficiency at

low output currents while keeping the output ripple below

15mV in a typical application. An internally compensated

current mode topology is used for fast transient response

and good loop stability. A high efficiency 0.44Ω switch

is included on the die along with a boost Schottky diode

and the necessary oscillator, control and logic circuitry.

An accurate 1V threshold enable pin can be used to shut

down the LT3991, reducing the input supply current to

700nA. A capacitor on the SS pin provides a controlled

inrush current (soft-start). A power good flag signals

when V

OUT

reaches 91% of the programmed output volt-

age. The LT3991 is available in small 10-pin MSOP and

3mm

×

3mm DFN packages with exposed pads for low

thermal resistance.

L,

LT, LTC, LTM, Burst Mode, Linear Technology and the Linear logo are registered trademarks

of Linear Technology Corporation. All other trademarks are the property of their respective

owners.

n

Ultralow Quiescent Current:

2.8µA I

Q

Regulating 12V

IN

to 3.3V

OUT

Fixed Output Voltages: 3.3V, 5V

2.1µA I

Q

Regulating 12V

IN

Low Ripple Burst Mode

®

Operation:

Output Ripple < 15mV

P-P

Wide Input Voltage Range: 4.3V to 55V

1.2A Maximum Output Current

Adjustable Switching Frequency: 200kHz to 2MHz

Synchronizable Between 250kHz to 2MHz

Fast Transient Response

Accurate 1V Enable Pin Threshold

Low Shutdown Current: I

Q

= 700nA

Power Good Flag

Soft-Start CapabilityV

Internal Compensation

Saturating Switch Design: 0.44Ω On-Resistance

Output Voltage: 1.19V to 30V

Small Thermally Enhanced 10-Pin MSOP Package

and (3mm

×

3mm) DFN Packages

Automotive Battery Regulation

Power for Portable Products

Industrial Supplies

applicaTions

n

Typical applicaTion

3.3V Step Down Converter

V

IN

INPUT CURRENT (µA)

V

IN

4.3V TO 55V

OFF ON

EN./UVLO

PG

4.7µF

SS

RT

BD

118k

SYNC

GND

V

OUT

47µF

3991 TA01a

No Load Supply Current

3.0

OUTPUT IN REGULATION

2.5

BOOST

0.47µF

12µH

SW

2.0

LT3991-5

LT3991-3.3

1.5

V

OUT

3.3V

1.2A

1.0

5

f = 400kHz

10 15 20 25 30 35 40 45 50 55

INPUT VOLTAGE (V)

3991 G06

3991fa

1

LT3991/LT3991-3.3/LT3991-5

absoluTe MaxiMuM raTings

(Note 1)

V

IN

, EN Voltage .........................................................55V

BOOST Pin Voltage ...................................................75V

BOOST Pin Above SW Pin .........................................30V

FB, V

OUT

, RT, SYNC, SS Voltage .................................6V

PG, BD Voltage .........................................................30V

Boost Diode Current....................................................1A

Operating Junction Temperature Range (Note 2)

LT3991E ............................................. –40°C to 125°C

LT3991I.............................................. –40°C to 125°C

Storage Temperature Range .............. –65°C to 150°C

Lead Temperature (Soldering, 10 sec)

(MSE Only) ....................................................... 300°C

pin conFiguraTion

LT3991

TOP VIEW

BD

BOOST

SW

V

IN

EN

1

2

3

4

5

11

GND

10 SYNC

9 PG

8 RT

7 SS

6 FB

TOP VIEW

BD

BOOST

SW

V

IN

EN

1

2

3

4

5

11

GND

10

9

8

7

6

SYNC

PG

RT

SS

FB

BD

BOOST

SW

V

IN

EN

1

2

3

4

5

TOP VIEW

11

GND

10

9

8

7

6

SYNC

PG

RT

SS

V

OUT

LT3991

LT3991-3.3, LT3991-5

DD PACKAGE

10-LEAD (3mm

×

3mm) PLASTIC DFN

θ

JA

= 45°C,

θ

JC

= 10°C/W

EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB

MSE PACKAGE

10-LEAD PLASTIC MSOP

θ

JA

= 45°C,

θ

JC

= 10°C/W

EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB

MSE PACKAGE

10-LEAD PLASTIC MSOP

θ

JA

= 45°C,

θ

JC

= 10°C/W

EXPOSED PAD (PIN 11) IS GND, MUST BE SOLDERED TO PCB

orDer inForMaTion

LEAD FREE FINISH

LT3991EDD#PBF

LT3991IDD#PBF

LT3991EMSE#PBF

LT3991IMSE#PBF

LT3991EMSE-3.3#PBF

LT3991IMSE-3.3#PBF

LT3991EMSE-5#PBF

LT3991IMSE-5#PBF

TAPE AND REEL

LT3991EDD#TRPBF

LT3991IDD#TRPBF

LT3991EMSE#TRPBF

LT3991IMSE#TRPBF

LT3991EMSE-3.3#TRPBF

LT3991IMSE-3.3#TRPBF

LT3991EMSE-5#TRPBF

LT3991IMSE-5#TRPBF

PART MARKING*

LFJR

LTFJS

LTFRS

LTFRV

PACKAGE DESCRIPTION

10-Lead (3mm

×

3mm) Plastic DFN

10-Lead (3mm

×

3mm) Plastic DFN

10-Lead Plastic MSOP

TEMPERATURE RANGE

–40°C to 125°C

Consult LTC Marketing for parts specified with wider operating temperature ranges. *The temperature grade is identified by a label on the shipping container.

Consult LTC Marketing for information on non-standard lead based finish parts.

For more information on lead free part marking, go to:

http://www.linear.com/leadfree/

For more information on tape and reel specifications, go to:

http://www.linear.com/tapeandreel/

2

3991fa

LT3991/LT3991-3.3/LT3991-5

elecTrical characTerisTics

PARAMETER

Minimum Input Voltage

Quiescent Current from V

IN

LT3991 FB Pin Current

Internal Feedback Resistor Divider

Feedback Voltage

l

The

l

denotes the specifications which apply over the full operating

temperature range, otherwise specifications are at T

A

= 25°C. V

IN

= 12V, V

EN

= 12V, V

BD

= 3.3V unless otherwise noted. (Note 2)

CONDITIONS

(Note 4)

V

EN

Low

V

EN

High, V

SYNC

Low

V

EN

High, V

SYNC

Low

V

FB

= 1.19V

l

MIN

TYP

4

0.7

1.7

MAX

4.3

1.2

2.7

4.5

12

1.205

1.215

3.35

3.376

5.07

5.11

0.01

2.4

1.2

240

200

2.9

1

1.8

33

1.07

20

140

12.5

1

1.0

1.6

UNITS

V

μA

nA

MΩ

V

%/V

MHz

kHz

ns

A

mV

μA

mV

μA

V

mA

V

mV

nA

mV

%

µA

μA

V

nA

μA

l

0.1

10

1.175

1.165

3.25

3.224

4.93

4.89

1.6

0.8

160

1.19

3.3

5

0.0002

2

1

200

110

150

1.7

2.3

440

0.02

800

0.02

LT3991-3.3 Output Voltage

l

LT3991-5 Output Voltage

l

FB Voltage Line Regulation

Switching Frequency

4.3V < V

IN

< 40V (Note 4)

R

T

= 11k

R

T

= 35.7k

R

T

= 255k

Minimum Switch On Time

Minimum Switch Off Time

Switch Current Limit

Switch V

CESAT

Switch Leakage Current

Boost Schottky Forward Voltage

Boost Schottky Reverse Leakage

Minimum Boost Voltage (Note 3)

BOOST Pin Current

EN Voltage Threshold

EN Voltage Hysteresis

EN Pin Current

LT3991 PG Threshold Offset from V

FB

LT3991 PG Hysteresis

LT3991-X PG Threshold Offset from V

OUT

LT3991X PG Hysteresis

PG Leakage

PG Sink Current

SYNC Threshold

SYNC Pin Current

SS Source Current

V

SS

= 1V

0.6

Note 1:

Stresses beyond those listed under Absolute Maximum Ratings

may cause permanent damage to the device. Exposure to any Absolute

Maximum Rating condition for extended periods may affect device

reliability and lifetime.

Note 2:

The LT3991E is guaranteed to meet performance specifications

from 0°C to 125°C junction temperature. Specifications over the –40°C

to 125°C operating junction temperature range are assured by design,

characterization, and correlation with statistical process controls.

V

PG

= 3V

V

PG

= 0.4V

l

I

SW

= 1A

I

SH

= 100mA

V

REVERSE

= 12V

V

IN

= 5V

I

SW

= 1A, V

BOOST

= 15V

EN Rising

l

1.4

25

0.95

1.01

30

0.2

V

FB

Rising

V

OUT

Rising

60

5.5

100

20

9

1.3

0.02

300

0.6

570

0.8

0.1

1

The LT3991I is guaranteed over the full –40°C to 125°C operating junction

temperature range. High junction temperatures degrade operating

lifetimes. Operating lifetime is derated at junction temperatures greater

than 125°C.

Note 3:

This is the minimum voltage across the boost capacitor needed to

guarantee full saturation of the switch.

Note 4:

Minimum input voltage depends on application circuit.

3991fa

3

LT3991/LT3991-3.3/LT3991-5

Typical perForMance characTerisTics

100

90

80

EFFICIENCY (%)

70

60

50

40 V

OUT

= 5V

R1 = 1M

R2 = 309k

30

0

0.2

V

IN

= 24V

V

IN

= 36V

V

IN

= 48V

T

A

= 25°C, unless otherwise noted.

Efficiency, V

OUT

= 5V

Efficiency, V

OUT

= 5V

V

IN

= 12V

90

80

70

60

50

40

30

Efficiency, V

OUT

= 3.3V

V

IN

= 12V

100

V

OUT

= 5V

90 R1 = 1M

R2 = 309k

80

70

60

50

40

30

20

10

V

IN

= 48V

V

IN

= 36V

V

IN

= 48V

EFFICIENCY (%)

V

IN

= 24V

V

IN

= 12V

V

IN

= 24V

V

IN

= 36V

0.4

0.6

0.8

LOAD CURRENT (A)

1

1.2

3991 G01

20

0

0.2

0.4

0.6

0.8

LOAD CURRENT (A)

1

1.2

3991 G02

0

0.01

0.1

1

10

100

LOAD CURRENT (mA)

1000

3991 G03

Efficiency, V

OUT

= 3.3V

90

80

70

EFFICIENCY (%)

60

50

40

30

20

10

0

0.01

0.1

1

10

100

LOAD CURRENT (mA)

1000

3991 G04

No Load Supply Current

100

DIODES, INC.

DFLS2100

3.0

No Load Supply Current

OUTPUT IN REGULATION

V

IN

= 12V

V

IN

= 36V

V

IN

= 48V

INPUT CURRENT (µA)

V

IN

= 24V

2.5

10

2.0

LT3991-5

LT3991-3.3

1.5

1

–55

–25

5

35

65

95

TEMPERATURE (°C)

125

155

1.0

5

3991 G05

10 15 20 25 30 35 40 45 50 55

INPUT VOLTAGE (V)

3991 G06

LT3991 Feedback Voltage

1.205

1.200

FEEDBACK VOLTAGE (V)

OUTPUT VOLTAGE (V)

1.195

1.190

1.185

1.180

1.175

–55

3.345

3.330

3.315

3.300

3.285

3.270

LT3991-3.3 Output Voltage

5.06

5.04

OUTPUT VOLTAGE (V)

155

5.02

5.00

4.98

4.96

LT3991-5 Output Voltage

–25

5

35

65

95

TEMPERATURE (°C)

125

155

3.255

–50 –25

3991 G07

65

35

95

5

TEMPERATURE (°C)

125

4.94

–50 –25

65

35

95

5

TEMPERATURE (°C)

125

155

3991 G28

3991 G29

4

3991fa

LT3991/LT3991-3.3/LT3991-5

Typical perForMance characTerisTics

Maximum Load Current

3.0

2.5

LOAD CURRENT (A)

2.0

1.5

1.0

0.5

0

TYPICAL

MINIMUM

LOAD CURRENT (A)

V

OUT

= 3.3V

T

A

= 25°C, unless otherwise noted.

Load Regulation

0.30

0.25

0.20

LOAD REGULATION (%)

0.15

0.10

0.05

0

–0.05

–0.10

–0.15

–0.20

–0.25

–0.30

REFERENCED FROM V

OUT

AT 0.5A LOAD

Maximum Load Current

2.5

V

OUT

= 5V

2.0

TYPICAL

1.5

MINIMUM

1.0

0.5

5

10 15 20 25 30 35 40 45 50 55

INPUT VOLTAGE (V)

3991 G08

0

5

10 15 20 25 30 35 40 45 50 55

INPUT VOLTAGE (V)

3991 G09

0

200

400

600

800 1000

LOAD CURRENT (mA)

1200

3991 G10

Switching Frequency

1000

950

900

FREQUENCY (kHz)

850

800

750

700

650

600

–55

–25

5

35

65

95

TEMPERATURE (°C)

125

155

SWITCH CURRENT LIMIT (A)

3.0

2.5

2.0

1.5

1.0

0.5

0

Switch Current Limit

2.5

2.4

SWITCH CURRENT LIMIT (A)

0

20

40

60

DUTY CYCLE (%)

80

100

3991 G12

Switch Current Limit

2.3

2.2

2.1

2.0

1.9

1.8

1.7

1.6

DUTY CYCLE = 30%

1.5

–55 –25

5

35

65

95

TEMPERATURE (°C)

125

155

3991 G11

3991 G13

Switch V

CESAT

700

600

500

V

CESAT

(mV)

400

300

200

100

0

250

500

750 1000 1250

SWITCH CURRENT (mA)

1500

BOOST PIN CURRENT (mA)

45

40

Boost Pin Current

900

800

SWITCHING FREQUENCY (kHz)

700

600

500

400

300

200

100

0

250

500

750 1000 1250

SWITCH CURRENT (mA)

1500

0

LT3991 Frequency Foldback

35

30

25

20

15

10

5

0

0.2

0.6

0.4

0.8

FB PIN VOLTAGE (V)

1

1.2

3991 G16

3991 G14

3991 G15

3991fa

5

参数名称	属性值
欧盟限制某些有害物质的使用	Compliant
ECCN (US)	EAR99
Part Status	Active
类型 Type	Synchronous Step Down
输出类型 Output Type	Adjustable
Switching Frequency (kHz)	160 to 2400
Switching Regulator	Yes
Number of Outputs	1
Output Voltage (V)	1.19 to 30
Maximum Output Current (A)	1.2
Minimum Input Voltage (V)	4.3
Maximum Input Voltage (V)	55
Operating Supply Voltage (V)	4.3 to 55
Typical Quiescent Current (uA)	1.7
Line Regulation	0.01%/V
Minimum Operating Temperature (°C)	-40
Maximum Operating Temperature (°C)	125
Supplier Temperature Grade	Industrial
系列 Packaging	Tube
Pin Count	10
Standard Package Name	SOP
Supplier Package	MSOP EP
Mounting	Surface Mount
Package Height	0.86
Package Length	3
Package Width	3
PCB changed	10
Lead Shape	Gull-wing

LT3991IMSE#PBF

LT3991IMSE#PBF概述

LT3991IMSE#PBF规格参数

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