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LTC3646/LTC3646-1

40V, 1A Synchronous

Step-Down Converter

FEATURES

n

DESCRIPTION

The

LTC

®

3646

is a high efficiency, step-down DC/DC

converter with internal high side and synchronous power

FETs. It draws only 140µA typical DC supply current in

Burst Mode operation at no load while maintaining output

voltage regulation.

The LTC3646 can supply up to a 1A load, and its combina-

tion of Burst Mode operation, integrated power switches

and low quiescent current provides high efficiency over a

broad range of load currents. Alternatively, it can be used

in forced continuous mode for ripple sensitive applications.

The LTC3646 has a wide 4.0V to 40V input range and its

patented controlled on-time architecture and 0.6V refer-

ence voltage allow for large step-down ratios without

the risk of output overvoltage. The frequency may be set

between 200kHz and 3.0MHz with a program resistor or

synchronized to an external clock.

The internal soft-start, short-circuit protection and volt-

age rating make the LTC3646 a robust part ideal for high

voltage applications.

L,

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

and Hot Swap is a trademark of Linear Technology Corporation. All other trademarks are the

property of their respective owners. Protected by U.S. Patents, including 6580258, 5481178,

5994885, 6304066, 5847554, 6476589, 6774611.

n

Wide Input Voltage Range: 4.0V to 40V

1A Guaranteed Output Current

High Efficiency: Up to 95%

Wide Output Voltage Range

n

LTC3646: 2.0V to 30V

n

LTC3646-1: 0.6V to 15V

±1% Accurate Reference Voltage

Internal or External Compensation

Switching Frequency Adjustable and Synchronizable:

200kHz to 3MHz

Selectable High Efficiency Burst Mode

®

Operation or

Forced Continuous Mode

14 Lead 3mm × 4mm DFN or Thermally Enhanced

16-Lead MSOP Packages

APPLICATIONS

n

Point of Load Power Supplies

Intermediate Bus Power

Automotive Applications

TYPICAL APPLICATION

Efficiency Curve

V

IN

40V MAX

PVIN

SVIN

RUN

10µF

INTV

CC

MODE/SYNC

ITH

RT

EXTV

CC

4.7µF

0.6V

SGND

SWITCH

CONTROL

V

ON

412k

LTC3646

SW

BOOST

0.1µF

3.3µH

100

90

80

EFFICIENCY (%)

V

OUT

5V

1A

V

IN

= 12V

f = 1MHz

1.0

V

OUT

= 5V

V

OUT

= 3.3V

0.8

POWER LOSS (W)

70

60

50

40

30

V

OUT

= 5V

V

OUT

= 3.3V

0.2

0.4

0.6

+ –

PGND

V

FB

56.2k

3646 TA01a

15µF

20

10

0

0.001

0.01

0.1

LOAD CURRENT (A)

1

3646 TA01b

0

36461fc

For more information

www.linear.com/LTC3646

1

LTC3646/LTC3646-1

ABSOLUTE MAXIMUM RATINGS

(Notes 1, 7)

PVIN, SVIN Supply Voltage ........................ –0.3V to 45V

SW Voltage (DC) ........................... –0.3V to PVIN + 0.3V

BOOST – SW Voltage ................................... –0.3V to 6V

V

ON

Voltage................................................ –0.3V to 33V

MODE/SYNC, RT, ITH,

V

FB

Voltage ................................–0.3V to INTV

CC

+ 0.3V

INTV

CC

Voltage ............................................ –0.3V to 6V

EXTV

CC

Voltage ........................................... –0.3V to 6V

RUN Voltage............................................... –0.3V to 45V

PGOOD.......................................–0.3V to INTV

CC

+ 0.3V

Operating Junction Temperature Range

(Notes 2, 7) ............................................ –40°C to 150°C

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

Lead Temperature (Soldering, 10 sec) MSE .......... 300°C

PIN CONFIGURATION

TOP VIEW

SGND

V

FB

ITH

RT

V

ON

PGOOD

MODE/SYNC

1

2

3

4

5

6

7

15

PGND

14 SVIN

13 RUN

12 EXTV

CC

11 INTV

CC

10 BOOST

9 SW

8 PVIN

TOP VIEW

SGND

V

FB

ITH

RT

V

ON

PGOOD

MODE/SYNC

NC

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

SVIN

RUN

EXTV

CC

INTV

CC

BOOST

SW

PVIN

17

PGND

DE PACKAGE

14-LEAD (4mm

×

3mm) PLASTIC DFN

T

JMAX

= 150°C,

θ

JA

= 43°C/W

EXPOSED PAD (PIN 15) IS PGND, MUST BE SOLDERED TO PCB

MSE PACKAGE

16-LEAD PLASTIC MSOP

T

JMAX

= 150°C,

θ

JA

= 38°C/W

EXPOSED PAD (PIN 17) IS PGND, MUST BE SOLDERED TO PCB

ORDER INFORMATION

LEAD FREE FINISH

LTC3646EDE#PBF

LTC3646IDE#PBF

LTC3646HDE#PBF

LTC3646EMSE#PBF

LTC3646IMSE#PBF

LTC3646HMSE#PBF

LTC3646EDE-1#PBF

LTC3646IDE-1#PBF

LTC3646HDE-1#PBF

LTC3646EMSE-1#PBF

LTC3646IMSE-1#PBF

LTC3646HMSE-1#PBF

TAPE AND REEL

LTC3646EDE#TRPBF

LTC3646IDE#TRPBF

LTC3646HDE#TRPBF

LTC3646EMSE#TRPBF

LTC3646IMSE#TRPBF

LTC3646HMSE#TRPBF

LTC3646EDE-1#TRPBF

LTC3646IDE-1#TRPBF

LTC3646HDE-1#TRPBF

LTC3646EMSE-1#TRPBF

LTC3646IMSE-1#TRPBF

PART MARKING

3646

36461

PACKAGE DESCRIPTION

14-Lead (4mm

×

3mm) Plastic DFN

14-Lead (4mm

×

3mm) Plastic DFN

14-Lead (4mm

×

3mm) Plastic DFN

16-Lead Plastic MSOP

14-Lead (4mm

×

3mm) Plastic DFN

14-Lead (4mm

×

3mm) Plastic DFN

14-Lead (4mm

×

3mm) Plastic DFN

16-Lead Plastic MSOP

TEMPERATURE RANGE

–40°C to 85°C

–40°C to 125°C

–40°C to 150°C

–40°C to 85°C

–40°C to 125°C

–40°C to 150°C

–40°C to 85°C

–40°C to 125°C

–40°C to 150°C

–40°C to 85°C

–40°C to 125°C

–40°C to 150°C

LTC3646HMSE-1#TRPBF 36461

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

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

36461fc

For more information

www.linear.com/LTC3646

LTC3646/LTC3646-1

ELECTRICAL CHARACTERISTICS

SYMBOL

PARAMETER

Input Supply (PVIN, SVIN)

Input Voltage Operating Range

V

IN

Input Supply Overvoltage Lockout

V

IN(OV)

V

IN(UV)

I

Q

Input Supply Undervoltage Lockout

The

l

denotes the specifications which apply over the specified operating

junction temperature range, otherwise specifications are at T

A

= 25°C (Note 2), PVIN = SVIN = 12V unless otherwise noted.

CONDITIONS

l

MIN

4.0

43.5

2.0

3.2

TYP

MAX

40

UNITS

V

mV

µA

V

%/V

%

nA

µS

ns

A

MHz

mΩ

µA

V

%

V

mV

V

mV

µA

%V

FB

%V

FB

%V

FB

%V

FB

36461fc

V

IN

Rising

Hysteresis (V

IN

Falling)

V

IN

Falling

Hysteresis (V

IN

Rising)

l

46

2.5

3.35

250

620

140

8

2.9

3.5

875

190

DC Supply Current (Note 3)

Forced Continuous

Sleep Mode

Shutdown Mode

Main Control Loop

Output Voltage Range (Note 4)

V

OUT

V

FB

Feedback Reference Voltage

Feedback Voltage Line Regulation

Feedback Voltage Load Regulation

Feedback Input Current

Error Amplifier Transconductance

Minimum On-Time

Minimum Off-Time

Valley Switch Current Limit

Negative Valley Switch Current Limit

Internal Oscillator Frequency

V

RUN

= 0V

LTC3646

LTC3646-1

–40°C < T

A

< 85°C

l

2.0

0.6

0.594

0.591

0.6

g

m(EA)

t

ON(MIN)

t

OFF(MIN)

I

LIM

V

IN

= 4.0V to 40V, I

TH

= 1.5V

I

TH

= 1.0V to 1.8V

V

FB

= 0.6V

External Comp

V

IN

= 40V, R

RT

= 30k, V

ON

= 2V

l

0.9

1.6

0.19

1.25

2.55

0.2

V

RT

= V

INTVCC

R

RT

= 450kΩ

R

RT

= 60kΩ

R

RT

= 30kΩ

V

IN

= 5.5V

V

IN

= 5.5V

V

IN

= V

SW

= 40V, V

RUN

= 0V

V

IN

= 40V, V

SW

= 0V, V

RUN

= 0V

I

INTVCC

= 5mA

I

INTVCC

= 0mA to 5mA

INTV

CC

Falling

EXTV

CC

Rising

l

0

300

30

80

1.2

–0.3

2.25

0.2

1.5

3.0

200

120

30

15

0.606

0.609

0.05

0.12

±20

1.5

2.95

0.27

1.75

3.45

3.0

R

DS(ON)

External Clock Frequency Range

Top Switch On-Resistance (Note 5)

Bottom Switch On-Resistance (Note 5)

Switch Leakage

±1

4.8

5.0

0.5

3.0

0.3

4.5

200

1.21

1.10

110

0

7.5

5

–7.5

–5

5.2

Internal V

CC

Regulator

INTV

CC

Voltage

V

INTVCC

INTV

CC

Load Regulation (Note 6)

INTV

CC

Undervoltage Lockout

INTV

CC

UVLO Hysteresis

EXTV

CC

Switchover Voltage

EXTV

CC

Hysteresis

Operation

RUN Pin Threshold

V

RUN

RUN Pin Leakage Current

PGOOD Overvoltage Threshold

PGOOD Undervoltage Threshold

4.25

4.65

V

PGOOD(UT)

V

PGOOD(LT)

RUN Rising

RUN Falling

Hysteresis

RUN = 1.3V

FB Rising

FB Falling

FB Rising

1.17

1.06

1.26

1.14

±1

10

–10

5.0

3.5

–5.0

–3.5

For more information

www.linear.com/LTC3646

3

LTC3646/LTC3646-1

ELECTRICAL CHARACTERISTICS

SYMBOL

t

PGOOD

R

PGOOD

t

SS

V

MODE/SYNC

PARAMETER

PGOOD Filter Time

PGOOD Pull-Down Resistance

PGOOD Leakage

Internal Soft-Start Time

Mode Threshold Voltage

SYNC Threshold Voltage

MODE/SYNC Input Current

Internal ITH Voltage Threshold

V

ON

Pin Input Impedance

The

l

denotes the specifications which apply over the specified operating

junction temperature range, otherwise specifications are at T

A

= 25°C (Note 2), PVIN = SVIN = 12V unless otherwise noted.

CONDITIONS

RT = INTV

CC

I

PGOOD

= 10mA

V

PGOOD

= V

INTVCC

Mode V

IH

Mode V

IL

SYNC

IH

SYNC

IL

l

MIN

15

TYP

30

63

250

MAX

1.0

500

0.3

1.2

1

0.3

2

l

INTV

CC

– 0.3V

520

600

LTC3646

LTC3646-1

UNITS

µs

Ω

µA

µs

V

µA

V

kΩ

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 LTC3646 is tested under pulsed load conditions such that

T

J

≈ T

A

. The LTC3646E is guaranteed to meet specifications from

0°C to 85°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. The

LTC3646I is guaranteed over the –40°C to 125°C operating junction

temperature range and the LTC3646H is guaranteed over the –40°C to

150°C operating junction temperature range. High junction temperatures

derate operating lifetimes; operating lifetime is derated for junction

temperatures greater than 125°C. Note that the maximum ambient

temperature consistent with these specifications is determined by specific

operating conditions in conjunction with board layout, the rated package

thermal impedance and other environmental factors.

Note 3:

Dynamic supply current is higher due to gate charging being

delivered at the switch frequency.

Note 4:

Limits to V

OUT

are a subject to PVIN, SVIN, t

ON(MIN)

, t

OFF(MIN)

,

and frequency constraints. See the Applications Information section for a

further discussion. These items are tested with appropriate combinations

of V

IN

, V

ON

and frequency.

Note 5:

R

DS(ON)

is guaranteed by correlation to wafer level measurements.

Note 6:

Maximum allowed current draw when used as a regulated output

is 5mA. This supply is only intended to provide additional DC load current

as needed and not to regulate large transient or AC behavior as such

waveforms may impact LTC3646 operation.

Note 7:

This IC includes overtemperature protection intended to protect

the device during momentary overload conditions. The maximum junction

temperature may be exceeded when overtemperature protection is active.

Continuous operation above the specified maximum operating junction

temperature may result in device degradation or failure.

4

36461fc

For more information

www.linear.com/LTC3646

LTC3646/LTC3646-1

TYPICAL PERFORMANCE CHARACTERISTICS

T

A

= 25°C, SVIN/PVIN = 12V, f

O

= 1MHz unless otherwise noted.

Efficiency vs Load Current,

Burst Mode Operation

100

V

OUT

= 1.8V

90 f

O

= 1.5MHz

80

EFFICIENCY (%)

70

60

50

40

30

20

10

0

0.001

0.01

0.1

LOAD CURRENT (A)

V

IN

= 5V

V

IN

= 8V

V

IN

= 12V

1

36461 G01

Efficiency vs Load Current,

Forced Continuous Mode Operation

100

V

OUT

= 1.8V

90 f

O

= 1.5MHz

80

EFFICIENCY (%)

70

60

50

40

30

20

10

0

0.001

0.01

0.1

LOAD CURRENT (A)

V

IN

= 5V

V

IN

= 8V

V

IN

= 12V

1

36461 G02

Efficiency vs Load Current

100

90

80

70

60

50

40

30

20

10

0

0.001

V

OUT

= 5V

V

OUT

= 3.3V

0.01

0.1

LOAD CURRENT (A)

1

36461 G03

Burst Mode OPERATION

FORCED CONTINUOUS

OPERATION

Efficiency vs Input Voltage,

Burst Mode Operation

100

95

90

EFFICIENCY (%)

85

80

75

70

65

60

0

L = 6.8µH

V

OUT

= 3.3V

5

10

15 20 25 30

INPUT VOLTAGE (V)

35

40

LOAD = 100mA

LOAD = 500mA

LOAD = 1A

608

606

604

V

REF

(mV)

602

600

598

596

594

Reference Voltage

vs Temperature

0.35

0.30

RESISTANCE ( )

0.25

0.20

0.15

0.10

0.05

R

DS(ON)

vs Temperature

MAIN SWITCH

SYNCHRONOUS SWITCH

592

–50 –30 –10 10 30 50 70 90 110 130 150

TEMPERATURE (°C)

36461 G05

0

–50 –30 –10 10 30 50 70 90 110 130 150

TEMPERATURE (°C)

36461 G06

36461 G04

Switch Pin Leakage

vs Temperature and Supply

20

18

SW LEAKAGE CURRENT (µA)

16

14

12

10

8

6

4

2

0

–50 –30 –10 10 30 50 70 90 110 130 150

TEMPERATURE (°C)

36461 G07

Oscillator Internal Set Frequency

vs Temperature

2.50

2.45

2.40

FREQUENCY (MHz)

2.35

2.30

2.25

2.20

2.15

2.10

2.05

2.00

–40 –20 0

20 40 60 80 100 120 140

TEMPERATURE (°C)

36461 G08

Oscillator Externally Set Frequency

vs Temperature

1.8

1.7

1.6

1.5

1.4

1.3

1.2

–40 –20 0

R

RT

= 60k

V

DS

= 12V, MAIN SWITCH

V

DS

= 12V, SYNCHRONOUS SWITCH

V

DS

= 40V, MAIN SWITCH

V

DS

= 40V, SYNCHRONOUS SWITCH

V

RT

= V

INTVCC

20 40 60 80 100 120 140

TEMPERATURE (°C)

36461 G09

36461fc

For more information

www.linear.com/LTC3646

5

参数名称	属性值
功能	降压
输出配置	正
拓扑	降压
输出类型	可调式
输出数	1
电压 - 输入（最小值）	4V
电压 - 输入（最大值）	40V
电压 - 输出（最小值/固定）	2V
电压 - 输出（最大值）	30V
电流 - 输出	1A
频率 - 开关	200kHz ~ 3MHz
同步整流器	是
工作温度	-40°C ~ 150°C（TJ）
安装类型	表面贴装
封装/外壳	16-TFSOP（0.118"，3.00mm 宽）裸露焊盘
供应商器件封装	16-MSOP-EP

LTC3646EMSE#PBF

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