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LTC3873-5

No R

SENSE

TM

Constant

Frequency Current Mode

Boost/Flyback/SEPIC

DC/DC Controller

FEATURES

n

DESCRIPTION

The LTC

®

3873-5 is a constant frequency current mode

controller for boost, ﬂyback or SEPIC DC/DC converters

designed to drive an N-channel MOSFET for high input

and output voltage converter applications.

The LTC3873-5 provides ±1.5% output voltage accuracy

and consumes only 300μA quiescent current during nor-

mal operation and only 50μA during micropower start-up.

Using a 9.3V internal shunt regulator, the LTC3873-5 can

be powered from a high input voltage through a resistor

or it can be powered directly from a low impedance DC

voltage of 9V or less. Soft-start can be programmed using

an external capacitor.

The LTC3873-5 is available in 8-lead ThinSOT and 2mm

×

3mm DFN packages.

PARAMETER

V

CC

UV

+

V

CC

UV

–

LTC3873

8.4V

4V

LTC3873-5

4.1V

2.9V

V

IN

and V

OUT

Limited Only by External Components

Internal or Programmable External Soft-Start

Constant Frequency 200kHz Operation

Adjustable Current Limit

Current Sense Resistor Optional

±1.5% Voltage Reference Accuracy

Current Mode Operation for Excellent Line and Load

Transient Response

4.1V Undervoltage Threshold for Logic Level

MOSFET Applications

Low Quiescent Current: 300μA

Low Proﬁle (1mm) ThinSOT

TM

and (0.75mm)

2mm

×

3mm DFN Package

APPLICATIONS

n

Telecom Power Supplies

Automotive Power Supplies

PoE Applications

L,

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

No R

SENSE

and ThinSOT are trademarks of Linear Technology Corporation.

All other trademarks are the property of their respective owners.

TYPICAL APPLICATION

High Efﬁciency 5V Input, 12V Output Boost Converter

1nF

4.7nF

11.8k

I

TH

47pF

LTC3873-5

IPRG

12k

GND

V

FB

108k

38735 TA01a

Efﬁciency and Power Loss vs Load Current

100

90

10000

RUN/SS

V

CC

10μH

SW

NGATE

22μF

10μF

80

EFFICIENCY (%)

V

IN

5V

70

60

50

40

30

20

10

0

10

100

I

OUT

(mA)

1000

3873 TA01b

1000

POWER LOSS (mW)

V

OUT

12V

2A

100

10

38735fb

1

LTC3873-5

ABSOLUTE MAXIMUM RATINGS

(Note 1)

V

CC

to GND

Low Impedance Source ........................... –0.3V to 9V

Current Fed ..........................................25mA Into V

CC

RUN/SS........................................................ –0.3V to 9V

IPRG Voltage.................................–0.3V to (V

CC

+ 0.3V)

V

FB

, I

TH

Voltages ....................................... –0.3V to 2.4V

SW Voltage ................................................ –0.3V to 60V

Operating Temperature Range (Note 2)

LTC3873E-5 ......................................... –40°C to 85°C

LTC3873I-5 ........................................ –40°C to 125°C

Junction Temperature (Note 3) ............................. 125°C

Storage Temperature Range................... –65°C to 125°C

Lead Temperature (Soldering, 10 sec)

TS8 Package ..................................................... 300°C

PIN CONFIGURATION

TOP VIEW

IPRG 1

I

TH

2

V

FB

3

GND 4

8 SW

7 RUN/SS

6 V

CC

5 NGATE

GND 1

V

FB

2

I

TH

3

IPRG 4

9

8

7

6

5

NGATE

V

CC

RUN/SS

SW

TS8 PACKAGE

8-LEAD PLASTIC TSOT-23

T

JMAX

= 125°C,

θ

JA

= 230°C/W

DDB PACKAGE

8-LEAD (3mm 2mm) PLASTIC DFN

T

JMAX

= 125°C,

θ

JA

= 76°C/W

EXPOSED PAD (PIN 9) IS GND, MUST BE SOLDERED TO PCB

ORDER INFORMATION

LEAD FREE FINISH

LTC3873ETS8-5#PBF

LTC3873ITS8-5#PBF

LTC3873EDDB-5#PBF

LTC3873IDDB-5#PBF

LEAD BASED FINISH

LTC3873ETS8-5

LTC3873ITS8-5

LTC3873EDDB-5

LTC3873IDDB-5

TAPE AND REEL

LTC3873ETS8-5#TRPBF

LTC3873ITS8-5#TRPBF

LTC3873EDDB-5#TRPBF

LTC3873IDDB-5#TRPBF

TAPE AND REEL

LTC3873ETS8-5#TR

LTC3873ITS8-5#TR

LTC3873EDDB-5#TR

LTC3873IDDB-5#TR

PART MARKING*

LTCSP

LCSM

PART MARKING*

LTCSP

LCSM

PACKAGE DESCRIPTION

8-Lead Plastic TSOT-23

8-Lead (3mm

×

2mm) Plastic DFN

8-Lead (3mm

×

2mm) Plastic DFN

PACKAGE DESCRIPTION

8-Lead Plastic TSOT-23

8-Lead (3mm

×

2mm) Plastic DFN

8-Lead (3mm

×

2mm) Plastic DFN

TEMPERATURE RANGE

–40°C to 85°C

–40°C to 125°C

–40°C to 85°C

–40°C to 125°C

TEMPERATURE RANGE

–40°C to 85°C

–40°C to 125°C

–40°C to 85°C

–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.

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/

38735fb

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LTC3873-5

ELECTRICAL CHARACTERISTICS

PARAMETER

Input DC Supply Current

Normal Operation

Shutdown

UVLO

Undervoltage Lockout Threshold

The

l

denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at T

A

= 25°C. V

CC

= 5V unless otherwise noted. (Note 2)

CONDITIONS

Typicals at V

CC

= 5V (Note 4)

V

ITH

= 1.9V

V

RUN/SS

= 0V

V

CC

= UVLO Threshold – 100mV, V

RUN/SS

= V

CC

V

CC

Rising

V

CC

Falling

V

CC

Hysteresis

V

RUN/SS

Falling

V

RUN/SS

Rising

(Note 5)

3.5V < V

CC

< 9V (Note 5)

V

ITH

= 1.6V (Note 5)

V

ITH

= 1V (Note 5)

(Note 5)

V

RUN/SS

= 0V

V

RUN/SS

= 1.3V

1.5

5

70

160

C

LOAD

= 3000pF (Note 6)

C

LOAD

= 3000pF (Note 6)

IPRG = GND

IPRG = Float

IPRG = V

IN

I

IN

= 1mA, I

IN

= 25mA, V

RUN/SS

= 0V

l

MIN

TYP

300

50

35

MAX

400

80

50

4.4

3.3

1.7

0.9

1.0

1.218

UNITS

μA

V

mV/V

%

3.8

2.5

0.9

0.5

0.6

1.182

4.1

2.9

1.25

0.7

0.8

1.2

0.1

0.05

–0.05

25

3

15

78

20

200

40

Shutdown Threshold (at RUN/SS)

Regulated Feedback Voltage

Feedback Voltage Line Regulation

Feedback Voltage Load Regulation

V

FB

Input Current

RUN/SS Pull Up Current

Maximum Duty Cycle

I

SLMAX

, Peak Slope Compensation Current

Oscillator Frequency

Gate Drive Rise Time

Gate Drive Fall Time

Peak Current Sense Voltage

50

4.5

25

84

240

nA

μA

%

μA

kHz

ns

95

165

265

9

110

185

295

9.3

3.3

125

210

325

9.6

mV

V

ms

V

IN

Shunt Regulator Voltage

Default Internal Soft-Start

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 LTC3873E-5 is guaranteed to meet performance speciﬁcations

from 0°C to 85°C. Speciﬁcations over the –40°C to 85°C operating

temperature range are assured by design, characterization and correlation

with statistical process controls. The LTC3873I-5 is guaranteed to meet

performance speciﬁcations over the full –40°C to 125°C operating

temperature range.

Note 3:

T

J

is calculated from the ambient temperature T

A

and power

dissipation P

D

according to the following formula:

T

J

= T

A

+ (P

D

•

θ

JA

)

Note 4:

The dynamic input supply current is higher due to power MOSFET

gate charging (Q

G

• f

OSC

). See Applications Information.

Note 5:

The LTC3873-5 is tested in a feedback loop which servos V

FB

to

the reference voltage with the I

TH

pin forced to the midpoint of its voltage

range (0.7V ≤ V

ITH

≤ 1.9V, midpoint = 1.3V).

Note 6:

Rise and fall times are measured at 10% and 90% levels.

V

CC

= 5.6V.

38735fb

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LTC3873-5

TYPICAL PERFORMANCE CHARACTERISTICS

Regulated Feedback Voltage vs

Temperature

1.25

1.24

1.23

1.22

1.21

1.20

1.19

1.18

–60 –40 –20

1.2025

1.2020

2.0

1.2015

V

FB

VOLTAGE (V)

I

TH

VOLTAGE (V)

1.2010

1.2005

1.2000

0.5

1.1995

1.1990

3

4

5

7

6

V

IN

(V)

8

9

0

1.5

V

FB

VOLTAGE (V)

Regulated Feedback Voltage Line

Regulation

2.5

I

TH

Voltage vs RUN/SS Voltage

V

IN

= 5V

1.0

40 60 80 100 120

TEMPERATURE (°C)

38735 G01

0

20

10

0

0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0

RUN/SS VOLTAGE (V)

38735 G03

38735 G02

Shutdown Mode I

Q

vs V

IN

70

65

SHUTDOWN MODE I

Q

(μA)

SHUTDOWN MODE I

Q

(μA)

60

55

50

45

40

35

30

25

20

3

4

5

7

6

V

IN

(V)

8

9

10

80

70

60

Shutdown I

Q

vs Temperature

100

90

80

70

TIME (ns)

60

50

40

30

20

10

0

–60 –40 –20 0 20 40 60 80 100 120

TEMPERATURE (°C)

3873-5 G05

Gate Drive Rise and Fall Time

vs C

LOAD

50

40

30

RISE TIME

FALL TIME

20

10

0

2000

6000

4000

C

LOAD

(pF)

8000

10000

38735 G06

3873-5 G04

RUN Threshold vs Temperature

1.0

10.2

10.1

REGULATION VOLTAGE (V)

0.9

RUN THRESHOLDS (V)

0.8

RISING

10.0

9.9

9.8

9.7

9.6

9.5

9.4

9.3

0.5

–60 –40 –20 0 20 40 60 80 100 120

TEMPERATURE (°C)

38735 G07

Shunt Regulator Voltage

vs I

SHUNT

0.7

FALLING

0.6

9.2

0

5

10

15

20 25 30

I

SHUNT

(mA)

35

40

45

3873-5 G08

38735fb

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LTC3873-5

TYPICAL PERFORMANCE CHARACTERISTICS

Frequency vs Temperature

250

300

V

IN

= 5V

MAXIMUM SENSE THRESHOLD (mV)

250

200

150

IPRG = GND

100

50

0

–60 –40 –20 0 20 40 60 80 100 120

TEMPERATURE (°C)

38735 G10

Maximum Sense Threshold

vs Temperature

IPRG = V

IN

230

FREQUECY (kHz)

IPRG = FLOAT

210

190

170

150

–60 –40 –20 0 20 40 60 80 100 120

TEMPERATURE (°C)

3873-5 G09

PIN FUNCTIONS

(TS8/DD8)

IPRG (Pin 1/Pin 4):

Current Sense Limit Select Pin.

I

TH

(Pin 2/Pin 3):

This pin serves as the error ampliﬁer

compensation point. Nominal voltage range for this pin

is 0.7V to 1.9V.

V

FB

(Pin 3/Pin 2):

This pin receives the feedback voltage

from an external resistor divider across the output.

GND (Pin 4/Pin 1):

Ground Pin.

NGATE (Pin 5/Pin 8):

Gate Drive for the External N-Channel

MOSFET. This pin swings from 0V to V

IN

.

V

CC

(Pin 6/Pin 7):

Supply Pin. This pin must be closely

decoupled to GND (Pin 4).

RUN/SS (Pin 7/Pin 6):

Shutdown and External Soft-Start

Pin. In shutdown, all functions are disabled and the NGATE

pin is held low.

SW (Pin 8/Pin 5):

Switch node connection to inductor and

current sense input pin through external slope compensa-

tion resistor. Normally, the external N-channel MOSFET’s

drain is connected to this pin.

Exposed Pad (NA/Pin 9):

Ground. Must be soldered to PCB

for electrical contact and rated thermal performance.

38735fb

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LTC3873ETS8-5-TRPBF

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