ANALOG DEVICES LT 3480 EMSE Datasheet

LT3480

36V, 2A, 2.4MHz Step-Down

Switching Regulator with

70µA Quiescent Current

FEATURES

n

Wide Input Range:

Operation from 3.6V to 36V
Over-Voltage Lockout Protects Circuits
through 60V Transients

n

2A Maximum Output Current

n

Low Ripple Burst Mode® Operation

70µA IQ at 12VIN to 3.3V

OUT

Output Ripple < 15mV

n

Adjustable Switching Frequency: 200kHz to 2.4MHz

n

Low Shutdown Current: IQ < 1µA

n

Integrated Boost Diode

n

Synchronizable Between 250kHz to 2MHz

n

Power Good Flag

n

Saturating Switch Design: 0.25 On-Resistance

n

0.790V Feedback Reference Voltage

n

Output Voltage: 0.79V to 20V

n

Soft-Start Capability

n

Small 10-Lead Thermally Enhanced MSOP and

(3mm × 3mm) DFN Packages

APPLICATIONS

n

Automotive Battery Regulation

n

Power for Portable Products

n

Distributed Supply Regulation

n

Industrial Supplies

DESCRIPTION

The LT®3480 is an adjustable frequency (200kHz to

2.4MHz) monolithic buck switching regulator that ac­cepts input voltages up to 36V (60V maximum). A high
efficiency 0.25
a boost Schottky diode and the necessary oscillator, con­trol, and logic circuitry. Current mode topology is used
for fast transient response and good loop stability. Low
ripple Burst Mode operation maintains high efficiency at
low output currents while keeping output ripple below
15mV in a typical application. In addition, the LT3480 can
further enhance low output current efficiency by draw­ing bias current from the output when V
Shutdown reduces input supply current to less than 1µA
while a resistor and capacitor on the RUN/SS pin provide a
controlled output voltage ramp (soft-start). A power good
flag signals when V
output voltage. The LT3480 is available in 10-lead MSOP
and 3mm × 3mm DFN packages with exposed pads for
low thermal resistance.

, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation. All other
trademarks are the property of their respective owners.

switch is included on the die along with

is above 3V.

OUT

reaches 86% of the programmed

OUT

TYPICAL APPLICATION

3.3V Step-Down Converter

V

IN

4.5V TO 36V
TRANSIENT

TO 60V

4.7µF

OFF ON

14k

470pF

40.2k

V

IN

RUN/SS BOOST

V

LT3480

C

RT

PG

SYNC

GND

Efficiency

V

OUT

3.3V

BD

0.47µF

SW

FB

For more information www.linear.com/LT3480

4.7µH

316k

100k

3480 TA01

2A

22µF

100

90

80

70

EFFICIENCY (%)

60

50

0

V

= 5V

OUT

V

= 3.3V

OUT

VIN = 12V
L = 5.6µH

0.5 1.0 1.5 2
LOAD CURRENT (A)

F = 800 kHz

3480 TA01b

3480fe

1

LT3480

ABSOLUTE MAXIMUM RATINGS

VIN, RUN/SS Voltage (Note 5) ...................................60V

BOOST Pin Voltage
BOOST Pin Above SW Pin
FB, RT, V

Voltage .......................................................5V

C

PG, BD, SYNC Voltage

...................................................56V

.........................................30V

..............................................30V

Operating Junction Temperature Range (Note 2)

LT3480E
LT3480I

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

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

LT3480H ............................................ –40°C to 150°C

LT3480MP.......................................... –55°C to 150°C

PIN CONFIGURATION

TOP VIEW

10

BD

1

BOOST

2

11

3

SW

4

V

IN

5

RUN/SS

10-LEAD (3mm × 3mm) PLASTIC DFN

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

DD PACKAGE

= 45°C/W, JC = 10°C/W

JA

RT

9

V

C

FB

8
7

PG

6

SYNC

(Note 1)

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

Lead Temperature (Soldering, 10 sec)

(MSE Only)

....................................................... 300°C

TOP VIEW

10

1

BD

2

BOOST

SW
V

IN

RUN/SS

10-LEAD PLASTIC MSOP

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

11

3
4
5

MSE PACKAGE

= 45°C/W, JC = 10°C/W

JA

RT

9

V

C

FB

8

PG

7

SYNC

6

ORDER INFORMATION

LEAD FREE FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LT3480EDD#PBF LT3480EDD#TRPBF LCTP

LT3480IDD#PBF LT3480IDD#TRPBF LCTP

10-Lead (3mm × 3mm) Plastic DFN

10-Lead (3mm × 3mm) Plastic DFN

LT3480EMSE#PBF LT3480EMSE#TRPBF LTCTM 10-Lead Plastic MSOP –40°C to 125°C

LT3480IMSE#PBF LT3480IMSE#TRPBF LTCTM 10-Lead Plastic MSOP –40°C to 125°C

LT3480HMSE#PBF LT3480HMSE#TRPBF LTCTM 10-Lead Plastic MSOP –40°C to 150°C

LT3480MPMSE#PBF LT3480MPMSE#TRPBF LTCTM 10-Lead Plastic MSOP –55°C to 150°C

LEAD BASED FINISH TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE

LT3480EDD LT3480EDD#TR LCTP

LT3480IDD LT3480IDD#TR LCTP

10-Lead (3mm × 3mm) Plastic DFN

10-Lead (3mm × 3mm) Plastic DFN

LT3480EMSE LT3480EMSE#TR LTCTM 10-Lead Plastic MSOP –40°C to 125°C

LT3480IMSE LT3480IMSE#TR LTCTM 10-Lead Plastic MSOP –40°C to 125°C

LT3480HMSE LT3480HMSE#TR LTCTM 10-Lead Plastic MSOP –40°C to 150°C

LT3480MPMSE LT3480MPMSE#TR LTCTM 10-Lead Plastic MSOP –55°C to 150°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/

–40°C to 125°C

–40°C to 125°C

–40°C to 125°C

–40°C to 125°C

3480fe

2

For more information www.linear.com/LT3480

LT3480

ELECTRICAL CHARACTERISTICS

The l denotes the specifications which apply over the full operating temperature
range, otherwise specifications are at TA = 25°C. VIN = 10V, V

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Input Voltage

Overvoltage Lockout

V

IN

V

Quiescent Current from V

IN

Quiescent Current from BD V

Minimum Bias Voltage (BD Pin) 2.7 3 V

Feedback Voltage

FB Pin Bias Current (Note 3) V

FB Voltage Line Regulation 4V < V

Error Amp g

m

Error Amp Gain 1000

Source Current 45 µA

V

C

Sink Current 45 µA

V

C

Pin to Switch Current Gain 3.5 A/V

V

C

Clamp Voltage 2 V

V

C

Switching Frequency R

Minimum Switch Off-Time

Switch Current Limit Duty Cycle = 5% 3 3.5 4 A

Switch V

CESAT

Boost Schottky Reverse Leakage V

Minimum Boost Voltage (Note 4)

BOOST Pin Current I

RUN/SS Pin Current V

RUN/SS Input Voltage High 2.5 V

RUN/SS Input Voltage Low 0.2 V

PG Threshold Offset from Feedback Voltage V

PG Hysteresis 12 mV

PG Leakage V

PG Sink Current V

SYNC Low Threshold 0.5 V

SYNC High Threshold 0.7 V

SYNC Pin Bias Current V

= 0.2V

RUN/SS

V

= 3V, Not Switching

BD

V

= 0, Not Switching

BD

= 0.2V

RUN/SS

V

= 3V, Not Switching

BD

V

= 0, Not Switching

BD

= 0.8V, VC = 0.4V

FB

IN

= 8.66k

T

R

= 29.4k

T

R

= 187k

T

ISW = 2A 500 mV

= 0V 0.02 2 µA

BD

= 1A 22 35 mA

SW

RUN/SS

Rising 100 mV

FB

= 5V 0.1 1 µA

PG

= 0.4V

PG

= 0V 0.1 µA

SYNC

RUN/SS

= 10V, V

= 15V, VBD = 3.3V unless otherwise noted. (Note 2)

BOOST

l

l

36 38 40 V

l

3 3.6 V

0.01
30

105

l

0.01
80

1

780

l

775

l

790
790

7 30 nA

0.5
100
160

0.5
120

5

800
805

µA
µA
µA

µA
µA
µA

mV
mV

< 36V 0.002 0.01 %/V

400 µMho

2.1

0.9

160

l

l

2.4
1

200

2.7

1.15
240

MHz
MHz

kHz

60 150 nS

1.5 2.1 V

= 2.5V 5 10 µA

l

100 600 µA

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.

For more information www.linear.com/LT3480

Note 2: The LT3480E is guaranteed to meet performance specifications
from 0°C to 125°C. Specifications over the –40°C to 125°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LT3480I specifications are

3480fe

3

LT3480

EFFICIENCY (%)

EFFICIENCY (%)

POWER LOSS (W)

SUPPLY CURRENT (µA)

120

SUPPLY CURRENT (µA)

LOAD CURRENT (A)

4.0

ELECTRICAL CHARACTERISTICS

guaranteed over the –40°C to 125°C temperature range. The LT3480H
specifications are guaranteed over the –40°C to 150°C temperature range.
The LT3480MP specifications are guaranteed over the –55°C to 150°C
temperature range.

Note 3: Bias current flows out of the FB pin.

TYPICAL PERFORMANCE CHARACTERISTICS

Efficiency

100

90

80

70

60

V

50

0

VIN = 12V

VIN = 24V

= 5V

OUT

0.2 0.4 0.6 0.8 1.2 1.4 1.6 1.8 2.01.0
LOAD CURRENT (A)

No Load Supply Current

100

80

60

40

20

0

5 10 20

0

15

INPUT VOLTAGE (V)

VIN = 34V

L: NEC PLC-0745-5R6
f: 800kHz

3480 G01

V

= 3.3V

OUT

25 30 35

3480 G04

Efficiency

90

85

80

75

70

65

EFFICIENCY (%)

60

55

50

0 0.2 0.4 0.6 0.8 1.2 1.4 1.6 1.8 2.01.0

400

350

300

250

200

150

100

50

Note 4: This is the minimum voltage across the boost capacitor needed to
guarantee full saturation of the switch.

Note 5: For operation at T
and RUN/SS pins is 40V for continuous operation and 60V for up to
1 second nonrepetitive transients. For operation at T
absolute maximum voltage at V

VIN = 7V

VIN = 12V

VIN = 24V

V

= 3.3V

OUT

LOAD CURRENT (A)

L: NEC PLC-0745-5R6
f: 800kHz

No Load Supply Current

CATCH DIODE: DIODES, INC. PDS360

VIN = 12V

= 3.3V

V

OUT

INCREASED SUPPLY
CURRENT DUE TO CATCH
DIODE LEAKAGE AT
HIGH TEMPERATURE

0

–50

–25 0 50

25

TEMPERATURE (°C)

VIN = 34V

3480 G02

75 100 150125

3480 G05

≤ 125°C, the absolute maximum voltage at VIN

J

> 125°C, the

and RUN/SS pins is 36V.

IN

J

Efficiency

90

80

70

60

50

VIN = 12V

= 3.3V

V

40

30

0

0.5 1.0 1.5 2
LOAD CURRENT (A)

OUT

L = 5.6µH
F = 800 kHz

3480 G27

Maximum Load Current

3.5

3.0

2.5

2.0

1.5

1.0
5

TYPICAL

MINIMUM

10 20

15

INPUT VOLTAGE (V)

V

OUT

= 25 °C

T

A

L = 4.7µH
f = 800 kHz

25 30

10

1

0.1

0.01

= 3.3V

3480 G06

4

3480fe

For more information www.linear.com/LT3480

4.0

SWITCH CURRENT LIMIT (A)

TYPICAL PERFORMANCE CHARACTERISTICS

BOOST PIN CURRENT (mA)

80

FEEDBACK VOLTAGE (mV)

FREQUENCY (MHz)

1.20

SWITCHING FREQUENCY (kHz)

1200

140

LT3480

Maximum Load Current

3.5

TYPICAL

3.0

2.5

MINIMUM

2.0

LOAD CURRENT (A)

1.5

1.0
10 20

5

INPUT VOLTAGE (V)

Switch Voltage Drop

700

600

500

400

300

VOLTAGE DROP (mV)

200

100

0

500 1000 2000 2500

0

SWITCH CURRENT (mA)

Switching Frequency

Switch Current Limit

3.5

3.0

2.5

2.0

V

= 5V

OUT

= 25 °C

T

A

L = 4.7µH
f = 800kHz

15

25 30

3480 G07

SWITCH CURRENT LIMIT(A)

1.5

1.0
20 60

0

40

DUTY CYCLE (%)

80 100

3480 G08

Boost Pin Current

70

60

50

40

30

20

10

1500

3480 G10

0

0 1500500 1000 2000 2500

SWITCH CURRENT (mA)

3480 G11

Frequency Foldback

Switch Current Limit

4.5

4.0

3.5

3.0

2.5

2.0

1.5

1.0

0.5

0

–50 25–25 0 50 75 100 150125

DUTY CYCLE = 10 %

DUTY CYCLE = 90 %

TEMPERATURE (°C)

Feedback Voltage

840

820

800

780

760

–50 25–25 0 50 75 100 150125

TEMPERATURE (°C)

Minimum Switch On-Time

3480 G09

4380 G12

1.15

1.10

1.05

1.00

0.95

0.90

0.85

0.80
–50 25–25 0 50 75 100 150125

TEMPERATURE (°C)

4380 G13

1000

800

600

400

200

0

0

200 400

100 300

FB PIN VOLTAGE (mV)

500

700 900

600

For more information www.linear.com/LT3480

800

3480 G14

120

100

80

60

40

MINIMUM SWITCH ON TIME (ns)

20

0

–50 25–25 0 50 75 100 150125

TEMPERATURE (˚C)

3480 G15

3480fe

5

LT3480

5.0

6.5

V

VOLTAGE (V)

2.50

95

4.0

RUN/SS PIN CURRENT (µA)

12

BOOST DIODE V

(V)

TYPICAL PERFORMANCE CHARACTERISTICS

Soft-Start

3.5

3.0

2.5

2.0

1.5

1.0

SWITCH CURRENT LIMIT (A)

0.5

0

0.5 1 2

0

1.5

RUN/SS PIN VOLTAGE (V)

Error Amp Output Current

50

40

30

20

10

0

–10

PIN CURRENT (µA)

C

–20

V

–30

–40

–50

–200

–100 100
FB PIN ERROR VOLTAGE (V)

Voltages

V

C

2.5 3 3.5

3480 G16

0 200

3480 G19

RUN/SS Pin Current

10

8

6

4

2

0

0

5 10

RUN/SS PIN VOLTAGE (V)

Minimum Input Voltage

4.5

4.0

3.5

3.0

INPUT VOLTAGE (V)

V

= 3.3V

OUT

2.5

= 25°C

T

A

L = 4.7µH
f = 800kHz

2.0
10 100 1000

1

LOAD CURRENT (A)

Power Good Threshold

20 30 35

15 25

3480 G17

10000

3480 G20

Boost Diode

1.4

1.2

1.0

f

0.8

0.6

0.4

0.2

0

0

0.5 1.0 1.5

BOOST DIODE CURRENT (A)

Minimum Input Voltage

6.0

5.5

5.0

INPUT VOLTAGE (V)

V

= 5V

OUT

4.5

= 25 °C

T

A

L = 4.7µH
f = 800kHz

4.0
1 1000010 100 1000

LOAD CURRENT (A)

Switching Waveforms; Burst Mode

2.0

3480 G18

3480 G21

2.00

1.50

1.00

C

0.50

0

–50 25–25 0 50 75 100 150125

6

CURRENT LIMIT CLAMP

SWITCHING THRESHOLD

TEMPERATURE (°C)

3480 G22

90

85

80

THRESHOLD VOLTAGE (%)

75

–50 25–25 0 50 75 100 150125

TEMPERATURE (°C)

For more information www.linear.com/LT3480

3480 G23

V

5V/DIV

0.2A/DIV

V

OUT

10mV/DIV

SW

I

L

5µs/DIV

VIN = 12V; FRONT PAGE APPLICATION

= 10mA

I

LOAD

3480 G24

3480fe

TYPICAL PERFORMANCE CHARACTERISTICS

LT3480

Switching Waveforms; Transition
from Burst Mode to Full Frequency

V

SW

5V/DIV

I

L

0.2A/DIV

V

OUT

10mV/DIV

1µs/DIV

VIN = 12V; FRONT PAGE APPLICATION
I

= 110mA

LOAD

3480 G25

PIN FUNCTIONS

BD (Pin 1): This pin connects to the anode of the boost
Schottky diode. BD also supplies current to the internal
regulator. BD must be locally bypassed when not tied to

with a low ESR capacitor (1µF).

V

OUT

BOOST (Pin 2): This pin is used to provide a drive
voltage, higher than the input voltage, to the internal bipolar
NPN power switch.

SW (Pin 3): The SW pin is the output of the internal power
switch. Connect this pin to the inductor, catch diode and
boost capacitor.

(Pin 4): The VIN pin supplies current to the LT3480’s

V

IN

internal regulator and to the internal power switch. This
pin must be locally bypassed.

RUN/SS (Pin 5): The RUN/SS pin is used to put the
LT3480 in shutdown mode. Tie to ground to shut down
the LT3480. Tie to 2.5V or more for normal operation. If
the shutdown feature is not used, tie this pin to the V
pin. RUN/SS also provides a soft-start function; see the
Applications Information section.

IN

Switching Waveforms; Full
Frequency Continuous Operation

V

SW

5V/DIV

I

L

0.5A/DIV

V

OUT

10mV/DIV

1µs/DIV

VIN = 12V; FRONT PAGE APPLICATION
I

= 1A

LOAD

3480 G26

SYNC (Pin 6): This is the external clock synchronization
input. Ground this pin for low ripple Burst Mode operation at
low output loads. Tie to a clock source for synchronization.
Clock edges should have rise and fall times faster than 1µs.
See synchronizing section in Applications Information.

PG (Pin 7): The PG pin is the open collector output of an
internal comparator. PG remains low until the FB pin is
within 14% of the final regulation voltage. PG output is
valid when V

is above 3.6V and RUN/SS is high.

IN

FB (Pin 8): The LT3480 regulates the FB pin to 0.790V.
Connect the feedback resistor divider tap to this pin.

(Pin 9): The VC pin is the output of the internal error

V

C

amplifier. The voltage on this pin controls the peak switch
current. Tie an RC network from this pin to ground to
compensate the control loop.

RT (Pin 10): Oscillator Resistor Input. Connecting a resistor
to ground from this pin sets the switching frequency.

Exposed Pad (Pin 11): Ground. The exposed pad must
be soldered to PCB.

For more information www.linear.com/LT3480

3480fe

7

LT3480

BLOCK DIAGRAM

V

V

IN

R

IN

4

C1

INTERNAL 0.79V REF

RUN/SS

5

RT

10

T

SYNC

6

SOFT-START

PG

7

+

0.7V

–

GND

11 8

ERROR AMP

FB

–

BOOST

SW

BD

1

2

3

V

C

9

C3

L1

D1

C

C

C

F

R

C

V

OUT

C2

+

Σ

SLOPE COMP

OSCILLATOR

200kHz–2.4MHz

SWITCH

LATCH

R

S

DISABLE

Burst Mode

DETECT

CLAMP

V

C

Q

+
–

R2

R1

OPERATION

The LT3480 is a constant frequency, current mode step­down regulator. An oscillator, with frequency set by RT,
enables an RS flip-flop, turning on the internal power
switch. An amplifier and comparator monitor the current
flowing between the V
off when this current reaches a level determined by the
voltage at V

. An error amplifier measures the output

C

voltage through an external resistor divider tied to the FB
pin and servos the V
increases, more current is delivered to the output; if it
decreases, less current is delivered. An active clamp on the

pin provides current limit. The VC pin is also clamped to

V

C

the voltage on the RUN/SS pin; soft-start is implemented
by generating a voltage ramp at the RUN/SS pin using an
external resistor and capacitor.

and SW pins, turning the switch

IN

pin. If the error amplifier’s output

C

3480 BD

(typically the regulated output voltage). This improves
efficiency. The RUN/SS pin is used to place the LT3480
in shutdown, disconnecting the output and reducing the
input current to less than 1µA.

The switch driver operates from either the input or from
the BOOST pin. An external capacitor and diode are used
to generate a voltage at the BOOST pin that is higher than
the input supply. This allows the driver to fully saturate the
internal bipolar NPN power switch for efficient operation.

To further optimize efficiency, the LT3480 automatically
switches to Burst Mode operation in light load situations.
Between bursts, all circuitry associated with controlling
the output switch is shut down, reducing the input supply
current to 70µA in a typical application.

An internal regulator provides power to the control circuitry.
The bias regulator normally draws power from the V

IN

pin,
but if the BD pin is connected to an external voltage higher
than 3V bias power will be drawn from the external source

8

For more information www.linear.com/LT3480

The oscillator reduces the LT3480’s operating frequency when
the voltage at the FB pin is low. This frequency foldback helps
to control the output current during startup and overload.

3480fe