LINEAR TECHNOLOGY LT3684 Technical data

36V, 2A, 2.8MHz Step-Down

Switching Regulator

FEATURES DESCRIPTION

LT3684

■

Wide Input Range: 3.6V to 34V Operating,

36V Maximum

■

2A Maximum Output Current

■

Adjustable Switching Frequency: 300kHz to 2.8MHz

■

Low Shutdown Current: IQ < 1µA

■

Integrated Boost Diode

■

Power Good Flag

■

Saturating Switch Design: 0.18Ω On-Resistance

■

1.265V Feedback Reference Voltage

■

Output Voltage: 1.265V to 20V

■

Soft-Start Capability

■

Small 10-Pin Thermally Enhanced MSOP and

(3mm × 3mm) DFN Packages

APPLICATIONS

■

Automotive Battery Regulation

■

Power for Portable Products

■

Distributed Supply Regulation

■

Industrial Supplies

■

Wall Transformer Regulation

The LT®3684 is an adjustable frequency (300kHz to 2.8MHz)
monolithic buck switching regulator that accepts input
voltages up to 34V (36V maximum). A high effi ciency

0.18Ω switch is included on the die along with 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. The LT3684’s
high operating frequency allows the use of small, low cost
inductors and ceramic capacitors resulting in low output
ripple while keeping total solution size to a minimum.
The low current shutdown mode 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 fl ag signals when V

reaches

OUT

90% of the programmed output voltage. The LT3684 is
available in 10-Pin MSOP and 3mm × 3mm DFN packages
with Exposed Pads for low thermal resistance.

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

All other trademarks are the property of their respective owners.

TYPICAL APPLICATION

3.3V Step-Down Converter

V

IN

4.5V TO
34V

OFF ON

16.2k

4.7µF

330pF

V

RUN/SS BOOST

V

C

RT

PG

60.4k

IN

LT3684

GND

BD

BIAS

SW

Effi ciency

V

OUT

3.3V
2A

0.47µF

FB

200k

4.7µH

324k

22µF

3684 TA01

90

80

70

60

EFFICIENCY (%)

50

40

30

0

VIN = 12V

= 3.3V

V

OUT

L = 4.7µH
f = 800kHz

0.5 1 1.5 2
LOAD CURRENT (A)

3684 TA01b

3684f

1

LT3684

ABSOLUTE MAXIMUM RATINGS

(Note 1)

VIN, RUN/SS Voltage .................................................36V

BOOST Pin Voltage ...................................................56V

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

FB, RT, V

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

C

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

Maximum Junction Temperature .......................... 125°C

Operating Temperature Range (Note 2)

LT3684E ............................................... –40°C to 85°C

LT3684I ............................................. –40°C to 125°C

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

Lead Temperature (Soldering, 10 sec)

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

PACKAGE/ORDER INFORMATION

TOP VIEW

BD

1

BOOST

2
3

SW

4

V

IN

5

RUN/SS

10-LEAD (3mm × 3mm) PLASTIC DFN

T

JMAX

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

DD PACKAGE

= 125°C, θJA = 45°C/W, θJC = 10°C/W

10

RT
V

9

11

C

FB

8
7

BIAS

6

PG

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

BD

BOOST

SW
V

RUN/SS

T

JMAX

ORDER PART NUMBER DD PART MARKING* ORDER PART NUMBER MSE PART MARKING*

TOP VIEW

10

1
2

11

3
4

IN

5

MSE PACKAGE

10-LEAD PLASTIC MSOP

= 125°C, θJA = 45°C/W, θJC = 10°C/W

RT

9

V

C

FB

8

BIAS

7

PG

6

LT3684EDD
LT3684IDD

LCVT
LCVT

LT3684EMSE
LT3684IMSE

LTCVS
LTCVS

Order Options Tape and Reel: Add #TR
Lead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBF
Lead Free Part Marking: http://www.linear.com/leadfree/

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

ELECTRICAL CHARACTERISTICS

The
temperature range, otherwise specifi cations are at T

= 25°C. VIN = 10V, V

A

●

denotes the specifi cations which apply over the full operating

RUNS/SS

= 10V, V

BOOST

= 15V, V

= 3.3V unless otherwise

BIAS

noted. (Note 2)

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Input Voltage

Quiescent Current from V

IN

Quiescent Current from BIAS V

●

V

= 0.2V 0.01 0.5 µA

RUN/SS

= 3V, Not Switching

V

BIAS

= 0, Not Switching 1.2 2.0 mA

V

BIAS

= 0.2V 0.01 0.5 µA

RUN/SS

= 3V, Not Switching

V

BIAS

= 0, Not Switching 00.1 mA

V

BIAS

●

●

3 3.6 V

0.4 0.8 mA

0.85 1.5 mA

2

3684f

LT3684

ELECTRICAL CHARACTERISTICS

The
temperature range, otherwise specifi cations are at T

= 25°C. VIN = 10V, V

A

noted. (Note 2)

PARAMETER CONDITIONS MIN TYP MAX UNITS

Minimum Bias Voltage 2.7 3 V

Feedback Voltage

FB Pin Bias Current (Note 3)

FB Voltage Line Regulation 4V < V

Error Amp g

Error Amp Gain 1000

Source Current 75 µA

V

C

Sink Current 100 µA

V

C

Pin to Switch Current Gain 3.5 A/V

V

C

Clamp Voltage 2V

V

C

Switching Frequency R

Minimum Switch Off-Time

Switch Current Limit Duty Cycle = 5% 3.1 3.6 4.0 A

Switch V

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 VFB Rising 100 mV

PG Hysteresis 10 mV

PG Leakage V

PG Sink Current V

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 LT3684E is guaranteed to meet performance specifi cations
from 0°C to 85°C. Specifi cations over the –40°C to 85°C operating
temperature range are assured by design, characterization and correlation
with statistical process controls. The LT3684I specifi cations are
guaranteed over the –40°C to 125°C temperature range.

m

CESAT

IN

= 8.66k

T

R

= 29.4k

T

R

= 187k

T

ISW = 2A 360 mV

= 10V, V

SW

= 1A 18 30 mA

SW

RUN/SS

= 5V 0.1 1 µA

PG

= 0.4V

PG

●

denotes the specifi cations which apply over the full operating

= 10V V

RUNS/SS

< 34V 0.002 0.02 %/V

= 0V 0.02 2 µA

BIAS

= 2.5V 5 10 µA

Note 3: Bias current measured in regulation. Bias current fl ows into the FB
pin.

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

BOOST

= 15V, V

●

●

●

●

●

= 3.3V unless otherwise

BIAS

1.25

1.24

2.7

1.25
250

100 300 µA

1.265

1.265

30 100 nA

330 µMho

3.0

1.4

300

100 150 nS

1.6 2.1 V

1.28

1.29

3.3

1.55
350

MHz
MHz

kHz

V
V

3684f

3

LT3684

TYPICAL PERFORMANCE CHARACTERISTICS

Effi ciency (V

100

90

80

70

EFFICIENCY (%)

60

50

0.2 0.4 0.6

0

OUT

0.8 1.0

LOAD CURRENT (A)

Maximum Load Current

4.0

3.5

3.0

= 5.0V)

VIN = 12V

VIN = 24V

L: NEC PLC-0745-4R7
f = 800kHz

1.2 1.4 1.8

TYPICAL

1.6

3684 G01

2.0

Effi ciency (V

90

85

80

75

70

65

EFFICIENCY (%)

60

55

50

0.2 0.4 0.6

0

Maximum Load Current

4.0

3.5

3.0

= 3.3V)

OUT

VIN = 24V

L: NEC PLC-0745-4R7
f = 800kHz

0.8 1.0

LOAD CURRENT (A)

TYPICAL

VIN = 7V

VIN = 12V

1.2 1.4 1.8

(TA = 25°C unless otherwise noted)

Effi ciency

90

85

1.6

3684 G02

2.0

80

75

70

65

EFFICIENCY (%)

60

55

50

0

VIN = 24V

0.5 1 2
SWITCHING FREQUENCY (MHz)

Switch Current Limit

4.0

3.5

3.0

VIN = 12V

1.5

V

= 3.3V

OUT

L = 10µH
LOAD = 1A

2.5 3

3684 G03

2.5

2.0

LOAD CURRENT (A)

1.5

1.0
5

MINIMUM

10 20

15

INPUT VOLTAGE (V)

Switch Current Limit

4.5

4.0

3.0

2.5

2.0

1.5

1.0

SWITCH CURRENT LIMIT (A)

0.5

0

–50

DUTY CYCLE = 10 %

DUTY CYCLE = 90 %

0–25 5025 10075

TEMPERATURE (°C)

V

= 3.3V

OUT

= 25°C

T

A

L = 4.7µH
f = 800kHz

25 30

3684 G04

3684 G07

125

2.5

2.0

LOAD CURRENT (A)

1.5

1.0
5

MINIMUM

10 20

Switch Voltage Drop

700

600

500

400

300

VOLTAGE DROP (mV)

200

100

0

0

500 1000

SWITCH CURRENT (mA)

15

INPUT VOLTAGE (V)

2000 3000 3500

1500 2500

V

= 5V

OUT

= 25°C

T

A

L = 4.7µH
f = 800kHz

25 30

3684 G05

3684 G08

2.5

2.0

SWITCH CURRENT LIMIT (A)

1.5

1.0
20 60

0

40

DUTY CYCLE (%)

Boost Pin Current

90

80

70

60

50

40

30

20

BOOST PIN CURRENT (mA)

10

0

500

0

1500 3500

1000
SWITCH CURRENT (mA)

2000

80 100

3684 G06

2500 3000

3684 G09

4

3684f

LT3684

TYPICAL PERFORMANCE CHARACTERISTICS

Feedback Voltage

1.290

1.285

1.280

1.275

1.270

1.265

FEEDBACK VOLTAGE (V)

1.260

1.255

1.250
–50

0 50 100–25 25 75

TEMPERATURE (°C)

125

3684 G10

Minimum Switch On-Time Soft-Start RUN/SS Pin Current

140

120

100

80

60

40

MINIMUM SWITCH ON-TIME (ns)

20

0

–50

–25 0 50 75 100 125

25

TEMPERATURE (˚C)

3684 G13

Switching Frequency Frequency Foldback

1.20
RT = 45.3k

1.15

1.10

1.05

1.00

0.95

FREQUENCY (MHz)

0.90

0.85

0.80

–50

4.0

3.5

3.0

2.5

2.0

1.5

1.0

SWITCH CURRENT LIMIT (A)

0.5

0

0

0 50 100–25 25 75

TEMPERATURE (°C)

0.5 1 2

1.5

RUN/SS PIN VOLTAGE (V)

2.5 3 3.5

(TA = 25°C unless otherwise noted)

1200

RT = 45.3k

1000

800

600

400

SWITCHING FREQUENCY (kHz)

200

0

3684 G11

3684 G14

125

0

200 400

12

10

8

6

4

RUN/SS PIN CURRENT (µA)

2

0

0

510

600 1000

FB PIN VOLTAGE (mV)

15 25

RUN/SS PIN VOLTAGE (V)

800 1200 1400

3684 G12

20 30 35

3684 G15

Boost Diode Error Amp Output Current

1.6

1.4

1.2

(V)

f

1.0

0.8

0.6

BOOST DIODE V

0.4

0.2

0

0

0.5

BOOST DIODE CURRENT (A)

1.0

1.5

2.0

3684 G16

100

80

60

40

20

0

PIN CURRENT (µA)

–20

C

V

–40

–60

–80

1.065

1.165 1.365

1 .265 1.465

FB PIN VOLTAGE (V)

3684 G17

Minimum Input Voltage

4.5

4.0

3.5

3.0

INPUT VOLTAGE (V)

2.5

2.0

0.001

0.01
LOAD CURRENT (A)

0.1

V

= 3.3V

OUT

= 25°C

T

A

L = 4.7µH
f = 800kHz

1

3684 G18

10

3684f

5

LT3684

TYPICAL PERFORMANCE CHARACTERISTICS

Minimum Input Voltage

6.5

6.0

5.5

5.0

INPUT VOLTAGE (V)

4.5

4.0

0.001

0.01
LOAD CURRENT (A)

0.5A/DIV

V

= 5V

OUT

= 25°C

T

A

L = 4.7µH
f = 800kHz

0.1

1

10

3684 G19

Switching Waveforms
(Discontinuous Operation)

I

L

VC Voltages

2.50

2.00

CURRENT LIMIT CLAMP

1.50

1.00

THRESHOLD VOLTAGE (V)

0.50

0

SWITCHING THRESHOLD

–25 0 50 100

–50

TEMPERATURE (°C)

25 75 125

0.5A/DIV

(TA = 25°C unless otherwise noted)

Power Good Threshold

1.200

PG RISING

1.180

1.160

1.140

THRESHOLD VOLTAGE (V)

1.120

1.100

3684 G20

–25 0 50 100

–50

TEMPERATURE (°C)

Switching Waveforms
(Continuous Operation)

I

L

25 75 125

3684 G21

V

SW

5V/DIV

V

OUT

10mV/DIV

VIN = 12V, FRONT PAGE APPLICATION
I

= 140mA

LOAD

1µs/DIV

3684 G22

V

RUN/SS

5V/DIV

V

OUT

10mV/DIV

VIN = 12V, FRONT PAGE APPLICATION
I

= 1A

LOAD

1µs/DIV

3684 G23

6

3684f

PIN FUNCTIONS

LT3684

BD (Pin 1): This pin connects to the anode of the boost
Schottky diode.

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 LT3684’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
LT3684 in shutdown mode. Tie to ground to shut down
the LT3684. Tie to 2.3V 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

PG (Pin 6): The PG pin is the open collector output of an
internal comparator. PG remains low until the FB pin is
within 10% of the fi nal regulation voltage. PG output is
valid when V

BIAS (Pin 7): The BIAS pin supplies the current to the
LT3684’s internal regulator. Tie this pin to the lowest
available voltage source above 3V (typically V
architecture increases effi ciency especially when the input
voltage is much higher than the output.

FB (Pin 8): The LT3684 regulates the FB pin to 1.265V.
Connect the feedback resistor divider tap to this pin.

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

V

C

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

(Pin 10): Oscillator Resistor Input. Connecting a resistor

RT

to ground from this pin sets the switching frequency.

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

is above 3.5V and RUN/SS is high.

IN

OUT

). This

3684f

7

LT3684

BLOCK DIAGRAM

V

V

IN

R

IN

4

C1

BIAS

7

RUN/SS

5

RT

10

T

SOFT-START

PG

6

INTERNAL 1.265V REF

+

1.12V

–

GND

11 8

R2

ERROR AMP

FB

R1

–
+

Σ

SLOPE COMP

OSCILLATOR

300kHz–2.8MHz

SWITCH

LATCH

R

S

VC CLAMP

Q

+
–

BD

BOOST

SW

1

2

C3

3

V

C

9

L1

D1

C

C

C

R

F

C

C2

3684 BD

V

OUT

8

3684f

OPERATION

LT3684

The LT3684 is a constant frequency, current mode step­down regulator. An oscillator, with frequency set by RT,
enables an RS fl ip-fl op, turning on the internal power
switch. An amplifi er and comparator monitor the current
fl owing between the V
off when this current reaches a level determined by the
voltage at V
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.

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

pin, but if the BIAS pin is connected to an external

V

IN

voltage higher than 3V bias power will be drawn from the
external source (typically the regulated output voltage).

. An error amplifi er measures the output

C

and SW pins, turning the switch

IN

pin. If the error amplifi er’s output

C

This improves effi ciency. The RUN/SS pin is used to place
the LT3684 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 effi cient
operation.

The oscillator reduces the LT3684’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.

The LT3684 contains a power good comparator which trips
when the FB pin is at 90% of its regulated value. The PG
output is an open-collector transistor that is off when the
output is in regulation, allowing an external resistor to pull
the PG pin high. Power good is valid when the LT3684 is
enabled and V

is above 3.6V.

IN

3684f

9

LT3684

APPLICATIONS INFORMATION

FB Resistor Network

The output voltage is programmed with a resistor divider
between the output and the FB pin. Choose the 1% resis­tors according to:

RR

12

V

⎛
⎜

⎝

1 265

OUT

.

⎞

–

1=

⎟

⎠

Reference designators refer to the Block Diagram.

Setting the Switching Frequency

The LT3684 uses a constant frequency PWM architecture
that can be programmed to switch from 300kHz to 2.8MHz
by using a resistor tied from the RT pin to ground. A table
showing the necessary R

value for a desired switching

T

frequency is in Figure 1.

SWITCHING FREQUENCY (MHz) RT VALUE (kΩ)

0.2

0.3

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

2.2

2.4

2.6

2.8

Figure 1. Switching Frequency vs RT Value

267
187
133

84.5

60.4

45.3

36.5

29.4

23.7

20.5

16.9

14.3

12.1

10.2

8.66

Operating Frequency Tradeoffs

Selection of the operating frequency is a tradeoff between
effi ciency, component size, minimum dropout voltage, and
maximum input voltage. The advantage of high frequency
operation is that smaller inductor and capacitor values may
be used. The disadvantages are lower effi ciency, lower
maximum input voltage, and higher dropout voltage. The
highest acceptable switching frequency (f

SW(MAX)

) for a

given application can be calculated as follows:

VV

+

D OUT

+

()

()

DINSW

–

f

SW MAX

=

()

tVVV

ON MIN

where VIN is the typical input voltage, V
voltage, is the catch diode drop (~0.5V), V

is the output

OUT

is the internal

SW

switch drop (~0.5V at max load). This equation shows
that slower switching frequency is necessary to safely
accommodate high V

IN/VOUT

ratio. Also, as shown in
the next section, lower frequency allows a lower dropout
voltage. The reason input voltage range depends on the
switching frequency is because the LT3684 switch has
fi nite minimum on and off times. The switch can turn on
for a minimum of ~150ns and turn off for a minimum of
~150ns. This means that the minimum and maximum
duty cycles are:

DC f t

DC f t

where fSW is the switching frequency, the t
minimum switch on time (~150ns), and the t

=

MIN SW

MAX SW

ON MIN

=

1–

()

OFF MIN

()

ON(MIN)

OFF(MIN)

is the

is
the minimum switch off time (~150ns). These equations
show that duty cycle range increases when switching
frequency is decreased.

A good choice of switching frequency should allow ad­equate input voltage range (see next section) and keep
the inductor and capacitor values small.

Input Voltage Range

The maximum input voltage for LT3684 applications de­pends on switching frequency, the Absolute Maximum Rat­ings on V

and BOOST pins, and on operating mode.

IN

If the output is in start-up or short-circuit operating modes,
then V

must be below 34V and below the result of the

IN

following equation:

VV

+

V

IN MAX

()

where V
V

OUT

IN(MAX)

is the output voltage, VD is the catch diode drop
(~0.5V), V
load), f
t

ON(MIN)

SW

is the minimum switch on time (~150ns). Note that

OUT D

=

ft

SW

ON MIN

()

is the maximum operating input voltage,

is the internal switch drop (~0.5V at max

SW

is the switching frequency (set by RT), and

VV

+–

DSW

a higher switching frequency will depress the maximum
operating input voltage. Conversely, a lower switching

10

3684f

APPLICATIONS INFORMATION

LT3684

frequency will be necessary to achieve safe operation at
high input voltages.

If the output is in regulation and no short-circuit or start-up
events are expected, then input voltage transients of up to
36V are acceptable regardless of the switching frequency.
In this mode, the LT3684 may enter pulse skipping opera­tion where some switching pulses are skipped to maintain
output regulation. In this mode the output voltage ripple
and inductor current ripple will be higher than in normal
operation.

The minimum input voltage is determined by either the
LT3684’s minimum operating voltage of ~3.6V or by its
maximum duty cycle (see equation in previous section).
The minimum input voltage due to duty cycle is:

V

IN MIN

()

where V

OUT D

=

ft

1–

SW

OFF MIN

()

is the minimum input voltage, and t

IN(MIN)

VV

+

–

DSW

OFF(MIN)

VV

+

is the minimum switch off time (150ns). Note that higher
switching frequency will increase the minimum input
voltage. If a lower dropout voltage is desired, a lower
switching frequency should be used.

Inductor Selection

For a given input and output voltage, the inductor value
and switching frequency will determine the ripple current.
The ripple current ΔI

increases with higher VIN or V

L

OUT

and decreases with higher inductance and faster switch­ing frequency. A reasonable starting point for selecting
the ripple current is:

= 0.4(I

ΔI

L

where I

OUT(MAX)

OUT(MAX)

)

is the maximum output load current. To
guarantee suffi cient output current, peak inductor current
must be lower than the LT3684’s switch current limit (I

LIM

).

The peak inductor current is:

I

L(PEAK)

where I

= I

L(PEAK)

OUT(MAX)

is the peak inductor current, I
the maximum output load current, and ΔI
ripple current. The LT3684’s switch current limit (I

+ ΔIL/2

LIM

is

) is

OUT(MAX)

is the inductor

L

at least 3.5A at low duty cycles and decreases linearly to

2.5A at DC = 0.8. The maximum output current is a func­tion of the inductor ripple current:

= I

I

OUT(MAX)

LIM

– ΔIL/2

Be sure to pick an inductor ripple current that provides
suffi cient maximum output current (I

OUT(MAX)

).

The largest inductor ripple current occurs at the highest

. To guarantee that the ripple current stays below the

V

IN

specifi ed maximum, the inductor value should be chosen
according to the following equation:

⎛

VV

OUT D

L

=

⎜

fI

∆

⎝

⎛

⎞

+

L

VV

1–

⎜

⎟

⎜

⎠

⎝

OUT D

V

IN MAX

()

⎞

+

⎟
⎟⎟

⎠

where VD is the voltage drop of the catch diode (~0.4V),
V

IN(MAX)

voltage, f

is the maximum input voltage, V

is the switching frequency (set by RT), and L

SW

is the output

OUT

is in the inductor value.

The inductor’s RMS current rating must be greater than the
maximum load current and its saturation current should be
about 30% higher. For robust operation in fault conditions
(start-up or short circuit) and high input voltage (>30V),
the saturation current should be above 3.5A. To keep the
effi ciency high, the series resistance (DCR) should be less
than 0.1Ω, and the core material should be intended for
high frequency applications. Table 1 lists several vendors
and suitable types.

Table 1. Inductor Vendors

VENDOR URL PART SERIES TYPE

Murata www.murata.com LQH55D Open

TDK www.componenttdk.com SLF7045

SLF10145

Toko www.toko.com D62CB

D63CB
D75C
D75F

Sumida www.sumida.com CR54

CDRH74
CDRH6D38
CR75

Shielded
Shielded

Shielded
Shielded
Shielded
Open

Open
Shielded
Shielded
Open

3684f

11

LT3684

APPLICATIONS INFORMATION

Of course, such a simple design guide will not always re­sult in the optimum inductor for your application. A larger
value inductor provides a slightly higher maximum load
current and will reduce the output voltage ripple. If your
load is lower than 2A, then you can decrease the value of
the inductor and operate with higher ripple current. This
allows you to use a physically smaller inductor, or one
with a lower DCR resulting in higher effi ciency. There are
several graphs in the Typical Performance Characteristics
section of this data sheet that show the maximum load
current as a function of input voltage and inductor value
for several popular output voltages. Low inductance may
result in discontinuous mode operation, which is okay
but further reduces maximum load current. For details of
maximum output current and discontinuous mode opera­tion, see Linear Technology Application Note 44. Finally,
for duty cycles greater than 50% (V
is a minimum inductance required to avoid subharmonic
oscillations. See AN19.

Input Capacitor

Bypass the input of the LT3684 circuit with a ceramic capaci­tor of X7R or X5R type. Y5V types have poor performance
over temperature and applied voltage, and should not be
used. A 4.7µF to 10µF ceramic capacitor is adequate to
bypass the LT3684 and will easily handle the ripple current.
Note that larger input capacitance is required when a lower
switching frequency is used. If the input power source has
high impedance, or there is signifi cant inductance due to
long wires or cables, additional bulk capacitance may be
necessary. This can be provided with a low performance
electrolytic capacitor.

Step-down regulators draw current from the input sup­ply in pulses with very fast rise and fall times. The input
capacitor is required to reduce the resulting voltage
ripple at the LT3684 and to force this very high frequency
switching current into a tight local loop, minimizing EMI.
A 4.7µF capacitor is capable of this task, but only if it is
placed close to the LT3684 and the catch diode (see the
PCB Layout section). A second precaution regarding the

OUT/VIN

> 0.5), there

ceramic input capacitor concerns the maximum input
voltage rating of the LT3684. A ceramic input capacitor
combined with trace or cable inductance forms a high
quality (under damped) tank circuit. If the LT3684 circuit
is plugged into a live supply, the input voltage can ring to
twice its nominal value, possibly exceeding the LT3684’s
voltage rating. This situation is easily avoided (see the Hot
Plugging Safety section).

For space sensitive applications, a 2.2µF ceramic capaci­tor can be used for local bypassing of the LT3684 input.
However, the lower input capacitance will result in in­creased input current ripple and input voltage ripple, and
may couple noise into other circuitry. Also, the increased
voltage ripple will raise the minimum operating voltage
of the LT3684 to ~3.7V.

Output Capacitor and Output Ripple

The output capacitor has two essential functions. Along
with the inductor, it fi lters the square wave generated by the
LT3684 to produce the DC output. In this role it determines
the output ripple, and low impedance at the switching
frequency is important. The second function is to store
energy in order to satisfy transient loads and stabilize the
LT3684’s control loop. Ceramic capacitors have very low
equivalent series resistance (ESR) and provide the best
ripple performance. A good starting value is:

C

OUT

where fSW is in MHz, and C
output capacitance in µF. Use X5R or X7R types. This
choice will provide low output ripple and good transient
response. Transient performance can be improved with
a higher value capacitor if the compensation network is
also adjusted to maintain the loop bandwidth. A lower
value of output capacitor can be used to save space and
cost but transient performance will suffer. See the Fre­quency Compensation section to choose an appropriate
compensation network.

100

=

Vf

OUT SW

is the recommended

OUT

12

3684f

APPLICATIONS INFORMATION

Table 2. Capacitor Vendors

VENDOR PHONE URL PART SERIES COMMANDS

Panasonic [phone] www.panasonic.com Ceramic,

Polymer,
Tantalum

Kemet [phone] www.kemet.com Ceramic,

Tantalum T494, T495

Sanyo [phone] www.sanyovideo.com Ceramic,

Polymer,
Tantalum

Murata [phone] www.murata.com Ceramic

AVX www.avxcorp.com Ceramic,

Tantalum TPS Series

Taiyo Yuden [phone] www.taiyo-yuden.com Ceramic

EEF Series

POSCAP

LT3684

When choosing a capacitor, look carefully through the
data sheet to fi nd out what the actual capacitance is under
operating conditions (applied voltage and temperature).
A physically larger capacitor, or one with a higher voltage
rating, may be required. High performance tantalum or
electrolytic capacitors can be used for the output capacitor.
Low ESR is important, so choose one that is intended for
use in switching regulators. The ESR should be specifi ed

by the supplier, and should be 0.05Ω or less. Such a
capacitor will be larger than a ceramic capacitor and will
have a larger capacitance, because the capacitor must be
large to achieve low ESR. Table 2 lists several capacitor
vendors.

Catch Diode

The catch diode conducts current only during switch off
time. Average forward current in normal operation can
be calculated from:

I

D(AVG)

where I

= I

OUT

OUT

(VIN – V

OUT

)/VIN

is the output load current. The only reason to
consider a diode with a larger current rating than necessary
for nominal operation is for the worst-case condition of
shorted output. The diode current will then increase to the
typical peak switch current. Peak reverse voltage is equal
to the regulator input voltage. Use a diode with a reverse
voltage rating greater than the input voltage. Table 3 lists
several Schottky diodes and their manufacturers.

Table 3. Diode Vendors

PART NUMBER

On Semicnductor
MBRM120E
MBRM140

Diodes Inc.
B120
B130
B220
B230
DFLS240L

International Rectifi er
10BQ030
20BQ030

V
(V)

20
40

20
30
20
30
40

30
30

R

I

AVE

(A)

1
1

1
1
2
2
2

1
2

AT 1A

V

F

(mV)

530
550

500
500

420 470

VF AT 2A

(mV)

595

500
500
500

470

Frequency Compensation

The LT3684 uses current mode control to regulate the
output. This simplifi es loop compensation. In particular, the
LT3684 does not require the ESR of the output capacitor
for stability, so you are free to use ceramic capacitors to
achieve low output ripple and small circuit size. Frequency
compensation is provided by the components tied to the

pin, as shown in Figure 2. Generally a capacitor (CC)

V

C

and a resistor (R

) in series to ground are used. In addi-

C

tion, there may be lower value capacitor in parallel. This
capacitor (C

) is not part of the loop compensation but

F

is used to fi lter noise at the switching frequency, and is
required only if a phase-lead capacitor is used or if the
output capacitor has high ESR.

3684f

13

LT3684

APPLICATIONS INFORMATION

LT3684

CURRENT MODE

POWER STAGE

= 3.5mho

g

m

3M

V

C

R

C

C

F

C

C

ERROR

AMPLIFIER

g

m

330µmho

SW

C

R1

FB

–

=

+

1.265V

POLYMER

GND

TANTALUM

R2

OUTPUT

PL

ESR

+

C1

OR

3684 F02

C1

CERAMIC

V

= 12V, FRONT PAGE APPLICATION

OUT

I

L

1A/DIV

V

OUT

100mV/DIV

10µs/DIV

3684 F03

Figure 3. Transient Load Response of the LT3684 Front Page
Application as the Load Current is Stepped from 500mA to
1500mA. V

OUT

= 3.3V

Figure 2. Model for Loop Response

Loop compensation determines the stability and transient
performance. Designing the compensation network is a
bit complicated and the best values depend on the ap­plication and in particular the type of output capacitor. A
practical approach is to start with one of the circuits in
this data sheet that is similar to your application and tune
the compensation network to optimize the performance.
Stability should then be checked across all operating
conditions, including load current, input voltage and
temperature. The LT1375 data sheet contains a more
thorough discussion of loop compensation and describes
how to test the stability using a transient load. Figure 2
shows an equivalent circuit for the LT3684 control loop.
The error amplifi er is a transconductance amplifi er with
fi nite output impedance. The power section, consisting of
the modulator, power switch and inductor, is modeled as
a transconductance amplifi er generating an output cur­rent proportional to the voltage at the V

pin. Note that

C

the output capacitor integrates this current, and that the
capacitor on the V

pin (CC) integrates the error ampli-

C

fi er output current, resulting in two poles in the loop. In
most cases a zero is required and comes from either the
output capacitor ESR or from a resistor R

. This simple model works well as long as the value

C

C

in series with

C

of the inductor is not too high and the loop crossover
frequency is much lower than the switching frequency.
A phase lead capacitor (C

) across the feedback divider

PL

may improve the transient response. Figure 3 shows the
transient response when the load current is stepped from
500mA to 1500mA and back to 500mA.

BOOST and BIAS Pin Considerations

Capacitor C3 and the internal boost Schottky diode (see
the Block Diagram) are used to generate a boost volt­age that is higher than the input voltage. In most cases
a 0.22µF capacitor will work well. Figure 2 shows three
ways to arrange the boost circuit. The BOOST pin must be
more than 2.3V above the SW pin for best effi ciency. For
outputs of 3V and above, the standard circuit (Figure 4a)
is best. For outputs between 2.8V and 3V, use a 1µF boost
capacitor. A 2.5V output presents a special case because it
is marginally adequate to support the boosted drive stage
while using the internal boost diode. For reliable BOOST pin
operation with 2.5V outputs use a good external Schottky
diode (such as the ON Semi MBR0540), and a 1µF boost
capacitor (see Figure 4b). For lower output voltages the
boost diode can be tied to the input (Figure 4c), or to
another supply greater than 2.8V. The circuit in Figure 4a
is more effi cient because the BOOST pin current and BIAS
pin quiescent current comes from a lower voltage source.
You must also be sure that the maximum voltage ratings
of the BOOST and BIAS pins are not exceeded.

The minimum operating voltage of an LT3684 application
is limited by the minimum input voltage (3.6V) and by the
maximum duty cycle as outlined in a previous section. For

3684f

14

APPLICATIONS INFORMATION

LT3684

V

OUT

BD

BOOST

V

4.7µF

V

4.7µF

V

4.7µF

IN

IN

IN

V

LT3684

IN

SW

GND

(4a) For V

V

LT3684

IN

BD

GND

OUT

BOOST

SW

(4b) For 2.5V < V

BD

BOOST

V

LT3684

IN

SW

GND

(4c) For V

OUT

C3

> 2.8V

C3

< 2.8V

OUT

C3

< 2.5V

V

OUT

D2

V

OUT

3684 FO4

Figure 4. Three Circuits For Generating The Boost Voltage

proper start-up, the minimum input voltage is also limited
by the boost circuit. If the input voltage is ramped slowly,
or the LT3684 is turned on with its RUN/SS pin when the
output is already in regulation, then the boost capacitor
may not be fully charged. Because the boost capacitor is
charged with the energy stored in the inductor, the circuit
will rely on some minimum load current to get the boost
circuit running properly. This minimum load will depend
on input and output voltages, and on the arrangement of
the boost circuit. The minimum load generally goes to
zero once the circuit has started. Figure 5 shows a plot
of minimum load to start and to run as a function of input

6.0
TO START

5.5

5.0

4.5

4.0

TO RUN

3.5

INPUT VOLTAGE (V)

3.0

2.5

2.0

8.0

7.0

6.0

5.0

4.0

INPUT VOLTAGE (V)

3.0

2.0

0.001

0.001

TO START

TO RUN

0.01

0.01

0.1

LOAD CURRENT (A)

0.1

LOAD CURRENT (A)

V

= 3.3V

OUT

= 25°C

T

A

L = 4.7µH
f = 800kHz

1

V

= 5V

OUT

= 25 °C

T

A

L = 4.7µH
f = 800kHz

1

3684 F05

10

10

Figure 5. The Minimum Input Voltage Depends on
Output Voltage, Load Current and Boost Circuit

voltage. In many cases the discharged output capacitor
will present a load to the switcher and the minimum input
to start will be the same as the minimum input to run.
This occurs, for example, if RUN/SS is asserted after V

IN

is applied. The plots show the worst-case situation where

is ramping very slowly. For lower start-up voltage, the

V

IN

boost diode can be tied to V

; however, this restricts the

IN

input range to one-half of the absolute maximum rating
of the BOOST pin.

At light loads, the inductor current becomes discontinu­ous and the effective duty cycle can be very high. This
reduces the minimum input voltage to approximately
300mV above V

. At higher load currents, the inductor

OUT

current is continuous and the duty cycle is limited by the
maximum duty cycle of the LT3684, requiring a higher
input voltage to maintain regulation.

3684f

15

LT3684

APPLICATIONS INFORMATION

Soft-Start

The RUN/SS pin can be used to soft-start the LT3684,
reducing the maximum input current during start-up.
The RUN/SS pin is driven through an external RC fi lter to
create a voltage ramp at this pin. Figure 7 shows the start­up and shut-down waveforms with the soft-start circuit.
By choosing a large RC time constant, the peak start-up
current can be reduced to the current that is required to
regulate the output, with no overshoot. Choose the value
of the resistor so that it can supply 20µA when the RUN/SS
pin reaches 2.3V.

I

L

RUN

0.22µF

15k

RUN/SS

GND

1A/DIV

V

RUN/SS

2V/DIV

V

OUT

2V/DIV

D4

MBRS140

V

IN

Figure 7. Diode D4 Prevents a Shorted Input from
Discharging a Backup Battery Tied to the Output. It Also
Protects the Circuit from a Reversed Input. The LT3684
Runs Only When the Input is Present

V

IN

RUN/SS

V

C

LT3684

GND FB

BOOST

SW

3684 F07

V

OUT

BACKUP

LT3684 can pull large currents from the output through
the SW pin and the V

pin. Figure 7 shows a circuit that

IN

will run only when the input voltage is present and that
protects against a shorted or reversed input.

PCB Layout

2ms/DIV

Figure 6. To Soft-Start the LT3684, Add a Resisitor
and Capacitor to the RUN/SS Pin

3481 F06

Shorted and Reversed Input Protection

If the inductor is chosen so that it won’t saturate exces­sively, an LT3684 buck regulator will tolerate a shorted
output. There is another situation to consider in systems
where the output will be held high when the input to the
LT3684 is absent. This may occur in battery charging ap­plications or in battery backup systems where a battery
or some other supply is diode OR-ed with the LT3684’s
output. If the V

pin is allowed to fl oat and the RUN/SS

IN

pin is held high (either by a logic signal or because it is
tied to V

), then the LT3684’s internal circuitry will pull

IN

its quiescent current through its SW pin. This is fi ne if
your system can tolerate a few mA in this state. If you
ground the RUN/SS pin, the SW pin current will drop to
essentially zero. However, if the V

pin is grounded while

IN

the output is held high, then parasitic diodes inside the

For proper operation and minimum EMI, care must be
taken during printed circuit board layout. Figure 8 shows
the recommended component placement with trace,
ground plane and via locations. Note that large, switched
currents fl ow in the LT3684’s V

and SW pins, the catch

IN

diode (D1) and the input capacitor (C1). The loop formed
by these components should be as small as possible. These
components, along with the inductor and output capacitor,
should be placed on the same side of the circuit board,
and their connections should be made on that layer. Place
a local, unbroken ground plane below these components.
The SW and BOOST nodes should be as small as possible.
Finally, keep the FB and V

nodes small so that the ground

C

traces will shield them from the SW and BOOST nodes.
The Exposed Pad on the bottom of the package must be
soldered to ground so that the pad acts as a heat sink. To
keep thermal resistance low, extend the ground plane as
much as possible, and add thermal vias under and near
the LT3684 to additional ground planes within the circuit
board and on the bottom side.

16

3684f

APPLICATIONS INFORMATION

LT3684

L1

V

OUT

D1

VIAS TO LOCAL GROUND PLANE

VIAS TO V

OUT

Figure 8. A Good PCB Layout Ensures Proper, Low EMI Operation

C1

C2

GND

VIAS TO RUN/SS

VIAS TO PG

C

R

RT

R

PG

C

R

C

R2

R1

VIAS TO V

IN

OUTLINE OF LOCAL
GROUND PLANE

3684 F08

Hot Plugging Safely

The small size, robustness and low impedance of ceramic
capacitors make them an attractive option for the input
bypass capacitor of LT3684 circuits. However, these capaci­tors can cause problems if the LT3684 is plugged into a
live supply (see Linear Technology Application Note 88 for
a complete discussion). The low loss ceramic capacitor,
combined with stray inductance in series with the power
source, forms an under damped tank circuit, and the
voltage at the V

pin of the LT3684 can ring to twice the

IN

nominal input voltage, possibly exceeding the LT3684’s
rating and damaging the part. If the input supply is poorly
controlled or the user will be plugging the LT3684 into an
energized supply, the input network should be designed
to prevent this overshoot. Figure 9 shows the waveforms
that result when an LT3684 circuit is connected to a 24V
supply through six feet of 24-gauge twisted pair. The
fi rst plot is the response with a 4.7µF ceramic capacitor
at the input. The input voltage rings as high as 50V and
the input current peaks at 26A. A good solution is shown
in Figure 9b. A 0.7Ω resistor is added in series with the

input to eliminate the voltage overshoot (it also reduces
the peak input current). A 0.1µF capacitor improves high
frequency fi ltering. For high input voltages its impact on
effi ciency is minor, reducing effi ciency by 1.5 percent for
a 5V output at full load operating from 24V.

High Temperature Considerations

The PCB must provide heat sinking to keep the LT3684
cool. The Exposed Pad on the bottom of the package must
be soldered to a ground plane. This ground should be tied
to large copper layers below with thermal vias; these lay­ers will spread the heat dissipated by the LT3684. Place
additional vias can reduce thermal resistance further. With
these steps, the thermal resistance from die (or junction)
to ambient can be reduced to θ

= 35°C/W or less. With

JA

100 LFPM airfl ow, this resistance can fall by another 25%.
Further increases in airfl ow will lead to lower thermal re­sistance. Because of the large output current capability of
the LT3684, it is possible to dissipate enough heat to raise
the junction temperature beyond the absolute maximum of
125°C. When operating at high ambient temperatures, the

3684f

17

LT3684

APPLICATIONS INFORMATION

+

LOW
IMPEDANCE
ENERGIZED

24V SUPPLY

+

CLOSING SWITCH

SIMULATES HOT PLUG

I

IN

STRAY
INDUCTANCE
DUE TO 6 FEET
(2 METERS) OF
TWISTED PAIR

0.7Ω

V

IN

V

IN

LT3684

4.7µF

20V/DIV

10A/DIV

I

IN

DANGER

20µs/DIV

MAY EXCEED

IN

RINGING V
ABSOLUTE MAXIMUM RATING

(9a)

V

IN

(9b)

20V/DIV

10A/DIV

I

IN

20µs/DIV

LT3684

4.7µF0.1µF

LT3684

+

22µF

35V

AI.EI.

+

4.7µF

(9c)

Figure 9. A Well Chosen Input Network Prevents Input Voltage Overshoot and
Ensures Reliable Operation when the LT3684 is Connected to a Live Supply

maximum load current should be derated as the ambient
temperature approaches 125°C.

Power dissipation within the LT3684 can be estimated by
calculating the total power loss from an effi ciency measure­ment and subtracting the catch diode loss and inductor
loss. The die temperature is calculated by multiplying the
LT3684 power dissipation by the thermal resistance from
junction to ambient.

V

IN

20V/DIV

I

IN

10A/DIV

20µs/DIV

3684 F09

Other Linear Technology Publications

Application Notes 19, 35 and 44 contain more detailed
descriptions and design information for buck regulators
and other switching regulators. The LT1376 data sheet
has a more extensive discussion of output ripple, loop
compensation and stability testing. Design Note 100
shows how to generate a bipolar output supply using a
buck regulator.

18

3684f

TYPICAL APPLICATIONS

V

IN

6.3V TO 34V

4.7µF

D: DIODES INC. DFLS240L
L: TAIYO YUDEN NP06DZB6R8M

20k

5V Step-Down Converter

ON OFF

330pF

RUN/SS BOOST

V

C

RT

PG

60.4k

f = 800kHz

V

IN

LT3684

GND

BD

SW

BIAS

LT3684

V

OUT

5V
2A

0.47µF

FB

200k

L

6.8µH

D

590k

22µF

3684 TA02

V

4.4V TO 34V

IN

4.7µF

16.2k

330pF

D: DIODES INC. DFLS240L
L: TAIYO YUDEN NP06DZB4R7M

3.3V Step-Down Converter

V

IN

ON OFF

RUN/SS BOOST

V

C

RT

PG

60.4k

f = 800kHz

LT3684

GND

BD

SW

BIAS

V

OUT

3.3V
2A

0.47µF

FB

200k

L

4.7µH

D

324k

22µF

3684 TA03

3684f

19

LT3684

TYPICAL APPLICATIONS

V

IN

4V TO 34V

4.7mF

D1: DIODES INC. DFLS240L
D2: MBR0540
L: TAIYO YUDEN NP06DZB4R7M

22.1k

220pF

2.5V Step-Down Converter

V

IN

ON OFF

RUN/SS BOOST

V

C

RT

PG

84.5k

f = 600kHz

LT3684

GND

BD

SW

BIAS

V

OUT

2.5V

D2

1mF

FB

200k

L

4.7mH

D1

196k

2A

47mF

3684 TA04

V

8.6V TO 22V

TRANSIENT TO 36V

IN

2.2mF

20k

330pF

D: DIODES INC. DFLS240L
L: SUMIDA CDRH4D22/HP-2R2

5V, 2MHz Step-Down Converter

LT3684

GND

BD

SW

BIAS

FB

ON OFF

V

IN

RUN/SS BOOST

V

C

RT

PG

16.9k

f = 2MHz

0.47mF

200k

D

590k

L

2.2mH

3684 TA05

V

OUT

5V
2A

10mF

20

3684f

TYPICAL APPLICATIONS

V

IN

15V TO 34V

10µF

D: DIODES INC. DFLS240L
L: NEC/TOKIN PLC-0755-100

30k

12V Step-Down Converter

V

ON OFF

330pF

RUN/SS BOOST

V

C

RT

PG

60.4k

f = 800kHz

IN

LT3684

GND

BD

SW

BIAS

LT3684

V

OUT

12V
2A

0.47µF

FB

100k

L

10µH

D

845k

22µF

3684 TA06

V

3.5V TO 27V

IN

ON OFF

4.7µF

15.4k

330pF

D: DIODES INC. DFLS240L
L: TAIYO YUDEN NP06DZB3R3M

1.8V Step-Down Converter

LT3684

GND

BD

SW

BIAS

FB

V

IN

RUN/SS BOOST

V

C

RT

PG

105k

f = 500kHz

0.47µF

200k

D

84.5k

L

3.3µH

3684 TA07

V

OUT

1.8V
2A

47µF

3684f

21

LT3684

PACKAGE DESCRIPTION

DD Package

10-Lead Plastic DFN (3mm × 3mm)

(Reference LTC DWG # 05-08-1699)

0.675 ±0.05

3.50 ±0.05

1.65 ±0.05
(2 SIDES)2.15 ±0.05

PACKAGE
OUTLINE

0.25 ± 0.05

2.38 ±0.05

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

PIN 1

TOP MARK

(SEE NOTE 6)

0.200 REF

NOTE:

1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).
CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

4. DIMENSIONS OF EXPOSED PAD ON BOTTOM OF PACKAGE DO NOT INCLUDE

MOLD FLASH. MOLD FLASH, IF PRESENT, SHALL NOT EXCEED 0.15mm ON ANY SIDE

5. EXPOSED PAD SHALL BE SOLDER PLATED

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE
TOP AND BOTTOM OF PACKAGE

0.50
BSC

(2 SIDES)

3.00 ±0.10

(4 SIDES)

0.75 ±0.05

1.65 ± 0.10

(2 SIDES)

0.00 – 0.05

R = 0.115

TYP

2.38 ±0.10

(2 SIDES)

BOTTOM VIEW—EXPOSED PAD

106

15

0.25 ± 0.05

0.50 BSC

0.38 ± 0.10

(DD) DFN 1103

22

3684f

PACKAGE DESCRIPTION

2.794 ± 0.102
(.110 ± .004)

MSE Package

10-Lead Plastic MSOP

(Reference LTC DWG # 05-08-1664)

0.889 ± 0.127

(.035 ± .005)

BOTTOM VIEW OF

EXPOSED PAD OPTION

1

LT3684

2.06 ± 0.102
(.081 ± .004)

1.83 ± 0.102
(.072 ± .004)

5.23

(.206)

MIN

0.305 ± 0.038

(.0120 ± .0015)

TYP

RECOMMENDED SOLDER PAD LAYOUT

0.254

(.010)

GAUGE PLANE

0.18

(.007)

NOTE:

1. DIMENSIONS IN MILLIMETER/(INCH)

2. DRAWING NOT TO SCALE

3. DIMENSION DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS.
MOLD FLASH, PROTRUSIONS OR GATE BURRS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

4. DIMENSION DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS.
INTERLEAD FLASH OR PROTRUSIONS SHALL NOT EXCEED 0.152mm (.006") PER SIDE

5. LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.102mm (.004") MAX

DETAIL “A”

DETAIL “A”

2.083 ± 0.102
(.082 ± .004)

0.50

(.0197)

BSC

0° – 6° TYP

0.53 ± 0.152
(.021 ± .006)

3.20 – 3.45

(.126 – .136)

SEATING

PLANE

3.00 ± 0.102

(.118 ± .004)

(NOTE 3)

4.90 ± 0.152

(.193 ± .006)

1.10

(.043)

MAX

0.17 – 0.27

(.007 – .011)

TYP

10

12

0.50

(.0197)

BSC

8910

3

7

6

45

0.497 ± 0.076

(.0196 ± .003)

REF

3.00 ± 0.102

(.118 ± .004)

(NOTE 4)

0.86

(.034)

REF

0.127 ± 0.076
(.005 ± .003)

MSOP (MSE) 0603

Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa­tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

3684f

23

LT3684

TYPICAL APPLICATION

V

IN

3.6V TO 27V

4.7mF

D: DIODES INC. DFLS240L
L: TAIYO YUDEN NP06DZB3R3M

1.265V Step-Down Converter

V

IN

ON OFF

13k

330pF

RUN/SS BOOST

V

C

RT

PG

105k

f = 500kHz

LT3648

GND

BD

SW

BIAS

V

OUT

1.265V
2A

0.47mF

FB

L

3.3mH

D

47mF

3648 TA08

RELATED PARTS

PART NUMBER DESCRIPTION COMMENTS

LT1933 500mA (I

), 500kHz Step-Down Switching Regulator in

OUT

SOT-23

LT3437 60V, 400mA (I

OUT

Converter with Burst Mode Operation

LT1936 36V, 1.4A (I

OUT

DC/DC Converter

LT3493 36V, 1.2A (I

OUT

DC/DC Converter

LT1976/LT1977 60V, 1.2A (I

OUT

Down DC/DC Converter with Burst Mode Operation

LT1767 25V, 1.2A (I

OUT

DC/DC Converter

LT1940 Dual 25V, 1.4A (I

DC/DC Converter

LT1766 60V, 1.2A (I

OUT

DC/DC Converter

LT3434/LT3435 60V, 2.4A (I

OUT

DC/DC Converter with Burst Mode Operation

LT3481 36V, 2A (I

), Micropower 2.8MHz, High Effi ciency

OUT

Step-Down DC/DC Converter

), MicroPower Step-Down DC/DC

), 500kHz High Effi ciency Step-Down

), 750kHz High Effi ciency Step-Down

), 200kHz/500kHz, High Effi ciency Step-

), 1.1MHz, High Effi ciency Step-Down

), 1.1MHz, High Effi ciency Step-Down

OUT

), 200kHz, High Effi ciency Step-Down

), 200/500kHz, High Effi ciency Step-Down

VIN: 3.6V to 36V, V
Package

VIN: 3.3V to 80V, V

VIN: 3.6V to 36V, V

VIN: 3.6V to 40V, V

V

: 3.3V to 60V, V

IN

Package

VIN: 3V to 25V, V

VIN: 3.6V to 25V, V
Package

VIN: 5.5V to 60V, V
Package

VIN: 3.3V to 60V, V
Package

VIN: 3.6V to 36V, V
DFN and MS10E Packages

= 12V, IQ = 1.6mA, ISD < 1µA, ThinSOTTM

OUT(MIN)

= 1.25V, IQ = 100µA, ISD < 1µA, DFN Package

OUT(MIN)

= 1.2V, IQ = 1.9mA, ISD < 1µA, MS8E Package

OUT(MIN)

= 0.8V, IQ = 1.9mA, ISD < 1µA, DFN Package

OUT(MIN)

= 1.20V, IQ = 100µA, ISD < 1µA, TSSOP16E

OUT(MIN)

= 1.20V, IQ = 1mA, ISD < 6µA, MS8E Package

OUT(MIN)

= 1.20V, IQ = 3.8mA, ISD < 30µA, TSSOP16E

OUT(MIN)

= 1.20V, IQ = 2.5mA, ISD < 25µA, TSSOP16E

OUT(MIN)

= 1.20V, IQ = 100µA, ISD < 1µA, TSSOP16E

OUT(MIN)

= 1.265V, IQ = 5µA, ISD < 1µA, 3mm × 3mm

OUT(MIN)

24

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

[phone] ● FAX: [phone]

●

www.linear.com

3684f

LT 0207 • PRINTED IN USA

© LINEAR TECHNOLOGY CORPORATION 2007