DC1570A-A - Linear Technology

LT3663

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OUTPUT CURRENT (A)

0.1

EFFICIENCY (%)

100

40 0.5 0.90.3 0.7 1.1

3663 TA01b

1.3

VIN = 15V

VIN = 8V

VIN = 30V

Typical applicaTion

DescripTion

1.2A Step-Down

Switching Regulator with

Output Current Limit

The LT

3663 is a current mode step-down switching regu-

lator with programmable output current limit. The current

limit accurately controls the system power dissipation and

reduces the size of the power path components.

The wide operating input voltage range of 7.5V to 36V (60V

transient) suits the LT3663 to a variety of input sources,

including unregulated 12V wall adapters, 24V industrial

supplies, and automotive power.

The LT3663 includes a low current shutdown mode, input

overvoltage and undervoltage lockout, and thermal shut-

down. Internal compensation and boost diode minimize the

number of external exponents. 3.3V and 5V ﬁxed output

voltage versions are available.

The LT3663 is available in 8-lead DFN and MSOP packages

with exposed pads for low thermal resistance.

L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks of Linear

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

5V Step-Down Converter

FeaTures

applicaTions

n Wide Input Range:

Operation from 7.5V to 36V

Overvoltage Lockout Protects Circuit through 60V

Transients

n Programmable Output Current Limit (0.4A to 1.2A)

n 3.3V and 5V Fixed Output Voltage Options

n Integrated Boost Diode

n Fixed Frequency, Peak Current Mode Control

LT3663 fSW = 1.5MHz

LT3663-X fSW = 1MHZ

n Low Switch VCESAT: 275mV at 1A

n Internally Compensated

n Thermal Protection

n Thermally Enhanced 8-Pin 2mm × 3mm DFN and

MSOP Packages

n Distributed Supply Regulation

n Automotive Battery Regulation

n Industrial Supplies

n Wall Transformer Regulation

Efﬁciency

3663 TA01

LT3663

VIN

RUN

ILIM

BOOST

GND

0.1µF

2.2µF

22µF59k28.7k

11k

6.8µH

ISENSE

VOUT V

OUT

ON OFF

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absoluTe MaxiMuM raTings

Input Voltage (VIN) (Note 2) ......................................60V

BOOST Pin Voltage ...................................................50V

BOOST Pin Above SW Pin .........................................25V

VOUTS, VOUT, ISENSE, FB Pins .......................................6V

RUN Pin (Note 2) ......................................................60V

(Note 1)

orDer inForMaTion

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

LT3663EDCB#PBF LT3663EDCB#TRPBF LDVK 8-Lead (2mm × 3mm) Plastic DFN –40°C to 125°C

LT3663IDCB#PBF LT3663IDCB#TRPBF LDVK 8-Lead (2mm × 3mm) Plastic DFN –40°C to 125°C

LT3663EDCB-3.3#PBF LT3663EDCB-3.3#TRPBF LFMW 8-Lead (2mm × 3mm) Plastic DFN –40°C to 125°C

LT3663IDCB-3.3#PBF LT3663IDCB-3.3#TRPBF LFMW 8-Lead (2mm × 3mm) Plastic DFN –40°C to 125°C

LT3663EDCB-5#PBF LT3663EDCB-5#TRPBF LFMY 8-Lead (2mm × 3mm) Plastic DFN –40°C to 125°C

LT3663IDCB-5#PBF LT3663IDCB-5#TRPBF LFMY 8-Lead (2mm × 3mm) Plastic DFN –40°C to 125°C

LT3663EMS8E#PBF LT3663EMS8E#TRPBF LTDWT 8-Lead Plastic MSOP –40°C to 125°C

LT3663IMS8E#PBF LT3663IMS8E#TRPBF LTDWT 8-Lead Plastic MSOP –40°C to 125°C

LT3663HMS8E#PBF LT3663HMS8E#TRPBF LTDWT 8-Lead Plastic MSOP –40°C to 150°C

LT3663EMS8E-3.3#PBF LT3663EMS8E-3.3#TRPBF LTFMX 8-Lead Plastic MSOP –40°C to 125°C

LT3663IMS8E-3.3#PBF LT3663IMS8E-3.3#TRPBF LTFMX 8-Lead Plastic MSOP –40°C to 125°C

LT3663HMS8E-3.3#PBF LT3663HMS8E-3.3#TRPBF LTFMX 8-Lead Plastic MSOP –40°C to 150°C

LT3663EMS8E-5#PBF LT3663EMS8E-5#TRPBF LTFMZ 8-Lead Plastic MSOP –40°C to 125°C

Operating Junction Temperature Range (Note 3)

LT3663E ............................................. –40°C to 125°C

LT3663I .............................................. –40°C to 125°C

LT3663H ............................................ –40°C to 150°C

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

pin conFiguraTion

TOP VIEW

BOOST

ISENSE

VOUT

VIN

RUN

ILIM

DCB PACKAGE

8-LEAD (2mm × 3mm) PLASTIC DFN

GND

θJA = 64°C/W

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

TOP VIEW

BOOST

ISENSE

VOUT

VIN

RUN

VOUTS

ILIM

DCB PACKAGE

8-LEAD (2mm × 3mm) PLASTIC DFN

GND

θJA = 64°C/W

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

VIN

RUN

ILIM

BOOST

ISENSE

VOUT

TOP VIEW

GND

MSE PACKAGE

8-LEAD PLASTIC MSOP

θJA = 35°C/W

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

VIN

RUN

VOUTS

ILIM

BOOST

ISENSE

VOUT

TOP VIEW

GND

MSE PACKAGE

8-LEAD PLASTIC MSOP

θJA = 35°C/W

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

LT3663

LT3663-X

LT3663

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elecTrical characTerisTics

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: Absolute Maximum Voltage at VIN and RUN pins is 60V for

nonrepetitive 1 second transients.

Note 3: The LT3663E 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 LT3663I speciﬁcations

The l denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at TA = 25°C. VIN = 12V, RILIM = 36.5k unless otherwise noted.

PARAMETER CONDITIONS MIN TYP MAX UNITS

VIN Undervoltage Lockout Rising l7 7.5 V

VIN Undervoltage Lockout Hysteresis 500 mV

VIN Overvoltage Lockout Rising l36 39 41 V

VIN Overvoltage Lockout Hysteresis 1 V

VIN Supply Current Not Switching 2.4 3.2 mA

VIN Supply Current in Shutdown VRUN = 0V 0.01 2 µA

Run Input Voltage High 2.5 V

Run Input Voltage Low 0.3 V

Run Pin Bias Current VRUN = 2.3V (Note4)

VRUN = 0V

0.01

0.1

µA

VOUT Current Limit Range l0.4 1.2 A

VOUT Current Limit l0.8 1 1.2 A

Operating Frequency LT3663

LT3663-X

1350

900

1500

1000

1650

1100

kHz

Maximum Duty Cycle l80 92 %

Feedback Voltage LT3663 l784 800 816 mV

FB Bias Current VFB = 0.8V, LT3663 50 150 nA

Regulated Output Voltage LT3663-3.3

LT3663-5

3.234

4.900

3.3

3.366

5.100

VOUTS Bias Current LT3663-X 90 120 µA

Switch Peak Current Limit (Note 5) l1.6 2 2.5 A

Switch VCESAT ISW = 1A 275 mV

Minimum BOOST Voltage ISW = 1A (Note 6) 1.85 2.2 V

Boost Diode Drop IDIODE = 60mA 0.9 1.2 V

Boost Pin Current ISW = 1A 28 mA

are guaranteed over the full –40°C to 125°C temperature range. The

LT3663H speciﬁcations are guaranteed over the –40°C to 150°C operating

temperature range. High junction temperatures degrade operating

lifetimes. Operating lifetime is derated at junction temperatures greater

than 125°C.

Note 4: Current ﬂows into pin.

Note 5: Switch Peak Current Limit guaranteed by design and/or correlation

to static test.

Note 6: This is the minimum voltage across the boost capacitor needed to

guarantee full saturation of the switch.

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

LT3663IMS8E-5#PBF LT3663IMS8E-5#TRPBF LTFMZ 8-Lead Plastic MSOP –40°C to 125°C

LT3663HMS8E-5#PBF LT3663HMS8E-5#TRPBF LTFMZ 8-Lead Plastic MSOP –40°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.

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/

orDer inForMaTion

LT3663

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Minimum Switch On-Time

RUN Pin Current Output Current Limit

Feedback Voltage

TEMPERATURE (°C)

–50

OUTPUT CURRENT LIMIT (A)

500 100

3663 G04

15012525–25 75

1.20

1.15

1.05

1.10

1.00

0.90

0.95

0.85

0.80

RILIM = 36.5k

TEMPERATURE (°C)

–50

FEEDBACK VOLTAGE (V)

500 100

3663 G05

15012525–25 75

0.84

0.82

0.80

0.78

0.76

TEMPERATURE (°C)

–50

MINIMUM SWITCH-ON TIME (ns)

500 100

3663 G10

15012525–25 75

140

120

100

RUN PIN VOLTAGE (V)

RUN PIN CURRENT (µA)

3010 50

3663 G11

20 40

TEMPERATURE (°C)

SWITCHING FREQUENCY (MHz)

1.6

3663 G02

0.9

1.0

1.1

1.2

1.3

1.4

1.5

–50 –25 0 25 50 75 100 150125

LT3663-X

LT3663

Switching Frequency

OUTPUT CURRENT (A)

OUTPUT VOLTAGE (V)

3663 G12

0 0.2 0.4 0.6 0.8 1 1.2

1.4

RILIM = 28.7k

Output Current Limit

Typical perForMance characTerisTics

TA = 25°C, unless otherwise noted.

VIN Shutdown Current

VIN Overvoltage Lockout

TEMPERATURE (°C)

–50

INPUT VOLTAGE (V)

500 100

3663 G06

15012525–25 75

RISING

FALLING

VIN VOLTAGE (V)

CURRENT (µA)

3010 50

3663 G08

20 40

800

700

500

600

400

200

300

100

VRUN = 0V

TEMPERATURE (°C)

INPUT VOLTAGE (V)

8.0

7.5

7.0

3663 G03

4.0

4.5

5.0

5.5

6.0

6.5

–50 –25 0 25 50 75 100 150125

RISING

FALLING

VIN Undervoltage Lockout

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Typical perForMance characTerisTics

BOOST Pin CurrentBoost Diode Vf

TA = 25°C, unless otherwise noted.

SWITCH CURRENT (A)

BOOST PIN CURRENT (mA)

3653 G07

0 0.2 0.4 0.5 0.8 1.0

1.2

DIODE CURRENT (mA)

BOOST DIODE V

(V)

1.4

1.2

0.8

3653 G09

0.2

0.6

0.4

0 50 100 150 200 250

300

SWITCH CURRENT (A)

SWITCH VOLTAGE DROP (mV)

400

350

3663 G01

100

150

200

250

300

0 0.2 0.4 0.6 0.8 1

1.2

125°C

–45°C

25°C

Switch Voltage Drop

pin FuncTions

BOOST: The BOOST pin is used to provide a drive voltage,

higher than the input voltage, to the internal power switch.

The BOOST pin is also internally connected to the cathode

of the BOOST diode.

GND (Exposed Pad Pin 9) : Ground. The exposed pad

must be soldered to the PCB and electrically connected

to ground. Use a large ground plane and thermal vias to

optimize thermal performance.

FB (LT3663): The LT3663 regulates the FB pin to 0.8V.

Connect the feedback resistor divider tap to this pin.

ILIM: Output Current Limit Program Pin. Connect a resistor

to ground to program the regulator output current limit.

ISENSE: The ISENSE pin is the positive input to the internal

output current limit sense resistor. The ISENSE pin is also

the anode to the internal BOOST diode.

RUN: The Run pin is used to put the LT3663 into shutdown

mode. Tie to ground to shut down the LT3663. Tie to 2.5V

or more for normal operation. If the shutdown feature is

not used, connect this pin to VIN.

SW: The SW pin is the output of the internal power switch.

Connect this pin to the inductor, catch diode and boost

capacitor.

VIN: The VIN pin supplies current to the LT3663’s internal

regulator and internal power switch. Capacitively bypass

the pin to ground.

VOUT: The VOUT pin is connected to the negative terminal

of the internal output current limit sense resistor.

VOUTS (LT3663-X): Output Voltage Sense Pin. Connect to

the positive terminal of the output capacitor.

LT3663

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FuncTional block DiagraM

2.5V INTERNAL

REGULATOR,

REFERENCE,

UVLO AND OVP OSCILLATOR

SLOPE

COMPENSATION

RSENSE1

VIN SWQ1

RSENSE2

R1 NOTE: RESISTOR DIVIDER

IS INTERNAL ON LT3663-X

VERSIONS.

EXPOSED PAD (GND)

3663 BD

BOOST

ISENSE

VOUT

RILIM

VIN

INTERNAL

COMPENSATION

–

DRIVER

VOUT

–

0.8V

–

ILIM

RUN

LT3663

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operaTion

The LT3663 is a constant frequency, current mode step

down regulator. A switch cycle is initiated when the os-

cillator enables the RS ﬂip ﬂop, turning on the internal

power switch, Q1. The sense ampliﬁer (A1) monitors the

switch current via the voltage dropped across the current

sense resistor RSENSE1. The comparator compares the

ampliﬁed current signal with the output (VC) of the error

ampliﬁer (G1). The switch is turned off when this current

exceeds a value determined by the VC voltage. The error

ampliﬁer monitors the VOUT voltage through an internal

resistor divider and, when not driven externally, servos

the VC voltage to regulate VOUT. If the VOUT voltage drops,

the VC voltage will be driven higher increasing the output

current and VOUT voltage. An active clamp (not shown)

on the VC node provides current limit. The LT3663 is

internally compensated with a pole-zero combination on

the VC node.

An external capacitor and internal diode, D2, generate a

voltage at the BOOST pin that is higher than the input supply.

(Refer to Block Diagram)

This allows the driver to fully saturate the internal bipolar

NPN power switch for efﬁcient operation. The switch driver

operates from either VIN or BOOST to ensure startup.

An internal regulator provides power to the control circuitry.

This regulator includes input undervoltage and overvoltage

protection which disables switching action when VIN is

out of range. When switching is disabled, the LT3663

safely sustains input voltages up to 60V. Note that while

switching is disabled the output will discharge.

Output current limiting is provided via the servo action of

ampliﬁer G2. The voltage across sense resistor, RSENSE2,

is compared to a voltage programmed by external resistor

RILIM on the ILIM pin. A capacitor averages the inductor

ripple current. If the average inductor current exceeds the

programmed value then the VC voltage is pulled low, reduc-

ing the current in the regulator. The output current limit

circuit allows for a lower current rated inductor and diode

and provides better control of system power dissipation.

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2.5µs/DIV 3663 F02

VSW

20V/DIV

1A/DIV

VOUT

200mV/DIV

AC-COUPLED

Figure 2. Pulse-Skip Mode

VSW

20V/DIV

1A/DIV

VOUT

200mV/DIV

AC-COUPLED

2.5µs/DIV 3663 F01

applicaTions inForMaTion

FB Resistor Network

The output voltage of the LT3663 is programmed with a

resistor divider. Choose the 1% resistors according to:

R1 = R2 (VOUT/0.8 – 1)

Reference designators refer to the Block Diagram.

The resistor divider is internal on the ﬁxed output voltage

versions, LT3663-X.

Minimum Duty Cycle

As the input voltage increases the duty cycle decreases. At

some point, the minimum duty cycle of the IC is reached

and pulse skipping begins. The output voltage continues to

regulate but the output voltage ripple increases. The input

voltage at which this occurs is calculated as follows:

VVV

IN OUT F

MINFS

()

+–

Where VF is the forward voltage drop of the catch diode,

D1, and VSW is the voltage drop on the internal switch,

Q1. LT3663 DCMIN is typically 0.12.

For VF = 0.4V, VSW = 0.3V, and VOUT = 3.3V pulse skipping

occurs at about 24.5V.

Figure 1 illustrates switching waveforms in normal mode

for a 3.3V output application with VIN = 20V.

Figure 2. illustrates switching waveforms in pulse skip

mode a 3.3V output application with VIN = 30V.

Figure 1. Normal Operation

Inductor Selection

A good ﬁrst choice for the inductor value is:

L = VOUT + VD (µH)

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

and L is in µH. With this value there is no sub-harmonic

oscillation for applications with 50% or greater duty

cycle. The inductor’s RMS current rating must be greater

than the maximum load current. Size the inductor so the

saturation current rating is about 30% higher than the

maximum load current. The output current limit circuit

tightly controls the maximum average inductor current,

therefore the inductor RMS current rating does not have

to be overrated to handle short circuit or overload condi-

tions. For high efﬁciency, keep the series resistance (DCR)

less than 0.1Ω. A higher value inductor is larger in size

and slows transient response but reduces output voltage

ripple. A lower value inductor has higher ripple currents

but is physically smaller or, for the same size, it has lower

DCR typically resulting in higher efﬁciency.

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Catch Diode

The catch diode conducts current only during switch-off

time. Average forward current in normal operation is

calculated from:

DAVG OUT IN OUT

()

–

where IOUT is the maximum output load current pro-

grammed by the ILIM resistor. Peak reverse voltage is equal

to the regulator input voltage. Use a Schottky diode with a

reverse voltage rating greater than the input voltage. The

overvoltage protection feature in the LT3663 keeps the

switch off when VIN > 39V (typical) allowing the use of a

45V rated Schottky even when VIN ranges up to 60V.

Input Capacitor

Bypass the input of the LT3663 circuit with a 1µF or higher

value ceramic capacitor of X7R or X5R type. Y5V types

have poor performance over temperature and applied volt-

age and are not recommended. If the input power source

has high impedance, or there is signiﬁcant inductance

due to long wires or cables, additional bulk capacitance

may be necessary. This can be provided with a low per-

formance 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 LT3663 and

to force this very high frequency switching current into

a tight local loop, minimizing EMI. Place the capacitor in

close proximity to the LT3663 and the catch diode; (see

the PCB Layout section).

Output Capacitor

A 10µF or greater ceramic capacitor is recommended to

provide low output ripple and good transient response.

Ceramic capacitors have very low equivalent series re-

sistance (ESR) and provide the best ripple performance.

Use X5R or X7R types and keep in mind that a ceramic

capacitor biased with VOUT has less than its speciﬁed

nominal capacitance.

High performance electrolytic capacitors can be used for

the output capacitor. Low ESR is important, so choose

one that is intended for use in switching regulators. Keep

the ESR less than 0.1Ω.

ILIM Resistor

The LT3663 output current limit controls the maximum

current delivered from the LT3663 regulator. This allows

tighter control of the system power dissipation and also

protects the inductor and diode from overheating during

an overload or short circuit condition. A resistor con-

nected from ILIM pin to GND programs the output current.

Table 1 details the ILIM resistor values for speciﬁc output

current limits.

Table 1. Output Current Limit vs RLIM Value

OUTPUT CURRENT LIMIT (A) RILIM VALUE (kΩ)

0.4 140

0.6 75

0.8 48.7

1.0 36.5

1.2 28.7

There may be a reason in some applications to move the

output current limit. The following simple circuit demon-

strates how the output current limit can be adjusted:

Figure 3. Circuit for Multiple Values of Output Current Limit

LT3663

ON, RILIM = RA

OFF, R

ILIM = RA + RB

ILIM

3663 F03

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applicaTions inForMaTion

BOOST and BIAS Pin Considerations

Capacitor C3 and the internal boost diode (see the Block

Diagram) are used to generate a boost voltage that is higher

than the input voltage. In most cases a 0.1µF capacitor

works well. Figure 4 shows three ways to arrange the boost

circuit. The BOOST pin must be more than 2.3V above the

SW pin for best efﬁciency. 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 connect an external Schottky

diode to the input (Figure 4c), or to another supply greater

than 2.8V. Using VIN reduces the maximum input voltage

to 25V. The circuit in Figure 4a is more efﬁcient because

the BOOST pin current comes from a lower voltage source.

Take care to ensure that the maximum voltage ratings of

the BOOST pin is not exceeded.

Figure 4. Three Circuits to Generate BOOST Pin Voltage

LT3663

(4c) For VOUT < 2.5V; VIN(MAX) = 25V

VIN

3663 F04

BOOST

ISENSE

VOUT VOUT

LT3663

(4b) For 2.5V < VOUT < 2.8V

VIN

VIN BOOST

ISENSE

VOUT VOUT

LT3663

(4a) For VOUT > 2.8V

VIN

VIN BOOST

ISENSE

VOUT VOUT

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PCB Layout

Proper operation and minimum EMI, requires careful

printed circuit board layout. Figure 5 shows the recom-

mended component placement with trace, ground plane

and via locations. Note that large, switched currents ﬂow

in the LT3663’s VIN and SW pins, the catch diode (D2)

and the input capacitor (C1). Keep the loop formed by

these components as small as possible and tied to system

ground in only one place. Locate these components, along

with the inductor and output capacitor, on the same side

of the circuit board, and keep their connections on that

layer. Place a local, unbroken ground plane below these

components, and tie this ground plane to system ground

at one location, ideally at the ground terminal of the output

capacitor C1. Make the SW and BOOST PCB trace as short

as possible. Include vias near the exposed GND pad of

the LT3663 to help remove heat from the LT3663 to the

ground plane.

High Temperature Considerations

The die temperature of the LT3663 must not exceed the

maximum rating. This is generally not a concern unless

the ambient temperature is above 85°C. For higher tem-

peratures, take care in the layout of the circuit to ensure

good heat sinking of the LT3663. De-rate the maximum

load current as the ambient temperature approaches the

maximum temperature rating. Calculate the die tempera-

ture by multiplying the LT3663 power dissipation by the

thermal resistance from junction to ambient. Estimate

the power dissipation within the LT3663 by calculating

the total power loss from an efﬁciency measurement

and subtracting the catch diode loss. Thermal resistance

depends on the layout of the circuit board, but 64°C/W is

typical for the (2mm × 3mm) DFN (DCB) package.

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.

3663 F05

VIN

RUN

RILIM C2

VOUT

GND

LT3663

Figure 5. LT3663 PCB Layout

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Typical applicaTions

2.5V Step-Down Converter

1.2V Step-Down Converter

5V Step-Down Converter

3663 TA02

LT3663

VIN

7.5V TO 36V

TRANSIENT

TO 60V

RUN

ILIM

BOOST

GND

0.1µF

4.7µF

D1: DIODES INC, DFLS260

L: TDK, VLCF5020T-6R8N1R3-1

22µF

59k

RILIM

28.7k

11k

6.8µH

ISENSE

VOUT V

OUT

1.2A

ON OFF

3663 TA04

LT3663

VIN

7.5V TO 36V

TRANSIENT

TO 60V

RUN

ILIM

BOOST

GND

1µF

4.7µF

D1: DIODES INC, DFLS260

D3: ON SEMI, MBR0560

L: TDK, VLCF5020T-3R3N2R0-1

22µF

210k

RILIM

28.7k

100k

3.3µH

ISENSE

VOUT V

OUT

2.5V

1.2A

ON OFF

3663 TA05

LT3663

VIN

7.5V TO 23V

RUN

ILIM

BOOST

GND

0.22µF

4.7µF

D1: DIODES INC, DFLS240

D3: ON SEMI, MBR0540

L: TDK, VLCF5020T-3R3N2R0-1

22µF

49.9k

RILIM

28.7k

100k

3.3µH

ISENSE

VOUT V

OUT

1.2V

1.2A

ON OFF

•

3663 TA07

LT3663-5

VIN

RUN

ILIM

BOOST

GND

0.1µF

16V

2.2µF

50V

1206

47µF

1206

10V

20%

L16-0017

BH ELECTRONICS

1761ES5-3.3

10k

DFLS260

60V

ISENSE

VOUT

2.2µF

0603

10V

10µH

3 4

1 3

100

0805

47pF

50V

0603

CMPSH-3E

SOT-23

VOUTS

100k

NOTE: 60V MAX

TRANSIENT VOLTAGE

RILIM

75k

VIN

7.5V TO 36V

HVBUCK

600mA

GND

SHDN

OUT

BYP

0.01µF

10V

0403

10µF

6.3V

0603

3.3V

50mA

RTN

LT3663-5 5V Step-Down Regulator

with Isolated 3.3V Output

LT3663

3663fc

For more information For more information www.linear.com/LT3663

package DescripTion

3.00 ±0.10

(2 SIDES)

2.00 ±0.10

(2 SIDES)

NOTE:

1. DRAWING IS NOT A JEDEC PACKAGE OUTLINE

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

0.40 ±0.10

BOTTOM VIEW—EXPOSED PAD

0.75 ±0.05

R = 0.115

TYP

R = 0.05

TYP

1.35 REF

PIN 1 BAR

TOP MARK

(SEE NOTE 6)

0.200 REF

0.00 – 0.05

(DCB8) DFN 0106 REV A

0.23 ±0.05

0.45 BSC

PIN 1 NOTCH

R = 0.20 OR 0.25

× 45° CHAMFER

0.25 ±0.05

1.35 REF

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

APPLY SOLDER MASK TO AREAS THAT ARE NOT SOLDERED

2.10 ±0.05

0.70 ±0.05

3.50 ±0.05

PACKAGE

OUTLINE

0.45 BSC

1.35 ±0.10

1.35 ±0.05

1.65 ±0.10

1.65 ±0.05

DCB Package

8-Lead Plastic DFN (2mm × 3mm)

(Reference LTC DWG # 05-08-1718 Rev A)

LT3663

3663fc

For more information www.linear.com/LT3663

MSOP (MS8E) 0911 REV J

0.53 ±0.152

(.021 ±.006)

SEATING

PLANE

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

6. EXPOSED PAD DIMENSION DOES INCLUDE MOLD FLASH. MOLD FLASH ON E-PAD

SHALL NOT EXCEED 0.254mm (.010") PER SIDE.

0.18

(.007)

0.254

(.010)

1.10

(.043)

MAX

0.22 – 0.38

(.009 – .015)

TYP

0.86

(.034)

REF

0.65

(.0256)

BSC

0° – 6° TYP

DETAIL “A”

GAUGE PLANE

1 2 34

4.90 ±0.152

(.193 ±.006)

BOTTOM VIEW OF

EXPOSED PAD OPTION

765

3.00 ±0.102

(.118 ±.004)

(NOTE 3)

3.00 ±0.102

(.118 ±.004)

(NOTE 4)

0.52

(.0205)

REF

1.68

(.066)

1.88

(.074)

5.23

(.206)

MIN

3.20 – 3.45

(.126 – .136)

1.68 ±0.102

(.066 ±.004)

1.88 ±0.102

(.074 ±.004) 0.889 ±0.127

(.035 ±.005)

RECOMMENDED SOLDER PAD LAYOUT

0.65

(.0256)

BSC

0.42 ±0.038

(.0165 ±.0015)

TYP

0.1016 ±0.0508

(.004 ±.002)

DETAIL “B”

CORNER TAIL IS PART OF

THE LEADFRAME FEATURE.

FOR REFERENCE ONLY

NO MEASUREMENT PURPOSE

0.05 REF

0.29

REF

MS8E Package

8-Lead Plastic MSOP, Exposed Die Pad

(Reference LTC DWG # 05-08-1662 Rev J)

LT3663

3663fc

For more information For more information www.linear.com/LT3663

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 representa-

tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

revision hisTory

REV DATE DESCRIPTION PAGE NUMBER

B 11/09 Additions to Features

Text Changes to Description

Addition of MSE Package to Pin Conﬁguration

Additions Made to Order Information

Changes to Electrical Characteristics

Expanded Temperature Range of Typical Performance Curves

Addition of Note to Functional Block Diagram

Text Changes to Applications Information

Addition of Typical Applications Drawing

Addition of MS8E Package Drawing

2, 3

4, 5

8, 11

C 05/13 Clariﬁed PCB Layout 11

(Revision history begins at Rev B)

LT3663

3663fc

For more information www.linear.com/LT3663

 LINEAR TECHNOLOGY CORPORATION 2009

LT 0513 REV C • PRINTED IN USA

Linear Technology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com/LT3663

relaTeD parTs

Typical applicaTion

3.3V Step-Down Converter

3663 TA03

LT3663

VIN

7.5V TO 36V

RUN

ILIM

BOOST

GND

0.1µF

4.7µF

D1: DIODES INC, DFLS240

L: TDK, VLCF5020T-4R7N1R7-1

22µF

316k

RILIM

28.7k

100k

4.7µH

ISENSE

VOUT V

OUT

3.3V

1.2A

ON OFF

Efﬁciency

OUTPUT CURRENT (A)

0.1

EFFICIENCY (%)

100

0.5 0.90.3 0.7 1.1

3663 TA06

1.3

VIN = 15V

VIN = 8V

VIN = 30V

PART NUMBER DESCRIPTION COMMENTS

LT1766 60V, 1.2A (IOUT), 200kHz, High Efﬁciency Step-Down DC/DC Converter VIN: 5.5V to 60V, VOUTMAX = 1.20V, IQ = 2.5mA, ISD = 25µA,

TSSOP16/TSSOP16E Packages

LT1933 500mA(IOUT), 500kHz Step-Down Switching Regulator in SOT-23 VIN: 3.6V to 36V, VOUTMAX = 1.2V, IQ = 1.6mA, ISD <1µA,

ThinSOT Package

LT1936 36V, 1.4A(IOUT) , 500kHz High Efﬁciency Step-Down DC/DC Converter VIN: 3.6V to 36V, VOUTMAX = 1.2V, IQ = 1.9mA, ISD <1µA,

MS8E Package

LT1940 Dual 25V, 1.4A (IOUT), 1.1MHz, High Efﬁciency Step-Down DC/DC

Converter

VIN: 3.6V to 25V, VOUTMAX = 1.20V, IQ = 3.8mA, ISD <30µA,

TSSOP16E Package

LT1976/LT1977 60V, 1.2A (IOUT), 200/500kHz, High Efﬁciency Step-Down DC/DC Converter

with BurstMode

Operation

VIN: 3.3V to 60V, VOUTMAX = 1.20V, IQ = 100µA, ISD <1µA,

TSSOP16E Package

LTC3407/

LTC3407-2

Dual 600mA/800mA, 1.5/2.25 MHz Syncronous Step-Down DC/DC

Converter

VIN: 2.5V to 5.5V, VOUTMAX = 0.6V, IQ = 40µA, ISD <1µA,

3mm × 3mm DFN, MS10E Packages

LT3434/LT3435 60V, 2.4A (IOUT), 200/500kHz, High Efﬁciency Step-Down DC/DC Converter

with BurstMode Operation

VIN: 3.3V to 60V, VOUTMAX = 1.20V, IQ = 100µA, ISD <1µA,

TSSOP16E Package

LT3437 60V, 400mA (IOUT),MicroPower Step-Down DC/DC Converter with

BurstMode Operation

VIN: 3.3V to 60V, VOUTMAX = 1.25V, IQ = 100µA, ISD <1µA,

3mm × 3mm DFN, TSSOP16E Packages

LT3493 36V, 1.4A(IOUT), 750kHz High Efﬁciency Step-Down DC/DC Converter VIN: 3.6V to 36V, VOUTMAX = 0.8V, IQ = 1.9mA, ISD <1µA,

2mm × 3mm DFN Package

LT3501 Dual 25V, 3A (IOUT), 1.5MHz, High Efﬁciency Step-Down DC/DC Converter VIN: 3.3V to 25V, VOUTMAX = 0.8V, IQ = 3.7mA, ISD <10µA,

TSSOP-20E Package

LT3503 20V, 1A (IOUT), 2.2MHz, High Efﬁciency Step-Down DC/DC Converter VIN: 3.6V to 20V, VOUTMAX = 0.78V, IQ = 1.9mA, ISD <1µA,

2mm × 3mm DFN, Package

LT3505 36V, 1.2A (IOUT), 3MHz, High Efﬁciency Step-Down DC/DC Converter VIN: 3.6V to 36V, VOUTMAX = 0.78V, IQ = 2mA, ISD <2µA,

3mm × 3mm DFN, MS8E Packages

LT3506/

LT3506A

Dual 25V, 1.6A (IOUT), 575kHz/1.1MHz, High Efﬁciency Step-Down DC/DC

Converter

VIN: 3.6V to 25V, VOUTMAX = 0.8V, IQ = 3.8mA, ISD <30µA,

4mm × 5mm DFN Package

LT3508 Dual 36V, 1.4A (IOUT), 2.5MHz, High Efﬁciency Step-Down DC/DC

Converter

VIN: 3.6V to 36V, VOUTMAX = 0.8V, IQ = 4.3mA, ISD <1µA,

4mm × 4mm QFN, TSSOP16E Packages

LT3510 Dual 25V, 2A (IOUT), 1.5MHz, High Efﬁciency Step-Down DC/DC Converter VIN: 3.3V to 25V, VOUTMAX = 0.8V, IQ = 3.7mA, ISD <10µA,

TSSOP-20E Package

LTC3548 Dual 400mA + 800mA, 2.25 MHz Syncronous Step-Down DC/DC Converter VIN: 2.5V to 5.5V, VOUTMAX = 0.6V, IQ = 40µA, ISD <1µA,

3mm × 3mm DFN, MS10E Packages

BurstMode is a registered trademark of Linear Technology Corporation.