LT3474-1_技术文档

LT3474/LT3474-1

Step-Down

1A LED Driver

FEATURES

DESCRIPTION

The LT^®3474/LT3474-1 are ﬁxed frequency step-down

DC/DCconvertersdesignedtooperateasconstant-current

sources. An internal sense resistor monitors the output

current allowing accurate current regulation, ideal for

driving high current LEDs. High output current accuracy

is maintained over a wide current range, from 35mA to

1A, allowing a wide dimming range.

n

True Color PWM™ Delivers Constant Color with

400:1 Dimming Range

n

Wide Input Range: 4V to 36V

n

Up to 1A LED Current

Adjustable 200kHz–2MHz Switching Frequency

n

Adjustable Control of LED Current

Integrated Boost Diode

n

High Output Current Accuracy is Maintained

Unique PWM circuitry allows a dimming range of 400:1,

avoiding the color shift normally associated with LED

current dimming.

Over a Wide Range from 35mA to 1A

n

Open LED (LT3474) and Short-Circuit Protection

n

High Side Sense Allows Grounded

Cathode Connection

The high switching frequency offers several advantages,

permitting the use of small inductors and ceramic capaci-

tors. Small inductors combined with the 16-lead TSSOP

surface mount package save space and cost versus

alternative solutions. The constant switching frequency

combined with low-impedance ceramic capacitors result

in low, predictable output ripple.

n

Uses Small Inductors and Ceramic Capacitors

n

LT3474-1 Drives LED Strings Up to 26V

n

Compact 16-Lead TSSOP Thermally Enhanced

Surface Mount Package

APPLICATIONS

With their wide input range of 4V to 36V, the LT3474/

LT3474-1 regulate a broad array of power sources, from

5V logic rails to unregulated wall transformers, lead acid

batteries and distributed power supplies. A current mode

PWM architecture provides fast transient response and

cycle-by-cycle current limiting. Frequency foldback and

thermal shutdown provide additional protection.

■

Automotive and Avionic Lighting

■

Architectural Detail Lighting

■

Display Backlighting

Constant Current Sources

■

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

True Color PWM is a trademark of Linear Technology Corporation. All other trademarks are

the property of their respective owners. Patent Pending

TYPICAL APPLICATION

Step-Down 1A LED Driver

Efﬁciency

95

V

IN

V

= 12V

IN

5V TO 36V

TWO SERIES CONNECTED

WHITE 1A LEDS

90

85

80

0.22μF

10μH

V

BOOST

SW

LT3474

IN

2.2μF

SHDN

ONE WHITE 1A LED

R

BIAS

OUT

T

75

70

REF

V

DIMMING*

CONTROL

PWM

ADJ

80.6k

0.1μF

2.2μF

65

60

55

V

LED

C

GND

LED1

*SEE APPLICATIONS SECTION FOR DETAILS

200

400

LED CURRENT (mA)

800

0

1000

600

3474 TA01a

3474 G02

3474fd

1

LT3474/LT3474-1

ABSOLUTE MAXIMUM RATINGS

PIN CONFIGURATION

(Note 1)

V Pin ........................................................(–0.3V), 36V

IN

BIAS Pin....................................................................25V

BOOST Pin Voltage ...................................................51V

BOOST above SW Pin ...............................................25V

OUT, LED Pins (LT3474)............................................15V

OUT, LED Pins (LT3474-1).........................................26V

PWM Pin...................................................................10V

TOP VIEW

DNC*

OUT

LED

1

2

3

4

5

6

7

8

16

15

14

13

12

11

10

9

DNC*

GND

PWM

V

17

V

ADJ

IN

SW

BOOST

BIAS

V

C

V

Pin .....................................................................6V

ADJ

REF

V , REF, R Pins ..........................................................3V

SHDN

C

T

SHDN Pin...................................................................V

GND

R

T

IN

BIAS Pin Current.........................................................1A

Maximum Junction Temperature (Note 2)............. 125°C

Operating Temperature Range (Note 3)

FE PACKAGE

16-LEAD PLASTIC TSSOP

θ

= 8°C/W, θ = 40°C/W

JA

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

JC

LT3474E, LT3474E-1............................ –40°C to 85°C

LT3474I, LT3474I-1............................ –40°C to 125°C

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

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

*DO NOT CONNECT EXTERNAL CIRCUITRY TO THESE PINS.

ORDER INFORMATION

LEAD FREE FINISH

LT3474EFE#PBF

LT3474IFE#PBF

TAPE AND REEL

PART MARKING

3474EFE

PACKAGE DESCRIPTION

TEMPERATURE RANGE

LT3474EFE#TRPBF

LT3474IFE#TRPBF

LT3474EFE-1#TRPBF

LT3474IFE-1#TRPBF

16-Lead TSSOP

–40°C to 85°C

–40°C to 125°C

–40°C to 85°C

–40°C to 125°C

3474IFE

LT3474EFE-1#PBF

LT3474IFE-1#PBF

3474EFE-1

3474IFE-1

Consult LTC Marketing for parts speciﬁed with wider operating temperature ranges.

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/

ELECTRICAL CHARACTERISTICS ^Thel denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at T_A= 25°C. V_IN= 12V, V_BOOST= 16V, V_OUT= 4V unless otherwise noted (Note 3).

PARAMETER

CONDITIONS

MIN

TYP

3.5

2.6

0.01

1

MAX

UNITS

V

l

Minimum Input Voltage

Input Quiescent Current

Shutdown Current

LED Pin Current

4

2

Not Switching

mA

μA

SHDN = 0.3V, V

= 0V, V

= 0V

OUT

BOOST

V

ADJ

Tied to V

0.98

0.968

0.193

0.186

1.02

1.025

0.207

0.210

A

REF

l

V

ADJ

Tied to V /5

0.2

REF

l

REF Voltage

1.23

1.25

1.265

V

3474fd

2

LT3474/LT3474-1

ELECTRICAL CHARACTERISTICS ^Thel denotes the speciﬁcations which apply over the full operating

temperature range, otherwise speciﬁcations are at T_A= 25°C. V_IN= 12V, V_BOOST= 16V, V_OUT= 4V unless otherwise noted (Note 3).

PARAMETER

CONDITIONS

5V < V < 36V

MIN

TYP

0.01

0.0002

20

MAX

UNITS

%/V

Reference Voltage Line Regulation

Reference Voltage Load Regulation

IN

0 < I

< 250μA

%/μA

nA

REF

l

V

ADJ

Pin Bias Current (Note 4)

400

Switching Frequency

R = 80.6k

470

450

500

530

540

kHz

T

l

Maximum Duty Cycle

R = 80.6k

90

95

76

98

%

T

R = 10k

T

R = 232k

T

Foldback Frequency

R = 80.6k, V

= 0V

OUT

70

2.65

10.3

0.9

0.8

100

1.5

1

kHz

V

T

SHDN Threshold (to Switch)

SHDN Pin Current (Note 5)

PWM Threshold

2.6

8.3

0.4

2.7

12.3

1.2

V

= SHDN Threshold

μA

SHDN

V

V Switching Threshold

C

V

V Source Current

C

V = 1V

C

μA

V Sink Current

C

V = 1V

C

μA

LED to V Current Gain

μA/mA

V/mA

A/V

V

C

LED to V Transresistance

C

V to Switch Current Gain

C

2

V Clamp Voltage

C

1.9

0.01

13.8

0.1

l

V Pin Current in PWM Mode

C

V = 1V, V = 0.3V

C PWM

1

μA

OUT Pin Clamp Voltage (LT3474)

OUT Pin Current in PWM Mode

Switch Current Limit (Note 6)

13.2

14.5

10

V

l

V

= 4V, V

= 0.3V

PWM

μA

OUT

–40°C to 85°C

LT3474I, LT3474I-1 at 125°C

1.6

1.5

2.1

3.2

A

Switch V

I

= 1A

380

30

500

50

1

mV

mA

μA

V

CESAT

SW

Boost Pin Current

Switch Leakage Current

Minimum Boost Voltage (Note 7)

Boost Diode Forward Voltage

0.01

1.9

2.5

I

= 100mA

600

mV

DIO

operating temperature range are assured by design, characterization and

correlation with statistical process controls. The LT3474I and LT3474I-1

are guaranteed to meet performance speciﬁcations over the –40°C to

125°C operating temperature range.

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 4: Current ﬂows out of pin.

Note 5: Current ﬂows into pin.

Note 6: Current limit is guaranteed by design and/or correlation to static

test. Slope compensation reduces current limit at higher duty cycles.

Note 7: This is the minimum voltage across the boost capacitor needed to

Note 2: This IC includes overtemperature protection that is intended

to protect the device during momentary overload conditions. Junction

temperature will exceed 125°C when overtemperature protection is active.

Continuous operation above the speciﬁed maximum operating junction

temperature may impair device reliability.

Note 3: The LT3474E and LT3474E-1 are guaranteed to meet performance

speciﬁcations from 0°C to 70°C. Speciﬁcations over the –40°C to 85°C

guarantee full saturation of the internal power switch.

3474fd

3

LT3474/LT3474-1

TYPICAL PERFORMANCE CHARACTERISTICS

LED Current vs V_ADJ

LED Current vs Temperature

Switch Voltage Drop

1200

1000

800

1000

800

600

400

200

0

700

600

500

400

300

200

100

0

T

= 25°C

T

= 25°C

A

V

ADJ

= V

REF

600

400

200

0

V

ADJ

= V /5

REF

50

100 125

–50 –25

0

25

75

0

0.25

0.5

V

0.75

(V)

1

1.25

1000

500

SWITCH CURRENT (mA)

1500

0

TEMPERATURE (°C)

ADJ

3474 GO3

3474 G05

3474 G04

Switch Current Limit vs

Temperature

Current Limit vs Duty Cycle

Current Limit vs Output Voltage

2.5

2

2.5

2

2.5

2

T

= 25°C

A

TYPICAL

MINIMUM (85°C)

1.5

1

1.5

1

1.5

1

MINIMUM (125°C)

0.5

0

0.5

0

4

6

8

10

12

2

–50 –25

0

25

50

75 100 125

0

20

40

60

80

100

V

(V)

TEMPERATURE (°C)

OUT

DUTY CYCLE (%)

3474 G08

3474 G07

3474 G06

Oscillator Frequency vs

Temperature

Oscillator Frequency vs R_T

Oscillator Frequency Foldback

600

550

500

450

600

500

R

T

= 80.6k

T

= 25°C

= 80.6k

T

= 25°C

A

T

A

R

1000

400

300

200

100

0

100

400

10

100

–50 –25

0

25

50

75 100 125

0

0.5

1

1.5

(V)

2

2.5

R

T

(kΩ)

TEMPERATURE (°C)

V

OUT

3474 G09

3474 G10

3474 G11

3474fd

4

LT3474/LT3474-1

TYPICAL PERFORMANCE CHARACTERISTICS

Boost Pin Current

Quiescent Current

Reference Voltage

1.260

1.255

1.250

1.245

1.240

1.235

3.0

2.5

2.0

1.5

1.0

0.5

0

60

50

40

30

20

10

0

T

= 25°C

T

= 25°C

A

0

12

18

(V)

24

30

36

–50 –25

0

25

50

75

125

0

500

750 1000 1250 1500

6

100

250

V

SWITCH CURRENT (mA)

TEMPERATURE (°C)

IN

3474 G13

3474 G14

3473 G12

Open-Circuit Output Voltage and

Input Current

Schottky Reverse Leakage

Schottky Forward Voltage Drop

500

400

300

200

100

0

20

15

10

5

60

50

8

V

= 5V

T

A

= 25°C

T

= 25°C

R

A

INPUT CURRENT

LT3474-1

7

6

5

4

3

2

1

40

30

20

10

LT3474

LT3474-1

LT3474

OUTPUT VOLTAGE

0

–50 –25

0

25

50

75 100 125

0

200

400

600

800

1000

0

10

20

(V)

30

40

TEMPERATURE (°C)

V

FORWARD VOLTAGE (mV)

IN

3474 G15

3474 G19

3474 G16

Minimum Input Voltage,

One White Luxeon III Star

Two Series Connected White

Luxeon III Stars

6

5

10

9

T

A

= 25°C

T = 25°C

A

TO START

TO RUN

4

3

8

LED VOLTAGE

TO START

TO RUN

7

LED VOLTAGE

2

1

0

6

5

0

200

400

600

800

1000

0

200

400

600

800

1000

LED CURRENT (mA)

3474 G17

3474 G18

3474fd

5

LT3474/LT3474-1

PIN FUNCTIONS

DNC(Pins1,16):Donotconnectexternalcircuitrytothese

pins, or tie them to GND. Leave the DNC pins ﬂoating.

SHDN (Pin 10): The SHDN pin is used to shut down the

switching regulator and the internal bias circuits. The

2.6V switching threshold can function as an accurate

under-voltage lockout. Pull below 0.3V to shut down the

LT3474/LT3474-1. Pull above 2.65V to enable the LT3474/

OUT (Pin 2): The OUT pin is the input to the current sense

resistor. Connect this pin to the inductor and the output

capacitor.

LT3474-1. Tie to V if the SHDN function is unused.

IN

LED (Pin 3): The LED pin is the output of the current sense

resistor. Connect the anode of the LED here.

REF (Pin 11): The REF pin is the buffered output of the

internal reference. Either tie the REF pin to the V pin for

ADJ

V (Pin 4): The V pin supplies current to the internal

a 1A output current, or use a resistor divider to generate a

IN

circuitry and to the internal power switch and must be

lower voltage at the V pin. Leave this pin unconnected

ADJ

locally bypassed.

if unused.

SW (Pin 5): The SW pin is the output of the internal power

switch. Connect this pin to the inductor and switching

diode.

V (Pin 12): The V pin is the output of the internal error

C

c

amp. The voltage on this pin controls the peak switch

current. Use this pin to compensate the control loop.

BOOST (Pin 6): The BOOST pin is used to provide a drive

voltage,higherthantheinputvoltage,totheinternalbipolar

NPN power switch.

V

(Pin 13): The V

pin is the input to the internal

ADJ

voltage to current ampliﬁer. Connect the V

pin to the

ADJ

REF pin for a 1A output current. For lower output cur-

rents, program the V pin using the following formula:

ADJ

BIAS (Pin 7): The BIAS pin connects through a Schottky

diode to BOOST. Tie to OUT.

I

= 1A • V /1.25V.

LED

ADJ

PWM (Pin 14): The PWM pin controls the connection of

GND (Pins 8, 15, Exposed Pad Pin 17): Ground. Tie both

GND pins and the Exposed Pad directly to the ground

plane.TheExposedPadmetalofthepackageprovidesboth

electrical contact to ground and good thermal contact to

the printed circuit board. It must be soldered to the circuit

board for proper operation.

the V pin to the internal circuitry. When the PWM pin is

C

low, the V pin is disconnected from the internal circuitry

C

and draws minimal current. If the PWM feature is unused,

leave this pin unconnected.

R (Pin 9): The R pin is used to set the internal oscilla-

T

tor frequency. Tie an 80.6k resistor from R to GND for a

T

500kHz switching frequency.

3474fd

6

LT3474/LT3474-1

BLOCK DIAGRAM

V

IN

V

4

IN

C

IN

BIAS

7

INT REG

AND

UVLO

SHDN

10

BOOST

∑

6

5

SLOPE

COMP

R

S

Q

C1

D1

C1

Q

Q1

DRIVER

L1

R

T

SW

OSC

9

R

T

FREQUENCY

FOLDBACK

OUT

LED

2

3

C2

–

100Ω

0.1Ω

+

2V

D

LED1

1.25V

g

m

REF

11

PWM

14

13

USE WITH

PWM DIMMING

V

C

ADJ

12

Q2

C

C2

C1

R

C

1.25k

GND

8

3474 BD

Figure 1. Block Diagram

3474fd

7

LT3474/LT3474-1

APPLICATIONS INFORMATION

Operation

acrossthe0.1Ωresistorisequaltothevoltagedropacross

the 100Ω resistor, the servo loop is balanced.

The LT3474 is a constant frequency, current mode regula-

tor with an internal power switch capable of generating

a constant 1A output. Operation can be best understood

by referring to the Block Diagram.

Tying the REF pin to the V pin sets the LED pin current

ADJ

to 1A. Tying a resistor divider to the REF pin allows the

programming of LED pin currents of less than 1A. LED

pin current can also be programmed by tying the V pin

ADJ

If the SHDN pin is tied to ground, the LT3474 is shut

down and draws minimal current from the input source

directly to a voltage source up to 1.25V.

An LED can be dimmed with pulse width modulation us-

ing the PWM pin and an external NFET. If the PWM pin is

unconnected or pulled high, the part operates nominally.

tied to V . If the SHDN pin exceeds 1.5V, the internal bias

IN

circuitsturnon, includingtheinternalregulator, reference,

and oscillator. The switching regulator will only begin to

operate when the SHDN pin exceeds 2.65V.

If the PWM pin is pulled low, the V pin is disconnected

C

from the internal circuitry and draws minimal current from

Theswitcherisacurrentmoderegulator.Insteadofdirectly

modulatingthedutycycleofthepowerswitch,thefeedback

loop controls the peak current in the switch during each

cycle. Compared to voltage mode control, current mode

control improves loop dynamics and provides cycle-by-

cycle current limit.

thecompensationcapacitor.Circuitrydrawingcurrentfrom

the OUT pin is also disabled. This way, the V pin and the

C

output capacitor store the state of the LED pin current

until PWM is pulled high again. This leads to a highly

linear relationship between pulse width and output light,

allowing for a large and accurate dimming range.

A pulse from the oscillator sets the RS ﬂip-ﬂop and turns

on the internal NPN bipolar power switch. Current in the

switch and the external inductor begins to increase. When

this current exceeds a level determined by the voltage at

TheR pinallowsprogrammingoftheswitchingfrequency.

T

Forapplicationsrequiringthesmallestexternalcomponents

possible, a fast switching frequency can be used. If very

low or very high input voltages are required, a slower

switching frequency can be programmed.

V , current comparator C1 resets the ﬂip-ﬂop, turning

C

off the switch. The current in the inductor ﬂows through

the external Schottky diode and begins to decrease. The

cycle begins again at the next pulse from the oscillator.

During startup V

will be at a low voltage. The NPN Q2

OUT

can only operate correctly with sufﬁcient voltage at V

,

OUT

around 1.7V. A comparator senses V

and forces the V

In this way, the voltage on the V pin controls the current

OUT

C

pin high until V

correctly.

rises above 2V, and Q2 is operating

through the inductor to the output. The internal error

OUT

ampliﬁer regulates the output current by continually

adjusting the V pin voltage. The threshold for switching

C

The switching regulator performs frequency foldback dur-

ing overload conditions. An ampliﬁer senses when V is

on the V pin is 0.8V, and an active clamp of 1.9V limits

C

OUT

the output current.

lessthan2Vandbeginsdecreasingtheoscillatorfrequency

down from full frequency to 20% of the nominal frequency

The voltage on the V

pin sets the current through the

ADJ

whenV

=0V.TheOUTpinislessthan2Vduringstartup,

LED pin. The NPN Q2 pulls a current proportional to the

voltage on the V pin through the 100Ω resistor. The

OUT

shortcircuit, andoverloadconditions. Frequencyfoldback

ADJ

helps limit switch current under these conditions.

g ampliﬁer servos the V pin to set the current through

m

C

the 0.1Ω resistor and the LED pin. When the voltage drop

3474fd

8

LT3474/LT3474-1

APPLICATIONS INFORMATION

An internal comparator will force the part into shutdown

The switch driver operates either from V or from the

IN

when V falls below 3.5V. If an adjustable UVLO threshold

BOOST pin. An external capacitor and internal Schottky

diode are used to generate a voltage at the BOOST pin

that is higher than the input supply. This allows the driver

to saturate the internal bipolar NPN power switch for ef-

ﬁcient operation.

IN

is required, the SHDN pin can be used. The threshold

voltage of the SHDN pin comparator is 2.65V. A internal

resistor pulls 10.3μA to ground from the SHDN pin at the

UVLO threshold.

Choose resistors according to the following formula:

Open Circuit Protection

2.65V

R2=

TheLT3474hasinternalopencircuitprotection.IftheLEDis

absent or fails open, the LT3474 clamps the voltage on the

LED pin at 14V. The switching regulator then skips cycles

to limit the input current. The LT3474-1 has no internal

open circuit protection. With the LT3474-1, be careful not

V_TH– 2.65V

–10.3μA

R1

V

= UVLO Threshold

TH

Example: Switching should not start until the input is

above 8V.

to violate the ABSMAX voltage of the BOOST pin; if V >

IN

25V, external open circuit protection circuitry (as shown in

Figure 2) may be necessary. The output voltage during an

open LED condition is shown in the Typical Performance

Characteristics section.

V

TH

= 8V

R1 = 100k

2.65V

8V – 2.65V

R2=

=61.9k

Undervoltage Lockout

–10.3μA

Undervoltagelockout(UVLO)istypicallyusedinsituations

wheretheinputsupplyiscurrentlimited,orhashighsource

resistance. A switching regulator draws constant power

from the source, so the source current increases as the

source voltage drops. This looks like a negative resistance

loadtothesourceandcancausethesourcetocurrentlimit

or latch low under low source voltage conditions. UVLO

prevents the regulator from operating at source voltages

where these problems might occur.

100k

Keep the connections from the resistors to the SHDN pin

short and make sure the coupling to the SW and BOOST

pins is minimized. If high resistance values are used, the

SHDN pin should be bypassed with a 1nF capacitor to

prevent coupling problems from switching nodes.

LT3474

V

IN

V

IN

OUT

10k

2.65V

R1

R2

V

C

SHDN

27V

V

C

10.3μA

C1

GND

100k

3474 F03

3474 F02

Figure 3. Undervoltage Lockout

Figure 2. External Overvoltage Protection

Circuitry for the LT3474-1.

3474fd

9

LT3474/LT3474-1

APPLICATIONS INFORMATION

Setting the Switching Frequency

V

+ V

F

(

)

OUT

DC =

The LT3474 uses a constant frequency architecture that

can be programmed over a 200kHz to 2MHz range with a

V – V + V

F

(

)

IN

SW

single external timing resistor from the R pin to ground.

T

where V is the forward voltage drop of the catch diode

The current that ﬂows into the timing resistor is used

F

(~0.4V) and V is the voltage drop of the internal switch

to charge an internal oscillator capacitor. A graph for

SW

(~0.4V at maximum load). This leads to a minimum input

selecting the value of R for a given operating frequency

T

voltage of:

is shown in the Typical Performance Characteristics

section. Table 1 shows suggested R selections for a

T

V

_OUT+ V

F

V

=

– V + V_SW

F

variety of switching frequencies.

IN MIN

(

)

DC_MAX

= 1–t

Table 1. Switching Frequencies

SWITCHING FREQUENCY (MHz)

with DC

where t

frequency.

• f

OFF(MIN)

MAX

R (kΩ)

T

is equal to 200ns and f is the switching

2

10

0FF(MIN)

1.5

1

18.7

33.2

52.3

80.6

147

232

Example: f = 500kHz, V

= 4V

OUT

0.7

0.5

0.3

0.2

DC_MAX=1− 200ns •500kHz = 0.90

4V + 0.4V

V

=

– 0.4V + 0.4V = 4.9V

IN MIN

(

)

0.9

The maximum operating voltage is determined by the

Operating Frequency Selection

absolute maximum ratings of the V and BOOST pins,

IN

The choice of operating frequency is determined by sev-

eral factors. There is a tradeoff between efﬁciency and

component size. Higher switching frequency allows the

useofsmallerinductorsatthecostofincreasedswitching

losses and decreased efﬁciency.

and by the minimum duty cycle.

V

_OUT+ V

DC_MIN

F

V

=

– V + V_SW

F

IN MAX

(

)

with DC

where t

= t

• f

MIN

ON(MIN)

Another consideration is the maximum duty cycle. In

certain applications, the converter needs to operate at a

high duty cycle in order to work at the lowest input voltage

possible. The LT3474 has a ﬁxed oscillator off-time and

a variable on-time. As a result, the maximum duty cycle

increases as the switching frequency is decreased.

is equal to 160ns and f is the switching

ON(MIN)

frequency.

Example: f = 500kHz, V

= 2.5V

OUT

DC_MIN=160ns •500kHz = 0.08

2.5V + 0.4V

V

=

– 0.4V + 0.4V = 36V

IN MAX

(

)

Input Voltage Range

0.08

Theminimumoperatingvoltageisdeterminedeitherbythe

LT3474’s undervoltage lockout of 4V, or by its maximum

duty cycle. The duty cycle is the fraction of time that the

internal switch is on and is determined by the input and

output voltages:

The minimum duty cycle depends on the switching fre-

quency. Running at a lower switching frequency might

allow a higher maximum operating voltage. Note that this

is a restriction on the operating input voltage; the circuit

will tolerate transient inputs up to the Absolute Maximum

Rating.

3474fd

10

LT3474/LT3474-1

APPLICATIONS INFORMATION

Inductor Selection and Maximum Output Current

The optimum inductor for a given application may differ

from the one indicated by this simple design guide. A

larger value inductor provides a higher maximum load

current, and reduces the output voltage ripple. If your

load is lower than the maximum load current, then you

can relax 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

efﬁciency. Be aware that if the inductance differs from

the simple rule above, then the maximum load current

will depend on input voltage. In addition, low inductance

mayresultindiscontinuousmodeoperation,whichfurther

reduces maximum load current. For details of maximum

output current and discontinuous mode operation, see

Linear Technology’s Application Note 44. Finally, for duty

A good first choice for the inductor value is

900kHz

L = (V_OUT+ V )•

F

f

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

F

is the switching frequency and L is in μH. With this value

the maximum load current will be 1.1A, independent of

input voltage. The inductor’s RMS current rating must be

greater than the maximum load current and its saturation

currentshouldbeatleast30%higher.Forhighestefﬁciency,

the series resistance (DCR) should be less than 0.2Ω.

Table 2 lists several vendors and types that are suitable.

For robust operation at full load and high input voltages

(V > 30V), use an inductor with a saturation current

IN

cycles greater than 50% (V /V > 0.5), a minimum

OUT IN

higher than 2.5A.

inductanceisrequiredtoavoidsub-harmonicoscillations.

See Application Note 19.

Table 2. Inductors

VALUE

(μH)

I

DCR

(Ω)

HEIGHT

(mm)

Thecurrentintheinductorisatrianglewavewithanaverage

value equal to the load current. The peak switch current

is equal to the output current plus half the peak-to-peak

inductor ripple current. The LT3474 limits its switch cur-

rentinordertoprotectitselfandthesystemfromoverload

faults. Therefore, the maximum output current that the

LT3474 will deliver depends on the switch current limit,

the inductor value, and the input and output voltages.

RMS

PART NUMBER

Sumida

(A)

CR43-3R3

3.3

4.7

3.3

4.7

10

1.44

1.15

1.1

0.086

0.109

0.063

0.049

0.072

0.048

0.076

0.072

0.13

3.5

1.8

3

CR43-4R7

CDRH4D16-3R3

CDRH4D28-3R3

CDRH4D28-4R7

CDRH5D28-100

CDRH5D28-150

CDRH73-100

CDRH73-150

Coilcraft

1.57

1.32

1.3

3

When the switch is off, the potential across the inductor

is the output voltage plus the catch diode drop. This gives

the peak-to-peak ripple current in the inductor

15

1.1

3

10

1.68

1.33

3.4

15

1–DC V + V

(

)(

)

OUT

F

ΔI_L=

DO1606T-332

DO1606T-472

DO1608C-332

DO1608C-472

MOS6020-332

MOS6020-472

3.3

4.7

3.3

4.7

3.3

10

1.3

1.1

2

0.1

0.12

0.08

0.09

0.046

0.05

2

L • f

(

)

2.9

2

where f is the switching frequency of the LT3474 and L

is the value of the inductor. The peak inductor and switch

current is

1.5

1.8

1.5

2

ΔI_L

2

I_{SW PK}=I_{L PK}=I_OUT

+

(

)

(

)

3474fd

11

LT3474/LT3474-1

APPLICATIONS INFORMATION

at the LT3474 input and to force this switching current into

a tight local loop, minnimizing EMI. The input capacitor

must have low impedance at the switching frequency to

do this effectively, and it must have an adequate ripple

current rating. The RMS input is:

To maintain output regulation, this peak current must be

less than the LT3474’s switch current limit I . For SW1,

LIM

I

is at least 1.6A (1.5A at 125°C) at low duty cycles and

LIM

decreases linearly to 1.15A (1.08A at 125°C) at DC = 0.8.

The maximum output current is a function of the chosen

inductor value:

V_OUTV – V

(

)

<

IN

OUT

I_OUT

2

ΔI_L

2

C_INRMS= I_OUT

•

I_{OUT MAX}= I_LIM

–

V

(

)

IN

ΔI_L

2

and is largest when V = 2V

sidering that the maximum load current is 1A, RMS ripple

current will always be less than 0.5A

(50% duty cycle). Con-

=1.6A • 1– 0.35•DC –

IN

OUT

(

)

Choosing an inductor value so that the ripple current is

small will allow a maximum output current near the switch

current limit.

The high switching frequency of the LT3474 reduces the

energystoragerequirementsoftheinputcapacitor, sothat

thecapacitancerequiredislessthan10μF.Thecombination

of small size and low impedance (low equivalent series

resistance or ESR) of ceramic capacitors makes them the

preferred choice. The low ESR results in very low voltage

ripple. Ceramic capacitors can handle larger magnitudes

of ripple current than other capacitor types of the same

value. Use X5R and X7R types.

One approach to choosing the inductor is to start with the

simple rule given above, look at the available inductors,

and choose one to meet cost or space goals. Then use

these equations to check that the LT3474 will be able to

deliver the required output current. Note again that these

equations assume that the inductor current is continuous.

Discontinuous operation occurs when I

is less than

OUT

An alternative to a high value ceramic capacitor is a lower

value ceramic along with a larger electrolytic capaci-

tor. The electrolytic capacitor likely needs to be greater

than 10μF in order to meet the ESR and ripple current

requirements. The input capacitor is likely to see high

surge currents when the input source is applied. Tanta-

lum capacitors can fail due to an over-surge of current.

Only use tantalum capacitors with the appropriate surge

current rating. The manufacturer may also recommend

operation below the rated voltage of the capacitor.

ΔI /2.

L

Input Capacitor Selection

Bypass the input of the LT3474 circuit with a 2.2μF or

higher ceramic capacitor of X7R or X5R type. A lower

value or a less expensive Y5V type will work if there is

additional bypassing provided by bulk electrolytic capaci-

tors or if the input source impedance is low. The following

paragraphs describe the input capacitor considerations in

more detail.

Step-down regulators draw current from the input sup-

ply in pulses with very fast rise and fall times. The input

capacitor is required to reduce the resulting voltage ripple

3474fd

12

LT3474/LT3474-1

APPLICATIONS INFORMATION

A ﬁnal caution is in order regarding the use of ceramic

capacitors at the input. A ceramic input capacitor can

combine with stray inductance to form a resonant tank

circuit.Ifpowerisappliedquickly(forexamplebyplugging

the circuit into a live power source), this tank can ring,

doubling the input voltage and damaging the LT3474. The

solution is to either clamp the input voltage or dampen the

tank circuit by adding a lossy capacitor in parallel with the

ceramic capacitor. For details, see Application Note 88.

You can estimate output ripple with the following

equation:

ΔI_L

8•f•C

V_RIPPLE

=

(

)

for ceramic capacitors

OUT

whereΔI isthepeak-to-peakripplecurrentintheinductor.

L

The RMS content of this ripple is very low so the RMS

current rating of the output capacitor is usually not of

concern. It can be estimated with the formula:

Output Capacitor Selection

ΔI_L

I_{C RMS}

=

(

)

12

For most LEDs, a 2.2μF 6.3V ceramic capacitor (X5R or

X7R)attheoutputresultsinverylowoutputvoltageripple

and good transient response. Other types and values will

also work; the following discusses tradeoffs in output

ripple and transient performance.

The low ESR and small size of ceramic capacitors make

them the preferred type for LT3474 applications. Not all

ceramic capacitors are the same, however. Many of the

higher value capacitors use poor dielectrics with high

temperature and voltage coefﬁcients. In particular, Y5V

and Z5U types lose a large fraction of their capacitance

with applied voltage and at temperature extremes.

Theoutputcapacitorﬁlterstheinductorcurrenttogenerate

an output with low voltage ripple. It also stores energy in

order to satisfy transient loads and stabilizes the LT3474’s

control loop. Because the LT3474 operates at a high

frequency, minimal output capacitance is necessary. In

addition, the control loop operates well with or without

the presence of output capacitor series resistance (ESR).

Ceramic capacitors, which achieve very low output ripple

and small circuit size, are therefore an option.

Because loop stability and transient response depend on

the value of C , this loss may be unacceptable. Use X7R

OUT

and X5R types. Table 3 lists several capacitor vendors.

Table 3. Low-ESR Surface Mount Capacitors

VENDOR

Taiyo-Yuden

AVX

TYPE

SERIES

X5R, X7R

Ceramic

TDK

3474fd

13

LT3474/LT3474-1

APPLICATIONS INFORMATION

Diode Selection

Table 4 lists several Schottky diodes and their

manufacturers.

The catch diode (D1 from Figure 1) conducts current only

during switch off time. Average forward current in normal

operation can be calculated from:

Table 4. Schottky Diodes

V

I

V at 0.5A

V at 1A

R

AVE

F

PART NUMBER

On Semiconductor

MBR0520L

MBR0540

(V)

(A)

(mV)

I_OUTV – V

(

)

IN

OUT

I_{D AVG}

=

(

)

V

20

40

20

40

0.5

1

385

510

IN

620

530

550

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 cur-

rent will then increase to one half the typical peak switch

current.

MBRM120E

MBRM140

Diodes Inc.

B0530W

1

30

20

30

40

0.5

1

430

B120

500

530

Peakreversevoltageisequaltotheregulatorinputvoltage.

Use a diode with a reverse voltage rating greater than the

input voltage.

B130

1

B140 HB

1

International Rectiﬁer

10BQ030

30

1

420

If using the PWM mode of the LT3474, select a diode with

low reverse leakage.

3474fd

14

LT3474/LT3474-1

APPLICATIONS INFORMATION

BOOST and BIAS Pin Considerations

can be tied to the input (Figure 4b). The circuit in Figure

4a is more efﬁcient because the BOOST pin current comes

from a lower voltage source. The BIAS pin can be tied to

another source that is at least 3V (Figure 4c). For example,

if a 3.3V source is on whenever the LED is on, the BIAS

pin can be connected to the 3.3V output. For LT3474-1

applications with higher output voltages, an additional

Zener diode may be necessary (Figure 4d) to maintain the

BOOST pin voltage below the absolute maximum. In any

case, be sure that the maximum voltage at the BOOST pin

is both less than 51V and the voltage difference between

the BOOST and SW pins is less than 25V.

The capacitor and internal diode tied to the BOOST pin

generate a voltage that is higher than the input voltage.

In most cases, a 0.22μF capacitor will work well. Figure 4

shows three ways to arrange the boost circuit. The BOOST

pin must be more than 2.5V above the SW pin for full ef-

ﬁciency. For outputs of 2.8V or higher, the standard circuit

(Figure 4a) is best. For lower output voltages, the BIAS pin

C3

BIAS

BOOST

SW

LT3474

V

OUT

IN

Programming LED Current

GND

– V ≈ V

OUT

3474 F04a

The LED current can be set by adjusting the voltage on

the V pin. For a 1A LED current, either tie V to REF

V

BOOST

SW

MAX V

≈ V + V

IN OUT

ADJ

BOOST

or to a 1.25V source. For lower output currents, program

(4a)

the V

using the following formula:

ADJ

1A •V_ADJ

1.25V

C3

BIAS

BOOST

I_LED

=

LT3474

V

SW

V

OUT

IN

Voltages less than 1.25V can be generated with a voltage

divider from the REF pin, as shown in Figure 5.

GND

3474 F04b

V

– V ≈ V

SW

BOOST

IN

MAX V

≈ 2V

BOOST

REF

(4b)

R1

R2

LT3474

GND

V

> 3V

IN2

IN

V

ADJ

C3

BIAS

BOOST

SW

LT3474

V

OUT

IN

3474 F04

GND

Figure 5. Setting V_ADJwith a Resistor Divider

3474 F04c

V

– V ≈ V

SW IN2

BOOST

MAX V

≈ V + V

IN2 IN

MINIMUM VALUE FOR V = 3V

IN2

In order to have accurate LED current, precision resistors

are preferred (1% or better is recommended). Note that

(4c)

the V

pin sources a small amount of bias current, so

ADJ

use the following formula to choose resistors:

C3

BIAS

BOOST

SW

LT3474

V_ADJ

1.25V – V_ADJ

V

IN

V

IN

V

OUT

R2 =

GND

– V ≈ V

+ 50nA

3474 F04d

R1

V

– V

Z

BOOST

MAX V

SW

OUT

≈ V + V

IN

– V

OUT Z

BOOST

(4d)

Figure 4. Generating the Boost Voltage

3474fd

15

LT3474/LT3474-1

APPLICATIONS INFORMATION

the C-RC string (tied to the V pin) shown in Figure 7 for

To minimize the error from variations in V pin current,

C

ADJ

properoperationduringstart-up. WhenthePWMpingoes

high again, the LED current returns rapidly to its previous

onstatesincethecompensationandoutputcapacitorsare

at the correct voltage. This fast settling time allows The

LT3474 to maintain diode current regulation with PWM

pulse widths as short as 40μs. If the NFET is omitted and

the cathode of the LED is instead tied to GND, use PWM

pulse widths of 1ms or greater. The maximmum PWM

use resistors with a parallel resistance of less than 4k. Use

resistors with a series resistance of 5.11k or greater so as

not to exceed the 250μA current limit on the REF pin.

Dimming Control

There are several different types of dimming control cir-

cuits. One dimming control circuit (Figure 6) changes the

voltage on the V pin by tying a low on-resistance FET to

ADJ

dimming ratio (PWM

) can be calculated from the

RATIO

the resistor divider string. This allows the selection of two

different LED currents. For reliable operation, program an

LED current of no less than 35mA. The maximum current

maximum PWM period (t

) and minimum PWM pulse

MAX

width (t ) as follows:

MIN

dimming ratio (I

) can be calculated from the maxi-

MAX

RATIO

mum LED current (I

t_MAX

t_MIN

= PWM_RATIO

) and the minimum LED current

(I ) as follows:

MIN

Total dimming ratio (DIM

dimming ratio and the current dimming ratio.

) is the product of the PWM

RATIO

I_MAX

I_MIN

= I_RATIO

Example: I

= 1A, I = 0.1A, t

= 12ms, t = 40μs

MAX

MIN

MAX

MIN

Another dimming control circuit (Figure 7) uses the PWM

pin and an external NFET tied to the cathode of the LED.

When the PWM signal goes low, the NFET turns off, turn-

ing off the LED and leaving the output capacitor charged.

The PWM pin is pulled low as well, which disconnects the

1A

0.1A

I_RATIO

=

=10:1

12ms

PWM_RATIO

=

=300:1

40μs

V pin, storing the voltage in the capacitor tied there. Use

C

DIM_RATIO=10•300=3000:1

REF

R1

R2

LT3474

GND

PWM

60Hz TO

10kHz

PWM

LED

V

ADJ

LT3474

GND

3474 F05

DIM

3.3nF 10k

0.1μF

3474 F06

Figure 6. Dimming with an NFET and Resistor Divider

Figure 7. Dimming Using PWM Signal

3474fd

16

LT3474/LT3474-1

APPLICATIONS INFORMATION

LED Voltage Range

as short as possible. To prevent electromagnetic interfer-

ence (EMI) problems, proper layout of the high frequency

switching path is essential. The voltage signal of the SW

and BOOST pins have sharp rise and fall edges. Minimize

the area of all traces connected to the BOOST and SW

pins and always use a ground plane under the switching

regulator to minimize interplane coupling. In addition, the

The LT3474 can drive LED voltages from 2.4V to 12V. The

LT3474-1 can drive LED voltages from 2.4V to 30V. Be

careful not to exceed the ABSMAX rating of the OUT, LED,

or BOOST pins of the LT3474-1 since the internal output

clamp is disabled. See the Typical Application section for

an example of adding an external output clamp. If the

LED voltage can drift below 2.4V due to temperature or

component variation, add extra series resistance to bring

the overall voltage above 2.4V.

ground connection for frequency setting resistor R (refer

T

to Figure 1) should be tied directly to the GND pin and

not shared with any other component, ensuring a clean,

noise-free connection.

Layout Hints

As with all switching regulators, careful attention must

be paid to the PCB layout and component placement. To

maximize efﬁciency, switch rise and fall times are made

PWM

SHDN

V

IN

GND

VIA TO LOCAL GND PLANE

VIA TO OUT

Figure 8. Recommended Component Placement

3474fd

17

LT3474/LT3474-1

TYPICAL APPLICATIONS

Step-Down 1A LED Driver with PWM Dimming

LED Current in PWM Mode

V

IN

I

LED1

500mA/DIV

6V TO 36V

C3

0.22μF

6.3V

C1

2.2μF

50V

L1

10μH

V

BOOST

SW

IN

SHDN

V(PWM)

5V/DIV

D1

LT3474

R

BIAS

OUT

T

REF

V

1ms/DIV

PWM

C2

2.2μF

6.3V

ADJ

R1

80.6k

V

LED

C

C4

GND

3.3nF

LED1

M1

R2

10k

PWM

C5

0.1μF

3474 TA01

D1: B140HB

C1 TO C3: X5R OR X7R

M1: Si2302ADS

Step-Down 1A LED Driver with

Two Series Connected LED Output

Efﬁciency, Two LED Output

95

V

IN

90

85

80

12V TO

36V

V

= 12V

= 24V

IN

C3

C1

2.2μF

50V

L1

10μH

0.22μF

V

BOOST

SW

IN

V

IN

10V

SHDN

D1

LT3474

75

70

R

T

BIAS

OUT

REF

V

R1

ADJ

C2

2.2μF

10V

PWM

LED

65

60

55

33.2k

V

C

C4

0.1μF

GND

LED1

LED2

1A

LED

CURRENT

200

400

LED CURRENT (mA)

800

0

1000

600

3474 G01

3474 TA02

D1: MBRM 140

C1 TO C3: X5R OR X7R

3474fd

18

LT3474/LT3474-1

PACKAGE DESCRIPTION

FE Package

16-Lead Plastic TSSOP (4.4mm)

(Reference LTC DWG # 05-08-1663)

Exposed Pad Variation BA

4.90 – 5.10*

(.193 – .201)

2.74

(.108)

2.74

(.108)

16 1514 13 12 1110

9

6.60 ±0.10

2.74

(.108)

4.50 ±0.10

6.40

2.74

SEE NOTE 4

(.252)

(.108)

0.45 ±0.05

BSC

1.05 ±0.10

0.65 BSC

5

7

8

1

2

3

4

6

RECOMMENDED SOLDER PAD LAYOUT

1.10

(.0433)

MAX

4.30 – 4.50*

(.169 – .177)

0.25

REF

0° – 8°

0.65

(.0256)

BSC

0.09 – 0.20

(.0035 – .0079)

0.50 – 0.75

(.020 – .030)

0.05 – 0.15

(.002 – .006)

FE16 (BA) TSSOP 0204

0.195 – 0.30

(.0077 – .0118)

TYP

NOTE:

1. CONTROLLING DIMENSION: MILLIMETERS 4. RECOMMENDED MINIMUM PCB METAL SIZE

FOR EXPOSED PAD ATTACHMENT

*DIMENSIONS DO NOT INCLUDE MOLD FLASH. MOLD FLASH

SHALL NOT EXCEED 0.150mm (.006") PER SIDE

MILLIMETERS

(INCHES)

2. DIMENSIONS ARE IN

3. DRAWING NOT TO SCALE

3474fd

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.

19

LT3474/LT3474-1

TYPICAL APPLICATION

Step-Down 1A LED Driver with Four Series Connected LED Output

V

IN

21V TO

36V

C3

0.22μF

16V

C1

2.2μF

50V

L1

47μH

V

BOOST

SW

IN

SHDN

LT3474-1

D1

D2

BIAS

R

T

REF

V

OUT

R1

C2

2.2μF

25V

ADJ

PWM

LED

80.6k

R2

10k

V

C

C4

0.1μF

GND

D3

Q1

12V TO 18V

LED VOLTAGE

R3

100k

1A LED

CURRENT

f

= 500kHz

SW

3474 TA02a

D1: MBRM 140

D2: 7.5V Zener Diode

D3: 22V Zener Diode

Q1: MMBT3904

C1 TO C3: X5R OR X7R

RELATED PARTS

PART NUMBER DESCRIPTION

COMMENTS

: 1.6V to 18V, V

LT1618

LT1766

LT1956

LT1961

Constant Current, 1.4MHz, 1.5A Boost Converter

V

= 36V, I = 1.8mA, I = <1μA,

Q SD

IN

OUT(MAX)

MS10 Package

60V, 1.2A (I ), 200kHz, High Efﬁciency Step-Down DC/DC Converter V : 5.5V to 60V, V

= 1.20V, I = 2.5mA, I = 25μA,

OUT

IN

Q

SD

TSSOP16/E Packages

60V, 1.2A (I ), 500kHz, High Efﬁciency Step-Down DC/DC Converter V : 5.5V to 60V, V

= 1.20V, I = 2.5mA, I = 25μA,

OUT

IN

OUT(MAX)

Q

SD

TSSOP16/E Packages

1.5A (I ), 1.25MHz, High Efﬁciency Step-Up DC/DC Converter

V

: 3V to 25V, V

= 35V, I = 0.9mA, I = 6μA,

OUT(MAX) Q SD

SW

IN

MS8E Package

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

V : 3.3V to 60V, V

= 1.20V, I = 100μA, I = <1μA,

Q SD

OUT

IN

OUT(MAX)

DC/DC Converters with BurstMode^®Operation

TSSOP16E Package

LT3430/LT3431 60V, 2.5A (I ), 200kHz, High Efﬁciency Step-Down DC/DC Converters

V

SD

: 5.5V to 60V, V

= 1.20V, I = 2.5μA,

OUT(MAX) Q

OUT

IN

I

= <25μA, TSSOP16/E Packages

LT3433

60V, 400mA (I ), 200kHz, High Efﬁciency Step-Up/Step-Down

V : 4V to 60V, V : 3.3V to 20V, I = 100μA,

SD

OUT

IN

OUT

Q

DC/DC Converters with Burst Mode Operation

I

= <1μA, TSSOP16E Package

LT3434/LT3435 60V, 2.5A (I ), 200kHz/500kHz, High Efﬁciency Step-Down

V : 3.3V to 60V, V

= 1.20V, I = 100μA, I = <1μA,

OUT(MAX) Q SD

OUT

IN

DC/DC Converters with Burst Mode Operation

TSSOP16E Package

LTC3453

1MHz, 800mA Synchronous Buck-Boost High Power LED Driver

V : 2.7V to 5.5V, V

= 5.5V, I = 2.5mA, I = <6μA,

Q SD

IN

OUT(MAX)

QFN Package

LT3467/LT3467A 1.1A (I ), 1.3MHz/2.1MHz, High Efﬁciency Step-Up DC/DC Converters V : 2.4V to 16V, V

= 40V, I = 1.2mA, I = <1μA,

Q SD

SW

IN

OUT(MAX)

with Integrated Soft-Start

ThinSOT™ Package

LT3477

LT3479

3A, 42V, 3MHz Step-Up Regulator with Dual Rail to Rail Current Sense

V

: 2.5V to 2.5V, V

= 40V, I = 5mA, I = <1μA,

OUT(MAX) Q SD

IN

QFN, TSSOP16E Packages

3A, Full Featured DC/DC Converter with Soft-Start and Inrush

Current Protection

V : 2.5V to 24V, V

DFN and TSSOP Packages

= 40V, I = 6.5mA, I = <1μA,

Q SD

IN

OUT(MAX)

Burst Mode is a registered trademark of Linear Technology Corporation.

ThinSOT is a trademark of Linear Technology Corporation.

3474fd

LT 1008 REV D • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

20

●

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


型号：	LT3474-1
厂家：	Linear
描述：	Step-Down 1A LED Driver 降压型1A LED驱动器驱动器
文件：	总20页 (文件大小：215K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

LT3474-1 [Linear]

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