LTC3454EDD#TR_技术文档

LTC3454

1A Synchronous Buck-Boost

High Current LED Driver

U

DESCRIPTIO

FEATURES

■

High Efﬁciency: >90% Typical in Torch Mode,

The LTC^®3454 is a synchronous buck-boost DC/DC

converter optimized for driving a single high power LED

at currents up to 1A from a single cell Li-Ion battery in-

put. The regulator operates in either synchronous buck,

synchronous boost, or buck-boost mode depending on

>80% in Flash Mode

■

Wide V Range: 2.7V to 5.5V

IN

■

Up to 1A Continuous Output Current

3.5% LED Current Programming Accuracy

Internal Soft-Start

Open/Shorted LED Protection

Constant Frequency 1MHz Operation

Zero Shutdown Current

Overtemperature Protection

Small Thermally Enhanced 10-Lead (3mm × 3mm)

DFN Package

inputvoltageandLEDforwardvoltage.P /P efﬁciency

LED IN

greater than 90% can be achieved over the entire usable

range of a Li-Ion battery (2.7V to 4.2V).

LED current is programmable to one of four levels, includ-

ingshutdown, withdualexternalresistorsanddualenable

inputs. In shutdown no supply current is drawn.

A high constant operating frequency of 1MHz allows the

use of small external components. The LTC3454 is offered

in a low proﬁle (0.75mm) thermally enhanced 10-lead

(3mm × 3mm) DFN package.

U

APPLICATIO S

■

Cell Phone Camera Flash

■

Cell Phone Torch Lighting

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

All other trademarks are the property of their respective owners.

■

Digital Cameras

PDAs

Misc Li-Ion LED Drivers

■

U

TYPICAL APPLICATIO

High Efﬁciency Torch/Flash LED Driver

L1

5 H

V

IN

1-CELL

Li-Ion

LED Power Efﬁciency vs V

IN

10 F

I

2.7V-4.2V

V

SW1

SW2

V

OUT

IN

LED

100

95

A

D

C

I

= 150mA

LED

90

EN2 EN1

I

LED

0 (SHUTDOWN)

150mA

850mA

1A

LED

B

0

1

0

1

0

1

85

I

= 1A

LED

EN1 (TORCH)

EN2 (FLASH)

80

75

1MHz

BUCK-BOOST

V

I

C

SET1

70

65

60

R

20.5k

1%

I

ISET1

0.1 F

SET2

T

= 25°C

A

LTC3454

EFFICIENCY = (V

– V )I /V I

LED LED IN IN

R

3.65k

1%

OUT

ISET2

GND (EXPOSED PAD)

LED: LUMILEDS LXL-PWF1

L1: SUMIDA CDRH6D28-5RONC

3453 TA01a

3.1 3.5 3.9

4.7

2.7

5.1 5.5

4.3

(V)

V

IN

3454 TA01b

3454f

1

LTC3454

W W U W

U

W

U

ABSOLUTE AXI U RATI GS

PACKAGE/ORDER I FOR ATIO

(Note 1)

TOP VIEW

V , SW1, SW2, V

Voltage......................–0.3V to 6V

IN

OUT

, I

EN1

EN2

1

2

3

4

5

10 SW1

V , EN1, EN2, I

C

SET1 SET2

9

8

7

6

V

IN

Voltage.............................–0.3V to (V + 0.3V) or 6V

IN

I

11

SET1

C

LED Peak Current...................................................1.25A

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

Operating Temperature Range (Note 2) ...–40°C to 85°C

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

SET2

LED

OUT

SW2

DD PACKAGE

10-LEAD (3mm × 3mm) PLASTIC DFN

T

= 125°C, θ = 40°C/W

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

JMAX

JA

ORDER PART NUMBER

LTC3454EDD

DD PART MARKING

LBQX

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 speciﬁed with wider operating temperature ranges.

The

●

denotes the speciﬁcations which apply over the full operating

ELECTRICAL CHARACTERISTICS

temperature range, otherwise speciﬁcations are at T = 25°C, V = 3.6V, R

= 20.5k unless otherwise noted. (Note 2)

A

IN

ISET

PARAMETER

CONDITIONS

MIN

TYP

MAX

UNITS

Input Supply Voltage (V )

●

2.7

5.5

V

IN

Input DC Supply Current

Normal Operation

Shutdown

(Typicals at V = 3.6V, R

= R = 20.5k)

ISET2

IN

ISET1

2.7V ≤ V ≤ 5.5V (Note 4)

825

0

5

1200

1

10

µA

IN

2.7V ≤ V ≤ 5.5V; V

= V

= 0V

EN2

EN1

UVLO

V

< UVLO Threshold; V = V = V

IN

EN1

EN2

IN

Undervoltage Lockout Threshold

V

Rising

Falling

●

2.05

1.90

0.68

0.66

2.3

1.2

V

µA

mV

IN

1.75

V

, V

DC Threshold for Normal Operation (V )

DC Threshold for Shutdown (V )

Input Current

●

EN1 EN2

IH

, V

0.2

–1

780

788

EN1 EN2

IL

, V

EN1 EN2

1

812

I

and I

Servo Voltage

3.08k ≤ R ||R ≤ 20.5k

ISET1 ISET2

800

SET1

SET2

LED Output Current to Programming Current Ratio

LED Pin Voltage

I

/(I

+ I

), I = 500mA (Note 5)

●

3725

3775

3850

3975

3925

mA/mA

LED ISET1

ISET2 LED

= 1A

105

5.15

170

130

3.4

mV

V

mΩ

A

mA

µA

LED

Regulated Maximum V

LED Pin Open, Programmed I

= 1A

LED

4.95

2.5

5.35

OUT

PMOS Switch R

Switches A and D (V

Switches B and C

Switch A

Switch D (V

Switches A, D

Switches B, C

= 3.6V)

ON

OUT

NMOS Switch R

ON

Forward Current Limit

Reverse Current Limit

PMOS Switch Leakage

NMOS Switch Leakage

Oscillator Frequency

Soft-Start Time

= 3.6V)

275

OUT

–1

0.9

1

1.15

1.0

200

MHz

µs

Note 1: Absolute Maximum Ratings are those values beyond which the life

of a device may be impaired.

Note 3: T is calculated from the ambient temperature T and power

dissipation PD according to the following formula:

J

A

Note 2: The LTC3454 is guaranteed to meet speciﬁcations from 0°C to

70°C. Speciﬁcations over the –40°C to 85°C operating temperature range

are assured by design, characterization and correlation with statistical

process controls.

T = T + (PD • θ °C/W).

J A JA

Note 4: Dynamic supply current is higher due to the gate charge being

delivered at the switching frequency.

Note 5: This parameter is tested using a feedback loop which servos V

C

to 1.8V.

3454f

2

LTC3454

U W

TYPICAL PERFOR A CE CHARACTERISTICS

Undervoltage Lockout Threshold

vs Temperature

Enable Thresholds

vs Temperature

Enable Thresholds vs V

IN

2.4

2.3

2.2

2.1

2.0

1.9

1.8

1.7

1.6

1.5

1.4

1200

1100

1000

900

800

700

600

500

400

300

200

1200

1100

1000

900

800

700

600

500

400

300

200

T

= 25°C

V

= 3.6V

A

IN

V

RISING

IN

V

IH

V

IH

V

IL

V

IL

V

FALLING

IN

–55 –35 –15

5

25 45 65 85 105 125

–55 –35 –15

5

25 45 65 85 105 125

2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5

(V)

TEMPERATURE (°C)

V

IN

3454 G01

3454 G02

3454 G03

I

Servo Voltage

SET1,2

vs Temperature

I

Servo Voltage vs V

I

Servo Voltage vs R

SET1,2 ISET

SET1,2

IN

812

808

812

808

804

800

812

808

804

800

V

= 3.6V

ISET1,2

T

= 25°C

ISET1

IN

V

T

= 3.6V

IN

A

R

= 15k

R

= R

= 15k

ISET2

= 25°C

804

800

796

792

788

796

792

788

792

788

4.3

(V)

5.1

5.5

2.7 3.1

3.5 3.9

V

4.7

–55 –35 –15

5

25 45 65 85 105 125

19

27

31

3

7

11

15

23

TEMPERATURE (°C)

R

(kΩ)

IN

ISET

3454 G05

3454 G04

3454 G06

LED Current Programming Ratio

vs Temperature

LED Current Programming Ratio

vs V

V

vs Temperature

IN

LED

4050

4000

3950

3900

3850

3800

3750

3700

3650

150

120

90

4050

4000

3950

3900

3850

3800

3750

3700

3650

V

= 3.6V

PROGRAMMED I

A

= 500mA

V

= 3.6V

IN

LED

T

= 25°C

PROGRAMMED

I

= 1A

LED

PROGRAMMED

= 500mA

I

LED

60

30

0

PROGRAMMED

= 100mA

PROGRAMMED I

= 1A

= 500mA

= 150mA

LED

I

LED

25 45

TEMPERATURE (°C)

–55 –35 –15

5

65 85 105 125

4.3

(V)

25

5

TEMPERATURE (°C)

2.7 3.1 3.5 3.9

4.7 5.1 5.5

–55 –35 –15

45 65 85 105 125

V

IN

3454 G07

3454 G08

3454 G09

3454f

3

LTC3454

U W

TYPICAL PERFOR A CE CHARACTERISTICS

Maximum Regulated V

vs Temperature

Maximum Regulated V

OUT

V

vs V

IN

vs V

LED

IN

60

58

56

54

52

50

48

46

44

42

40

5.40

5.35

5.30

5.25

5.20

5.15

5.10

5.05

5.00

4.95

4.90

5.40

5.35

5.30

5.25

5.20

5.15

5.10

5.05

5.00

4.95

4.90

PROGRAMMED I

T

= 500mA

LED

PROGRAMMED I

A

= 1A

PROGRAMMED I

IN

= 1A

LED

= 25°C

A

T

= 25°C

V

= 3.6V

2.7

3.5 3.9 4.3

(V)

4.7 5.1 5.5

3.1

3.5 3.9

V

2.7 3.1

4.3 4.7 5.1 5.5

(V)

25 45

–55 –35 –15

5

65 85 105 125

V

IN

TEMPERATURE (°C)

IN

3454 G10

3454 G12

3454 G11

Maximum Regulated V

OUT

PMOS R

vs Temperature

NMOS R

vs Temperature

DS(ON)

vs Programmed LED Current

DS(ON)

300

270

240

210

180

150

120

90

200

180

160

140

120

100

80

5.40

5.35

5.30

5.25

5.20

5.15

5.10

5.05

5.00

4.95

4.90

MEASURED AT 500mA

V

A

= 3.6V

IN

= 25°C

T

V

= 2.7V

IN

V

= 3.6V

IN

V

= 2.7V

V

IN

V

= 5.5V

IN

V

= 3.6V

IN

V

= 4.2V

IN

= 5.5V

IN

V

= 4.2V

IN

60

40

500 600

100 200 300 400

700 800 900 1000

(mA)

–55 –35 –15

5

25 45

125

–55 –35 –15

5

25 45

125

65 85 105

TEMPERATURE (°C)

PROGRAMMED I

LED

3454 G13

3454 G14

3454 G15

Oscillator Frequency

vs Temperature

LED Power Efﬁciency

vs LED Current

1100

1080

1060

1040

1020

1000

980

100

V

= 3V

OUT

95

90

85

80

75

70

65

60

V

= 5.5V

= 2.7V

IN

V

= 4.2V

= 3.6V

IN

V

IN

5

960

V

A

= 3.6V

IN

940

T

= 25°C

EFFICIENCY = (V

– V )I /V I

LED LED IN IN

920

OUT

FRONT PAGE APPLICATION

900

500 600

100 200 300 400

700 800 900 1000

–55 –35 –15

25 45 65 85 105 125

TEMPERATURE (°C)

I

(mA)

LED

3454 G17

3454 G16

3454f

4

LTC3454

U W

TYPICAL PERFOR A CE CHARACTERISTICS

Output Voltage Ripple

Back Page Application

Start-Up Transient

Back Page Application

CH1, V

1V/DIV

OUT

CH2, I

LED

500mA

FINAL VALUE

20mV/DIV

0V, 0A

0V

CH3, V

1V/DIV

EN1

3454 G19

V

I

= 3.6V

LED

5ms/DIV

V

I

= 3.6V

LED

500ns/DIV

IN

= 500mA

U

PI FU CTIO S

V

(Pin7):Buck-BoostOutputRail. BypasstoGNDwith

EN1 (Pin 1): Enable Input Pin for I

Current.

OUT

SET1

SET2

a ceramic capacitor. Recommended value is 10µF.

EN2 (Pin 2): Enable Input Pin for I

Current.

V (Pin 8): Compensation Point for the Internal Error

C

I

(Pin 3): LED Current Programming Pin. A resistor

SET1

Ampliﬁer Output. Connect a ceramic capacitor from V

C

to ground programs the current through the LED to I

LED

to GND. Recommended value is 0.1µF.

= 3850(0.8V/R

amount set by EN2/I

). This amount of current adds to any

ISET1

V (Pin 9): Voltage Input Supply Pin (2.7V ≤ V ≤ 5.5V).

if used.

IN

SET2

Bypass to GND with a ceramic capacitor. Recommended

I

(Pin 4): LED Current Programming Pin. A resistor

SET2

value is 10µF.

to ground programs the current through the LED to I

LED

SW1 (Pin 10): Switching Node. External inductor con-

nects between SW1 and SW2. Recommended value is

4.7µH/5µH.

= 3850(0.8V/R

amount set by EN1/I

). This amount of current adds to any

ISET2

if used.

SET1

LED (Pin 5): Low Dropout Output for LED Current Biasing.

Connect the LED between V and the LED pin.

Exposed Pad (Pin 11): Ground Pin. Solder to PCB ground

for electrical contact and optimal thermal performance.

OUT

SW2 (Pin 6): Switching Node. External inductor con-

nects between SW1 and SW2. Recommended value is

4.7µH/5µH.

3454f

5

LTC3454

W

BLOCK DIAGRA

OPTIONAL

10

6

V

7

SW1

SW2

OUT

V

SWITCH A

SWITCH D

IN

9

V

IN

2.7V TO 5.5V

GATE

DRIVERS

AND

ANTICROSS-

CONDUCTION

SWITCH B

SWITCH C

UNDERVOLTAGE

LOCKOUT

UV

FORWARD

CURRENT

LIMIT

REVERSE

CURRENT

LIMIT

+

–

+

–

OVERTEMP

PROTECTION

OT

3.4A

275mA

BANDGAP

REFERENCE

1.23V

+

–

LOGIC

+

–

AB PWM

COMPARATOR

CD PWM

COMPARATOR

UV

OT

1MHz

OSCILLATOR

V

C

8

SAFETY

ERROR AMP

AUTOZEROING

ERROR AMP

V

LED

OUT

1.23V

–

+

–

+

5

377k

123k

R

SOFT

1.23V

START

CLAMP

LED CURRENT

SETTING AMP 1

800mV

+

–

CURRENT

MIRROR

I

ISET1

I

SET1

∑

3

I

3850 I

R

ISET1

LED CURRENT

SETTING AMP 2

+

–

ISET2

SET2

4

1

EN1

EN2

ISET2

SHUTDOWN

2

EXPOSED PAD (GND)

11

3454 BD

3454f

6

LTC3454

U

OPERATIO

Buck-Boost DC-DC Converter

each cycle. During the off time of switch A, synchronous

rectiﬁer switch B turns on for the remainder of the cycle.

Switches A and B will alternate conducting similar to a

typical synchronous buck regulator. As the control volt-

age increases, the duty cycle of switch A increases until

the maximum duty cycle of the converter in buck mode

The LTC3454 employs an LTC proprietary buck-boost

DC/DCconvertertogeneratetheoutputvoltagerequiredto

drive a high current LED. This architecture permits high-

efﬁciency, low noise operation at input voltages above,

below or equal to the output voltage by properly phasing

fourinternalpowerswitches.Theerrorampoutputvoltage

reaches DC

|max given by:

BUCK

on the V pin determines the duty cycle of the switches.

DC

|max = 100% – DC

BUCK 4SW

C

Since the V pin is a ﬁltered signal, it provides rejection

C

where DC

equals the duty cycle in % of the “four

4SW

switch” range.

of frequencies well below the factory trimmed switching

frequency of 1MHz. The low R

, low gate charge

DS(ON)

DC = (150ns • f) • 100%

synchronousswitchesprovidehighfrequencypulsewidth

modulation control at high efﬁciency. Schottky diodes

across synchronous rectiﬁer switch B and synchronous

rectiﬁer switch D are not required, but if used do provide

a lower voltage drop during the break-before-make time

(typically 20ns), which improves peak efﬁciency by typi-

cally 1% to 2% at higher loads.

4SW

where f is the operating frequency in Hz.

Beyond this point the “four switch” or buck-boost region

is reached.

Buck-Boost or Four-Switch Mode (V ≈ V

)

IN

OUT

Referring to Figure 2, when the control voltage V is above

C

Figure1showsasimpliﬁeddiagramofhowthefourinternal

voltage V2, switch pair AD continue to operate for duty

power switches are connected to the inductor, V , V

IN OUT

cycle DC

|max, and the switch pair AC begins to phase

BUCK

and GND. Figure 2 shows the regions of operation of the

in. As switch pair AC phases in, switch pair BD phases out

buck-boost as a function of the control voltage V . The

C

accordingly. When the V voltage reaches the edge of the

C

outputswitchesareproperlyphasedsotransitionsbetween

regionsofoperationarecontinuous, ﬁlteredandtranspar-

buck-boostrangeatvoltageV3, switchpairACcompletely

phases out switch pair BD and the boost region begins at

enttotheuser.WhenV approachesV ,thebuck-boost

IN

OUT

duty cycle DC . The input voltage V where the four

4SW

IN

region is reached where the conduction time of the four

switch region is typically 150ns. Referring to Figures 1

switch region begins is given by:

and 2, the various regions of operation encountered as V

V = V /[1 – (150ns • f)]

C

IN

OUT

increaseswillnowbedescribed.

and the input voltage V where the four switch region

IN

ends is given by

Buck Mode (V > V

)

OUT

IN

V = V

• (1 – DC

) = V • [1 – (150ns • f)]

OUT

IN

OUT

4SW

In buck mode, switch D is always on and switch C is

always off. Referring to Figure 2, when the control

75%

voltage V is above voltage V1, switch A begins to turn on

C

D

MAX

V4 (2.1V)

BOOST

A ON, B OFF

BOOST REGION

BUCK REGION

V

IN

OUT

7

PWM CD SWITCHES

D

9

MIN

V3 (1.65V)

BOOST

BUCK/BOOST REGION

FOUR SWITCH PWM

D

MAX

PMOS A

PMOS D

NMOS C

V2 (1.55V)

BUCK

0%

SW1

10

SW2

6

D ON, C OFF

PWM AB SWITCHES

V1 (0.9V)

NMOS B

DUTY

CYCLE

CONTROL

VOLTAGE, V

3454 F02

3454 F01

C

Figure 2. Switch Control vs Control Voltage, V

Figure 1. Simpliﬁed Diagram of Internal Power Switches

C

3454f

7

LTC3454

U

W U U

APPLICATIO S I FOR ATIO

Boost Mode (V < V

)

limiting the rate of duty cycle change as V transitions

IN

OUT

C

from the buck region through the buck-boost region into

the boost region. Once the soft-start times out, it can only

be reset by entering shutdown, or by an undervoltage or

overtemperature condition.

Inboostmode,switchAisalwaysonandswitchBisalways

off. Referring to Figure 2, when the control voltage V is

C

above voltage V3, switches C and D will alternate conduct-

ing similar to a typical synchronous boost regulator. The

maximum duty cycle of the converter is limited to 88%

Autozero Error Amp

typical and is reached when V is above V4.

C

The error ampliﬁer is an autozeroing transconductance

amp with source and sink capability. The output of this

Forward Current Limit

ampliﬁer drives a capacitor to GND at the V pin. This

C

If the current delivered from V through PMOS switch A

IN

capacitor sets the dominant pole for the regulation loop.

(See the Applications Information section for selecting

the capacitor value). The feedback signal to the error

amp is developed across a resistor through which LED

current ﬂows.

exceeds 3.4A (typical), switch A is shut off immediately.

Switches B and D are turned on for the remainder of the

cycle in order to safely discharge the forward inductor

current at the maximum rate possible.

Reverse Current Limit

Safety Error Amp

If the current delivered from V

backwards through

OUT

The safety error ampliﬁer is a transconductance ampliﬁer

with sink only capability. In normal operation, it has no

effectontheloopregulation.However,iftheLEDpinopen-

circuits, the output voltage will keep rising, and the safety

errorampwilleventuallytakeovercontroloftheregulation

PMOS switch D exceeds 275mA (typical), switch D is

shut off immediately. Switches A and C are turned on for

the remainder of the cycle in order to safely discharge the

reverse inductor current at the maximum rate possible.

looptopreventV runaway.TheV thresholdatwhich

OUT

Undervoltage Lockout

this occurs is approximately 5.15V.

TopreventoperationofthepowerswitchesathighR

,

DS(ON)

an undervoltage lockout is incorporated on the LTC3454.

Whentheinputsupplyvoltagedropsbelowapproximately

1.90V, the four power switches and all control circuitry

are turned off except for the undervoltage block, which

draws a few microamperes.

LED Current Programming and Enable Circuit

Two enable pins work in conjunction with dual external

resistors to program LED current to one of three nonzero

settings. The table below explains how the current can

be set.

Overtemperature Protection

EN1

EN2

GND

I

(A)

LOAD

GND

0 (SHUTDOWN)

If the junction temperature of the LTC3454 exceeds 130°C

for any reason, all four switches are shut off immediately.

The overtemperature protection circuit has a typical hys-

teresis of 11°C.

V

3850 • 0.8V/R

IN

ISET1

ISET2

GND

V

IN

V

3850 • (0.8V/R

+ 0.8V/R

)

IN

ISET1

ISET2

Soft-Start

With either enable pin pulled high, the buck-boost will

regulate the output voltage at the current programmed

The LTC3454 includes an internally ﬁxed soft-start which

is active when powering up or coming out of shutdown.

by R

and/or R

.

ISET1

ISET2

The soft-start works by clamping the voltage on the V

C

With both enable pins pulled to GND, the LTC3454 is in

shutdown and draws zero current. The enable pins are

high impedance inputs and should not be ﬂoated.

node and gradually releasing it such that it requires 200µs

to linearly slew from 0.9V to 2.1V. This has the effect of

3454f

8

LTC3454

U

W U U

APPLICATIO S I FOR ATIO

Input Capacitor Selection

COMPONENT SELECTION

SincetheV pinisthesupplyvoltagefortheICitisrecom-

IN

mendedtoplaceatleasta2.2µF,lowESRbypasscapacitor

Inductor Selection

toground.SeeTable2foralistofcomponentsuppliers.

The high frequency operation of the LTC3454 allows the

use of small surface mount inductors. The inductor cur-

rent ripple is typically set to 20% to 40% of the maximum

averageinductorcurrent. Foragivenrippletheinductance

term in Boost mode is:

Table 2. Capacitor Vendor Information

SUPPLIER

AVX

Sanyo

Taiyo Yuden

TDK

WEB SITE

www.avxcorp.com

www.sanyovideo.com

www.t-yuden.com

www.component.tdk.com

V

²• V_OUT– V

•100%

(

)

IN(MIN)

L >

2

f •I_OUT(MAX)•%Ripple• V_OUT

Output Capacitor Selection

The bulk value of the capacitor is set to reduce the ripple

due to charge into the capacitor each cycle. The steady

state ripple due to charge is given by:

and in Buck mode is:

V

_IN(MAX)– V_OUT• V_OUT•100%

(

)

L >

f • V_IN(MAX)•%Ripple •I _OUT

I_OUT(MAX)• V_OUT– V

•100%

(

)

IN(MIN)

C_OUT• V_OUT²• f

%Ripple_Boost =

where f = operating frequency, Hz

%Ripple = allowable inductor current ripple, %

V

_IN(MAX)– V_OUT•100%

(

)

V

= minimum input voltage, V

= maximum input voltage, V

IN(MIN)

IN(MAX)

%Ripple_Buck =

8• V_IN(MAX)• f²•L •C_OUT

where C

= output ﬁlter capacitor, F

= output voltage, V

OUT

The output capacitance is usually many times larger in

ordertohandlethetransientresponseoftheconverter.For

a rule of thumb, the ratio of operating frequency to unity-

gain bandwidth of the converter is the amount the output

capacitance will have to increase from the above calcula-

tions in order to maintain desired transient response.

I

= maximum output load current

OUT(MAX)

For high efﬁciency, choose an inductor with a high fre-

quencycorematerial, suchasferrite, toreducecoreloses.

The inductor should have low ESR (equivalent series

2

resistance) to reduce the I R losses, and must be able

to handle the peak inductor current without saturating.

Molded chokes or chip inductors usually do not have

enough core to support peak inductor currents >1A. To

minimize radiated noise, use a toroid, pot core or shielded

bobbin inductor. For white LED application, a 4.7µH/5µH

inductor value is recommended. See Table 1 for a list of

component suppliers.

The other component of ripple is due to ESR (equivalent

series resistance) of the output capacitor. Low ESR ca-

pacitors should be used to minimize output voltage ripple.

For surface mount applications, Taiyo Yuden, TDK, AVX

ceramic capacitors, AVX TPS series tantalum capacitors

or Sanyo POSCAP are recommended. For the white LED

application, a 10µF capacitor value is recommended. See

Table 2 for a list of component suppliers.

Table 1. Inductor Vendor Information

SUPPLIER

WEB SITE

Coilcraft

www.coilcraft.com

Optional Schottky Diodes

Cooper/Coiltronics www.cooperet.com

Murata

Sumida

Toko

www.murata.com

www.japanlink.com/sumida

www.toko.com

Schottky diodes across the synchronous switches B and

D are not required, but provide a lower drop during the

break-before-make time (typically 20ns) of the NMOS to

PMOS transition, improving efﬁciency. Use a Schottky

Vishay-Dale

www.vishay.com

diode such as an MBRM120T3 or equivalent. Do not use

3454f

9

LTC3454

U

W U U

APPLICATIO S I FOR ATIO

ordinary rectiﬁer diodes, since the slow recovery times where g is the error amp transconductance (typically

m

will compromise efﬁciency.

1/5.2k) and C is the external capacitor to GND at the

VC

V pin. For the white LED application, a 0.1µF or greater

C

In applications in which V is greater than 4V and V

to

OUT

IN

capacitor value is recommended.

GND short-circuit protection is needed, a Schottky diode

such as MBRM12OT3 or equivalent may be used from

SW1 to GND and/or a 2Ω/1nF series snubber from SW1

to GND. The Schottky diode should be added as close

to the pins as possible. Neither of these is required for

shorted LED protection.

Maximum LED Current

As described in the Operation section, the output LED

current with both enable pins logic high is equal to

I

= 3850 [0.8V/(R

|| R )]

ISET2

LED

ISET1

Sincethemaximumcontinuousoutputcurrentislimitedto

1A, this sets a minimum limit on the parallel combination

Closing the Feedback Loop

The LTC3454 incorporates voltage mode PWM control.

The control to output gain varies with operation region

(Buck, Boost, Buck/Boost), but is usually no greater

than 15. The output ﬁlter exhibits a double pole response

givenby:

of R

and R

equal to

ISET1

ISET2

R

MIN

= (R

|| R

)|

= 3850(0.8V/1A)

ISET1

= 3080Ω

ISET2 MIN

Although the LTC3454 can safely provide this current

continuously, the external LED may not be rated for this

high a level of continuous current. Higher current levels

are generally reserved for pulsed applications, such as

LED camera ﬂash. This is accomplished by programming

1

f_{FILTER_POLE}

=

Hz

2 • π • L •C_OUT

where C

is the output ﬁlter capacitor.

OUT

a high current with one of the R

the appropriate enable pin.

resistors and pulsing

ISET

The output ﬁlter zero is given by:

1

f_{FILTER_ZERO}

=

Hz

Varying LED Brightness

2 • π •R_ESR•C_OUT

Continuously variable LED brightness control can be

achieved by interfacing directly to one or both of the I

whereR isthecapacitorequivalentseriesresistance.

ESR

SET

A troublesome feature in Boost mode is the right-half

plane zero (RHP), and is given by:

pins. Figure 3 shows four such methods employing a

voltage DAC, a current DAC, a simple potentiometer or a

PWM input. It is not recommended to control brightness

by PWMing the enable pins directly as this will toggle

the LTC3454 in and out of shutdown and result in erratic

operation.

2

V

IN

f_RHPZ

=

Hz

2• π •I_OUT•L•V_OUT

The loop gain is typically rolled off before the RHP zero

frequency.

LED Failure Modes

AsimpleTypeIcompensationnetworkcanbeincorporated

to stabilize the loop but at a cost of reduced bandwidth

and slower transient response. To ensure proper phase

margin, the loop is required to be crossed over a decade

before the LC double pole.

IftheLEDfailsasanopencircuit, thesafetyampliﬁertakes

control of the regulation loop to prevent V

runaway.

OUT

The V

threshold at which this occurs is about 5.15V.

OUT

The safety ampliﬁer has no effect on loop regulation at

less than 5.15V.

V

OUT

The unity-gain frequency of the error ampliﬁer with the

Type I compensation is given by:

If the LED fails as a short-circuit, the current limiting

circuitry detects this condition and limits the peak input

current to a safe level.

g_m

2 • π •C_VC

f_UG

=

3454f

10

LTC3454

U

W U U

APPLICATIO S I FOR ATIO

V

IN

V

OUT

IN

ENx

LTC3454

I

SETx

LED

SETx

LED

0.8V – V

DAC

I

= 3850

I

= 3850 • IDAC

LED

0.8V

R

≥ R

R

SET

MIN

SET

IDAC ≤

R

MIN

VOLTAGE

DAC

CURRENT

DAC

V

DAC

(3a)

(3b)

V

IN

V

OUT

IN

ENx

LTC3454

I

SETx

LED

SETx

LED

0.8V

+ R

0.8V – V

PWM

R

SET

R

100

R

SET

MIN

POT

I

= 3850

I

= 3850

R

≥ R

MIN

LED

SET

R

MIN

POT

V

PWM

0.8V – (DC% • V

)

R

DVCC

R

SET

DV

CC

f

≥ 10kHz

PWM

(3c)

(3d)

3454 F03

Figure 3. Brightness control Methods: (a) Using Voltage DAC, (b) Using Current DAC, (c) Using Potentiometer, (d) Using PWM Input

U

PACKAGE DESCRIPTIO

DD Package

10-Lead Plastic DFN (3mm × 3mm)

(Reference LTC DWG # 05-08-1699)

R = 0.115

0.38 0.10

TYP

6

10

0.675 0.05

3.50 0.05

2.15 0.05 (2 SIDES)

1.65 0.05

3.00 0.10

(4 SIDES)

1.65 0.10

(2 SIDES)

PIN 1

TOP MARK

(SEE NOTE 6)

PACKAGE

OUTLINE

(DD10) DFN 1103

5

1

0.25 0.05

0.50 BSC

0.75 0.05

0.200 REF

0.25 0.05

0.50

BSC

2.38 0.10

(2 SIDES)

2.38 0.05

(2 SIDES)

0.00 – 0.05

BOTTOM VIEW—EXPOSED PAD

RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS

NOTE:

1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2).

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

CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 5. EXPOSED PAD SHALL BE SOLDER PLATED

2. DRAWING NOT TO SCALE

3. ALL DIMENSIONS ARE IN MILLIMETERS

6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE

TOP AND BOTTOM OF PACKAGE

3454f

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 represen-

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

11

LTC3454

U

TYPICAL APPLICATIO

500mA LED Flashlight Driver

L1

4.7 H

LED Power Efﬁciency vs V

IN

100

95

90

85

80

75

70

65

60

I

= 500mA

LED

V

SW1

SW2

SWD

V

OUT

2.2 F

4.7 F

LED

IN

3-CELL

ALKALINE

4.5V

SWA

SWB

EN1

LED

EN2

SWC

1MHz

BUCK-BOOST

I

= 500mA

V

C

I

LED

A

SET1

T

= 25°C

R

6.19k

1%

I

ISET1

0.1 F

EFFICIENCY = (V

– V )I /V

I

SET2

OUT

LED LED IN IN

LTC3454

4.3 4.7

(V)

2.7 3.1 3.5 3.9

5.1 5.5

GND (EXPOSED PAD)

3453 TA02

V

IN

3454 TA02b

LED: LUMILEDS, LXCL LW3C

L1: TOKO A997AS-4R7M

RELATED PARTS

PART NUMBER

DESCRIPTION

COMMENTS

V : 1.6V to 18V, V

MS10 Package/EDD Package

LT1618

Constant Current, Constant Voltage 1.4MHz, High Efﬁciency

Boost Regulator

= 34V, I = 1.8mA, I = <1µA,

OUT(MAX) Q SD

IN

LT1930/LT1930A 1A (I ), 1.2MHz/2.2MHz, High Efﬁciency Step-Up

V : 2.6V to 16V, V

ThinSOT Package

= 34V, I = 4.2mA/5.5mA, I = <1µA,

OUT(MAX) Q SD

SW

IN

DC/DC Converter

LT1932

Constant Current, 1.2MHz, High Efﬁciency White LED

Boost Regulator

V : 1V to 10V, V

ThinSOT Package

= 34V, I = 1.2mA, I = <1µA,

OUT(MAX) Q SD

IN

LT1937

Constant Current, 1.2MHz, High Efﬁciency White LED

Boost Regulator

V : 2.5V to 10V, V

ThinSOT Package/SC70 Package

= 34V, I = 1.9mA, I = <1µA,

OUT(MAX) Q SD

IN

LTC3205

LTC3215

LTC3216

High Efﬁciency, Multi-Display LED Controller

V : 2.8V to 4.5V, V

QFN-24 Package

= 6V, I = 50µA, I = <1µA,

Q SD

IN

OUT(MAX)

700mA Low Noise Charge Pump LED Driver

V : 2.9V to 4.4V, V

= 5.5V, I = 300µA, I = <2.5µA,

Q SD

IN

DFN Package

1A Low Noise High Current Charge Pump LED

Driver with Independent Flash/Torch Current

V : 2.9V to 4.4V, V

= 5.5V, I = 300µA, I = <2.5µA,

Q SD

IN

DFN Package

LTC3440/

LTC3441

600mA/1.2A I , 2MHz/1MHz, Synchronous Buck-Boost

V : 2.4V to 5.5V, V

= 5.25V, I = 25µA/50µA, I = <1µA,

Q SD

OUT

IN

DC/DC Converter

MS-10 Package/DFN Package

LTC3443

LTC3490

LTC3453

600mA/1.2A I , 600kHz, Synchronous Buck-Boost

DC/DC Converter

V : 2.4V to 5.5V, V

DFN Package

= 5.25V, I = 28µA, I = <1µA,

OUT(MAX) Q SD

OUT

IN

Single Cell 350mA LED Driver

V : 1V to 3.2V, V

IN

= 4V, I = 20µA, I = 20µA,

OUT(MAX) Q SD

DFN Package

Synchronous Buck-Boost High Power White LED Driver

V : 2.7V to 5.5V, Up to 500mA Continuous Output Current,

IN

QFN-16 Package

LT3465/LT3465A Constant Current, 1.2MHz/2.7MHz, High Efﬁciency White LED

Boost Regulator with Integrated Schottky Diode

V : 2.7V to 16V, V

ThinSOT Package

= 34V, I = 1.9mA, I = <1µA,

Q SD

IN

OUT(MAX)

LT3466

Dual Constant Current, 2MHz, High Efﬁciency White LED

Boost Regulator with Integrated Schottky Diode

V : 2.7V to 24V, V

= 40V, I = 5mA, I = <16µA,

Q SD

IN

DFN Package

LT3479

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

Inrush Current Protection

V : 2.5V to 24V, V

= 40V, I = 6.5mA, I = <1µA,

Q SD

IN

DFN Package/TSOPP Package

3454f

LT 1105 • PRINTED IN USA

LinearTechnology Corporation

1630 McCarthy Blvd., Milpitas, CA 95035-7417

12

●

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


型号：	LTC3454EDD#TR
厂家：	Linear
描述：	LTC3454 - 1A Synchronous Buck-Boost High Current LED Driver; Package: DFN; Pins: 10; Temperature Range: -40°C to 85°C 驱动器
文件：	总12页 (文件大小：206K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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