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SC635

Charge Pump

Flash LED Driver

Twoselectablemodes-FlashandSpotlight

200mAmaxoutput-FlashMode

Spotlightmodesetto40%ofFlashCurrent

3.0Vto5.25VInputRange

Externalpinsforcontrolofflashandspotlightmodes

forsynchronizationtoacameramoduleorgraphics

controller

Shortcircuit,over-voltage,andover-temperature

protection

Soft-startfunctionality

MicroLeadPackageMLPD-0,3mmx3mm

December2,2005

Description

Features

TypicalApplicationCircuit

TheSC635isahigh-currentchargepumpdesignedspe-

cificallyforusewithwhiteLEDsusedincameraflashap-

plications.Onlytwosmallbucketcapacitorsarerequired

todeveloptheoutputdrive,providingalowEMIsolution

comparedtoinductiveboostregulators.

TheSC635hastwomodesofoperation:Flashmodeand

Spotlightmode.InFlashmode,theSC635iscapableof

delivering 200mA to a high-intensity LED during image

capture.InSpotlightmodetheSC635outputs40%ofthe

Flashmodecurrentforgeneralpurposelightingorstatus

indication.

AnexternalresistorisconnectedinserieswiththeLEDto

setthecurrent.InFlashmode,thisresistorcandissipate

upto50mW,reducingthepowerdissipationrequirement

oftheSC635.Theflashinput(FLASH)overridesthecon-

trolinput(CTRL)tomakesuretheflashfunctionisacti-

vatedwhencalledfor.

ThethermallyefficientMLPD-10packageandceramicby-

passandbucketcapacitorsmaketheSC635ahighout-

putcurrentdriverthatrequiresminimalPCBarea.

MobileCameraPhones

DigitalCameras

PDAswithBuilt-inCameras

VBAT

SC635

VIN

C2-

C2+

C1-

C1+

VOUT

FLASH

CTRL

GND

ISET

1礔

FLASH

CTRL

1礔

white LED

RSET

10礔

TypicalApplicationCircuit

Applications

Features

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SC635

AbsoluteMaximumRatings

Exceedingthespecificationsbelowmayresultinpermanentdamagetothedeviceordevicemalfunction.Operationoutsideoftheparametersspecifiedinthe

ElectricalCharacteristicssectionisnotimplied.

Unlessotherwisespecified:TA=25癈forTYP,-40癈to+60癈forMINandMAX;

BUCKET

OUT

=1.0F(ESR<0.1);C

=10.0F;V

VIN

=3.0Vto5.25V;V

VOUT

=2.8Vto4.25V;R

SET

=0.5(0.1%).

(1)Calculatedfrompackageinstillair,mountedto3"x4.5",4layerFR4PCBwiththermalviasundertheexposedpadasperJESD51standards.

(2)TestedaccordingtoJEDECstandardJESD22-A114-B.

Parameter

Symbol

Maximum

Units

Input Supply Voltage

VIN

-0.3 to +6.5

Output Voltage

VOUT

-0.3 to +6.5

Pin Voltage - FLASH, CTRL, ISET, C1-, C2-

-0.3 to V

VIN

+ 0.3

Pin Voltage - C1+, C2+

-0.3 to V

VOUT

+ 0.3

Thermal Resistance, Junction to Ambient

(JESD51 Standard Method)

(1)

癈/W

VOUT Short Circuit Duration

Indefinite

Operating Ambient Temperature Range

-40 to +85

癈

Junction Temperature Range

-40 to +150

癈

Storage Temperature Range

STG

-60 to +150

癈

Peak IR Flow Temperature

LEAD

260

癈

ESD Protection Level

(2)

ESD

Parameter

Symbol

Conditions

Min

Typ

Max

Units

Output Current

OUT

FLASH high, R

ISET

= 1.25W

3.3V < V

VIN

< 4.2V

2.8V < V

VOUT

= 4.25V

184

200

216

FLASH low, CTRL high, R

ISET

= 1.25W

3.0V < V

VIN

< 4.5V

2.8V < V

VOUT

< 4.5V

ISET Reference Voltage

ISET

FLASH high, R

ISET

= 1.25W

3.3V < V

VIN

< 4.2V

2.8V < V

VOUT

< 4.25V

230

250

270

FLASH low, CTRL high, R

ISET

= 1.25W

3.0V < V

VIN

< 4.5V

2.8V < V

VOUT

< 4.5V

100

115

Quiescent Current

FLASH high

3.4

5.0

FLASH low, CTRL high

2.0

4.5

FLASH low, CTRL low

0.1

2.0

礎

AbsoluteMaximumRatings

ElectricalCharacteristics

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SC635

Parameter

Symbol

Conditions

Min

Typ

Max

Units

Flash Mode Start-up Time

(1)

F-SU

t = 0 when FLASH goes high to I

OUT

= 90%

of final value

Flash Mode Pulse Duration

FLASH

3.3V < V

VIN

< 4.2V

OUT

= 200mA, V

VOUT

> 2.8V

indefinite

Spotlight Mode Start-up Time

(1)

S-SU

t = 0 when CTRL goes high to I

OUT

= 90%

of final value

Oscillator Frequency

OSC

Device enabled

250

kHz

Oscillator Frequency Accuracy

OSC

-15

Short-circuit Output Current

Limit

VOUT shorted to GND

465

Input Current Limit

LIMIT

3.3V < V

VIN

< 4.2V

1.0

2.1

Over-temperature Protection

(1)

150

癈

Hysteresis

Logic Input High Threshold

FLASH, CTRL

1.5

Logic Input Low Threshold

FLASH, CTRL

0.4

Logic Input High Current

FLASH

礎

CTRL

Logic Input High Current

FLASH, CTRL

0.1

2.0

礎

ISET Ripple Voltage

(1)

ISET(P-P)

Spotlight mode - I

OUT

= 80mA

FLASH mode - I

OUT

= 200mA

100

Notes:

(1)Guaranteedbydesign-nottestedinproduction.

ElectricalCharacteristics(Cont.)

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SC635

DEVICE

PACKAGE

(1)

SC635MLTRT

(2)(1)

(1)(2)

MLPD-10 3x3

SC635EVB

Evaluation Board

Notes:

(1) Available in tape and reel only. A reel contains 3,000 devices.

(2) Available in lead-free package only. Device is WEEE and

RoHS compliant.

Pin#

Pin Name Pin Function

VIN

Input voltage.

C2-

Negative terminal of bucket capacitor 2.

GND

Ground - connect to ground plane using multiple vias.

C1-

Negative terminal of bucket capacitor 1.

FLASH

Flash mode enable pin - puts the device in active Flash mode when high and also overrides

CTRL.

ISET

Current-setting reference pin - connect to the LED cathode and the current setting resistor.

CTRL

Control input bit - used to enable and set the output current in Spotlight mode when high.

C1+

Positive terminal of bucket capacitor 1.

VOUT

Output pin.

C2+

Positive terminal of bucket capacitor 2.

Thermal

Pad

Pad for heat sinking purposes - not connected internally. Connect to ground plane using

multiple vias.

PinConfiguration

OrderingInformation

PinDescriptions

TOPVIEW

MLP10:3X310LEAD

VIN

C2-

GND

C1-

FLASH

C2+

VOUT

C1+

CTRL

ISET

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SC635

PinConfiguration

ApplicationsInformation

GeneralOperation

The SC635 is a powerful 2X charge pump designed to

driveahigh-intensitywhiteLEDwithaconstantcurrent

(Spotlightmode)orwithapulsedcurrentofhigherinten-

sity(Flashmode)usedforcameraflash.

In Flash mode the SC635 output can drive 200mA at

4.25V into an LED for an unlimited duration under all

temperatureandinputconditions.TheFLASHpinisused

totriggerthismode(activehigh).InSpotlightmodethe

SC635regulatestheoutputcurrentto40%oftheFlash

mode current setting when the CTRL pin is pulled high

andtheFLASHpinislow.NotethatFlashmodehasprior-

ityoverSpotlightmode,i.e.,theFLASHpintriggersFlash

moderegardlessofthestateoftheCTRLpin.

OutputcurrentisregulatedbyattachingtheISETpinto

thecathode(s)oftheLEDpackageandalowresistance

sense resistor (typically 1.25). The ISET pin monitors

thevoltageatthecathodeandsignalsthechargepump

toincreaseordecreasetheoutputcurrentuntiltheISET

voltage reaches the programmed setting. The resistor

valueischosentosetthecurrentthroughtheLEDbased

onthisreferencevoltage.

FlashMode

FlashmodeisenabledwhenevertheFLASHpinispulled

highandremainsactiveuntiltheFLASHpinisreleased.

ThismodehashigherprioritythanSpotlightmode,sothe

stateoftheCTRLpinisoverriddenwhenevertheFLASH

pinisactivated.WhileinFlashmodethereferencevolt-

ageontheISETpinissetto250mV.

Outputcurrentsotherthantheratedmaximumof200mA

canbesetbychangingtheR

ISET

value.InFlashmode,

IOUT=250mV/R

ISET

SpotlightMode

SpotlightmodeisenabledbysettingtheCTRLpinhigh

andkeepingtheFLASHpinlow.WheninSpotlightmode,

theSC635canmaintainaconstantcurrentindefinitelyto

driveanLEDorbankofLEDs.TheISETreferencevoltage

issetto00mVsothattheoutputcurrentismaintained

at80mAwhena1.25resistorisused.Spotlightcurrent

isalways40%offlashcurrentforanygivenvalueofR

ISET

Inspotlightmode,IOUT=100mV/R

ISET

.Theresistorval-

ueshouldnotexceed2,however,toensuretheSC635

doesnotbecomeunstablewhileinSpotlightmodedueto

theoutputcurrentbeingsettoolow.

ProtectionCircuitry

TheSC635alsoprovidesprotectioncircuitrythatprevents

thedevicefromoperatinginanunspecifiedstate.These

functions include Input Over-Voltage Protection (IOVP),

Output Over-Voltage Protection (OVP), Over-Temperature

(OT)Protection,Over-CurrentProtection(OCP),andShort-

CircuitCurrentProtection(SCCP).

Input Over-Voltage Protection

Inputover-voltageprotectionisincludedtopreventopera-

tionathighinputvoltagesthatcoulddamagethedevice.

TheIOVPcircuitsensestheinputvoltageanddetermines

whenthesupplyexceeds6V.Hysteresisisincludedinthis

circuittoavoidchatteringbetweenstates.Whenthevolt-

agerisesabovethisthreshold,thedeviceisdisabledun-

tiltheinputvoltagedropstoalevelwithinthespecified

range.

Output Over-Voltage Protection

Outputover-voltageprotectionisincludedtopreventthe

SC635fromgeneratinganoutputvoltagethatcoulddam-

ageotherdevicesconnectedtoitsuchasloadLEDsand

bypasscapacitors.Whentheoutputvoltageexceeds5.5V,

theOVPcircuitdisablesthechargepumpuntilthevoltage

decreases to a level within the acceptable range. This

circuitallowsthedevicetodriveLEDswithhighforward

voltagesatareducedlevelwithoutexceedingtheoutput

voltagelimitsspecifiedforthedevice.Note,however,that

thiseffectisaconsequenceoftheOVPcircuitandisnot

itsintendedpurpose.

Over-Temperature Protection

The over-temperature circuit helps prevent the device

from overheating and experiencing a catastrophic fail-

ure.Whenthejunctiontemperatureexceeds150癈the

deviceisdisabled.Itremainsdisableduntilthejunction

temperaturedropsbelowthisthreshold.AswiththeUVLO

andOVPcircuits,hysteresisisincludedtopreventtoggling

betweenmodes.

Over-Current Protection

When the SC635 is in 2X mode, the input current will

beapproximatelydoubletherequiredoutput.Whenthe

steady-stateloadrequiresthemaximumcurrentavailable

in2Xmode,theOCPcircuitpreventsthedevicefromover-

heatingduetoexcessivepowerdissipation.

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SC635

Short-Circuit Current Protection

Short-circuitcurrentprotectionisprovidedtolimitthecur-

rentthatcanbesourcedwhentheoutputisshortedto

ground.WhenashortcircuitforcesVOUTtodropbelow

2V,theSCCPdetectstheconditionandlimitstheoutput

current.

ResistorSelection

TheISETresistorselectioniscriticalingeneratingthecor-

rectcurrent.ThevaluecanbechosentosettheSpotlight

modecurrentortheFlashmodecurrent,butitmustbe

notedthatthetwocurrentsettingsaredependentonthe

sameresistance.Itisrecommendedthattheresistorbe

selectedtomatchthedesiredLEDcurrentforFlashmode.

ThisallowsthedesignertosettheSC635'smaximumcur-

rent and select the resistor package size necessary for

thepowerdissipationrequiredinFlashmode.Thetypical

applicationshownonpage1usesa1.25resistortoset

aflashmodecurrentof200mAandspotlightmodecur-

rentof80mA.Ahighprecisionresistorshouldbeusedto

ensurethespecifiedaccuracyforLEDcurrent.

To avoid malfunction of the charge pump, it is recom-

mendedthattheresistanceseenattheISETpinremain

constant while the device is active (Flash or Spotlight

mode). Changing the resistance value or the load cur-

rentwhilethedeviceisactivecouldcauseinstabilitythat

wouldresultinnon-compliantbehavior.

TheloadcurrentreturnpathisfromtheISETsensepoint

throughtheresistorandbacktothegroundpins.Resis-

tanceinthispathaddstothetotalresistanceandhasthe

effectofreducingtheLEDcurrentbyabout4%per0mV

ApplicationsInformation(Cont.)

ofDCdropacrossthereturncoppertraceinflashmode.

Forthisreason,itiscrucialtohavealowresistancereturn

path.Placeandgroundtheresistorascloseaspossible

tothegroundpinoftheSC635.ThetracefromtheISET

pinhasvirtuallynocurrent.TheISETtraceshouldmake

contactatthepadofthepowersenseresistortominimize

theeffectofvoltagedropbetweentheLEDcathodeand

theresistor.

CapacitorSelection

TheSC635isdesignedtouselow-ESRceramiccapaci-

torsfortheinputandoutputbypasscapacitorsaswellas

thechargepumpbucketcapacitors.Idealperformance

isachievedwhenCisexactlyequaltoC2.Itisrecom-

mendedthatX5RorX7Rceramiccapacitorsbeusedfor

bestperformance.

ThermalResistance

TheSC635packageisthermallyefficientwhenthecircuit

boardlayoutconnectsthethermalpadthoughmultiple

viastothegroundplane.Thethermalresistanceisrated

at49癈/W,andthisratingisdependentontheconnec-

tionbetweenthethermalpadandthegroundplane.A

layoutthatisdonecorrectlyshouldkeepthejunctiontem-

perature below the OT limit while operating the SC635

withinthespecifiedelectricalconditionsforIOUTandV

ISET

Apoorlayoutmayallowthejunctiontemperaturetoreach

theOTlimitwhileinFlashorSpotlightmode.Itiscritical

tomaintainadequategroundplanearoundthedeviceto

maximizeheattransferandavoidover-temperatureshut-

down.

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SC635

TypicalCharacteristics

80mASpotlightCurrent,RISET=1.25W,VOUT=2.96V

195.0

197.0

199.0

201.0

203.0

205.0

100

200

300

400

500

Pulse Duration [ms]

LED Current [mA]

VIN = 4.2V

VIN = 3.7V
VIN = 3.3V

200mAFlashDuration,RISET=1.25W,

VOUT=3.30V(start)to3.25V(LEDheated500ms)

195.0

197.0

199.0

201.0

203.0

205.0

3.3

3.45

3.6

3.75

3.9

4.05

4.2

VIN [V]

LED Current [mA]

FlashCurrentat10ms,RISET=1.25W,VOUT=3.30V

195.0

197.0

199.0

201.0

203.0

205.0

3.3

3.45

3.6

3.75

3.9

4.05

4.2

VIN [V]

LED Current [mA]

FlashCurrentat100ms,RISET=1.25W,VOUT=3.28V

195.0

197.0

199.0

201.0

203.0

205.0

3.3

3.45

3.6

3.75

3.9

4.05

4.2

VIN [V]

LED Current [mA]

FlashCurrentat500ms,RISET=1.25W,VOUT=3.25V

75.0

77.0

79.0

81.0

83.0

85.0

3.45

3.9

4.35

4.8

5.25

VIN [V]

LED Current [mA]

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SC635

SuggestedLayout

ThesensetracebetweenPin6andRisroutedaround

thegroundvias,allowingtheshortestgroundreturnpath

possible.ThesensetraceisconnectedtoRattheposi-

tiveterminalpadforthemostaccurateoutputpossible.

Thebottomcopperlayerismostlyagroundplanewithno

obstructionsbetweenthegroundvias.Thesmallerrect-

angletotheleftconnectstheinputpowertoVINpin1and

inputcapacitorC4.Thetwotracesatthelowerleftarefor

logicinputsFLASHandCTRL.Thetracetotherightisthe

ISETpin"sense"trace.Thesensetraceisroutedoutof

thepathofthereturninggroundcurrent.

LayoutGuidelines

Thefollowinglayoutissuggestedforatwo-layerdesign.

ThecapacitorsCandC2arethebucketcapacitorsand

eachconductsthefullloadcurrentofupto200mApulsed

foronehalfclockcycle.C3istheoutputdecouplingca-

pacitorplacedneartheSC635VOUTpin.C4isthein-

putdecouplingcapacitorplacedneartheSC635VINpin.

Multipleviasshouldbeusedwheneveritisnecessaryto

changelayersonnetsconnectingtopinsVIN,VOUT,GND,

C1-,C1+,C2-andC2+.ResistorR1isroutedwithavery

low resistance connection between R1 and GND pin 3.

BottomCopper

TopCopper

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SC635

MarkingInformation

635

yyww

xxxx

Top Mark

yyww = Datecode (Example = 0552)

xxxx = Semtech Lot Number

OutlineDrawing-MLPD-0

MIN

aaa
bbb

e
L

DIM

MILLIMETERS

NOM

DIMENSIONS

MAX

NOM

INCHES

MIN

MAX

.114 .118 .122 2.90 3.00 3.10

(LASER MARK)

INDICATOR

PIN 1

NOTES:

CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES).
COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS TERMINALS.

.003

.007

.042

.009

.048

.000

.031

(.008)

0.08

0.23

.011

.052

0.18

1.06

.039

.002

0.00

0.80

1.31

0.30

1.21

0.05

1.00

(0.20)

.004

0.10

0.50 BSC

.020 BSC

0.30

.012

.020

.016

0.40 0.50

aaa C

SEATING

PLANE

bxN

bbb

C A B

LxN

.074 .079 .083 1.87 2.02 2.12

协谢械泻褌褉芯薪薪褘泄 泻芯屑锌芯薪械薪褌: SC635

协谢械泻褌褉芯薪薪褘泄泻芯屑锌芯薪械薪褌: SC635