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1 1LT34913491fa Cellular Phones PDAs, Handheld Computers Digital Cameras MP3 Players GPS ReceiversLi-Ion Driver for Four White LEDsWhite led driver withIntegrated Schottky in SC70and 2mm 2mm DFN Drives Up to Six White LEDs from a 3V Supply High Side Sense Allows One Wire Current Source Internal Schottky Diode One Pin Dimming and Shutdown 27V Open LED Protection Switching Frequency 5% Reference Accuracy VIN Range: to 12V Requires Only 1 F Output Capacitor Wide 300:1 True Color PWMTM Dimming Range 8-Lead SC70 Package Low Profile 6-Lead DFN Package(2mm 2mm )EfficiencyFEATURESDESCRIPTIOUAPPLICATIO SUTYPICAL APPLICATIOUCTRLVINL110 HVIN3V TO 5 VRSENSE10 3491 TA01aLT3491 SHUTDOWN ANDDIMMING CONTROLSWCAPLEDGNDC21 FC11 FC1: TAIYO YUDEN LMK212BJ105 MDC2: TAIYO YUDEN GMK316BJ105 MLL1: MURATA LQH32CN100 The LT 3491 is a fixed frequency step-up DC/DC converterspecifically designed to drive up to six white LEDs in seriesfrom a Li-Ion cell.

2 Series connection of the LEDs providesidentical LED currents resulting in uniform brightness andeliminating the need for ballast resistors. The devicefeatures a unique high side LED current sense that enablesthe part to function as a one wire current source; oneside of the LED string can be returned to ground anywhere,allowing a simpler one wire LED connection. TraditionalLED drivers use a grounded resistor to sense LED current,requiring a 2-wire connection to the LED switching frequency allows the use of tinyinductors and capacitors.

3 A single pin performs bothshutdown and accurate LED dimming control. Few exter-nal components are needed: open-LED protection and theSchottky diode are all contained inside the tiny SC70 and2mm 2mm DFN packages. With such a high level ofintegration, the LT3491 provides a high efficiency LEDdriver solution in the smallest of CURRENT (mA)0 EFFICIENCY (%)5060203491 TA01b4051015807055654575 VIN = LEDs, LTC, LT and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective Voltage (VIN).

4 12 VSW Voltage .. 32 VCAP Voltage .. 32 VCTRL Voltage .. 12 VConsult LTC Marketing for parts specified with wider operating temperature AXI U RATI GSWWWUPACKAGE/ORDER I FOR ATIOUUW(Note 1)LT3491 ESC8 LBXQTJMAX = 125 C, JA = 270 C/ WPARAMETERCONDITIONSMINTYPMAXUNITSM inimum Operating Current Sense Voltage (VCAP VLED)VCAP = 30V 190200210mVCAP, LED Pin Bias CurrentVCAP = 16V, VLED = 16V2040 AVCAP, VLED Common Mode Minimum CurrentVCAP = 16V, VLED = 15V, CTRL = = 0V810 ASwitching Duty Cycle 8892%Switch Current Limit 260350mASwitch VCESATISW = 200mA200mVSwitch Leakage CurrentVSW = AVCTRL for Full LED CurrentVCAP = 30V to Shut Down IC50mVVCTRL to Turn On IC 100mVCTRL Pin Bias Current100nACAP Pin Overvoltage Protection 262728 VSchottky Forward DropISCHOTTKY = Leakage CurrentVR = 20V4 AThe denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25 = 3V, VCTRL = 3V.

5 Unless otherwise CHARACTERISTICSSW 1 GND 2 GND 3 GND 48 CAP7 LED6 CTRL5 VINTOP VIEWSC8 PACKAGE8-LEAD PLASTIC SC70 LED Voltage .. 32 VOperating Temperature Range (Note 2) .. 40 C to 85 CMaximum Junction Temperature .. 125 CStorage Temperature Range .. 65 C to 150 CLead Temperature (Soldering, 10sec, SC-70).. 300 CTOP VIEWCTRLLEDCAPVINGNDSWDC PACKAGE6-LEAD (2mm 2mm) PLASTIC DFN4576321 TJMAX = 125 C, JA = 102 C/W, JC = 20 C/ WEXPOSED PAD (PIN 7) SHOULD BE CONNECTED TO PCB GROUNDO rder Options Tape and Reel: Add #TRLead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBFLead Free Part Marking.

6 PART NUMBERDC PART MARKINGLT3491 EDCLCHJORDER PART NUMBERDC PART MARKING3LT34913491faTYPICAL PERFOR A CE CHARACTERISTICS UWSwitch Saturation Voltage (VCESAT)Schottky Forward Voltage DropShutdown Current (VCTRL = 0V)Sense Voltage (VCAP VLED)vs VCTRLOpen-Circuit Output ClampVoltageInput Current in Output OpenCircuitSwitching WaveformTransient Response(TA = 25 C unless otherwise specified)SWITCH CURRENT (mA)03503002502001501005001503003491 G0150100200400250350 SWITCH SATURATION VOLTAGE (mV)SCHOTTKY FORWARD DROP (mV)0 SCHOTTKY FORWARD CURRET (mA)15020025060010003491 G021005002004008003003504001200 VIN (V)0 SHUTDOWN CURRENT ( A)91215123491 G03630369 VCTRL (mV)0 SENSE VOLTAGE (mV)8012020003491 G0440050010001500240200160 VIN (V)0 OUTPUT CLAMP VOLTAGE (V)2728123491 G0526253693029 VIN (V)00 INPUT CURRENT (mA)12345636 9123491 G06 VSW10V/DIVVCAP50mV/DIVIL100mA/DIVVIN = PAGE APPLICATION CIRCUIT200ns/DIV3491 G07 VCTRL5V/DIVVCAP5V/DIVIL200mA/DIVVIN = PAGE APPLICATION CIRCUIT1ms/DIV3491 G08 Note 1.

7 Stresses beyond those listed under Absolute Maximum Ratingsmay cause permanent damage to the device. Exposure to any AbsoluteMaximum Rating condition for extended periods may affect devicereliability and 2: The LT3491E is guaranteed to meet performance specificationsfrom 0 C to 85 C. Specifications over the 40 C to 85 C operatingtemperature range are assured by design, characterization and correlationwith statistical process CHARACTERISTICS4LT34913491faQuiescent Current (VCTRL = 3V)Switching Current Limtvs Duty CycleSchottky Leakage Currentvs TemperatureOpen-Circuit Output Clamp Voltagevs TemperatureInput Current in Output Open Circuitvs TemperatureSwitching Frequencyvs TemperatureTYPICAL PERFOR A CE CHARACTERISTICS UW(TA = 25 C unless otherwise specified)Sense Voltage (VCAP VLED)

8 Vs VCTRLS ense Voltage (VCAP VLED)vs VCAPS ense Voltage (VCAP VLED)vs TemperatureVIN (V)00 QUIESCENT CURRENT (mA) 9123491 G09 DUTY CYCLE (%)300 CURRENT LIMIT (mA)50150200250704503491 G10100504080609030035040025 CTEMPERATURE ( C) 500 SCHOTTKY LEAKAGE CURRENT ( A)3691215 25025503491 G1175100VR = 10 VVR = 16 VVR = 20 VTEMPERATURE ( C) 50 2525 OUTPUT CLAMP VOLTAGE (V)2730050753491 G1226292825100125 TEMPERATURE ( C) 50 INPUT CURRENT (mA)45625753491 G1332 2505010012510 VIN = 3 VTEMPERATURE ( C) 50 FREQUENCY (MHz) (mV)00 SENSE VOLTAGE (mV)40801201602002405001000150020003491 G15 50 C25 C85 CVCAP (V)5 SENSE VOLTAGE (mV)200204253491 G16196192101520212208 TEMPERATURE ( C) 50 25192 SENSE VOLTAGE (mV)200212050753491 G17196208204251001255LT34913491fa1 + +RSW5 VINCAPQSDRIVER ++8 LED3491 F01 CTRLGNDPINS 2, 3, 476 +A = NUMBERS CORRESPOND TO THE 8-PIN SC70 PACKAGEUUUPI FU CTIO SSW (Pin 1/Pin 3): Switch Pin.

9 Minimize trace area at thispin to minimize EMI. Connect the inductor at this (Pins 2, 3, 4/Pin 2): Ground Pins. All three pinsshould be tied directly to local ground (Pin 5/Pin 1): Input Supply Pin. Must be (Pin 6/Pin 6): Dimming and Shutdown Pin. Connectthis pin below 50mV to disable the driver. As the pinvoltage is ramped from 0V to , the LED current rampsfrom 0 to ILED ( = 200mV/RSENSE). The CTRL pin must notbe left (Pin 7/Pin 5): Connection Point for the Anode of theFirst LED and the Sense Resistor.

10 The LED current can beprogrammed by :ImVRLEDSENSE=200 CAP (Pin 8/Pin 4): Output of the Driver. This pin isconnected to the cathode of internal Schottky. Connect theoutput capacitor to this pin and the sense resistor fromthis pin to the LED PAD (NA/Pin 7): The Exposed Pad should besoldered to the PCB ground to achieve the rated DIAGRA WFigure 1. Block Diagram(SC70/DFN)6LT34913491faOPERATIOUT he LT3491 uses a constant frequency, current modecontrol scheme to provide excellent line and load regula-tion.