UTorch and Flash Mode Efficiency95939189878583817977752.73.13.53.94.3VIN (V)4.75.15.5FLASH MODE AT 200mATA = 25°C(V – VLEDx) • ILEDxEFFICIENCY = Σ OUTVIN • IINTORCH MODE AT 100mA3452 TA01bU3452f
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LTC3452
ABSOLUTE AXI U RATI GS(Note 1)UUWPACKAGE/ORDER I FOR ATIOTOP VIEWUF PACKAGE20-LEAD (4mm × 4mm) PLASTIC QFNTJMAX = 125°C, θJA = 40°C/WEXPOSED PAD (PIN 21) IS GND, MUST BE SOLDERED TO PCBORDER PART NUMBERLTC3452EUFUF PART MARKING3452Order Options Tape and Reel: Add #TRLead Free: Add #PBF Lead Free Tape and Reel: Add #TRPBFLead Free Part Marking: http://www.linear.com/leadfree/Consult LTC Marketing for parts specified with wider operating temperature ranges.ELECTRICAL CHARACTERISTICSThe ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.VIN = PVIN = VOUT = 3.6V unless otherwise specified. (Note 2)PARAMETERInput Supply Voltage (VIN)Input DC Supply Current Normal Operation Shutdown UVLOUndervoltage Lockout ThresholdENL,H DC Threshold for Normal Operation (VIH)ENL,H DC Threshold for Shutdown (ILEDx = 0)(VIL)ENL,H Input Current (IIH, IIL)ENL PWM FrequencyISETL,H Servo VoltageLEDHx Output Current Ratio (ILEDHx/ISETH)LEDHx Output Current MatchingLEDHx Pin Voltage2.7V ≤ VIN ≤ 5.5V, RISETL = RISETH = 51.1k, ILEDx = 0 (Note 4)2.7V ≤ VIN ≤ 5.5V, VENL = VENH = 0VVIN < UVLO ThresholdVIN RisingVIN Falling2.7V ≤ VIN ≤ 5.5V, VENL,H Rising2.7V ≤ VIN ≤ 5.5V, VENL,H Falling2.7V ≤ VIN ≤ 5.5V2.7V ≤ VIN ≤ 5.5V (Note 5)RISETL = RISETH = 20k●●CONDITIONS●MIN2.7LEDH1LEDL3LEDL4LEDL5GNDVIN, PVIN, SW1, SW2, VOUT Voltage........... –0.3V to 6VLEDL1 to LEDL5 Voltage... –0.3V to (VOUT + 0.3V) or 6VLEDH1, LEDH2 Voltage..... –0.3V to (VOUT + 0.3V) or 6VVC, ENL, ENH,ISETL, ISETH Voltage............ –0.3V to (VIN + 0.3V) or 6VLEDL1 to LEDL5 Current....................................... 50mALEDH1, LEDH2 Current....................................... 250mAOperating Temperature Range (Note 2)..–40°C to 85°CJunction Temperature (Note 3)............................ 125°CStorage Temperature Range................ –65°C to 125°CPGND2019181716VIN1ENL2ISETL3LEDL14LEDL256789102115VC14ENH13ISETH12LEDH211GNDVOUTSW1SW2PVINILEDHx = 100mA, VLEDHx = 300mV●(Max – Min)/[(Max + Min)/2] • 100%, ILEDHx = 100mA,VLEDHx = 300mV, 2.7V ≤ VIN ≤ 5.5VILEDHx = 100mAhttp://oneic.com/
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UWWWTYPMAX5.5UNITSVmAµAµAVVVV0.66.531.6●●●●11852.31.22.01.870.540.520.2–110788780730714180080076876812508128128068066µAkHzmVmVmA/mAmA/mA%mV3452f
LTC3452
ELECTRICAL CHARACTERISTICSThe ● denotes specifications which apply over the full operating temperature range, otherwise specifications are TA = 25°C.VIN = PVIN = VOUT = 3.6V unless otherwise specified. (Note 2)PARAMETERLEDLx Output Current Ratio (ILEDLx/ISETL)(Note 6)CONDITIONSILEDLx|MAX = 20mA, VLEDLx = 300mVPWM Duty Cycle = 6%●MIN1.81.753.663.567.327.1214.7214.3229.4428.6458.8857.92TYP2244881616323264641281282562452.5130MAX2.162.214.284.388.568.7617.0417.4433.9234.5667.268.16134.4137.6268.8272.648UNITSmA/mAmA/mAmA/mAmA/mAmA/mAmA/mAmA/mAmA/mAmA/mAmA/mAmA/mAmA/mAmA/mAmA/mAmA/mAmA/mA%mVPWM Duty Cycle = 19%●PWM Duty Cycle = 31%●PWM Duty Cycle = 44%●PWM Duty Cycle = 56%●PWM Duty Cycle = 69%●PWM Duty Cycle = 81%PWM Duty Cycle = 94%LEDLx Output Current MatchingLEDLx Pin VoltageRegulated Maximum VOUTPMOS Switch RONNMOS Switch RONForward Current LimitReverse Current LimitPMOS Switch LeakageNMOS Switch LeakageOscillator FrequencySoft-Start TimeNote 1: 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 lifetime.Note 2: The LTC3452E is guaranteed to meet specifications from 0°C to70°C. Specifications over the –40°C to 85°C operating temperature rangeare assured by design, characterization and correlation with statisticalprocess controls.(Max – Min)/[(Max + Min)/2] • 100%, ILEDLx = 20mA,VLEDLx = 300mVILEDLx = 20mAVLEDLx = VLEDHy = 0VSwitches A and D at 100mASwitches B and C at 100mASwitch ASwitch DSwitches A and DSwitches B and C117.12●114.56234.24●229.12●4.354.52102054.75VmΩmΩ1000–1–10.91600200240011mAmAµAµAMHzµs16501.1Note 3: TJ is calculated from the ambient temperature TA and powerdissipation PD according to the following formula:TJ = TA + (PD • θJA°C/W).Note 4: Dynamic supply current is higher due to the gate charge beingdelivered at the switching frequency.Note 5: Do not exceed 50kHz PWM frequency in the application.Note 6: This parameter is tested in a setup which forces conditionsequivalent to those programmed by the indicated duty cycle.3452f
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LTC3452
TYPICAL PERFOR A CE CHARACTERISTICS Shutdown Current vs Temperature2018SHUTDOWN CURRENT (µA)SHUTDOWN CURRENT (µA)1210864202.7161412108642VIN = 2.7VVIN = 3.6VVIN = 5.5VVIN = 4.2VUVLO THRESHOLD (V)0–55–35–15525456585105125TEMPERATURE (°C)3452 G01Enable Thresholds vs Temperature120011001000VIN = 3.6V900ENABLE THRESHOLDS (mV)ENABLE THRESHOLDS (mV)1000900800700600500400300200–55–35–15525456585105125TEMPERATURE (°C)3452 G04VISETL,H (mV)VIHVILISETL,H Servo Voltage vs VIN812808804TA = 25°C4.604.584.564.54VISETL,H (mV)VOUT (V)8007967927887847802.73.13.53.94.3VIN (V)4.75.15.5http://oneic.com/4
UWShutdown Current vs VINTA = 25°C2.5Undervoltage Lockout Thresholdvs Temperature2.32.1VIN RISING1.9VIN FALLING1.73.13.53.94.3VIN (V)4.75.15.51.5–55–35–15525456585105125TEMPERATURE (°C)3452 G033452 G02Enable Thresholds vs VINTA = 25°CISETL,H Servo Voltagevs Temperature812808804800796792788784VIN = 3.6VRISETL = 10.2kRISETH = 4.99k8007006005004003002002.73.13.53.94.3VIN (V)4.75.15.5VIHVIL780–55–35–15525456585105125TEMPERATURE (°C)3452 G063452 G05Maximum Regulated VOUTvs TemperatureVIN = 3.6V4.524.504.484.464.444.424.40–55–35–15525456585105125TEMPERATURE (°C)3452 G083452 G073452f
LTC3452
TYPICAL PERFOR A CE CHARACTERISTICS PMOS RDS(ON) vs Temperature325300275VIN = 2.7VVIN = 3.6V325300275250225200175150525456585105125TEMPERATURE (°C)3452 G10250225200175150125–55–35–15FREQUENCY (kHz)RDS(ON) (mΩ)RDS(ON) (mΩ)VIN = 5.5VVIN = 4.2VOutput Voltage Ripple(Front Page Application)VIN = 3VVOUT = 3.1VILED = 100mAhttp://oneic.com/
UWNMOS RDS(ON) vs Temperature105010401030VIN = 2.7VVIN = 3.6VVIN = 5.5VVIN = 4.2VOscillator Frequencyvs TemperatureVOUT = 3V102010101000990980970960VIN = 4.2VVIN = 5.5VVIN = 3.6VVIN = 2.7V125–55–35–15525456585105125TEMPERATURE (°C)3452 G11950–55–35–15525456585105125TEMPERATURE (°C)3452 G12
Start-Up TransientCH1, VOUT1V/DIVCH2, ILED300mA FINAL VALUECH3, ENH1V/DIV3452 G13VIN = 3.6VILEDH = 300mA3452 G143452f
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LTC3452
PI FU CTIO SVIN (Pin 1): Signal Voltage Input Supply Pin (2.7V ≤ VIN ≤5.5V). Recommended bypass capacitor to GND is 2.2µFceramic or larger. Connect to PVIN (Pin 20).ENL (Pin 2): Enable Input Pin and PWM Brightness Controlfor Low Power LED Bank. Active high. For constant IMAXLoperation, connect the ENL pin to VIN (or any voltage>1.2V). For ENL voltage <0.2V, all low power bank LEDcurrent source outputs are Hi-Z (if both ENL and ENH are<0.2V, the part is in shutdown and the input supply currentdrops to ~6µA). For brightness control between zerocurrent and IMAXL, drive the ENL pin with a PWM waveformof frequency ≥10kHz. The low power LED bank currentswill be equal to a percentage of IMAXL as given in Table 1.The ENL pin is high impedance and should not be floated.ISETL (Pin 3): Low Power LED Bank Current ProgrammingPin. A resistor to ground programs each low power bankcurrent source output maximum to ILEDLx|MAX = 256 •(0.8V/RISETL). Enabled by ENL (Pin 2). PWM brightnesscontrol also via ENL.LEDL1 to LEDL5 (Pins 4 to 8): Individual Low DropoutCurrent Source Outputs for Low Power LED Bank CurrentBiasing. Connect each low power LED between VOUT andan individual LEDLx pin. Unused LEDLx outputs should beconnected to VOUT.GND (Pins 9 and 11): Signal Ground Pins. Connecttogether and to PGND (Pin 18) and Exposed Pad ground(Pin 21).LEDH1, LEDH2 (Pins 10, 12): Individual Low DropoutCurrent Source Outputs for High Power LED Bank CurrentBiasing. Connect each high power LED between VOUT andan individual LEDHx pin. Unused LEDHx outputs should beconnected to VOUT.ISETH (Pin 13): High Power LED Bank Current Program-ming Pin. A resistor to ground programs each high powerbank current source output to ILEDHx = 768(0.8V/RISETH).Enabled by ENH (Pin 14).ENH (Pin 14): Enable Input Pin for High Power LED Bank.Active high. The ENH pin is high impedance and should notbe floated.VC (Pin 15): Compensation Point for the Internal ErrorAmplifier Output. Recommended compensation capacitorto GND is 0.1µF ceramic or larger.VOUT (Pin 16): Buck-Boost Output Pin. Recommendedbypass capacitor to GND is 4.7µF ceramic.SW2 (Pin 17): Switching Node Pin. Connected to internalpower switches C and D. External inductor connectsbetween SW1 and SW2. Recommended value is 4.7µH.PGND (Pin 18): Power Ground Pin. Connect to GND (Pins9 and 11).SW1 (Pin 19): Switching Node Pin. Connected to internalpower switches A and B. External inductor connectsbetween SW1 and SW2. Recommended value is 4.7µH.PVIN (Pin 20): Power Voltage Input Supply Pin. Connect toVIN (Pin 1).Exposed Pad (Pin 21): Heat Sink Ground. Connect to GND(Pins 9 and 11) and solder to PCB ground for electricalcontact and rated thermal performance.http://oneic.com/
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UUU3452f
LTC3452
BLOCK DIAGRA VIN2.7V TO 5.5VVIN1PVIN20SW119SW217164UVSWITCHASWITCHBGATEDRIVERSANDANTI-CROSS-FORWARDCONDUCTIONCURRENTLIMITSWITCHDSWITCHCLEDDETECTREVERSECURRENTLIMIT6LEDDETECT5LEDL2LOWPOWERLEDBANKLEDL1VOUTVOUTUNDERVOLTAGELOCKOUTOVERTEMPERATUREPROTECTIONBANDGAPREFERENCEVC15VBIASVFB800mVISETLRISETLENL2ENH14+–LOW POWERLED CURRENTSETTING AMP3SDL800mVISETH+–HIGH POWERLED CURRENTSETTING AMPIMAXH768SDH911182113RISETHhttp://oneic.com/
WOT1.23V+1600mA+–200mALEDDETECT7LEDL3–AB PWMCOMPARATORLOGICCD PWMCOMPARATOR+–+–LEDDETECT8LEDDETECTLEDL4UV1MHzOSCILLATOROTLEDL5–+MAIN ERROR AMPSAFETY ERROR AMP1.23V–+VOUT327k123k1.23VSOFT-STARTCLAMPIMAXL256EXPONENTIALBRIGHTNESSCONTROL8 LEVELS10SDLLEDDETECTSHUTDOWNSDHLEDDETECT12LEDH2LEDH1HIGHPOWERLEDBANKSHUTDOWNCIRCUITGNDGNDPGNDEXPOSEDPAD3452 BD3452f
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LTC3452
UOPERATIOBuck-Boost DC-DC ConverterThe LTC3452 employs an LTC proprietary buck-boostDC/DC converter to generate the output voltage requiredto drive the LEDs. This architecture permits high-effi-ciency, low noise operation at input voltages above, belowor equal to the output voltage by properly phasing fourinternal power switches. The error amp output voltage onthe VC pin determines the duty cycle of the switches. Sincethe VC pin is a filtered signal, it provides rejection offrequencies well below the factory trimmed switchingfrequency of 1MHz. The low RDS(ON), low gate chargesynchronous switches provide high frequency pulse widthmodulation control at high efficiency. Schottky diodesacross synchronous rectifier switch B and synchronousrectifier switch D are not required, but if used, do providea lower voltage drop during the break-before-make time(typically 20ns), which improves peak efficiency by typi-cally 1% to 2% at higher loads.Figure 1 shows a simplified diagram of how the fourinternal power switches are connected to the inductor, VIN= PVIN, VOUT and GND. Figure 2 shows the regions ofoperation of the buck-boost as a function of the controlvoltage VC. The output switches are properly phased sotransitions between regions of operation are continuous,filtered and transparent to the user. When VIN approachesVOUT, the buck-boost region is reached where the conduc-tion time of the four switch region is typically 150ns.Referring to Figures 1 and 2, the various regions ofoperation encountered as VC increases will now bedescribed.Buck Mode (VIN > VOUT)In buck mode, switch D is always on and switch C is alwaysoff. Referring to Figure 2, when the control voltage VC isabove voltage V1, switch A begins to turn on each cycle.During the off time of switch A, synchronous rectifierswitch B turns on for the remainder of the cycle. SwitchesA and B will alternate conducting similar to a typicalsynchronous buck regulator. As the control voltage in-creases, the duty cycle of switch A increases until themaximum duty cycle of the converter in buck modereaches DCBUCK|max given by:DCBUCK|max = 100% – DC4SWwhere DC4SW equals the duty cycle in % of the “fourswitch” range.DC4SW = (150ns • f) • 100%where f is the operating frequency in Hz.Beyond this point the “four switch” or buck-boost regionis reached.Buck-Boost or Four-Switch Mode (VIN ≈ VOUT)Referring to Figure 2, when the control voltage VC is abovevoltage V2, switch pair AD continue to operate for dutycycle DCBUCK|max, and the switch pair AC begins to phasein. As switch pair AC phases in, switch pair BD phases outaccordingly. When the VC voltage reaches the edge of thebuck-boost range at voltage V3, switch pair AC completelyphases out switch pair BD and the boost region begins at75%DMAXBOOSTPVIN20PMOS ASW119NMOS BSW217NMOS CVOUT16PMOS DV4 (≈2.1V)A ON, B OFFBOOST REGIONPWM CD SWITCHESDMINBOOSTDMAXBUCKFOUR SWITCH PWMV3 (≈1.65V)BUCK/BOOST REGIONV2 (≈1.55V)D ON, C OFFPWM AB SWITCHESBUCK REGION0%DUTYCYCLEV1 (≈0.9V)CONTROLVOLTAGE, VC3452 F013452 F02Figure 1. Simplified Diagram of Internal Power SwitchesFigure 2. Switch Control vs Control Voltage, VC3452f
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LTC3452
UOPERATIOduty cycle DC4SW. The input voltage VIN where the fourswitch region begins is given by:Overtemperature ProtectionIf the junction temperature of the LTC3452 exceeds 130°Cfor any reason, all four switches are shut off immediately.The overtemperature protection circuit has a typical hys-teresis of 11°C.Soft-StartThe LTC3452 includes an internally fixed soft-start whichis active when powering up or coming out of shutdown.The soft-start works by clamping the voltage on the VCnode and gradually releasing it such that it requires 650µsto linearly slew from 0.9V to 2.1V. This has the effect oflimiting the rate of duty cycle change as VC transitionsfrom the buck region through the buck-boost region intothe boost region. Once the soft-start times out, it can onlybe reset by entering shutdown, or by an undervoltage orovertemperature condition.Main Error AmpThe main error amplifier is a transconductance amplifierwith source and sink capability. The output of the mainerror amplifier drives a capacitor to GND at the VC pin. Thiscapacitor sets the dominant pole for the regulation loop.(See the Applications Information section for selecting thecapacitor value.) The error amp gets its feedback signalfrom a proprietary circuit which monitors all 7 LED currentsources to determine which LED to close the regulationloop on.Safety Error AmpThe safety error amplifier is a transconductance amplifierwith sink only capability. In normal operation, it has noeffect on the loop regulation. However, if any of the LEDpins open-circuits, the output voltage will keep rising, andsafety error amp will eventually take over control of theregulation loop to prevent VOUT runaway. The VOUT thresh-old at which this occurs is approximately 4.5V.VIN=VOUT1–(150ns•f)and the input voltage VIN where the four switch regionends is given by: VIN=VOUT•1–(150ns•f)Boost Mode (VIN < VOUT)In boost mode, switch A is always on and switch B isalways off. Referring to Figure 2, when the control voltageVC is above voltage V3, switches C and D will alternateconducting similar to a typical synchronous boost regula-tor. The maximum duty cycle of the converter is limited to88% typical and is reached when VC is above V4.Forward Current LimitIf the current delivered from VIN through PMOS switch Aexceeds 1600mA (typical), switch A is shut off immedi-ately. Switches B and D are turned on for the remainder ofthe cycle in order to safely discharge the forward inductorcurrent at the maximum rate possible.Reverse Current LimitIf the current delivered from VOUT backwards throughPMOS switch D exceeds 200mA (typical), switch D is shutoff immediately. Switches A and C are turned on for theremainder of the cycle in order to safely discharge thereverse inductor current at the maximum rate possible.Undervoltage LockoutTo prevent operation of the power switches at high RDS(ON),an undervoltage lockout is incorporated on the LTC3452.When the input supply voltage drops below approximately1.9V, the four power switches and all control circuitry areturned off except for the undervoltage block, which drawsonly a few microamperes.[]3452f
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LTC3452
UOPERATIOLED Current Setting AmpsThe maximum forward current per LED for all LEDs in agiven bank is programmed by a single external resistor toground at the corresponding ISETL,H pin according to thefollowing formulas:implemented results in “smoother” brightness and dim-ming control as perceived by the human eye, which islogarithmic in nature.Table 1. Low Power Bank Brightness ControlENL DUTY CYCLE (% LOGIC HIGH)0% (Logic Low)0% < Duty Cycle < 12.5%12.5% < Duty Cycle < 25%25% < Duty Cycle < 37.5%37.5% < Duty Cycle < 50%50% < Duty Cycle < 62.5%62.5% < Duty Cycle < 75%75% < Duty Cycle < 87.5%87.5% < Duty Cycle ≤ 100%LEDLx CURRENT0 (Shutdown)1/128 • IMAXL1/64 • IMAXL1/32 • IMAXL1/16 • IMAXL1/8 • IMAXL1/4 • IMAXL1/2 • IMAXLIMAXL⎛0.8⎞⎛0.8⎞IMAXL=256⎜⎟⎟,IMAXH=768⎜⎝RISETH⎠⎝RISETL⎠For operation at currents below IMAXL in the low powerbank, refer to the Exponential Brightness Control sectionand also to external circuit options given in the Applica-tions Section. For operation at currents below IMAXH in thehigh power bank, refer only to the external circuit optionsgiven in the Applications Section.Shutdown CircuitThe shutdown circuit monitors the voltages at the ENL,Hpins. Logic high on either/both inputs enables the part andlogic low on both puts the part in shutdown. Since the ENLpin doubles as a PWM input for LED brightness control, anoutput filter in the shutdown circuit is employed to preventthe part from toggling in and out of shutdown for normalPWMing of the ENL input when ENH is low. If ENH is low,the LTC3452 is enabled immediately after a rising edge atthe ENL pin, but waits 200µs (typical) after a falling edgeto enter shutdown. Consequently, a minimum PWM fre-quency is required for smooth brightness control at cur-rents below IMAXL. The recommended PWM frequency is10kHz to 50kHz.Exponential Brightness Control(Low Power LED Bank Only)The LTC3452 implements an exponential brightness con-trol function for the low power LED bank only in which theLEDLx current is a function of the PWM duty cycle at theENL pin. The LED current will be equal to a fraction ofIMAXL as given in Table 1. As the duty cycle (that the PWMwaveform is logic high) increases linearly, the LED cur-rent will increase exponentially from 1/128th IMAXL to128/128ths IMAXL in seven binary steps. The functionLED Current SourcesEach LED pin is driven by a current source specificallydesigned for low dropout. The LTC3452 employs a propri-etary architecture that determines which of the sevenLEDs requires the largest forward voltage drop at itsprogrammed current, and then generates a feedbackvoltage based on this one for closing the buck-boostregulation loop. This results in the lowest output voltagerequired for regulating all of the LEDs and thus the highestLED power efficiency. The voltage present at the LED pinof the “controlling LED” will be typically 130mV at 20mA(low power bank) or 250mA at 100mA (high power bank)of current.LED Detect CircuitIf fewer than five LED outputs in the low power bank and/or fewer than two LED outputs in the high power bank arerequired, unused outputs should be connected to VOUT.Each LED pin has an internal LED detect circuit thatdisables the output current source to save power if anoutput is not needed. A small current is employed to detectthe presence of an LED at startup. This current is typically10µA for the low power bank and 30µA for the high powerbank.3452f
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LINEAR-TECHNOLOGYLTC3452EUF#PBF
LTC3452EUF#TRPBF
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