LTC3205EUF资料

LTC3205MultidisplayLED ControllerFEATURESssDESCRIPTIOssssssssssStep-Up/Step-Down Fractional Charge Pump for Upto 92% EfficiencyIndependent Current and Dimming Control for1-4 LED Main, 1-2 LED Sub and RGB LED DisplaysLED Currents Programmable Using 3-Wire SerialInterfaceUp to 250mA of Continuous LED Current0.7% LED Current MatchingLow Noise Constant Frequency Operation*Minimal Component CountAutomatic Soft-Start Limits Inrush CurrentFour Programmable Dimming States for Main andSub DisplaysUp to 4096 Color Combinations for RGB DisplayLow Shutdown Current: ICC < 1µATiny 24-Lead (4mm × 4mm) QFN PackageThe LTC®3205 is a highly integrated multidisplay LED con-troller. The part contains a high efficiency, low noise frac-tional step-up/step-down charge pump to provide powerfor both main and sub white LED displays plus an RGBcolor LED display. The LTC3205 requires only four smallceramic capacitors plus two resistors to form a complete3-display LED power supply and current controller.Maximum currents for the main/sub and RGB displays areset independently with a single resistor. Current for eachLED is controlled with an internal current source. Dim-ming and ON/OFF control for all displays are achieved viaa 3-wire serial interface. Four dimming states exist for themain and sub displays and 16 dimming states are availablevia internal PWM for the red, green and blue LEDs result-ing in up to 4096 color combinations.The LTC3205 charge pump optimizes efficiency based onVIN and LED forward voltage conditions. The part powersup in step-down mode and automatically switches to step-up mode once any enabled LED current source begins toenter dropout. Internal circuitry prevents inrush current andexcess input noise during start-up and mode switching.The LTC3205 is available in a low profile 24-lead(4mm × 4mm × 0.8mm) QFN package.UAPPLICATIOSsssCellular PhonesWireless PDAsMultidisplay Handheld Devices, LTC and LT are registered trademarks of Linear Technology Corporation.* U.S. Patent 6,411,531TYPICAL APPLICATIO1µFVIN2.8V TO4.5V1µF1µF1µFLTC3205MAIN1-4SUB1-24233205 TA01aEFFICIENCY (PLED/PIN) (%)VINCPOMAIN DISPLAYSUB DISPLAYRGB ILLUMINATORREDGREENBLUESERIALINTERFACE3RGBSERIAL PORTIMSIRGBU4-LED Main Panel Efficiencyvs Input Voltage100908070605040302010FOUR LEDs AT 15mA/LED(TYP VF AT 15mA = 3.2V)TA = 25°C3.33.63.9INPUT VOLTAGE (V)4.203.0 3205 TA01b U3205f1

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LTC3205ABSOLUTE AXIU RATIGS(Note 1)WUPACKAGE/ORDER IFORATIOTOP VIEWGREENMAIN3MAIN4SUB1SUB2BLUEUSTEPUPENRGBVIN, DVCC, CPO to GND............................. –0.3V TO 6VDIN, SCLK, LD, STEPUP,ENRGB...................................... –0.3V to (DVCC + 0.3V)ICPO (Note 4)...................................................... 250mAIMAIN1-4, ISUB1,2 (Note 4)..................................... 50mAIRED,GREEN,BLUE (Note 4).....................................100mAIMS, IRGB (Note 4).................................................. 1mACPO Short-Circuit Duration............................ IndefiniteOperating Temperature Range (Note 2)..–40°C to 85°CStorage Temperature Range.................–65°C to 125°CSCLKLDDVCCDINThe q denotes the specifications which apply over the full operatingtemperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, DVCC = 1.8V unless otherwise noted.SYMBOLPARAMETERInput Power SupplyVIN Operating VoltageDVCC Operating VoltageIVIN Operating CurrentIDVCC Operating CurrentVIN Shutdown CurrentDVCC Shutdown CurrentWhite LED Current (MAIN1-MAIN4, SUB1, SUB2)IMS Servo VoltageFull-Scale LED Current Ratio (ILED/IMS)Half-Scale LED Current Ratio (ILED/IMS)LED Current MatchingRGB LED Current (RED, GREEN, BLUE)IRGB Servo VoltageLED Current Ratio (ILED/IRGB)RGB PWM FrequencyRGB LED Switching FrequencyRGB PWM (Duty Factor) Range0/153.515/15kHz%3205fELECTRICAL CHARACTERISTICSCONDITIONSqqICPO, IMS, IIRGB = 0µA, Step-Down ModeICPO = 0µA, Step-Up ModeSerial Port Idle25µA < IMS < 75µAqMAIN1-MAIN4, SUB1, SUB2 Voltage = 1VMAIN1-MAIN4, SUB1, SUB2 Voltage = 1VAny Two MAIN or SUB Outputs25µA < IRGB < 75µAQuarter-Scale LED Current Ratio (ILED/IMS)MAIN1-MAIN4, SUB1, SUB2 Voltage = 1VRED, GREEN, BLUE Voltage = 1V2

UWWWORDER PARTNUMBER18RED17SGND16VIN15CPO14IMS13IRGB242322212019MAIN21MAIN12C2–C1+C2+LTC3205EUF35678C1–4259101112UF PARTMARKING3205UF PACKAGE24-LEAD (4mm × 4mm) PLASTIC QFNTJMAX = 150°C, θJA = 37°C/W, θJC = 2°C/WEXPOSED PAD IS PGND (PIN 25)MUST BE SOLDERED TO PCBConsult LTC Marketing for parts specified with wider operating temperature ranges.MIN2.81.5TYPMAX4.55.5UNITSVVµAmA704.21111.1931.175368184921.2231.2234002001000.71.1931.1753601.2231.2234001.2531.2714401.2531.271432216108µAµAµAVVmA/mAmA/mAmA/mA%VVmA/mAqqqq元器件交易网www.cecb2b.com

LTC3205The q denotes the specifications which apply over the full operatingtemperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, DVCC = 1.8V unless otherwise noted.SYMBOLPARAMETERCharge Pump (CPO)1:1 Mode Output Impedance2:3 Mode Output ImpedanceCPO Regulation VoltageCLK FrequencyDIN, SCLK, LD, STEPUP, ENRGBVILVIHIIHIILtDStDHtLtHtLWtCLtLCLow Level Input VoltageHigh Level Input VoltageInput CurrentInput CurrentDIN Valid to SCLK SetupDIN Valid to SCLK HoldSCLK Low TimeSCLK High TimeLD Pulse WidthSCLK to LDLD to SCLKDIN, SCLK, LD, STEPUP, ENRGB = DVCCDIN, SCLK, LD, STEPUP, ENRGB = 0Vqq0.85 • DVCCqqELECTRICAL CHARACTERISTICSCONDITIONSMINTYP0.8MAXUNITSΩΩVVIN = 3V, VCPO = 4.2V (Note 3)ICPO = 20mA, 2:3 Mode0.62.54.70.81.10.15 • DVCC–1–1353535353535011MHzVVµAµAnsnsnsnsnsnsnsSerial Port TimingNote 1: Absolute Maximum Ratings are those values beyond which the lifeof a device may be impaired.Note 2: The LTC3205E is guaranteed to meet performance specificationsfrom 0°C to 70°C. Specifications over the –40°C to 85°C operatingtemperature range are assured by design, characterization and correlationwith statistical process controls.Note 3: 2:3 mode output impedance is defined as (1.5VIN – VCPO)/ICPO.Note 4: Based on long term current density limitations.TYPICAL PERFOR A CE CHARACTERISTICS LED Pin Sink Currentvs LED Pin VoltageVINAC COUPLED(20mV/DIV)VOUTAC COUPLED(50mV/DIV)ILED3mA/DIV(100%SETTING)EFFICIENCY (PLED/PIN) (%)0mA200mV/DIV3205 G01UWInput and OutputCharge Pump Noise1009080706050403020104-LED Main Panel Efficiencyvs Input VoltageICPO = 150mA500ns/DIVVIN = 3.6VCIN = CCPO = 0.7µF3205 G0203.0FOUR LEDs AT 15mA/LED(TYP VF AT 15mA = 3.2V)TA = 25°C3.33.63.9INPUT VOLTAGE (V)4.2 3205 TA01b 3205f3

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LTC3205TYPICAL PERFOR A CE CHARACTERISTICS 1:1 Mode Switch Resistancevs Temperature1.0ICPO = 100mAOUTPUT RESISTANCE (Ω)3.2VIN = 3.3VSWITCH RESISTANCE (Ω)0.9VIN = 3.6V0.8VIN = 3.9V2.82.62.42.2CPO VOLTAGE (V)0.70.6–40–153510TEMPERATURE (°C)2:3 Mode CPO Voltage inCurrent Limit5.04.54.09001000DVCC SHUTDOWN CURRENT (µA)CPO VOLTAGE (V)FREQUENCY (kHz)3.53.02.52.01.51.00.500VIN = 4.2VTA = 25°C100200400300LOAD CURRENT (mA)5006003205 G13VIN Shutdown Currentvs Input Voltage1.0DVCC = VINVIN SHUTDOWN CURRENT (µA)0.0SUPPLY CURRENT (µA)0.6TA = 25°CTA = –40°CTA = 85°CSUPPLY CURRENT (mA)0.40.202.73.04.23.33.63.9VIN INPUT VOLTAGE (V)4

UW603205 G043205 G092:3 Mode Charge Pump Open-Loop Output Resistance vsTemperature (3/2VIN – VCPO)/ICPO3.0VIN = 3VVCPO = 4.2VCIN = CCPO = CFLY1 = CFLY2 = 1µF2:3 Mode CPO Voltagevs Load Current4.84.74..54.44.34.24.14.03.9VIN = 3.1VVIN = 3.2VVIN = 3.3VVIN = 3.4VVIN = 3.0V050150200100LOAD CURRENT (mA)2503205 G06TA = 25°CVIN = 3.6VVIN = 3.5V852.0–40–151035TEMPERATURE (°C)60853205 G053.8Oscillator Frequencyvs VIN Voltage0.5DVCC Shutdown Currentvs DVCCVIN = DVCCTA = 25°CTA = –40°C0.40.3TA = 25°CTA = –40°CTA = 85°C800TA = 85°C7000.20.106002.73.03.33.63.9VIN VOLTAGE (V)4.24.53205 G072.73.03.33.63.9DVCC VOLTAGE (V)4.24.53205 G081:1 Mode No Load Supply Currentvs VINTA = 25°CIMS = IRGB = 0µA102:3 Mode Supply Currentvs ICPO (IIN – 3/2ICPO)VIN = 3.6V9TA = 25°C876543218070604.5502.733.33.63.9INPUT VOLTAGE (V)4.24.53205 G120010050150LOAD CURRRENT (mA)2003205 G103205f元器件交易网www.cecb2b.com

LTC3205TYPICAL PERFOR A CE CHARACTERISTICS Input Supply Voltage Required forHigher LED Currents3.93.7INPUT VOLTAGE (V)LED CURRENT (mA)TA = 25°C3.53.33.12.92.72.5IMSIRGB255075100125175200225250IMS OR IRGB CURRENT (µA)3205 G14PI FUCTIOSMAIN1-MAIN4 (Pins 2, 1, 24, 23): Current SourceOutputs for the Main Display White LEDs. The current forthe main display is controlled by the resistor on the IMSpin. The LEDs on the main display can be set to 100%,50%, 25% or 0% of full-scale programmed current undersoftware control. See Tables 1 and 2.C1+, C1–, C2+, C2– (Pins 5, 4, 6, 3): Charge Pump FlyingCapacitor Pins. A 1µF X7R or X5R ceramic capacitor should beconnected from C1+ to C1– and another from C2+ to C2–.DIN (Pin 7): Input Data for the 16-Bit Serial Port. Serial datais shifted in one bit per clock to control the LTC3205 (seeTable 1). The logic level for DIN is referenced to DVCC.SCLK (Pin 8): Clock Input for the 16-Bit Serial Port (seeFigure 3). The logic level for SCLK is referenced to DVCC.LD (Pin 9): Load Input for the 16-Bit Serial Port. Commanddata is loaded into the command latch on the falling edgeof LD (see Figure 3). The logic level for LD is referenced toDVCC.ENRGB (Pin 10): This pin is used to enable and disable thered, green and blue current sources. Once ENRGB is broughthigh, the LTC3205 illuminates the RGB display with the colorcombination that was previously programmed via the serialport. When the main and sub displays are off and ENRGB islow, the LTC3205 will be in shutdown. The logic level forENRGB is referenced to DVCC.STEPUP (Pin 11): A logic high on this pin forces theLTC3205’s charge pump to operate in 2:3 step-up mode,thereby eliminating any possibility of the device switchingfrom 1:1 mode to 2:3 mode during critical communicationperiods. The logic level for STEPUP is referenced to DVCC.DVCC (Pin 12): This pin sets the logic reference level of theLTC3205.IRGB (Pin 13): This pin controls the amount of LED currentat the RED, GREEN and BLUE LED pins. The IRGB pinservos to 1.223V when there is a resistor to ground. Thecurrent in the RED, GREEN and BLUE LEDs will be 400times the current at the IRGB pin when programmed to fullscale (see Tables 1 and 3).IMS (Pin 14): This pin controls the maximum amount ofLED current in both the main and sub LED displays. TheIMS pin servos to 1.223V when there is a resistor toground. The currents in the main and sub display LEDs willbe 100, 200 or 400 times the current at the IMS pindepending on which setting is chosen from the serial port.CPO (Pin 15): Output of the Charge Pump. This outputshould be used to power white, blue and “true” greenLEDs. Red LEDs can be powered from VIN or CPO. An X5Ror X7R low impedance (ceramic) 1µF charge storagecapacitor is required on CPO.3205fUWCompliance Voltage for HigherLED Currents120100806040200IRGB = 150µAIRGB = 100µA0mAIRGB = 50µAVIN = 3.6VTA = 25°CIRGB = 250µAIRGB = 200µAILED3mA/DIVRGB LED Turn On and OffCharacteristics5µs/DIV3205 G01100.20.40.60.8LED PIN VOLTAGE (V)1.03205 G15UUU5

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LTC3205PI FUCTIOSVIN (Pin 16): Supply Voltage for the Charge Pump. The VINpin should be connected directly to the battery and by-–passed with a 1µF X5R or X7R ceramic capacitor.SGND (Pin 17): Ground for the Control Logic. This pinshould be connected directly to a low impedance ground–plane.RED, GREEN, BLUE (Pins 18, 19, 20): Current Source+Outputs for the RGB Illuminator LEDs. The currents for–the RGB LEDs are controlled by the resistor on the IRGBpin. The RGB LEDs can independently be set to any dutycycle from 0/15 through 15/15 under software controlgiving a total of 16 shades per LED and a total of 4096++BLOCK DIAGRA6

WUUUcolors for the illuminator. See Tables 1 and 3. The RGBLEDs are modulated at 1/240 the speed of the chargepump oscillator.SUB1, SUB2 (Pins 22, 21): Current Source Outputs forthe Sub Display White LEDs. The current for the subdisplay is controlled by the resistor on the IMS pin. TheLEDs on the sub display can be set to 100%, 50%, 25% or0% of full scale under software control. See Tables 1and␣2.PGND (Pin 25, Exposed Pad): Power Ground for theCharge Pump. The exposed pad should be connecteddirectly to a low impedance ground plane.C1+5C1–4C2+6C2–3800kHzOSCILLATORVIN161:1 AND 2:3 CHARGE PUMP25PGND15CPOENABLECP2MAIN11MAIN2IMS1424MAIN323MAIN42IRGB13SGND17222SUB121SUB218REDDVCC12STEPUP11ENRGB10LD9CONTROLLOGIC22COMMAND LATCH16DIN7SCLK8SHIFT REGISTER3205 BD19GREENPWM44420BLUE3205f元器件交易网www.cecb2b.com

LTC3205UOPERATIOPower ManagementTo optimize efficiency, the power management section ofthe LTC3205 provides two methods of supplying power tothe CPO pin: 1:1 direct connect mode or 2:3 boost mode.When either the main or sub displays of the LTC3205 areenabled, the power management system connects the CPOpin directly to VIN with a low impedance switch. If the voltagesupplied at VIN is high enough to power all of the LEDs withthe programmed current, the system will remain in this“direct connect” mode providing maximum efficiency.Internal circuits monitor all MAIN and SUB current sourcesfor the onset of “dropout,” the point at which the currentsources can no longer supply programmed current. As thebattery voltage falls, the LED with the largest forward volt-age will reach the “drop out” threshold first. When any ofthe four main or two sub display LEDs reach the dropoutthreshold, the LTC3205 will switch to boost mode and au-tomatically soft-start the 2:3 boost charge pump. The con-stant frequency charge pump is designed to minimize theamount of noise generated at the VIN supply.The 2:3 step-up charge pump uses a patented constantfrequency architecture to combine the best efficiency withthe maximum available power at the lowest noise level.OUTPUT RESISTANCE (Ω)However, for a given ROL, the amount of current availablewill be directly proportional to the advantage voltage 1.5VIN– VCPO. Consider the example of driving white LEDs froma 3.1V supply. If the LED forward voltage is 3.8V and thecurrent sources require 100mV, the advantage voltage is3.1V • 1.5V – 3.8V – 0.1V or 750mV. Notice that if the inputvoltage is raised to 3.2V, the advantage voltage jumps to900mV—a 20% improvement in available strength.From Figure 1, the available current is given by:IOUT=1.5VIN–VCPOROLTypical values of ROL as a function of temperature areshown in Figure 2.ROL+CPO+–1.5VIN–3205 F01Figure 1. Equivalent Open-Loop Circuit3.23.02.82.62.42.22.0–40VIN = 3VVCPO = 4.2VCIN = CCPO = CFLY1 = CFLY2 = 1µFIf the red, green or blue LEDs are programmed to be on atany duty cycle, the charge pump runs continuously.Soft-StartTo prevent excessive inrush current and supply droopwhen switching into step-up mode, the LTC3205 employsa soft-start feature on its charge pump. The currentavailable to the CPO pin is increased linearly over a periodof 1.2ms.Charge Pump StrengthWhen the LTC3205 operates in 2:3 boost mode, thecharge pump can be modeled as a Thevenin-equivalentcircuit to determine the amount of current available fromthe effective input voltage, 1.5VIN and the effective open-loop output resistance, ROL (Figure 1).ROL is dependent on a number of factors including theswitching term, 1/(2fOSC • CFLY), internal switch resis-tances and the nonoverlap period of the switching circuit.–151035TEMPERATURE (°C)60853205 F02Figure 2. Typical ROL vs TemperatureZero Shutdown CurrentAlthough the LTC3205 is designed to have very low shut-down current, it will draw about 400nA on VIN when inshutdown. For applications that require zero shutdowncurrent, the DVCC pin can be grounded. This will reduce theVIN current to very near zero. Internal logic ensures that the3205f7

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LTC3205UOPERATIOLTC3205 is in shutdown when DVCC is grounded. Note,however, that all of the logic signals that are referenced toDVCC (DIN, SCLK, LD, ENRGB and STEPUP) will need to beat DVCC or below (i.e., ground) to keep from violating theabsolute maximum specifications on these pins.Serial PortThe microcontroller compatible serial port provides all ofthe command and control inputs for the LTC3205. Data onthe DIN input is loaded on the rising edge of SCLK. D15 isloaded first and D0 last. Once all bits have been clocked intothe shift register, the command data is loaded into thecommand register by bringing LD low. At this time, thecommand register is latched and the LTC3205 will beginto act upon the new command set. The serial port uses staticlogic registers so there is no minimum speed at which it canbe operated. Figure 3 shows the operation of the serial port.Table 1 shows the mapping of the serial port bits to theoperation of the various displays. Bits D15 and D14control the brightness of the four LEDs in the main display.Bits D13 and D12 control the brightness of the two LEDsin the sub display. The red, green and blue LEDs each havefour bits assigned giving a linear range of 16 brightnesslevels to each of the LEDs.Programming the MAIN and SUB LED CurrentsTable 2 indicates the decoding of the Main and Sub displaycontrol bits.tLCtDStDHtHThe current levels of both the main and sub displays arecontrolled by precisely mirroring a multiple of the currentat the IMS pin.The main and sub display LED currents will follow therelationship:IMAIN/SUB=N1.223VRMAIN/SUBwhere N is equal to 400, 200, 100 or 0 depending on whichcurrent setting is selected. RMAIN/SUB is the value of theresistor on the IMS pin. The scale factors are spaced pseudoexponentially to compensate for the vision perception ofthe human eye (zero is a special case needed forshutdown).The LTC3205 can power up to six white LEDs (four for themain display, two for the sub display), however, it is notnecessary to have all six in each application. Any of the fourmain or two sub LED outputs can be disabled by connect-ing the unused output to CPO.Table 2. Main and Sub Display Current LevelsD15D130011tLtCLD14D120101tLWFRACTION OFFULL-SCALECURRENT (%)02550100SCLKDINXD15D14D2D1D0XLD3205 F03Figure 3. Serial Port Timing DiagramTable 1. Serial Port MappingD15D14D13D12D11D10D9D8D7D6D5D4D3D2D1D0MAIN1-MAIN4CurrentLevel(Table 2)SUB1-SUB2CurrentLevel(Table 2)Blue LED Duty Cycle(Table 3)Green LED Duty Cycle(Table 3)Red LED Duty Cycle(Table 3)3205f8

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LTC3205UOPERATIOUnused MAIN or SUB Display LED PinsAny of the six white LED pins (MAIN1-MAIN4, SUB1 andSUB2) can cause the LTC3205 to switch from 1:1 mode to2:3 charge pump mode if they drop out. If an unused LEDpin is left unconnected or grounded, it will automaticallydrop out and force the LTC3205 into charge pump mode.To avoid this problem, unused LED pins on the MAIN andSUB displays should be connected to CPO. However, poweris not wasted in this configuration. When the LED pin voltageis within approximately 1V of CPO, its LED current is–switched off and only a small 10µA test current remains.Figure 4 shows a block diagram of each of the MAIN and+SUB LED pins. The RED, GREEN and BLUE pins do not affectthe state of the charge pump so they can be left floating orgrounded if unused.CPO~1VTable 3. RGB Duty CyclesD11D7D30000000011111111D10D6D20000111100001111D9D5D10011001100110011D8D4D00101010101010101HEXCODE01234567ABCDEFDUTYCYCLE (%)0/151/152/153/154/155/156/157/158/159/1510/1511/1512/1513/1514/1515/15–+MAIN1-MAIN4SUB1, SUB2total of 4096 colors. Table 3 indicates the decoding of thered, green and blue LEDs.ENABLEILED3205 F0410µAFigure 4. Internal MAIN and SUB Panel LED Disable CircuitRGB Illuminator DriversThe red, green and blue LEDs can be individually set tohave a duty cycle ranging from 0/15 (off) to 15/15 (full on)with 1/15 increments in between. The combination of 16possible brightness levels gives the RGB indicator LED aThe full-scale currents in the red, green and blue LEDs arecontrolled by the current at the IRGB pin in a similar mannerto those in the main and sub panels. The IRGB pin isregulated at 1.223V and the LED current is a precisemultiple of the IRGB current.The RGB display LED currents will follow the relationship:1.223VRRGBwhere RRGB is the value of the resistor on the IRGB pin.IRED,GREENBLUE=400,APPLICATIO S I FOR ATIOInterfacing to a MicrocontrollerThe serial port of the LTC3205 can be connected directlyto an MC68HC11 style microcontroller’s serial port. Themicrocontroller should be configured as the master deviceand its clock’s idle state should be set to high (MSTR = 1,CPOL = 1 and CPHA = 1 for the MC68HC11 family).Figure␣5 shows the recommended configuration anddirecton of data flow. Note that an additional I/O line isUµCONTROLLERMOSISCKGPIOLTC3205DINSCLKLD3205 F05WUUFigure 5. Microcontroller Interface3205f9

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LTC3205APPLICATIO S I FOR ATIOnecessary for LD to load the data once it has shifted intothe device. Command data is latched into the commandregister on the falling edge of the LD signal. The LTC3205will begin to act on new command data as soon as LD goeslow. Any general purpose microcontroller I/O line can beconfigured to control the LD pin if the microcontrollerdoesn’t provide this feature automatically.VIN, CPO Capacitor SelectionThe style and value of capacitors used with the LTC3205determine several important parameters such as regulatorcontrol-loop stability, output ripple and charge pumpstrength. To reduce noise and ripple, it is recommendedthat low equivalent series resistance (ESR) multilayerceramic capacitors be used on both VIN and CPO. Tanta-lum and aluminum capacitors are not recommended be-cause of their high ESR. The value of the capacitor on CPOdirectly controls the amount of output ripple for a givenload current. Increasing the size of this capacitor willreduce the output ripple. The peak-to-peak output ripple isapproximately given by the expression:VRIPPLEP-PIOUT≅3fOSC•COUTwhere fOSC is the LTC3205’s oscillator frequency (typically800kHz) and COUT is the output charge storage capacitoron CPO. Both the style and value of the output capacitorcan significantly affect the stability of the LTC3205. TheLTC3205 uses a linear control loop to adjust the strengthof the charge pump to match the current required at theoutput. The error signal of this loop is stored directly onthe output charge storage capacitor. The charge storagecapacitor also serves to form the dominant pole for thecontrol loop. To prevent ringing or instability, it is impor-tant for the output capacitor to maintain at least 0.6µF ofcapacitance over all conditions. Likewise, excessive ESRon the output capacitor will tend to degrade the loopstability of the LTC3205. The closed-loop output resis-tance of the LTC3205 is designed to be 0.6Ω. For a 100mAload current change, the error signal will change by about60mV. If the output capacitor has 0.6Ω or more of ESR,the closed-loop frequency response will cease to roll off ina simple one-pole fashion and poor load transient re-sponse or instability could result. Multilayer ceramic chip10

Ucapacitors typically have exceptional ESR performance.MLCCs combined with a tight board layout will yield verygood stability. As the value of COUT controls the amount ofoutput ripple, the value of CIN controls the amount of ripplepresent at the input pin (VIN). The input current to theLTC3205 will be relatively constant while the charge pumpis on either the input charging phase or the output charg-ing phase but will drop to zero during the clock nonoverlaptimes. Since the nonoverlap time is small (~25ns), thesemissing “notches” will result in only a small perturbationon the input power supply line. Note that a higher ESRcapacitor such as tantalum will have higher input noisedue to the input current change times the ESR. Therefore,ceramic capacitors are again recommended for their ex-ceptional ESR performance. Input noise can be furtherreduced by powering the LTC3205 through a very smallseries inductor as shown in Figure 6. A 10nH inductor willreject the fast current notches, thereby presenting a nearlyconstant current load to the input power supply. Foreconomy, the 10nH inductor can be fabricated on the PCboard with about 1cm (0.4\") of PC board trace.10nHVINVIN0.1µF1µFLTC3205GND3205 F06WUUFigure 6. 10nH Inductor Used for Input NoiseReduction (Approximately 1cm of Wire)Flying Capacitor SelectionWarning: A polarized capacitor such as tantalum or alumi-num should never be used for the flying capacitors sincetheir voltage can reverse upon start-up of the LTC3205.Ceramic capacitors should always be used for the flyingcapacitors.The flying capacitor controls the strength of the chargepump. In order to achieve the rated output current it isnecessary to have at least 0.7µF of capacitance for each ofthe flying capacitors. Capacitors of different materials losetheir capacitance with higher temperature and voltage atdifferent rates. For example, a ceramic capacitor made ofX7R material will retain most of its capacitance from–40°C to 85°C whereas a Z5U or Y5V style capacitor will3205f元器件交易网www.cecb2b.com

LTC3205APPLICATIO S I FOR ATIOlose considerable capacitance over that range. Z5U and Y5Vcapacitors may also have a very strong voltage coefficientcausing them to lose 60% or more of their capacitance whenthe rated voltage is applied. Therefore, when comparing dif-ferent capacitors, it is often more appropriate to comparethe amount of achievable capacitance for a given case sizerather than comparing the specified capacitance value. Forexample, over rated voltage and temperature conditions,a 1µF, 10V, Y5V ceramic capacitor in a 0603 case may notprovide any more capacitance than a 0.22µF, 10V, X7Ravailable in the same 0603 case. The capacitormanufacturer’s data sheet should be consulted to determinewhat value of capacitor is needed to ensure minimumcapacitances at all temperatures and voltages.Table 4 shows a list of ceramic capacitor manufacturersand how to contact them:Table 4. Recommended Capacitor VendorsAVXKemetMurataTaiyo YudenVishaywww.avxcorp.comwww.kemet.comwww.murata.comwww.t-yuden.comwww.vishay.comFor very light load applications, the flying capacitors maybe reduced to save space or cost. The theoretical mini-mum output resistance of a 2:3 fractional charge pump isgiven by:ROL(MIN)≡1.5VIN–VOUT1=IOUT2fOSCCFLYwhere fOSC is the switching frequency (800kHz typ) andCFLY is the value of the flying capacitors. Note that thePIN 1Figure 7. Optimum Single Layer PCB Layout3205fUcharge pump will typically be weaker than the theoreticallimit due to additional switch resistance, however for verylight load applications, the above expression can be usedas a guideline in determining a starting capacitor value.Layout Considerations and NoiseDue to its high switching frequency and the transientcurrents produced by the LTC3205, careful board layout isnecessary. A true ground plane and short connections toall capacitors will improve performance and ensure properregulation under all conditions. Figure 7 shows the recom-mended layout configuration.The flying capacitor pins C1+, C2+, C1– and C2– will havevery high edge rate waveforms. The large dv/dt on these pinscan couple energy capacitively to adjacent printed circuitboard runs. Magnetic fields can also be generated if theflying capacitors are not close to the LTC3205 (i.e., the looparea is large). To decouple capacitive energy transfer, aFaraday shield may be used. This is a grounded PC tracebetween the sensitive node and the LTC3205 pins. For a highquality AC ground, it should be returned to a solid groundplane that extends all the way to the LTC3205Power EfficiencyTo calculate the power efficiency (η) of a white LED driverchip, the LED power should be compared to the inputpower. The difference between these two number repre-sents lost power whether it is in the charge pump or thecurrent sources. Stated mathematically, the power effi-ciency is given by:WUUη≡PLEDPINGNDVINCPO3205 F0711

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LTC3205APPLICATIO S I FOR ATIOThe efficiency of the LTC3205 depends upon the mode inwhich it is operating. Recall that the LTC3205 operates asa pass switch, connecting VIN to CPO until one of the LEDson the main or sub displays drops out. This featureprovides the optimum efficiency available for a given inputvoltage and LED forward voltage. When it is operating asa switch, the efficiency is approximated by:η≡PLEDVLED•ILEDVLED=≅PINVIN•IINVINsince the input current will be very close to the LEDcurrent.At moderate to high output power, the quiescent currentof the LTC3205 is negligible and the expression above isvalid. For example, with VIN = 3.9V, IOUT = 20mA • 6 LEDsand VLED equal to 3.6V, the measured efficiency is 92.2%,which is very close to the theoretical 92.3% calculation.Once an LED drops out, the LTC3205 switches into step-up mode. Employing the fractional ratio 2:3 charge pump,the LTC3205 provides more efficiency than would beachieved with a voltage doubling charge pump.In 2:3 boost mode, the efficiency is similar to that of alinear regulator with an effective input voltage of 1.5 timesthe actual input voltage. This is because the input current120100VIN = 3.6VTA = 25°CIRGB = 250µAIRGB = 200µA806040200IRGB = 150µAIRGB = 100µAIRGB = 50µAINPUT VOLTAGE (V)LED CURRENT (mA)00.20.40.60.8LED PIN VOLTAGE (V)1.03205 F08Figure 8. Compliance Voltage Required to get HigherLED Currents12

Ufor a 2:3 fractional charge pump is approximately 1.5times the load current. In an ideal 2:3 charge pump, thepower efficiency would be given by:ηIDEAL≡PLEDVLED•ILEDV=≅LEDPINV•3I1.5VININLED2Using the RED, GREEN and BLUE Pins with HigherCurrentsThe RED, GREEN and BLUE current source pins can beused at higher current levels to provide features such as aflash or camera light. Given that the output impedance ofthe currrent source is approximately 3.3Ω when in satu-ration, more compliance voltage will be necessary tooperate the device at higher LED currents. Figure 8 showsthe current source accuracy of the RED, GREEN and BLUEpins as a function of the pin voltage for various highcurrent settings.Programming the IMS or IRGB pins for more than 75µArequires a higher supply voltage to support the extracurrent. Figure 9 shows the minimum input supply voltagerequired to support various levels of current on the IMS andIRGB pins.3.93.73.53.33.12.92.72.5IRGBIMSTA = 25°C255075100125175200225250IMS OR IRGB CURRENT (µA)3205 F09WUUFigure 9. Input Supply Voltage Required to SupportHigher Currents3205f元器件交易网www.cecb2b.com

LTC3205APPLICATIO S I FOR ATIOIf the desired input voltage range is below the data shownin Figure 9, and a precise control of the LED current isdesired, then a precision current source may be added toeither the IMS or IRGB pins as shown in Figure 10.LTC3205IMS1.8V80kIRGB1413+24.3k–10k800Ω3205 F10Figure 10. Precision Reference CurrentBrightness ControlAlthough the LTC3205 has three exponentially spacedbrightness settings for the main and sub displays, it ispossible to control the brightness by alternative means.Figure 11 shows an example of how an external voltagesource can be use to inject a current into the IMS or IRGBpins to control brightness. For example, if R1 and R2 are50k, then the LED current would range from 20mA to 0mAas VCNTRL is swept from 0V to 2.5V.Alternatively, if only digital outputs are available, thenumber of settings can be doubled from 3 to 6 by simplyconnecting VCNTRL to a digital signal. With a 1.8V logicsupply, the circuit shown in Figure 12 has LED currentsettings of 2.5mA, 5mA, 7.5mA, 10mA, 15mA and 20mA.This topology can be extended to any number of bits andcan also be applied to the RGB panel.Finally, PWM brightness control can be achieved byapplying a PWM signal to the IMS programming resistor asshown in Figure 13. The signal should range from 0V (fullon) to any voltage above 1.3V (full off).UThermal ManagementFor higher input voltages and maximum output current,there can be substantial power dissipation in the LTC3205.If the junction temperature increases above approximately160°C the thermal shutdown circuitry will automaticallydeactivate the output. To reduce the maximum junctiontemperature, a good thermal connection to the PC boardis recommended. Connecting the PGND pin (exposedcenter pad) to a ground plane and maintaining a solidground plane under the device can reduce the thermalresistance of the package and PC board considerably.VILED = 4001.223V–CNTRLR2R1||R2LTC3205IMSIRGB141324.9k3205 F11WUU()VCNTRLR2R1Figure 11. Alternative Linear Brightness ControlLTC3205IMSIRGB141324.9k71.5k38.3kVDIG0V TO 1.3VOR HIGHER3205 F12Figure 12. Alternative Digital Brightness ControlLTC3205IMSIRGB1424.9k1324.9kPWM SIGNAL0V TO 1.3V OR HIGHERBRIGHTNESS = 1 – D3205 F13Figure 13. PWM Brightness Control of the MAIN and SUB Displays3205f13

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LTC3205TYPICAL APPLICATIO SUltralow Brightness MAIN and SUB DisplaysLTC3205IMSIRGB141324.9k24.9kBRIGHT DIM3205 TA08All Charge Pump Main, Sub, RGB and Camera Light ControllerCAMERA LIGHTCPOLTC3205MAIN1MAIN2MAIN3MAIN4SUB1SUB2REDGREENBLUEIMS1412.4k41µF108C1+VINLTC3202D0FB2WHITE30Ω1D1GND5, 11WHITE30ΩWHITE30ΩWHITE30Ω3205 TA02151µF2124232221181920WHITEWHITEWHITEWHITEILED = 40mAWHITEWHITEILED = 20mAREDGREENBLUEIRGB1324.9kMAIN DISPLAYCPOLTC3205MAIN1MAIN2MAIN3MAIN4SUB1SUB2REDGREENBLUEIMS1424.9k2124232221181920WHITEWHITEWHITEWHITE15IRGB1316.6k14

U487kPWM SIGNAL0V TO 1.3V OR HIGHER50Hz TO 15kHzBRIGHTNESS = 1 – DSUB DISPLAY(DUTY CYCLE = 50%)ILLUMINATOR1µF79C1C2–1µF6+C2–3VOUTMAIN DISPLAY1µFMain, Sub and Keypad IlluminationSUB DISPLAYKEYPAD1µFWHITEWHITEBLUE39ΩBLUE39ΩBLUE39ΩBLUE39ΩBLUE39ΩBLUE39Ω3205 TA033205f元器件交易网www.cecb2b.com

LTC3205TYPICAL APPLICATIO S4-LED Main Display Plus 160mA 4-LED Camera LightMAIN DISPLAYCPOLTC3205MAIN1MAIN2MAIN3MAIN4SUB1SUB2REDGREENBLUEIRGB1312.4kIMS1424.9k2124232221181920WHITEWHITEWHITEWHITEILED = 20mAWHITEILED = 40mAWHITEWHITEWHITE151µFCAMERA LIGHTCPOLTC3205MAIN1MAIN2MAIN3MAIN4SUB1SUB2REDGREENBLUEIMS14151µF2124232221181920WHITEWHITEWHITEWHITEWHITEWHITEREDGREENBLUEWHITE39ΩWHITE39ΩFLASH11STEPUPIRGB1324.9k24.9k3205 TA06PACKAGE DESCRIPTIO4.50 ± 0.052.45 ± 0.05(4 SIDES)3.10 ± 0.050.25 ±0.050.50 BSCRECOMMENDED SOLDER PAD PITCH AND DIMENSIONSNOTE:1.DRAWING PROPOSED TO BE MADE A JEDEC PACKAGE OUTLINE MO-220 VARIATION (WGGD-X)—TO BE APPROVED2.DRAWING NOT TO SCALE3.ALL DIMENSIONS ARE IN MILLIMETERSInformation 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.UU3205 TA05Main, Sub, RGB and Camera Light ControllerMAIN DISPLAYSUB DISPLAYRGBCAMERA LIGHTUF Package24-Lead Plastic QFN (4mm × 4mm)(Reference LTC DWG # 05-08-1697)4.00 ± 0.10(4 SIDES)0.75 ± 0.05BOTTOM VIEW—EXPOSED PAD0.23 TYPR = 0.115(4 SIDES)TYP23240.38 ± 0.10122.45 ± 0.10(4-SIDES)0.70 ±0.05PIN 1TOP MARK(NOTE 6)PACKAGE OUTLINE(UF24) QFN 11030.200 REF0.00 – 0.050.25 ± 0.050.50 BSC4. 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, IF PRESENT5. EXPOSED PAD SHALL BE SOLDER PLATED6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE3205f15

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LTC3205TYPICAL APPLICATIOLi-Ion41µF1µF1µF151µFMAIN1ENRGBDVCCDINSCLKLDLTC3205MAIN2MAIN3MAIN4SUB1SUB2REDGREENBLUESGNDSTEPUPIMS17111424.9kIRGB1324.9kSi1406DH6.2kIFLASH = 100mA PER R, G, B, LEDFLASH21242322211819203205 TA0754C1+C1–1012FROMMICROCONTROLLER7RELATED PARTSPART NUMBERLT®1618LTC1911-1.5LT1932LT1937LTC3200-5LTC3201LTC3202LTC3251LTC3405/LTC3405ALTC3406/LTC3406BLTC3440LT3465/LT3465ADESCRIPTIONConstant Current, Constant Voltage, 1.4MHzHigh Efficiency Boost Regulator250mA (IOUT), 1.5MHz High EfficiencyStep-Down Charge PumpConstant Current, 1.2MHz High Efficiency WhiteLED Boost RegulatorConstant Current, 1.2MHz High Efficiency WhiteLED Boost RegulatorLow Noise, 2MHz Regulated Charge PumpWhite LED DriverLow Noise, 1.7MHz Regulated Charge PumpWhite LED DriverLow Noise, 1.5MHz Regulated Charge PumpWhite LED Driver500mA (IOUT), 1MHz to 1.6MHz Spread SpectrumStep-Down Charge Pump300mA (IOUT), 1.5MHz Synchronous Step-DownDC/DC Converter600mA (IOUT), 1.5MHz Synchronous Step-DownDC/DC Converter600mA (IOUT), 2MHz Synchronous Buck-BoostDC/DC Converter1.2MHz/2.7MHz with Internal SchottkyCOMMENTSUp to 16 White LEDs, VIN: 1.6V to 18V, VOUT(MAX): 34V, IQ: 1.8mA, ISD: ≤1µA,10-Lead MS75% Efficiency, VIN: 2.7V to 5.5V, VOUT(MIN): 1.5V/1.8V, IQ: 180µA,ISD: ≤10µA, MS8Up to 8 White LEDs, VIN: 1V to 10V, VOUT(MAX): 34V, IQ: 1.2mA, ISD: ≤1µA,ThinSOTTMUp to 4 White LEDs, VIN: 2.5V to 10V, VOUT(MAX): 34V, IQ: 1.9mA, ISD: ≤1µA,ThinSOT, SC70Up to 6 White LEDs, VIN: 2.7V to 4.5V, VOUT(MAX): 5V, IQ: 8mA, ISD: ≤1µA,ThinSOTUp to 6 White LEDs, VIN: 2.7V to 4.5V, VOUT(MAX): 5V, IQ: 6.5mA, ISD: ≤1µA,10-Lead MSUp to 8 White LEDs, VIN: 2.7V to 4.5V, VOUT(MAX): 5V, IQ: 5mA, ISD: ≤1µA,10-Lead MS85% Efficiency, VIN: 3.1V to 5.5V, VOUT(MIN): 0.9V to 1.6V, IQ: 9µA, ISD: ≤1µA,10-Lead MS95% Efficiency, VIN: 2.7V to 6V, VOUT(MIN): 0.8V, IQ: 20µA, ISD: ≤1µA,ThinSOT95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 0.6V, IQ: 20µA, ISD: ≤1µA,ThinSOT95% Efficiency, VIN: 2.5V to 5.5V, VOUT(MIN): 2.5V, IQ: 25µA, ISD: ≤1µA,10-Lead MSUp to 6 White LEDs, VIN: 12.7V to 16V, VOUT(MAX): 34V, IQ: 1.9mA, ISD: <1µA,ThinSOT3205fThinSOT is a trademark of Linear Technology Corporation.16

Linear Technology Corporation1630 McCarthy Blvd., Milpitas, CA 95035-7417

(408) 432-1900 q FAX: (408) 434-0507 q www.linear.comUUsing the RGB Display as a Camera LightL12.2µH5VINSHDNLT1930AGND6316VINCPO21SWFB38.3k310k10µFD1VRGB = 6V IRGB = 300mA TOTAL2.2µFC2+C2–WHITEWHITEWHITEWHITEWHITEWHITEILED = 20mAREDGREENBLUELT/TP 0504 1K • PRINTED IN USA

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