LTC3217 600mA Low Noise Multi-LED Camera Light Charge Pumps FEATURES DESCRIPTION n Charge Pump Provides High Effi ciency with The LTC®3217 is a low noise charge pump DC/DC converter Automatic Mode Switching designed to power four high current LEDs. The LTC3217 n Multimode Operation: 1x, 1.5x, 2x requires only four small ceramic capacitors and two cur- n Four Low Dropout LED Outputs rent set resistors to form a complete LED power supply n Up to 600mA Total Output Current and current controller. n Independent Torch and Flash I and Enable Pins SET Built-in soft-start circuitry prevents excessive inrush cur- n Low Noise Constant Frequency Operation* rent during start-up and mode changes. High switching n PWM Brightness Control via the EN2 Pin frequency enables the use of small external capacitors. n Low Shutdown Current: 4μA Independent high and low current settings are programmed n Internal Soft-Start Limits Inrush Current During by two external resistors. Shutdown mode and current Start-Up and Mode Switching output levels are selected via two logic inputs. n Open/Short LED Protection n No Inductors The current through the LEDs is programmed via I SET1 n (3mm x 3mm) 16-Lead QFN Plastic Package and I . In addition, the brightness can be controlled SET2 by pulse width modulation of the EN2 pin. APPLICATIONS The charge pump optimizes effi ciency based on the volt- age across the LED current sources. The part powers up n Multi-LED Camera Light Supply for Cellphones/ in 1x mode and will automatically switch to boost mode DSCs/PDAs whenever any enabled LED current source begins to enter L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other dropout. The fi rst dropout switches the part into 1.5x trademarks are the property of their respective owners. *Protected by U.S. Patents including 6411531. mode and a subsequent dropout switches the part into 2x mode. The LTC3217 resets to 1x mode whenever the part is shut down. The LTC3217 is available in a low profile 16-lead (3mm × 3mm × 0.75mm) QFN package. TYPICAL APPLICATION C2 C3 Effi ciency vs V 2.2μF 2.2μF BAT 100 100mA 200mA 90 C1P C1MC2P C2M 400mA VBAT VBAT CPO %) 80 2.2CμF1 LTC3217 C2.42μF AOT-2015HPW-1751B /PIN) (D 7600 LED1 PLE 50 LED2 NCY ( 40 EN1 (TORCH) EN1 LED3 CIE 30 EN2 (FLASH) EN2 LED4 EFFI 20 ISET1 ISET2 GND TOTAL OUTPUT CURRENT EN1 EN2 ILED 10 PLED/PIN 19.6k 6.49k 0 0 0 (SHUTDOWN) 0 LED = 2015 HPW AOT 1% 1% 10 01 2755mmAA//LLEEDD 3 3.2 3.4 3.6 3.8 4 4.2 4.4 1 1 100mA/LED VBAT (V) 3217 TA01 3217 TA01b 3217fa 1

LTC3217 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW V , CPO to GND .........................................–0.3V to 6V ENBA1T, EN2 ......................................–0.3V to (VBAT + 0.3V) C2P VBAT C1M GND1 16 15 14 13 I (Note 2) ........................................................600mA CPO C1P 1 12 C2M I (Note 3) ...................................................150mA ILED1-4 CPO 2 11 EN2 CPO Short-Circuit Duration ..............................Indefi nite 17 EN1 3 10 ISET2 Operating Temperature Range (Note 4)....–40°C to 85°C LED1 4 9 ISET1 Storage Temperature Range ...................–65°C to 125°C 5 6 7 8 2 3 4 2 D D D D E E E N L L L G UD PACKAGE 16-LEAD (3mm (cid:115) 3mm) PLASTIC QFN TJMAX = 125°C, θJA = 68°C/W EXPOSED PAD (PIN 17) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LTC3217EUD#PBF LTC3217EUD#TRPBF LBTQ 16-Lead (3mm × 3mm) Plastic QFN –40°C to 85°C Consult LTC Marketing for parts specifi ed with wider operating temperature ranges. Consult LTC Marketing for information on non-standard lead based fi nish parts. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifi cations, go to: http://www.linear.com/tapeandreel/ ELECTRICAL CHARACTERISTICS The l denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at T = 25°C. V = 3.6V, C1 = C2 = C3 = C4 = 2.2μF, unless otherwise noted. A BAT PARAMETER CONDITIONS MIN TYP MAX UNITS V Operating Voltage ● 2.9 4.5 V BAT I Operating Current R = R = 20k, EN1 = EN2 = High VBAT ISET1 ISET2 I = 0mA, 1x Mode 1 mA CPO I = 0mA, 1.5x Mode 4 mA CPO I = 0mA, 2x Mode 6 mA CPO V Shutdown Current 4 μA BAT LED 1-4 Current LED Current Ratio (I /I ) I = 25mA to 100mA ● 370 400 430 mA/mA LED SET1/2 LED LED Dropout Voltage Mode Switch Threshold, I = 100mA 330 mV LED Mode Switching Delay EN1 Only 2.5 ms LED Current Matching Any Two Outputs, I = 100mA 1 % LED Charge Pump (CPO) 1x Mode Output Voltage I = 0mA V V CPO BAT 1.5x Mode Output Voltage I = 0mA 4.5 V CPO 2x Mode Output Voltage I = 0mA 5.05 V CPO 1x Mode Output Impedance 0.5 Ω 1.5x Mode Output Impedance V = 3.4V, V ≤ 4.6V (Note 5) 2.8 Ω BAT CPO 2x Mode Output Impedance V = 3.2V, V ≤ 5.1V (Note 5) 3.2 Ω BAT CPO CLOCK Frequency ● 0.6 0.85 1.15 MHz 3217fa 2

LTC3217 ELECTRICAL CHARACTERISTICS The l denotes the specifi cations which apply over the full operating temperature range, otherwise specifi cations are at T = 25°C. V = 3.6V, C1 = C2 = C3 = C4 = 2.2μF, unless otherwise noted. A BAT CPO Short Circuit Detection Threshold Voltage ● 0.4 1.3 V Test Current CPO = 0V, EN1 = EN2 = Low ● 10 30 mA Unused LED Detection Threshold Voltage V – LED ● 0.5 1.5 V CPO Test Current LED Tied to CPO ● 4 16 μA EN1, EN2 Low Level Input Voltage (V ) ● 0.4 V IL High Level Input Voltage (V ) ● 1.4 V IH Input Current (I ) ● 7 30 μA IH Input Current (I ) ● –1 1 μA IL Minimum PWM On-Time EN2 Only ● 50 μs Maximum PWM Off-Time EN2 to Remain Enabled, EN1 = Low ● 1 ms I , I SET1 SET2 V , I = 12.5mA ● 1.175 1.215 1.255 V ISET1 ISET2 LED1-4 I , Current Range ● 31.25 375 μA ISET1 ISET2 I , Short-Circuit Current 800 μA ISET1 ISET2 Note 1: Stresses beyond those listed under Absolute Maximum Ratings maximum conditions for durations less than 10 seconds. Maximum may cause permanent damage to the device. Exposure to any Absolute current for continuous operation is 100mA. Maximum Rating condition for extended periods may affect device Note 4: The LTC3217E is guaranteed to meet performance specifi cations reliability and lifetime. from 0°C to 85°C. Specifi cations over the –40°C to 85°C ambient Note 2: Based on charge pump long-term current density limitations. operating temperature range are assured by design, characterization and Assumes an operating duty cycle of ≤10% under absolute maximum correlation with statistical process controls. conditions for durations less than 10 seconds. Maximum current for Note 5: 1.5x mode output impedance is defi ned as (1.5V – V )/I . BAT CPO OUT continuous operation is 300mA. 2x mode output impedance is defi ned as (2V – V )/I . BAT CPO OUT Note 3: Based on LED current source long-term current density limitations. Assumes an operating duty cycle of ≤10% under absolute TYPICAL PERFORMANCE CHARACTERISTICS T = 25°C unless otherwise noted. A LED Dropout Voltage LED Pin Current vs LED Current vs LED Pin Voltage I vs R LED ISET 400 120 120 VBAT = 3.6V VBAT = 3.6V 100 100 V) AGE (m300 T (mA) 80 80 D DROPOUT VOLT120000 LED PIN CURREN 4600 I (mA)LED 4600 E L 20 20 0 0 0 10 20 30 40 50 60 70 80 90 100 0 0.2 0.4 0.6 0.8 1.0 0 5 10 15 20 25 30 35 40 45 50 LED CURRENT (mA) LED PIN VOLTAGE (V) RISET (kΩ) 3217 G01 3217 G02 3217 G03 3217fa 3

LTC3217 TYPICAL PERFORMANCE CHARACTERISTICS T = 25°C unless otherwise noted. A 1.5x Mode Charge Pump Open-Loop 2x Mode Charge Pump Open-Loop 1x Mode Switch Resistance Output Resistance vs Temperature Output Resistance vs Temperature vs Temperature (1.5V – V )/I (2V – V )/I BAT CPO CPO BAT CPO CPO 0.65 3.2 3.8 ICPO = 200mA VBAT = 3V VBAT = 3V VCPO = 4.2V VCPO = 4.8V 0.60 3.0 C2 = C3 = C4 = 2.2μF 3.6 C2 = C3 = C4 = 2.2μF Ω) Ω) Ω) CE (0.55 CE ( 2.8 CE ( 3.4 AN VBAT = 3.6V AN AN T T T S S S SI0.50 SI 2.6 SI 3.2 RE VBAT = 3.3V RE RE TCH 0.45 VBAT = 3.9V TCH 2.4 TCH 3.0 WI WI WI S S S 0.40 2.2 2.8 0.35 2.0 2.6 –40 –15 10 35 60 85 –40 –15 10 35 60 85 –40 –15 10 35 60 85 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) 3217 G04 3217 G05 3217 G06 V Shutdown Current Oscillator Frequency BAT vs V Voltage vs Supply Voltage Effi ciency vs V BAT BAT 7.5 980 100 100mA 200mA 970 90 HUTDOWN CURRENT (μA) 4563....5555 TA =T A8 5=° –C40°C TA = 25°C FREQUENCY (kHz)999999412356000000 TA = –T4A0 °=C 25°C TA = 85°C CIENCY (P/PIN) (%)LED 345786000000 400mA V SBAT2.5 900 EFFI 20 TOTAL OUTPUT CURRENT 890 10 PLED/PIN LED = 2015 HPW AOT 1.5 880 0 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 3 3.2 3.4 3.6 3.8 4 4.2 4.4 VBAT VOLTAGE (V) VBAT SUPPLY VOLTAGE (V) VBAT (V) 3217 G07 3217 G08 3217 G09 Charge Pump Mode Switching and Input Current to Ground 1.5x Mode CPO Output Ripple 2x Mode CPO Output Ripple (400mA Load) 2x 1VV/CDPIVO NO 1LxOAD 1x 1.5x (5V) VCPO VCPO IVBAT DROPOUT 50mV/DIV 20mV/DIV 500mA/DIV DROPOUT AC-COUPLED AC-COUPLED 0 EN1 5V/DIV VBAT = 3.6V 500ns/DIV 3217 G10 VBAT = 3.6V 500ns/DIV 3217 G11 VIN = 3.6V 1ms/DIV 3217 G12 ICPO = 400mA ICPO = 400mA CCPO = 2.2μF CCPO = 2.2μF 3217fa 4

LTC3217 TYPICAL PERFORMANCE CHARACTERISTICS T = 25°C unless otherwise noted. A 1.5x Mode CPO Voltage 2x Mode CPO Voltage vs Load Current vs Load Current 4.8 5.2 C2 = C3 = C4 = 2.2μF C2 = C3 = C4 = 2.2μF 5.1 4.6 5.0 3.4V 3.6V V) 4.4 3.5V V) 4.9 E ( 3.6V E ( 4.8 AG AG 3.3V LT 4.2 LT 4.7 O O 3.2V V V O 3.3V O 4.6 CP 4.0 CP 3.1V 3.2V 4.5 VBAT = 3V 4.4 3.8 3.1V 4.3 VBAT = 3V 3.6 4.2 0 100 200 300 400 500 0 100 200 300 400 500 LOAD CURRENT (mA) LOAD CURRENT (mA) 3217 G13 3217 G14 PIN FUNCTIONS C1P, C2P, C1M, C2M (Pins 1, 16, 14, 12): Charge Pump in between CPO (anodes) and LED1 – 4 (cathodes). The Flying Capacitor Pins. A 2.2μF X7R or X5R ceramic capacitor current to each LED output is set via the EN1 and EN2 should be connected from C1P to C1M and C2P to C2M. inputs, and the programming resistors connected from I and I to GND. With the LTC3217, any of the four CPO (Pin 2): Output of the charge pump used to power SET1 SET2 LED outputs can be disabled by connecting the output all LEDs. This pin is enabled or disabled using the EN1 directly to CPO. 10μA of current will fl ow through each and EN2 inputs. A 2.2μF X5R or X7R ceramic capacitor directly connected LED output. For single LED applications, should be connected to ground. all four LED pins may be tied together and will accurately EN1, EN2 (Pins 3, 11): Inputs. The EN1 and EN2 pins are share current. used to select which current level is being supplied to the GND2 (Pin 8): Analog Ground. This pin should be con- LEDs, as well as to put the part into shutdown mode. The nected directly to a low impedance ground plane. truth table for these pins is as follows: I /I (Pins 9, 10): LED Current Programming Re- SET1 SET2 Truth Table sistor Pins. The I and I pins will servo to 1.22V. SET1 SET2 EN1 EN2 MODE Resistors connected between each of these pins and 0 0 Shutdown GND are used to set the high and low LED current levels. 1 0 Low Current Connecting a resistor 2k or less will cause the LTC3217 0 1 High Current to enter overcurrent shutdown. 1 1 Low + High Current GND1 (Pin 13): Charge Pump Ground. This pin should be connected directly to a low impedance ground plane. EN2 can be used for PWM of the LED currents. For proper V (Pin 15): Supply Voltage. This pin should be bypassed operation, the minimum pulse width should be 50μs and BAT with a 2.2μF, or greater low ESR ceramic capacitor. the maximum low time should be 1ms if EN1 is low. If EN1 is high then the 1ms low time limitation does not apply. Exposed Pad (Pin 17): This pad should be connected directly to a low impedance ground plane for optimal LED1, LED2, LED3, LED4 (Pins 4, 5, 6, 7): LED1 to LED4 thermal and electrical performance. are the current source outputs. Each LED is connected 3217fa 5

LTC3217 BLOCK DIAGRAM 1 14 16 12 C1P C1M C2P C2M 850kHz OSCILLATOR GND1 VBAT 13 15 CPO 2 CHARGE PUMP – + ENABLE CP + CPO + SHORT-CIRCUIT PROTECTION – ISET1 – +– 0.8V LED1 9 4 LED2 5 LED CURRENT 4 MUX SOURCES LED3 6 ISET2 1.22V LED4 10 7 EN1 GND2 3 CONTROL LOGIC 8 250k EN2 THERMAL 11 PWM TIMING SHUTDOWN 250k 3217 BD OPERATION Power Management cause the part to enter the 2x mode. The CPO voltage will attempt to reach 2x V up to 5.05V. The LTC3217 will be The LTC3217 uses a switched capacitor charge pump to BAT reset to 1x mode whenever the part is shut down. boost CPO to as much as 2 times the input voltage up to 5.1V. The parts start up in 1x mode. In this mode, V is A two phase non-overlapping clock activates the charge BAT connected directly to CPO. This mode provides maximum pump switches. In the 2x mode the fl ying capacitors are effi ciency and minimum noise. The LTC3217 will remain in charged on alternate clock phases from V to minimize BAT 1x mode until an LED current source drops out. Dropout input current ripple and CPO voltage ripple. In 1.5x mode occurs when a current source voltage becomes too low the fl ying capacitors are charged in series during the fi rst for the programmed current to be supplied. When dropout clock phase and stacked in parallel on V during the BAT is detected, the LTC3217 will switch into 1.5x mode. The second phase. This sequence of charging and discharging CPO voltage will then start to increase and will attempt to the fl ying capacitors continues at a constant frequency reach 1.5x V up to 4.5V. Any subsequent dropout will of 850kHz. BAT 3217fa 6

LTC3217 OPERATION The LED currents are delivered by the four programmable Charge Pump Strength and Regulation current sources. Three discrete current settings (Low, High, Regulation is achieved by sensing the voltage at the CPO Low + High) are available and may be selected via the EN1 pin and modulating the charge pump strength based and EN2 pins. The values of these currents may be selected on the error signal. The CPO regulation voltages are set by choosing the appropriate programming resistors. Each internally, and are dependent on the charge pump modes resistor is connected between the I or I pin to SET1 SET2 as shown in Table 1. ground. The resistor values required to attain the desired current levels can be determined by Equation 1. When the LTC3217 operates in either 1.5x mode or 2x mode, the charge pump can be modeled as a Thevenin-equivalent 488 R = (1) circuit to determine the amount of current available from SET1/2 I LEDx the effective input voltage and effective open-loop output resistance, R (Figure 1). An R resistor value of 2k or less (i.e., short-circuit) will OL SETx cause the LTC3217 to enter overcurrent shutdown mode. Table 1. Charge Pump Output Regulation Voltages This mode prevents damage to the part and external LEDs CHARGE PUMP MODE REGULATED V CPO by shutting down the high power sections of the part. 1.5x 4.5V Each LED output can be disabled by connecting the pin 2x 5.05V directly to CPO. Do not leave pins open as this will cause dropout and subsequently mode changing. R is dependent on a number of factors including the OL switching term, 1/(2f • C ), internal switch resistances OSC FLY Pulse Width Modulation Option and the non-overlap period of the switching circuit. However, EN2 can be pulse width modulated to control the for a given ROL, the amount of current available will be directly LED brightness. The minimum allowable pulse width is proportional to the advantage voltage of 1.5VBAT – VCPO for 50μs and the maximum low time is 1ms. Pulse width 1.5x mode and 2VBAT – VCPO for 2x mode. Consider the modulating the EN2 input can be performed with EN1 high example of driving white LEDs from a 3.1V supply. If the or low. If EN1 is high then there is no limitation on the LED forward voltage is 3.8V and the current sources require EN2 low time. When EN1 is low the part would normally 100mV, the advantage voltage for 1.5x mode is 3.1V • 1.5 go into shutdown whenever EN2 goes low. Prevention – 3.8V – 0.1V or 750mV. Notice that if the input voltage is of shutdown in this case is achieved by an internal timer raised to 3.2V, the advantage voltage jumps to 900mV—a which delays shutdown until EN2 has remained low for 20% improvement in available strength. at least 1ms. From Figure 1, for 1.5x mode the available current is given by: Soft-Start 1.5V –V Initially, when the part is in shutdown, a weak switch I = BAT CPO (2) OUT R connects V to CPO. This allows V to slowly charge OL BAT BAT the CPO output capacitor and prevent large charging For 2x mode, the available current is given by: currents to occur. 2V –V The LTC3217 also employs a soft-start feature on its I = BAT CPO (3) OUT R charge pump to prevent excessive inrush current and OL supply droop when switching into the step-up modes. The Notice that the advantage voltage in this case is current available to the CPO pin is increased linearly over 3.1V • 2 – 3.8V – 0.1V = 2.3V. R is higher in 2x mode a typical period of 125μs. Soft-start occurs at the start of OL but a signifi cant overall increase in available current is both 1.5x and 2x mode changes. achieved. 3217fa 7

LTC3217 OPERATION Shutdown Current ROL + In shutdown mode all the circuitry is turned off and the +– 1.5VBAT OR 2VBAT CPO LTC3217 draws a very low current from the VBAT sup- ply. Furthermore, CPO is weakly connected to V . The BAT – LTC3217 enters shutdown mode when both the EN1 and 3217 F01 EN2 pins are brought low. EN1 and EN2 have 250k pull- down resistors to ground. Figure 1. Equivalent Open-Loop Circuit Thermal Protection V in calculating Equations 2 and 3 is the minimum re- CPO quired voltage for the LED and not the regulated voltage. The LTC3217 has built-in overtemperature protection. At internal die temperatures of around 150°C thermal Typical values of R as a function of temperature are OL shutdown will occur. This will disable all of the current shown in Figures 2 and 3. sources and charge pump until the die has cooled by about 15°C. This thermal cycling will continue until the 3.2 VBAT = 3V fault has been corrected. VCPO = 4.2V 3.0 C2 = C3 = C4 = 2.2μF Ω) CPO Short-Circuit Protection CE ( 2.8 N A The LTC3217 has internal CPO short-circuit protection. T S SI 2.6 An internal comparator senses when CPO is below 0.8V E R H which forces the part into shutdown. A pull-up device TC 2.4 WI ensures start-up. S 2.2 Mode Switching 2.0 –40 –15 10 35 60 85 The LTC3217 will automatically switch from 1x mode TEMPERATURE (°C) 3217 F02 to 1.5x mode and subsequently to 2x mode whenever a Figure 2. 1.5x Mode Charge Pump Open-Loop Output dropout condition is detected at an LED pin. Dropout oc- Resistance vs Temperature (1.5V – V )/I BAT CPO CPO curs when a current source voltage becomes too low for the programmed current to be supplied. The time from 3.8 dropout detection and mode switching is about 2.5ms. This VBAT = 3V VCPO = 4.8V delay allows for the LED to warm up and reduce its forward 3.6 C2 = C3 = C4 = 2.2μF voltage which may remove the dropout condition. Ω) NCE ( 3.4 If PWM is used on the EN2 pin, then the dropout time is A T SIS 3.2 dependent on one to two PWM clock pulses. E R H The part is reset back to 1x mode when the part is shut TC 3.0 WI down (EN1 = EN2 = Low). The part may be set to the S 2.8 desired output current level via EN1 and EN2. An internal comparator will not allow the main switches to connect 2.6 –40 –15 10 35 60 85 V and CPO in 1x mode until the voltage at the CPO BAT TEMPERATURE (°C) 3217 F03 pin has decayed to less than or equal to the voltage at Figure 3. 2x Mode Charge Pump Open-Loop Output the VBAT pin. Resistance vs Temperature (2V – V )/I BAT CPO CPO 3217fa 8

LTC3217 APPLICATIONS INFORMATION V , CPO Capacitor Selection current will be relatively constant while the charge pump BAT is either in the input charging phase or the output charging The style and value of the capacitors used with the LTC3217 phase but will drop to zero during the clock non-overlap determine several important parameters such as regulator times. Since the non-overlap time is small (~25ns), these control loop stability, output ripple, charge pump strength missing “notches” will result in only a small perturbation and minimum start-up time. on the input power supply line. Note that a higher ESR To reduce noise and ripple, it is recommended that low capacitor such as tantalum will have higher input noise equivalent series resistance (ESR) ceramic capacitors are due to the higher ESR. Therefore, ceramic capacitors are used for both CVBAT and CCPO. Tantalum and aluminum recommended for low ESR. Input noise can be further capacitors are not recommended due to high ESR. reduced by powering the LTC3217 through a very small series inductor as shown in Figure 4. A 10nH inductor The value of C directly controls the amount of output CPO will reject the fast current notches, thereby presenting a ripple for a given load current. Increasing the size of C CPO nearly constant current load to the input power supply. will reduce output ripple at the expense of higher start-up For economy, the 10nH inductor can be fabricated on the current. The peak-to-peak output ripple of the 1.5x mode PC board with about 1cm (0.4") of PC board trace. is approximately given by the expression: I I = OUT (4) RIPPLEP-P (3fOSC (cid:129)CCPO) VBAT LTC3217 Where f is the LTC3217 oscillator frequency or typically OSC 850kHz and C is the output storage capacitor. CPO GND The output ripple in 2x mode is very small due to the fact 3217 F04 that load current is supplied on both cycles of the clock. Figure 4. 10nH Inductor Used for Input Noise Reduction (Approximately 1cm of Board Trace) Both style and value of the output capacitor can signifi cantly affect the stability of the LTC3217. As shown in the Block Flying Capacitor Selection Diagram, the LTC3217 uses a control loop to adjust the Warning: Polarized capacitors such as tantalum or strength of the charge pump to match the required output aluminum should never be used for the fl ying capaci- current. The error signal of the loop is stored directly on tors since their voltage can reverse upon start-up of the the output capacitor. The output capacitor also serves as LTC3217. Ceramic capacitors should always be used for the dominant pole for the control loop. To prevent ringing the fl ying capacitors. or instability, it is important for the output capacitor to maintain at least 1μF of capacitance over all conditions. The fl ying capacitors control the strength of the charge pump. In order to achieve the rated output current it is In addition, excessive output capacitor ESR will tend to necessary to have at least 1.6μF of capacitance for each degrade the loop stability. The ESR of the output capacitor of the fl ying capacitors. Capacitors of different materials should be <100mΩ. Multilayer ceramic chip capacitors lose their capacitance with higher temperature and voltage typically have exceptional ESR performance. MLCCs at different rates. For example, a ceramic capacitor made combined with a tight board layout will result in very of X7R material will retain most of its capacitance from good stability. As the value of C controls the amount CPO –40°C to 85°C whereas a Z5U or Y5V style capacitor will of output ripple, the value of CV controls the amount of BAT lose considerable capacitance over that range. Z5U ripple present at the input pin (V ). The LTC3217 input BAT 3217fa 9

LTC3217 APPLICATIONS INFORMATION and Y5V capacitors may also have a very poor voltage The following guidelines should be followed when design- coeffi cient causing them to lose 60% or more of their ing a PCB layout for the LTC3217: capacitance when the rated voltage is applied. There- 1. The Exposed Pad should be soldered to a large fore, when comparing different capacitors, it is often copper plane that is connected to a solid, low imped- more appropriate to compare the amount of achievable ance ground plane using plated through-hole vias for capacitance for a given case size rather than comparing proper heat sinking and noise protection. the specifi ed capacitance value. For example, over rated voltage and temperature conditions, a 1μF, 10V, Y5V 2. Input and output capacitors must be placed close to ceramic capacitor in a 0603 case may not provide any the part. more capacitance than a 0.22μF, 10V, X7R available in 3. The fl ying capacitors must be placed close to the the same case. The capacitor manufacturer’s data sheet part. The traces from the pins to the capacitor pad should be consulted to determine what value of ca- should be as wide as possible. pacitor is needed to ensure minimum capacitances at all 4. V , CPO traces must be wide to minimize induc- temperatures and voltages. BAT tance and handle high currents. Table 2 shows a list of ceramic capacitor manufacturers 5. LED pads must be large and connected to other lay- and how to contact them: ers of metal to ensure proper LED heat sinking. Table 2. Recommended Capacitor Vendors AVX www.avxcorp.com Power Effi ciency Kemet www.kemet.com To calculate the power effi ciency (η) of a white LED Murata www.murata.com driver chip, the LED power should be compared to the Taiyo Yuden www.t-yuden.com input power. The difference between these two numbers Vishay www.vishay.com represents lost power whether it is in the charge pump or the current sources. Stated mathematically, the power effi ciency is given by: Layout Considerations and Noise P Due to its high switching frequency and the transient η= LED (5) P currents produced by the LTC3217, careful board layout IN is necessary. A true ground plane and short connections The effi ciency of the LTC3217 depends upon the mode in to all capacitors will improve performance and ensure which it is operating. Recall that the LTC3217 operates proper regulation under all conditions. as a pass switch, connecting V to CPO, until dropout BAT The fl ying capacitor pins C1P, C2P, C1M and C2M will have is detected at the LED pin. This feature provides the op- very high edge rate waveforms. The large dv/dt on these timum effi ciency available for a given input voltage and pins can couple energy capacitively to adjacent PCB runs. LED forward voltage. When it is operating as a switch, the Magnetic fi elds can also be generated if the fl ying capacitors effi ciency is approximated by: are not close to the LTC3217 (i.e., the loop area is large). P (V (cid:129)I ) V To decouple capacitive energy transfer, a Faraday shield η= LED = LED LED = LED (6) P (V (cid:129)I ) V may be used. This is a grounded PCB trace between the IN BAT BAT BAT sensitive node and the LTC3217 pins. For a high quality since the input current will be very close to the sum of AC ground, it should be returned to a solid ground plane the LED currents. that extends all the way to the LTC3217. 3217fa 10

LTC3217 PACKAGE DESCRIPTION At moderate to high output power, the quiescent current of 2 times the actual input voltage. In an ideal 2x charge of the LTC3217 is negligible and the expression shown in pump, the power effi ciency would be given by: Equation 6 is valid. P (V (cid:129)I ) V η = LED = LED LED = LED (8) Once dropout is detected at the LED pin, the LTC3217 IDEAL P (V (cid:129)(2)(cid:129)I ) (2(cid:129) V ) IN BAT LED BAT enables the charge pump in 1.5x mode. In 1.5x boost mode, the effi ciency is similar to that of a Thermal Management linear regulator with an effective input voltage of 1.5 times For higher input voltages and maximum output current, the actual input voltage. This is because the input current there can be substantial power dissipation in the LTC3217. for a 1.5x charge pump is approximately 1.5 times the If the junction temperature increases above approximately load current. In an ideal 1.5x charge pump, the power 150°C the thermal shutdown circuitry will automatically effi ciency would be given by: deactivate the output current sources and charge pump. P (V (cid:129)I ) V To reduce maximum junction temperature, a good thermal η = LED = LED LED = LED (7) IDEAL P (V (cid:129)(1.5)(cid:129)I ) (1.5(cid:129)V ) connection to the PC board is recommended. Connecting IN BAT LED BAT the Exposed Pad to a ground plane and maintaining a solid Similarly, in 2x boost mode, the effi ciency is similar to ground plane under the device will reduce the thermal that of a linear regulator with an effective input voltage resistance of the package and PC board considerably. PACKAGE DESCRIPTION UD Package 16-Lead Plastic QFN (3mm × 3mm) (Reference LTC DWG # 05-08-1691) BOTTOM VIEW—EXPOSED PAD 3.00 ± 0.10 0.75 ± 0.05 R = 0.T1Y1P5 POIRN 01. 2N5O ×T C4H5° R C =H A0M.2F0E TRYP (4 SIDES) 15 16 0.70 ±0.05 PIN 1 0.40 ± 0.10 TOP MARK (NOTE 6) 1 3.50 ± 0.05 1.45 ± 0.05 1.45 ± 0.10 2 2.10 ± 0.05 (4 SIDES) (4-SIDES) PACKAGE OUTLINE (UD16) QFN 0904 0.25 ±0.05 0.200 REF 0.25 ± 0.05 0.50 BSC 0.00 – 0.05 0.50 BSC RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS NOTE: 1. DRAWING CONFORMS TO JEDEC PACKAGE OUTLINE MO-220 VARIATION (WEED-2) 5. EXPOSED PAD SHALL BE SOLDER PLATED 2. DRAWING NOT TO SCALE 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION 3. ALL DIMENSIONS ARE IN MILLIMETERS ON THE TOP AND BOTTOM OF PACKAGE 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 3217fa Information furnished by Linear Technology Corporation is believed to be accurate and reliable. 11 However, no responsibility is assumed for its use. Linear Technology Corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.

LTC3217 TYPICAL APPLICATION 500mA Camera Flash with PWM Brightness Control C2 C3 2.2μF 2.2μF C1P C1MC2P C2M VBAT VBAT CPO C1 C4 2.2μF LTC3217 2.2μF LED1 EN1 LED2 ILED 500mA (MAX) 1kHz LED3 PWM EN2 LED4 (5% TO 100% DC) ISET1 ISET2 GND 3217 TA02 NC 3.92k 1% RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT®1618 Constant Current, Constant Voltage, 1.4MHz High Up to 16 White LEDs, V : 1.6V to 18V, V = 34V, I = 1.8mA, IN OUT(MAX) Q Effi ciency Boost Regulator I ≤1μA, 10-Lead MS Package SD LTC1911-1.5 250mA (I ), 1.5MHz High Effi ciency Step-Down 75% Effi ciency, V : 2.7V to 5.5V, V = 1.5V/1.8V, I = 180μA, OUT IN OUT(MAX) Q Charge Pump I ≤10μA, MS8 Package SD LT1932 Constant Current, 1.2MHz High Effi ciency White LED Up to 8 White LEDs, V : 1V to 10V, V = 34V, I = 1.2mA, IN OUT(MAX) Q Boost Regulator I ≤1μA, ThinSOT™ Package SD LT1937 Constant Current, 1.2MHz High Effi ciency White LED Up to 4 White LEDs, V : 2.5V to 10V, V = 34V, I = 1.9mA, IN OUT(MAX) Q Boost Regulator I ≤1μA, ThinSOT, SC70 Packages SD LTC3200-5 Low Noise, 2MHz Regulated Charge Pump White LED Up to 6 White LEDs, V : 2.7V to 4.5V, V = 5V, I = 8mA, IN OUT(MAX) Q Driver I ≤1μA, ThinSOT Package SD LTC3201 Low Noise, 1.7MHz Regulated Charge Pump White LED Up to 6 White LEDs, V : 2.7V to 4.5V, V = 5V, I = 6.5mA, IN OUT(MAX) Q Driver I ≤1μA, 10-Lead MS Package SD LTC3202 Low Noise, 1.5MHz Regulated Charge Pump White LED Up to 8 White LEDs, V : 2.7V to 4.5V, V = 5V, I = 5mA, IN OUT(MAX) Q Driver I ≤1μA, 10-Lead MS Package SD LTC3205 Multidisplay LED Controller 92% Effi ciency, V : 2.8V to 4.5V, I = 50μA, I ≤1μA, IN Q SD (4mm × 4mm) QFN Package LTC3206 I2C Multidisplay LED Controller 92% Effi ciency, 400mA Continuous Output Current. Up to 11 White LEDs in (4mm × 4mm) QFN Package LTC3208 High Current Software Confi gurable Multidisplay LED 95% Effi ciency, V : 2.9V to 4.5V, 1A Output Current, Up to 17 LEDs for IN Controller 5 Displays, (5mm × 5mm) QFN Package LTC3214 500mA Camera LED Charge Pump 93% Effi ciency, V : 2.9V to 4.4V, 1x/1.5x/2x Boost Modes, IN 3mm × 3mm DFN Package LTC3215 700mA High Current, Low Noise, White LED Driver 93% Effi ciency, V : 2.9V to 4.4V, 1x/1.5x/2x Boost Modes, IN 3mm × 3mm DFN Package LTC3216 1A High Current, Low Noise, White LED Driver 93% Effi ciency, V : 2.9V to 4.4V, 1x/1.5x/2x Boost Modes, Independent IN Low/High Current Programming, 3mm × 4mm DFN Package LTC3251 500mA (I ), 1MHz to 1.6MHz Spread Spectrum 85% Effi ciency, V : 3.1V to 5.5V, V : 0.9V to 1.6V, I = 9μA, I ≤1μA, OUT IN OUT Q SD Step-Down Charge Pump 10-Lead MS Package LTC3405/LTC3405A 300mA (I ), 1.5MHz Synchronous Step-Down DC/DC 95% Effi ciency, V : 2.7V to 6V, V = 0.8V, I = 20μA, I ≤1μA, OUT IN OUT(MIN) Q SD Converter ThinSOT Package LTC3406/LTC3406A 600mA (I ), 1.5MHz Synchronous Step-Down DC/DC 95% Effi ciency, V : 2.7V to 5.5V, V = 0.6V, I = 20μA, I ≤1μA, OUT IN OUT(MIN) Q SD Converter ThinSOT Package ThinSOT is a trademark of Linear Technology Corporation. 3217fa 12 Linear Technology Corporation LT 0208 REV A • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2005