LTC3215 700mA Low Noise High Current LED Charge Pump U FEATURES ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ DESCRIPTIO High Efficiency Operation: 1x, 1.5x or 2x Boost Modes with Automatic Mode Switching Ultralow Dropout ILED Current Control Output Current up to 700mA Low Noise Constant Frequency Operation* Wide VIN Range: 2.9V to 4.4V Open/Shorted LED Protection LED Disconnect in Shutdown Low Shutdown Current: 2.5µA 4% LED Current Programming Accuracy Automatic Soft-Start Limits Inrush Current No Inductors Tiny Application Circuit (All Components <1mm Profile) 3mm × 3mm 10-Lead DFN Package U APPLICATIO S ■ LED Torch/Camera Light Supply for Cell Phones, PDAs and Digital Cameras General Lighting and/or Flash/Strobe Applications Built-in soft-start circuitry prevents excessive inrush current during start-up. High switching frequency enables the use of small external capacitors. LED current is programmed with an external resistor. The LED is disconnected from VIN during shutdown. An ultralow dropout current source maintains accurate LED current at very low ILED voltages. Automatic mode switching optimizes efficiency by monitoring the voltage across the LED current source and switching modes only when ILED dropout is detected. The LTC3215 is available in a low profile 3mm × 3mm 10-Lead DFN package. , LTC and LT are registered trademarks of Linear Technology Corporation. *Protected by U.S. Patent 6411531. U ■ The LTC®3215 is a low noise, high current charge pump DC/DC converter designed to power high current LEDs. The part includes an accurate programmable current source capable of driving loads up to 700mA from a 2.9V to 4.4V input. Low external parts count (two flying capacitors, one programming resistor and two bypass capacitors) makes the LTC3215 ideally suited for small, batterypowered applications. TYPICAL APPLICATIO C1 2.2µF Efficiency vs VIN C2 2.2µF 100 C1+ 2.9V TO 4.4V CIN 2.2µF C1– C2+ VIN C2– CPO LED1 LTC3215 ILED DISABLE ENABLE EN ISET ILED 200mA CCPO 4.7µF EFFICIENCY (PLED/PIN) (%) 90 70 60 50 40 30 20 10 20k 1% ILED = 200mA 80 LED = AOT2015 HPW 1751B VF = 3V TYP AT 200mA 0 2.8 3.0 3215 TA01a LED1: AOT2015 HPW 1751B 3.2 3.4 3.6 3.8 VIN (V) 4.0 4.2 4.4 3215 TA01b 3215f 1 LTC3215 U W W W ABSOLUTE AXI U RATI GS U W U PACKAGE/ORDER I FOR ATIO (Note 1) VIN to GND ............................................... –0.3V to 5.5V CPO to GND ............................................. –0.3V to 5.5V EN ................................................... –0.3V to VIN + 0.3V ICPO, IILED (Note 2) ........................................... 1000mA CPO Short-Circuit Duration ............................ Indefinite Storage Temperature Range ................. –65°C to 125°C Operating Temperature Range (Note 3) .. –40°C to 85°C ORDER PART NUMBER TOP VIEW C2+ 1 C1+ 2 10 C1– CPO 3 ILED 4 7 VIN ISET 5 6 EN LTC3215EDD 9 GND 11 8 C2– DD PART MARKING DD PACKAGE 10-LEAD (3mm × 3mm) PLASTIC DFN TJMAX = 125°C, θJA = 43°C/W EXPOSED PIN (PIN 11) IS GND MUST BE SOLDERED TO PCB LBPX Consult LTC Marketing for parts specified with wider operating temperature ranges. ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, CIN = C1 = C2 = 2.2µF, CCPO = 4.7µF. PARAMETER CONDITIONS MIN TYP MAX UNITS 4.4 V Input Power Supply ● VIN Operating Voltage 2.9 IVIN Operating Current ICPO = 0mA, 1x Mode ICPO = 0mA, 1.5x ICPO = 0mA, 2x Mode 300 7 9.2 IVIN Shutdown Current EN = LOW 2.5 7 3270 3400 µA mA mA µA LED Current ● LED Current Ratio (ILED/ISET) ILED = 200mA to 600mA ILED Dropout Voltage Mode Switch Threshold, ILED = 200mA 3139 120 mV 2.5 ms EN to LED Current On 130 µs 1x Mode Output Voltage ICPO = 0mA VIN V 1.5x Mode Output Voltage ICPO = 0mA 4.6 V 2x Mode Output Voltage ICPO = 0mA Mode Switching Delay (LED Warmup Time) LED Current On Time mA/mA Charge Pump (CPO) 1x Mode Output Impedance 5.1 V 0.25 Ω 1.5x Mode Output Impedance VIN = 3.4V, VCPO < 4.6V, C1 = C2 = 2.2µF 1.5 Ω 2x Mode Output Impedance VIN = 3.2V, VCPO < 5.1V, C1 = C2 = 2.2µF 1.7 Ω ● 0.6 High Level Input Voltage (VIH) ● 1.4 Low Level Input Voltage (VIL) ● 0.4 V Input Current (IIH) ● –1 1 µA Input Current (IIL) ● –1 1 µA CLK Frequency 0.9 1.2 MHz EN V 3215f 2 LTC3215 ELECTRICAL CHARACTERISTICS The ● denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 3.6V, CIN = C1 = C2 = 2.2µF, CCPO = 4.7µF. PARAMETER CONDITIONS MIN TYP MAX UNITS 1.195 1.22 1.245 V 225 µA ISET VISET ● ISET = 50µA ● IISET Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: Based on long-term current density limitations. Assumes an operating duty cycle of ≤ 10% under absolute maximum conditions for durations less than 10 seconds. Max current for continuous operation is 350mA. Note 3: The LTC3215E is guaranteed to meet performance specifications from 0°C to 70°C. Specifications over the –40°C to 85°C ambient operating temperature range are assured by design, characterization and correlation with statistical process controls. U W TYPICAL PERFOR A CE CHARACTERISTICS ILED Dropout Voltage vs LED Current ILED Pin Current vs ILED Pin Voltage VIN = 3.6V 1000 ILED = 500mA 500 0.6 ILED PIN CURRENT (mA) DROPOUT VOLTAGE (V) 0.7 0.5 0.4 0.3 0.2 800 400mA 400 300mA 300 200mA 200 0 200 400 600 LED CURRENT (mA) 0 800 0.2 0.4 0.6 0.8 ILED PIN VOLTAGE (V) VIN = 3.9V 0.25 0.23 0.21 0.19 0.17 0.15 –40 1.8 2.0 1.6 1.8 1.4 1.6 1.2 1.0 0.8 0.6 0.4 0.2 –15 10 35 TEMPERATURE (°C) 60 85 3216 G07 10 15 20 25 RSET (kΩ) 35 30 VIN = 3V VCPO = 4.2V CIN = C1 = C2 = 2.2µF CCPO = 4.7µF 0 –40 –15 35 10 TEMPERATURE (°C) 1.4 1.2 1.0 0.8 0.6 0.4 0.2 60 85 3216 G05 40 2x Mode Charge Pump Open-Loop Output Resistance (2VIN – VCPO)/ICPO vs Temperature OUTPUT RESISTANCE (Ω) OUTPUT RESISTANCE (Ω) OUTPUT RESISTANCE (Ω) VIN = 3.3V VIN = 3.6V 5 1573 G06 1.5x Mode Charge Pump Open-Loop Output Resistance (1.5VIN – VCPO)/ICPO vs Temperature ICPO = 200mA 0.27 0 1.0 3216 G02 1x Mode Charge Pump Open-Loop Output Resistance vs Temperature 0.29 400 0 0 3216 G01 0.31 600 200 100mA 100 0.1 0 ILED vs RSET 600 ILED (mA) 0.8 (TA = 25°C unless otherwise specified) VIN = 3V VCPO = 4.8V CIN = C1 = C2 = 2.2µF CCPO = 4.7µF 0 –40 –15 35 10 TEMPERATURE (°C) 60 85 3216 G06 3215f 3 LTC3215 U W TYPICAL PERFOR A CE CHARACTERISTICS Input Shutdown Current vs Input Voltage Oscillator Frequency vs Supply Voltage TA = 25°C TA = –40°C 2.0 1.5 1.0 920 90 TA = 25°C 900 TA = –40°C 890 TA = 85°C 880 870 860 0.5 0 2.9 100 910 TA = 85°C 2.5 Efficiency vs VIN 930 EFFICIENCY (PLED/PIN) (%) 3.5 FREQUENCY (kHz) INPUT SHUTDOWN CURRENT (µA) 4.0 3.0 (TA = 25°C unless otherwise specified) 840 3.3 3.5 3.7 3.9 4.1 INPUT VOLTAGE (V) 4.3 3.1 2.9 4.5 3.3 3.5 3.7 3.9 4.1 SUPPLY VOLTAGE (V) 4.3 3216 G04 400mA 70 600mA 60 50 40 30 20 10 LED = LXCL-PWF1 LUMILED VF = 3V TYP AT 200mA 0 2.8 3.0 3.2 3.4 3.6 3.8 VIN (V) 850 3.1 200mA 80 4.5 4.0 4.2 4.4 3216 G11 3216 G03 ISET/ILED Current Ratio vs ILED Current Efficiency vs VIN 100 3400 3350 80 70 CURRENT RATIO EFFICIENCY (PLED/PIN) (%) 90 60 50 40 100mA 200mA 400mA AOT2015 HPW 1751B VF = 3V TYP AT 100mA 30 20 10 0 2.8 3.0 3.2 3300 25°C –40°C 3250 85°C 3200 3150 3100 3.4 3.6 3.8 VIN (V) 4.0 4.2 0 4.4 600 200 400 ILED CURRENT (mA) 3215 G16 3215 G15 Charge Pump Mode Switching and Input Current (ILED = 400mA) 2x Mode CPO Output Ripple 1.5x Mode CPO Output Ripple 800 VCPO 1V/DIV VCPO 50mV/DIV A/C COUPLED VCPO 20mV/DIV A/C COUPLED IVIN 500mA/ DIV EN2 5V/DIV VIN = 3.6V ICPO = 200mA 500ns/DIV 3216 G12 VIN = 3.6V ICPO = 400mA 500ns/DIV 3216 G13 VIN = 3V 1ms/DIV 3215 G14 3215f 4 LTC3215 U U U PI FU CTIO S C2+, C1+, C2–, C1– (Pins 1, 2, 8, 10): Charge Pump Flying Capacitor Pins. A 2.2µF X5R or X7R ceramic capacitor should be connected from C1+ to C1– and from C2+ to C2 –. CPO (Pin 3): Output. CPO is the output of the Charge Pump. This pin may be enabled or disabled using the EN input. A 4.7µF X5R or X7R ceramic capacitor is required from CPO to GND. ILED (Pin 4): Output. ILED is the LED current source output. The LED is connected between CPO (anode) and ILED (cathode). The current into the ILED pin is set by the programming resistor connected from ISET to GND. ISET (Pin 5): LED Current Programming Resistor Pin. The ISET pin will servo to 1.22V. A resistor connected between this pin and GND is used to set the LED current level. Connecting a resistor of 2k or less will cause the LTC3215 to enter overcurrent shutdown mode. EN (Pin 6): Input. The EN is used to enable the part or put it into shutdown mode. VIN (Pin 7): Power. Supply voltage for the LTC3215. VIN should be bypassed with a 2.2µF or greater low impedance ceramic capacitor to GND. GND (Pin 9): Charge Pump Ground. This pin should be connected directly to a low impedance ground plane. EXPOSED PAD (Pin 11): Control Signal Ground. This pad must be soldered to a low impedance ground plane for optimum thermal and electrical performance. W BLOCK DIAGRA 2 10 C1+ 1 C1– 8 C2+ C2– CPO 3 1X MODE: CPO = VIN 1.5X MODE: CPO = 4.6V 2X MODE: CPO = 5.1V OSCILLATOR – + MODE CONTROL 7 6 VREF ILED DROPOUT DETECTOR 4 VIN EN CONTROL LOGIC CURRENT SOURCE CONTROL ISET GND 9 5 GND 11 3215 BD 3215f 5 LTC3215 U OPERATIO The LTC3215 uses a fractional switched capacitor charge pump to power a high current LED with a programmed regulated current. The part starts up into the 1x mode. In this mode, VIN is directly connected to CPO. This mode provides maximum efficiency and minimum noise. The LTC3215 will remain in this mode until the LED current source begins to dropout. When dropout is detected, the LTC3215 will switch to 1.5x mode after a soft-start period. Any subsequent dropout detected will cause the part to enter 2x mode. The part may be reset to 1x mode by bringing the part into shutdown mode and then reenabling the part. A two phase nonoverlapping clock activates the charge pump switches. In the 2x mode, the flying capacitors are charged on alternate clock phases from VIN. While one capacitor is being charged from VIN, the other is stacked on top of VIN and connected to the output. Alternatively, in the 1.5x mode the flying capacitors are charged in series during the first clock phase, and stacked in parallel on top of VIN on the second clock phase. This sequence of charging and discharging the flying capacitors continues at a free running frequency of 900kHz (typ). The current delivered to the LED load is controlled by the internal programmable current source. The value of this current may be selected by choosing the appropriate programming resistor. The resistor is connected between the ISET pin and GND. The resistor value needed to attain the desired current level can be determined by Equation 1. RSET = 3990/ILED (1) A resistor value of 2k or less (e.g., a short-circuit) will cause the LTC3215 to enter overcurrent shutdown mode. This mode will prevent damage to the part by shutting down the high power sections of the chip. Regulation is achieved by sensing the voltage at the CPO pin and modulating the charge pump strength based on the error signal. The CPO regulation voltages are set internally, and are dependent on the charge pump mode as shown in Table 1. Table 1. Charge Pump Output Regulation Voltages CHARGE PUMP MODE VCPO 1.5x 4.6V 2x 5.1V In shutdown mode all circuitry is turned off and the LTC3215 draws a very low current from the VIN supply. Furthermore, CPO is weakly connected to VIN. The LTC3215 enters shutdown mode when the EN pin is brought low. Since EN is a high impedance CMOS input it should never be allowed to float. To ensure that its state is defined, it must always be driven with valid logic levels. Thermal Protection The LTC3215 has built-in overtemperature protection. Thermal shutdown circuitry will shutdown the ILED output when the junction temperature exceeds approximately 150°C. It will re-enable the ILED output once the junction temperature drops back to approximately 135°C. The LTC3215 will cycle in and out of thermal shutdown indefinitely without latch up or damage until the heat source is removed. Soft-Start To prevent excessive inrush current during start-up and mode switching, the LTC3215 employs built-in soft-start circuitry. Soft-start is achieved by increasing the amount of current available to the output charge storage capacitor linearly over a period of approximately 250µs. Charge Pump Strength When the LTC3215 operates in either the 1.5x mode or 2x mode, the charge pump can be modeled as a Theveninequivalent circuit to determine the amount of current available from the effective input voltage and effective open-loop output resistance, ROL(Figure 1). 3215f 6 LTC3215 U OPERATIO ROL 1.5VIN OR 2VIN + + – CPO 3215 F01 – Figure 1. Charge Pump Open-Loop Thevenin-Equivalent Circuit ROL is dependent on a number of factors including the oscillator frequency, flying capacitor values and switch resistances. From Figure 1, we can see that the output current is proportional to: (1.5VIN – CPO)/ROL or (2VIN – CPO)/ROL (2) in the 1.5x mode or 2x mode respectively. LED Current Programming The LTC3215 includes an accurate, programmable current source that is capable of driving LED currents up to 350mA continuously and up to 700mA for pulsed operation. Pulsed operation may be achieved by toggling the EN pin. In either continuous or pulsed operation, proper board layout is required for effective heat sinking. The current may be programmed using a single external resistor. Equation 1, used to calculate the resistor value from the desired current level is repeated below: RSET = 3990/ILED Mode Switching The LTC3215 will automatically switch from 1x mode to 1.5x mode, and subsequently from 1.5x mode to 2x mode whenever a dropout condition is detected at the ILED pin. The part will wait approximately 2ms before switching to the next mode. This delay allows the LED to warm up and reduce its forward voltage which may remove the dropout condition. In order to reset the part back into 1x mode, the LTC3215 must be brought into shutdown (EN = LOW). Immediately after the part has been brought to shutdown, it may be enabled into the 1x mode via the EN pin. An internal comparator will not allow the main switches to connect VIN and CPO in 1x mode until the voltage at the CPO pin has decayed to less than or equal to the voltage at the VIN pin. (1) 2.2µF C1+ 2.2µF C1– C2+ VIN 2.9V TO 4.4V µP VIO For applications requiring multiple current levels, several schemes may be used to change the resistance for the RSET resistor. Figure 2 shows two such schemes. The circuit in Figure 2a uses the I/O output of a microcontroller to switch a second resistor (R2) in parallel or series with R1, changing the effective ISET current. Alternatively, the circuit in Figure 2b uses a pulse-width modulator (PWM) to vary the current through RSET, which changes the LED current. 2.2µF C2– C1+ 2.9V TO 4.4V CPO 2.2µF 4.7µF LTC3215 ILED ON/OFF R2 C1– C2+ VIN C2– CPO 2.2µF 4.7µF LTC3215 ILED ILED* EN VIO 2.2µF EN ISET ISET TORCH/FLASH 9.31k 1% R1 1k 3215 F02b PWM 9.31k 1% 3215 F02a *ITORCH = [(1.22V/R1) – ((VIO – 1.22V)/R2)] • 3270 IFLASH = [(1.22V/(R1 • R2/(R1 + R2))] • 3270 (2a) 1µF (2b) Figure 2 3215f 7 LTC3215 U W U U APPLICATIO S I FOR ATIO VIN, CPO Capacitor Selection The value and type of capacitors used with the LTC3215 determine several important parameters such as regulator control loop stability, output ripple, charge pump strength and minimum start-up time. To reduce noise and ripple, it is recommended that low equivalent series resistance (ESR) ceramic capacitors be used for both CVIN and CCPO. Tantalum and aluminum capacitors are not recommended because of their high ESR. The value of CCPO directly controls the amount of output ripple for a given load current. Increasing the size of CCPO will reduce the output ripple at the expense of higher start-up current. The peak-to-peak output ripple for 1.5x mode is approximately given by the expression: VRIPPLE(P-P) = IOUT/(3fOSC • CCPO) (3) charging phase or the output charging phase but will drop to zero during the clock nonoverlap times. Since the nonoverlap time is small (~15ns), these missing “notches” will result in only a small perturbation on the input power supply line. Note that a higher ESR capacitor such as tantalum will have higher input noise due to the input current change times the ESR. Therefore, ceramic capacitors are again recommended for their exceptional ESR performance. Input noise can be further reduced by powering the LTC3215 through a very small series inductor as shown in Figure 3. A 10nH inductor will reject the fast current notches, thereby presenting a nearly constant current load to the input power supply. For economy, the 10nH inductor can be fabricated on the PC board with about 1cm (0.4") of PC board trace. Flying Capacitor Selection Where fOSC is the LTC3215’s oscillator frequency (typically 900kHz) and CCPO is the output storage capacitor. Both the style and value of the output capacitor can significantly affect the stability of the LTC3215. As shown in the block diagram, the LTC3215 uses a control loop to adjust the strength of the charge pump to match the current required at the output. The error signal of this loop is stored directly on the output charge storage capacitor. The charge storage capacitor also serves as the dominant pole for the control loop. To prevent ringing or instability, it is important for the output capacitor to maintain at least 2.2µF of actual capacitance over all conditions. Likewise, excessive ESR on the output capacitor will tend to degrade the loop stability of the LTC3215. The closed loop output resistance of the LTC3215 is designed to be 76mΩ. For a 100mA load current change, the error signal will change by about 7.6mV. If the output capacitor has 76mΩ or more of ESR, the closed-loop frequency response will cease to roll off in a simple one-pole fashion and poor load transient response or instability could result. Multilayer ceramic chip capacitors typically have exceptional ESR performance. MLCCs combined with a tight board layout will yield very good stability. As the value of CCPO controls the amount of output ripple, the value of CVIN controls the amount of ripple present at the input pin (VIN). The input current to the LTC3215 will be relatively constant while the charge pump is on either the input 8 10nH VIN 0.1µF LTC3215 2.2µF GND 3215 F03 Figure 3. 10nH Inductor Used for Input Noise Reduction (Approximately 1cm of Wire) Warning: Polarized capacitors such as tantalum or aluminum should never be used for the flying capacitors since their voltage can reverse upon start-up of the LTC3215. Ceramic capacitors should always be used for the flying capacitors. The flying capacitors control the strength of the charge pump. In order to achieve the rated output current it is necessary to have at least 2.2µF of actual capacitance for each of the flying capacitors. Capacitors of different materials lose their capacitance with higher temperature and voltage at different rates. For example, a ceramic capacitor made of X7R material will retain most of its capacitance from – 40oC to 85oC whereas a Z5U or Y5V style capacitor will lose considerable capacitance over that range. Z5U and Y5V capacitors may also have a very poor voltage coefficient causing them to lose 60% or more of their capacitance when the rated voltage is applied. Therefore, when comparing different capacitors, it is often more appropriate to 3215f LTC3215 U W U U APPLICATIO S I FOR ATIO compare the amount of achievable capacitance for a given case size rather than comparing the specified capacitance value. For example, over rated voltage and temperature conditions, a 1µF, 10V, Y5V ceramic capacitor in a 0603 case may not provide any more capacitance than a 0.22µF, 10V, X7R available in the same case. The capacitor manufacturer’s data sheet should be consulted to determine what value of capacitor is needed to ensure minimum capacitances at all temperatures and voltages. Table 2 shows a list of ceramic capacitor manufacturers and how to contact them. Table 2. Recommended Capacitor Vendors AVX www.avxcorp.com Kemet www.kemet.com Murata www.murata.com Taiyo Yuden www.t-yuden.com Vishay www.vishay.com TDK www.tdk.com pins can couple energy capacitively to adjacent PCB runs. Magnetic fields can also be generated if the flying capacitors are not close to the LTC3215 (i.e., the loop area is large). To decouple capacitive energy transfer, a Faraday shield may be used. This is a grounded PCB trace between the sensitive node and the LTC3215 pins. For a high quality AC ground, it should be returned to a solid ground plane that extends all the way to the LTC3215. The following guidelines should be followed when designing a PCB layout for the LTC3215. • The Exposed Pad should be soldered to a large copper plane that is connected to a solid, low impedance ground plane using plated, through-hole vias for proper heat sinking and noise protection. • Input and output capacitors (CIN and CCPO) must also be placed as close to the part as possible. • The flying capacitors must also be placed as close to the part as possible. The traces running from the pins to the capacitor pads should be as wide as possible. Layout Considerations and Noise Due to its high switching frequency and the transient currents produced by the LTC3215, careful board layout is necessary. A true ground plane and short connections to all capacitors will improve performance and ensure proper regulation under all conditions. The flying capacitor pins C1+, C2+, C1– and C2– will have very high edge rate waveforms. The large dv/dt on these • VIN, CPO and ILED traces must be made as wide as possible. This is necessary to minimize inductance, as well as provide sufficient area for high current applications. • LED pads must be large and should be connected to as much solid metal as possible to ensure proper heat sinking. C1 PIN 1 C2 CIN RSET CCPO 3215 F04 Figure 4. Example Board Layout 3215f 9 LTC3215 U W U U APPLICATIO S I FOR ATIO Power Efficiency To calculate the power efficiency (η) of a white LED driver chip, the LED power should be compared to the input power. The difference between these two numbers represents lost power whether it is in the charge pump or the current sources. Stated mathematically, the power efficiency is given by: P η ≡ LED PIN ηIDEAL ≡ (4) The efficiency of the LTC3215 depends upon the mode in which it is operating. Recall that the LTC3215 operates as a pass switch, connecting VIN to CPO, until dropout is detected at the ILED pin. This feature provides the optimum efficiency available for a given input voltage and LED forward voltage. When it is operating as a switch, the efficiency is approximated by: η≡ PLED VLED • ILED VLED = ≈ PIN VIN • IIN VIN In 1.5x boost mode, the efficiency is similar to that of a linear regulator with an effective input voltage of 1.5 times the actual input voltage. This is because the input current for a 1.5x charge pump is approximately 1.5 times the load current. In an ideal 1.5x charge pump, the power efficiency would be given by: (5) since the input current will be very close to the LED current. At moderate to high output power, the quiescent current of the LTC3215 is negligible and the expression above is valid. Once dropout is detected at the ILED pin, the LTC3215 enables the charge pump in 1.5x mode. PLED V •I V = LED LED ≈ LED PIN VIN • 1.5ILED 1.5VIN (6) Similarly, in 2x boost mode, the efficiency is similar to that of a linear regulator with an effective input voltage of 2 times the actual input voltage. In an ideal 2x charge pump, the power efficiency would be given by: ηIDEAL ≡ PLED V •I V = LED LED ≈ LED PIN VIN • 2 • ILED 2 • VIN (7) Thermal Management For higher input voltages and maximum output current, there can be substantial power dissipation in the LTC3215. If the junction temperature increases above approximately 150°C, the thermal shutdown circuitry will automatically deactivate the output. To reduce maximum junction temperature, a good thermal connection to the PC board is recommended. Connecting the Exposed Pad to a ground plane and maintaining a solid ground plane under the device can reduce the thermal resistance of the package and PC board considerably. 3215f 10 LTC3215 U PACKAGE DESCRIPTIO DD Package 10-Lead Plastic DFN (3mm × 3mm) (Reference LTC DWG # 05-08-1698) 0.675 ±0.05 3.50 ±0.05 1.65 ±0.05 2.15 ±0.05 (2 SIDES) PACKAGE OUTLINE 0.25 ± 0.05 0.50 BSC 2.38 ±0.05 (2 SIDES) RECOMMENDED SOLDER PAD PITCH AND DIMENSIONS R = 0.115 TYP 6 3.00 ±0.10 (4 SIDES) 0.38 ± 0.10 10 1.65 ± 0.10 (2 SIDES) PIN 1 TOP MARK (SEE NOTE 6) (DD10) DFN 1103 5 0.200 REF 1 0.25 ± 0.05 0.50 BSC 0.75 ±0.05 0.00 – 0.05 2.38 ±0.10 (2 SIDES) BOTTOM VIEW—EXPOSED PAD NOTE: 1. DRAWING TO BE MADE A JEDEC PACKAGE OUTLINE M0-229 VARIATION OF (WEED-2). CHECK THE LTC WEBSITE DATA SHEET FOR CURRENT STATUS OF VARIATION ASSIGNMENT 2. DRAWING NOT TO SCALE 3. ALL DIMENSIONS ARE IN MILLIMETERS 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 5. EXPOSED PAD SHALL BE SOLDER PLATED 6. SHADED AREA IS ONLY A REFERENCE FOR PIN 1 LOCATION ON THE TOP AND BOTTOM OF PACKAGE 3215f Information 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 representation that the interconnection of its circuits as described herein will not infringe on existing patent rights. 11 LTC3215 U TYPICAL APPLICATIO High Power Camera Light and Flash 2.2µF C1+ 2.9V TO 4.4V µP 2.8V 2.2µF C1– C2+ VIN C2– CPO 2.2µF 4.7µF LTC3215 ILED ON/OFF EN 2.8V 30k 1% ILED 200mA/500mA ISET TORCH/FLASH 10.5k 1% 3215 TA02 RELATED PARTS PART NUMBER DESCRIPTION COMMENTS LT1618 Constant Current, 1.4MHz, 1.5A Boost Converter VIN: 1.6V to 18V, VOUT(MAX) = 36V, IQ = 1.8mA, ISD < 1µA MS Package LT1961 1.5A (ISW), 1.25MHz, High Efficiency Step-Up DC/DC Converter VIN: 3V to 25V, VOUT(MAX) = 35V, IQ = 0.9mA, ISD < 6µA MS8E Package LTC3205 250mA, 1MHz, Multi-Display LED Controller VIN: 2.8V to 4.5V, VOUT(MAX) = 5.5V, IQ = 50µA, ISD < 1µA DFN Package LTC3206 400mA, 800kHz, Multi-Display LED Controller VIN: 2.8V to 4.5V, VOUT(MAX) = 5.5V, IQ = 50µA, ISD < 1µA DFN Package LTC3216 1A Low Noise High Current LED Charge Pump with Independent Flash/Torch Current Control VIN: 2.9V to 4.4V, VOUT(MAX) = 5.5V, IQ = 300µA, ISD < 2.5µA DFN Package LTC3440/LTC3441 600mA/1.2A IOUT, 2MHz/1MHz, Synchronous Buck-Boost DC/DC Converter VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, IQ = 25µA/50µA, ISD <1µA MS/DFN Packages LTC3443 600mA/1.2A IOUT, 600kHz, Synchronous Buck-Boost DC/DC Converter VIN: 2.4V to 5.5V, VOUT(MAX) = 5.25V, IQ = 28µA, ISD <1µA DFN Package LTC3453 1MHz, 800mA Synchronous Buck-Boost High Power LED Driver VIN(MIN): 2.7V to 5.5V, VIN(MAX): 2.7V to 4.5V, IQ = 2.5mA, ISD < 6µA QFN Package LT3467/LT3467A 1.1A (ISW), 1.3/2.1MHz, High Efficiency Step-Up DC/DC Converters with Integrated Soft-Start VIN: 2.4V to 16V, VOUT(MAX) = 40V, IQ = 1.2mA, ISD < 1µA ThinSOT Package LT3479 3A, 42V, 3.5MHz Boost Converter VIN: 2.5V to 24V, VOUT(MAX) = 40V, IQ = 2µA, ISD < 1µA DFN, TSSOP Packages 3215f 12 Linear Technology Corporation LT/TP 0305 1K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 ● FAX: (408) 434-0507 ● www.linear.com © LINEAR TECHNOLOGY CORPORATION 2005