SC615 Charge Pump Flash LED Driver POWER MANAGEMENT Description Features The SC615 is a high-current charge pump designed specifically for use with white LEDs used in camera flash applications. Only two small bucket capacitors are required to develop the output drive, providing a low EMI solution compared to inductive boost regulators. The SC615 has two modes of operation: Flash mode and Spotlight mode. The SC615 is capable of delivering 500mA of peak current for a duration of 500ms in Flash mode. In Spotlight mode the SC615 outputs 100mA and can remain enabled continuously. A minimum 0.5Ω sense resistor is used to set the current through the LED in both modes. This resistor dissipates up to 0.125W, reducing the power dissipation requirement of the SC615. The flash input (FLASH) overrides the control input (CTRL) to make sure the flash function is activated when called for. 500mA Output Current - Flash Mode 3.0V to 5.25V Input Range Two Selectable Modes - Flash and Spotlight External Flash Control Pin for Synchronization to a Camera Module or Graphics Controller Spotlight Mode Current Setting - 100mA Short Circuit, Over-Voltage, and Over-Temperature Protection Soft-Start Functionality Two Control Inputs for Maximum Versatility Shutdown Current < 2µA Micro Lead-frame Package MLPD-10, 3mm x 3mm Applications The thermally efficient MLPD-10 package and ceramic bypass and bucket capacitors help make the SC615 a high output current driver that requires a minimal amount of PCB area. Mobile Camera Phones Digital Cameras PDAs with Built-in Cameras Multi-LED Backlit LCDs Application Circuit 1 3.0V to 5.25V 10µF 8 1µF 4 10 1µF 2 SC615 VIN VOUT C1+ GND C1- ISET C2+ CTRL C2- FLASH 9 white LED 3 1µF 6 7 5 0.5Ω FLASH CTRL July 11, 2005 1 www.semtech.com SC615 POWER MANAGEMENT Absolute Maximum Ratings Exceeding the specifications below may result in permanent damage to the device or device malfunction. Operation outside of the parameters specified in the Electrical Characteristics section is not implied. Parameter Symbol Maximum Units Supply Voltage VIN -0.3 to 6.5 V Output Voltage VOUT -0.3 to 6.5 V -0.3 to VIN + 0.3 V -0.3 to VOUT + 0.3 V Pin Voltage - FLASH, CTRL, ISET, C1-, C2Pin Voltage - C1+, C2+ VOUT Short Circuit Duration SC Indefinite Thermal Resistance, Junction to Ambient (JESD51 Standard Method)(1) θJA 49 °C/W Operating Ambient Temperature Range TA -40 to +85 °C Junction Temperature Range TJC -40 to +150 °C Storage Temperature Range TSTG -65 to +150 °C IR Reflow Temperature TLEAD 260 °C ESD Protection Level(2) V ESD 2 kV Notes: 1) Calculated from package in still air, mounted to 3”x 4.5”, 4 layer FR4 PCB with thermal vias under the exposed pad per JESD51 standards. 2) Tested according to JEDEC standard JESD22-A114-B Electrical Characteristics Unless otherwise specified: TA = 25°C for TYP, -40°C to +60°C for MIN and MAX; CBUCKET = COUT = 1.0µF (ESR < 0.1Ω); CIN = 10.0µF; VIN = 3.0V to 5.25V; RISET = 0.5Ω (0.1%). Parameter Output Current ISET Reference Voltage 2005 Semtech Corp. Symbol IOUT VISET Conditions Min Typ Max FLASH high, RISET = 0.5Ω 3.3V < VIN < 4.2V 2.8V < VOUT < 4.25V 460 500 540 FLASH low, RISET = 0.5Ω CTRL high, 2.8V < VOUT < 4.5V 3.0V < VIN < 4.5V 75 100 125 FLASH high, RISET = 0.5Ω 3.3V < VIN < 4.2V 2.8V < VOUT < 4.25V 230 250 270 FLASH low, CTRL high, 2.8V < VOUT < 4.5V 3.0V < VIN < 4.5V 37.5 2 Units mA mV 50 62.5 www.semtech.com SC615 POWER MANAGEMENT Electrical Characteristics (Cont.) Unless otherwise specified: TA = 25°C for TYP, -40°C to +60°C for MIN and MAX; CBUCKET = COUT = 1.0µF (ESR < 0.1Ω); VIN = 3.0V to 5.25V; CIN = 10.0µF; RISET = 0.5Ω (0.1%). Parameter Symbol Conditions Typ Max Units FLASH high 3.4 5 mA FLASH low, CTRL high 2.0 4.5 mA FLASH low, CTRL low 0.1 2 µA Quiescent Current IQ Min Flash Mode Pulse Duration(1) tFLASH 3.3V < VIN < 4.2V IOUT = 500mA, VOUT > 2.8V 500 ms Flash Mode Start-Up Time(1) tF-ST t = 0 when FLASH goes high to IOUT = 90% of final value 1 ms Spotlight Mode Start-Up Time(1) tS-ST t = 0 when CTRL goes high to IOUT = 90% of final value 1 ms Oscillator Frequency fOSC Device Enabled Oscillator Frequency Accuracy ∆fOSC 250 -15 Short-Circuit Output Current Limit ISC VOUT = 0V Input Current Limit ILIMIT VIN = 3.7V, VOUT = 4.0V 1.0 kHz 15 % 465 mA 2.1 A 150 °C Hysteresis 10 °C 1.5 V TOT Over-Temperature Protection Logic Input High Threshold VIH FLASH, CTRL Logic Input Low Threshold VIL FLASH, CTRL Logic Input High Current IIH FLASH, CTRL Logic Input Low Current IIL ISET Ripple Voltage(1) V PP 0.4 V 20 35 µA FLASH, CTRL 0.1 2 µA Spotlight mode - IOUT = 100mA 25 FLASH mode - IOUT = 500mA 100 1 mV Notes: (1) Guaranteed by design - not tested in production. 2005 Semtech Corp. 3 www.semtech.com SC615 POWER MANAGEMENT Pin Configuration Ordering Information DEVICE SC615IMLTRT (1) VIN 1 C2- 2 GND 10 C2+ 9 VOUT 3 8 C1+ C1- 4 7 CTRL FLASH 5 6 ISET TOP VIEW T S C 615E V B PACKAGE MLPD-10 3x3 (2) Evaluation Board Notes: (1) Available in tape and reel only. A reel contains 3000 devices. (2) Available in lead-free package only. This product is fully WEEE and RoHS compliant. MLP10: 3X3 10 LEAD Pin Descriptions Pin Pin Name Pin Function 1 VIN Input voltage. 2 C 2- Negative terminal of bucket capacitor 2. 3 GND Ground - connect to ground plane using multiple vias. 4 C 1- Negative terminal of bucket capacitor 1. 5 F LA S H 6 ISET Current-setting reference pin - connect to the LED cathode and the current setting resistor. 7 CTRL Control input bit - used to enable and set the output current in Spotlight mode when high. 8 C 1+ 9 VOUT 10 C 2+ T Thermal P ad 2005 Semtech Corp. Flash mode enable pin - puts the device in active Flash mode when high and also overrides CTRL. Positive terminal of bucket capacitor 1. Output pin. Positive terminal of bucket capacitor 2 . Pad for heat sinking purposes -not connected internally. Connect to ground plane using multiple vias. 4 www.semtech.com SC615 POWER MANAGEMENT Applications Information General Operation The SC615 is a powerful 2X charge pump designed to drive a high-intensity white LED with a constant current (Spotlight mode) or with a pulsed current of higher intensity (Flash mode) used for camera flash. Spotlight Mode Spotlight mode is enabled by setting the CTRL pin high and keeping the FLASH pin low. When in Spotlight mode, the SC615 can maintain a constant current indefinitely to drive an LED or bank of LEDs. The ISET reference voltage is set to 50mV so that the output current is mainIn Flash mode the SC615 output can drive 500mA at tained at 100mA when a 0.5Ω resistor is used. 4.25V into an LED for a minimum duration of 500ms. The FLASH pin is used to trigger this mode (active high). Protection Circuitry In spotlight mode the SC615 regulates the output cur- The SC615 also provides protection circuitry that prerent to 100mA when the CTRL pin is pulled high and the vents the device from operating in an unspecified state. FLASH pin is low. Note that Flash mode has priority over These funtions include Input Over-Voltage Protection Spotlight mode, i.e., the FLASH pin triggers Flash mode (IOVP), Output Over-Voltage Protection (OVP), Over-Temregardless of the state of the CTRL pin. perature (OT) Protection, Over-Current Protection (OCP), and Short-Circuit Current Protection (SCCP). Output current is regulated by attaching the ISET pin to the cathode(s) of the LED package and a low resistance Input Over-Voltage Protection sense resistor (typically 0.5Ω). The ISET pin monitors Input over-voltage protection is included to prevent opthe voltage at the cathode and signals the charge pump eration at high input voltages that could damage the to increase or decrease the output current until the ISET device. The IOVP circuit senses the input voltage and voltage reaches the programmed setting. The resistor determines when the supply exceeds 6V. Hysteresis is value is chosen to set the current through the LED based included in this circuit to avoid chattering between states. on this reference voltage. The resistor can be chosen to When the voltage rises above this threshold, the device set either the flash mode current or spotlight mode cur- is disabled until the input voltage drops to a level within rent, but it should not be less than 0.5Ω due to output the specified range. current limitations of the device. Output Over-Voltage Protection Flash Mode Output over-voltage protection is included to prevent the Flash mode is enabled whenever the FLASH pin is pulled SC615 from generating an output voltage that could damhigh and remains active until the FLASH pin is released. age other devices connected to it such as load LEDs and This mode has higher priority than Spotlight mode, so bypass capacitors. When the output voltage exceeds the state of the CTRL pin is overridden whenever the 5.5V, the OVP circuit disables the charge pump until the FLASH pin is activated. While in flash mode the refer- voltage decreases to a level within the acceptable range. ence voltage on the ISET pin is set to 250mV. The duration of the pulse is limited by the amount of power that This circuit allows the device to drive LEDs with high forcan be dissipated in the SC615 before it exceeds the ward voltages at a reduced level without exceeding the maximum operating temperature. Note that if an output output voltage limits specified for the device. Note, howcurrent less than the rated 500mA is desired, the dura- ever, that this effect is a consequence of the OVP circuit tion of the pulse can increase proportionally. However, and is not its intended purpose. great care should be taken to insure the FLASH pin is not held high for an extended amount of time so that Over-Temperature Protection overheating does not occur. Extending flash mode be- The over-temperature circuit helps prevent the device yond the 500ms pulse limit could adversely affect the from overheating and experiencing a catastrophic faillong term reliability of the SC615. ure. When the junction temperature exceeds 150°C the device is disabled. It remains disabled until the junction temperature drops below this threshold. As with the UVLO and OVP circuits, hysteresis is included to prevent toggling between modes. 2005 Semtech Corp. 5 www.semtech.com SC615 POWER MANAGEMENT Applications Information (Cont.) through the resistor and back to the ground pins. Resistance in this path adds to the total resistance and has the effect of reducing the LED current by about 4% per 10mV of DC drop across the return copper trace in flash mode. For this reason, it is crucial to have a low resistance return path. Place and ground the resistor as close as possible to the ground pin of the SC615. The trace from the ISET pin has virtually no current. The ISET trace should make contact at the pad of the power sense resistor to minimize the effect of voltage drop between the LED cathode and the resistor. Over-Current Protection When the SC615 is in 2X charge pump mode, the input current will be approximately doubled the required output. When the steady-state load requires the maximum current available in 2X mode, the OCP circuit prevents the device from overheating due to excessive power dissipation. Short-Circuit Current Protection Short-circuit current protection is provided to limit the current that can be sourced when the output is shorted to ground. When a short circuit forces VOUT to drop below 2V, the SCCP detects the condition and limits the output current. Capacitor Selection The SC615 is designed to use low-ESR ceramic capacitors for the input and output bypass capacitors as well as the charge pump bucket capacitors. Ideal performance is achieved when C1 is exactly equal to C2. It is recommended that X5R or X7R ceramic capacitors be used for best performance. Resistor Selection The ISET resistor selection is critical in generating the correct current. The value can be chosen to set the Spotlight mode current or the Flash mode current, but it must be noted that the two current settings are dependent on the same resistor. It is recommended that the resistor be selected to match the desired LED current for Flash mode. This allows the designer to set the SC615’s maximum current and select the package size necessary for the power dissipation required in Flash mode. The typical application shown on page 1, uses a 0.5Ω resistor to set a flash mode current of 500mA and spotlight mode current of 100mA. A high precision resistor should be used to ensure the specified accuracy for LED current. Thermal Resistance The SC615 package is thermally efficient when the circuit board layout connects the thermal pad though multiple vias to the ground plane. The thermal resistance is rated at 49°C/W and this rating is dependent on the connection between the thermal pad and the ground plane. A layout that is done correctly should keep the junction temperature below the OT limit while operating the SC615 within the specified electrical conditions for IOUT and VISET. A poor layout may allow the junction temperature to reach the OT limit while in Flash or Spotlight mode. So, it is important to maintain adequate ground plane around the device to maximize heat transfer to the PCB. To avoid malfunction of the charge pump, it is recommended that the resistance seen at the ISET pin remain constant while the device is active (Flash or Spotlight mode). Changing the resistance value or the load current while the device is active could cause instability that would result in non-compliant behavior. The load current return path is from the ISET sense point 2005 Semtech Corp. 6 www.semtech.com SC615 POWER MANAGEMENT Block Diagram VIN 10µF C1+ LDO 1µF 250kHz VBAT C1C2+ CTRL 1µF Logic Control CHARGE PUMP FLASH CTRL C2VOUT Reference Voltage Generator white LED 1µF FLASH GND ISET 0.5Ω 2005 Semtech Corp. 7 www.semtech.com SC615 POWER MANAGEMENT Typical Characteristics Flash Duration Flash Current at 500ms VOUT = 3.53V(start) to 3.40V(LED heated 500ms) VOUT = 3.4V 540 520 520 VIN=4.2V VIN=3.75V VIN=3.3V Current [mA] LED Current [mA] 540 500 480 500 480 460 0 100 200 300 400 460 3.30 500 3.45 3.60 Pulse Duration [ms] Flash Current at 100ms 3.90 4.05 4.20 Flash Current at 10ms VOUT = 3.46V VOUT = 3.53V 540 520 520 Current [mA] Current [mA] 540 500 500 480 480 460 3.30 3.75 VIN [V] 3.45 3.60 3.75 3.90 4.05 460 3.30 4.20 VIN [V] 3.45 3.60 3.75 3.90 4.05 4.20 VIN [V] 100mA Spotlight Current VOUT = 2.93V 130.0 Current [mA] 115.0 100.0 85.0 70.0 3.00 3.45 3.90 4.35 4.80 5.25 VIN [V] 2005 Semtech Corp. 8 www.semtech.com SC615 POWER MANAGEMENT Typical Characteristics (Cont.) Flash Mode VISET Ripple Startup Flash Mode 500mA Ch1 100mV/div Ch2 2V/div Ch3 2V/div 4us/div Ch1 100mV/div Ch2 2V/div Ch3 2V/div 40us/div 2005 Semtech Corp. 9 www.semtech.com SC615 POWER MANAGEMENT Layout Guidelines The following layout is suggested for a two-layer design. The capacitors C1 and C2 are the bucket capacitors and each conducts the full load current of up to 500mA pulsed for one half clock cycle. C3 is the output decoupling capacitor placed near the SC615 VOUT pin. C4 is the input decoupling capacitor placed near the SC615 VIN pin. Multiple vias should be used whenever it is necessary to change layers on nets connecting to pins VIN, VOUT, GND, C1-, C1+, C2- and C2+. Resistor R1 is routed with a very low resistance connection between R1 and GND pin 3. The sense trace between Pin 6 and R1 is routed around the ground vias, allowing the shortest ground return path possible. The sense trace is connected to R1 at the positive terminal pad for the most accurate output possible. The bottom copper layer is mostly a ground plane with no obstructions between the ground vias. The smaller rectangle to the left connects the input power to VIN pin 1 and input capacitor C4. The two traces at the lower left are for logic inputs FLASH and CTRL. The trace to the right is the ISET pin "sense" trace. The sense trace is routed out of the path of the returning ground current. Bottom Copper 2005 Semtech Corp. Top Copper 10 www.semtech.com SC615 POWER MANAGEMENT Outline Drawing -MLPD-10 3x3 A E DIMENSIONS INCHES MILLIMETERS DIM MIN NOM MAX MIN NOM MAX B A A1 A2 b C D E e L N aaa bbb E PIN 1 INDICATOR (LASER MARK) A aaa C A1 C 1 .039 .031 .000 .002 (.008) .007 .009 .011 .074 .079 .083 .042 .048 .052 .114 .118 .122 .020 BSC .012 .016 .020 10 .003 .004 0.80 1.00 0.00 0.05 (0.20) 0.18 0.23 0.30 1.87 2.02 2.12 1.06 1.21 1.31 2.90 3.00 3.10 0.50 BSC 0.30 0.40 0.50 10 0.08 0.10 SEATING PLANE C A2 2 LxN D N e bxN bbb C A B NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. COPLANARITY APPLIES TO THE EXPOSED PAD AS WELL AS TERMINALS. Marking Diagram Top Mark 615 yyww xxxx yyww = Datecode (Example = 0552) xxxx = Semtech Lot Number 2005 Semtech Corp. 11 www.semtech.com SC615 POWER MANAGEMENT Land Pattern - MLPD-10 pin K DIM (C) H G C G H K P X Y Z Z Y X DIMENSIONS INCHES MILLIMETERS (.112) .075 .055 .087 .020 .012 .037 .150 (2.85) 1.90 1.40 2.20 0.50 0.30 0.95 3.80 P NOTES: 1. THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. Contact Information Semtech Corporation Power Management Products Division 200 Flynn Road, Camarillo, CA 93012 Phone: (805) 498-2111 FAX (805)498-3804 Visit us at: www.semtech.com 2005 Semtech Corp. 12 www.semtech.com