SC615A Charge Pump Flash LED Driver POWER MANAGEMENT Description Features The SC615A 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 SC615A has two modes of operation: Flash mode and Spotlight mode. In Flash mode, the SC615A is capable of delivering 500mA of regulated current for a duration of 500ms or up to 700mA for a reduced duration. In Spotlight mode the SC615A outputs 40% of the Flash mode current and can remain enabled continuously. An external resistor is connected in series with the LED to set the current. In Flash mode, this resistor can dissipate up to 175mW, reducing the power dissipation requirement of the SC615A. The flash input (FLASH) overrides the control input (CTRL) to make sure the flash function is activated when called for. Two Selectable Modes - Flash and Spotlight Up to 700mA Output - Flash Mode Up to 280mA Output - Spotlight Mode 500mA Over Temperature Range and Voltage Range - Flash Mode Spotlight mode set to 40% of Flash Current 3.0V to 5.25V Input Range External Flash Control Pin for Synchronization to a Camera Module or Graphics Controller Short Circuit, Over-Voltage, and Over-Temperature Protection Soft-Start Functionality Two Control Inputs for Maximum Versatility Shutdown Current < 2μA Micro Lead Package MLPD-10, 3mm x 3mm Applications Mobile Camera Phones Digital Cameras PDAs with Built-in Cameras The thermally efficient MLPD-10 package and ceramic bypass and bucket capacitors make the SC615A a high output current driver that requires minimal PCB area. Typical Application Circuit 1 3.0V to 5.25V 10μF 8 1μF 4 10 1μF 2 SC615A VIN VOUT C1+ GND C1- ISET C2+ CTRL C2- FLASH 9 3 1μF white LED 6 7 5 0.5Ω FLASH CTRL March 5, 2008 www.semtech.com 1 SC615A 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 TPKG 260 °C ESD Protection Level(2) VESD 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; VOUT = 2.8V to 4.25V; RISET = 0.5Ω (0.1%). Parameter Symbol Conditions Min FLASH high, RISET = 0.357W 3.7V < VIN < 4.2V, VOUT = 3.7V (1) IOUT Output Current FLASH high, RISET = 0.5W 3.3V < VIN < 4.2V 2.8V < VOUT < 4.25V VISET ISET Reference Voltage VISET Max 700 460 FLASH low, CTRL high, RISET = 0.357W 3.7V < VIN < 4.2V, VOUT = 3.4V (1) ISET Reference Voltage Typ 500 Units mA 540 mA 280 FLASH low, CTRL high, RISET = 0.5W 2.8V < VOUT < 4.5V 3.0V < VIN < 4.5V 170 200 230 FLASH high, RISET = 0.5W 3.3V < VIN < 4.2V 2.8V < VOUT < 4.25V 230 250 270 mV FLASH low, CTRL high, RISET = 0.5Ω 2.8V < VOUT < 4.5V, 3.0V < VIN < 4.5V 85 100 115 mV © 2008 Semtech Corp. www.semtech.com 2 SC615A POWER MANAGEMENT Electrical Characteristics (Cont.) Parameter Quiescent Current Symbol Conditions IQ Min 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 Flash Mode Pulse Duration(2) tFLASH 3.3V < VIN < 4.2V IOUT = 500mA, VOUT > 2.8V 500 ms Flash Mode Start-Up Time(2) tF-ST t = 0 when FLASH goes high to IOUT = 90% of final value 1 ms Spotlight Mode Start-Up Time(2) tS-ST t = 0 when CTRL goes high to IOUT = 90% of final value 1 ms Oscillator Frequency fOSC Device Enabled Oscillator Frequency Accuracy ΔfOSC Short-Circuit Output Current Limit ISC Input Current Limit -15 ILIMIT % VOUT = 0V 465 mA 3.3V < VIN < 4.2V 2.1 TOT 1.53 °C Hysteresis 10 °C 1.5 VIH FLASH, CTRL Logic Input Low Threshold VIL FLASH, CTRL Logic Input High Current IIH Logic Input Low Current IIL VPP A 1.38 150 Logic Input High Threshold ISET Ripple Voltage(2) kHz 15 VIN = 3.7V, VOUT = 3.7V, TA = 25°C Over-Temperature Protection(2) 250 V 0.4 V FLASH 1 20 35 μA CTRL 2 40 70 μA FLASH, CTRL 0.1 2 μA Spotlight mode - IOUT = 200mA 25 FLASH mode - IOUT = 500mA 100 mV Notes: (1) VOUT required by the typical LED at this current. (2) Guaranteed by design - not tested in production. © 2008 Semtech Corp. www.semtech.com 3 SC615A POWER MANAGEMENT Pin Configuration Ordering Information DEVICE PACKAGE 10 C2+ SC615AMLTRT (1) MLPD-10 3x3 (2) 9 VOUT SC615AEVB Evaluation Board 3 8 C1+ C1- 4 7 CTRL FLASH 5 6 ISET VIN 1 C2- 2 GND TOP VIEW T 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 C2- Negative terminal of bucket capacitor 2. 3 GND 4 C1- 5 FLASH Flash mode enable pin - puts the device in active Flash mode when high and also overrides CTRL. 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 C1+ 9 VOUT 10 C2+ T Thermal Pad Ground - connect to ground plane using multiple vias. Negative terminal of bucket capacitor 1. 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. © 2008 Semtech Corp. www.semtech.com 4 SC615A POWER MANAGEMENT Block Diagram VIN 10μF C1+ LDO 1μF 250 kHz VBAT C1C2+ CTRL 1μF Logic Control CHARGE PUMP FLASH CTRL C2VOUT Reference Voltage Generator 1μF FLASH white LED GND ISET 0.5 Ω © 2008 Semtech Corp. www.semtech.com 5 SC615A POWER MANAGEMENT Applications Information Flash Current [mA] General Operation Flash mode, IOUT = 250mV/RISET. The plot below shows The SC615A is a powerful 2X charge pump designed to drive maximum Flash mode current for extended duration times. a high-intensity white LED with a constant current (Spotlight 800 mode) or with a pulsed current of higher intensity (Flash 700 mode) used for camera flash. In Flash mode the SC615A output can drive 500mA at 4.25V into an LED for a minimum duration of 500ms under all temperature and input conditions. The FLASH pin is used to trigger this mode (active high). In spotlight mode the SC615A regulates the output current to 40% of the Flash mode current setting when the CTRL pin is pulled high and the FLASH pin is low. Note that Flash mode has priority over Spotlight mode, i.e., the FLASH pin triggers Flash mode regardless of the state of the CTRL pin. 600 500 400 300 200 100 0 0 100 200 300 400 500 600 700 800 900 1000 Flash Duration [ms] Spotlight Mode Spotlight mode is enabled by setting the CTRL pin high and keeping the FLASH pin low. When in Spotlight mode, the SC615A can maintain a constant current indefinitely to drive an LED or bank of LEDs. The ISET reference voltage is set to 100mV so that the output current is maintained at 200mA when a 0.5Ω resistor is used. Spotlight current is always 40% of flash current for any given value of RISET. Output current is regulated by attaching the ISET pin to the cathode(s) of the LED package and a low resistance sense resistor (typically 0.5Ω). The ISET pin monitors the voltage at the cathode and signals the charge pump to increase or decrease the output current until the ISET voltage reaches the programmed setting. The resistor value is chosen to set the current through the LED based on this reference voltage. The resistor can be chosen to set either the flash mode current or spotlight mode current, but it should not In spotlight mode, IOUT = 100mV/RISET. be less than 0.35Ω due to output current limitations of Protection Circuitry the device. The SC615A also provides protection circuitry that prevents the device from operating in an unspecified state. These Flash Mode Flash mode is enabled whenever the FLASH pin is pulled funtions include Input Over-Voltage Protection (IOVP), Outhigh and remains active until the FLASH pin is released. put Over-Voltage Protection (OVP), Over-Temperature (OT) This mode has higher priority than Spotlight mode, so the Protection, Over-Current Protection (OCP), and Short-Circuit state of the CTRL pin is overridden whenever the FLASH Current Protection (SCCP). pin is activated. While in Flash mode the reference voltage on the ISET pin is set to 250mV. The duration of the pulse Input Over-Voltage Protection is limited by the amount of power that can be dissipated Input over-voltage protection is included to prevent operain the SC615A before it exceeds the maximum operating tion at high input voltages that could damage the device. temperature. Note that if an output current less than the The IOVP circuit senses the input voltage and determines rated 500mA is desired, the duration of the pulse can when the supply exceeds 6V. Hysteresis is included in this circuit to avoid chattering between states. When the increase proportionally. voltage rises above this threshold, the device is disabled Extending Flash mode beyond the 500ms pulse limit could until the input voltage drops to a level within the specified adversely affect the long term reliability of the SC615A. range. Flash duration must be derated at higher currents. For example, 700mA derates to a maximum of 350ms. In © 2008 Semtech Corp. www.semtech.com 6 SC615A POWER MANAGEMENT Applications Information (Cont.) Output Over-Voltage Protection Output over-voltage protection is included to prevent the SC615A from generating an output voltage that could damage other devices connected to it such as load LEDs and bypass capacitors. When the output voltage exceeds 5.5V, the OVP circuit disables the charge pump until the voltage decreases to a level within the acceptable range. shown on page 1 uses a 0.5Ω resistor to set a flash mode current of 500mA and spotlight mode current of 200mA. A high precision resistor should be used to ensure the specified accuracy for LED current. 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. This circuit allows the device to drive LEDs with high forward voltages at a reduced level without exceeding the output voltage limits specified for the device. Note, however, that this effect is a consequence of the OVP circuit and is not its intended purpose. The load current return path is from the ISET sense point 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 SC615A. 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-Temperature Protection The over-temperature circuit helps prevent the device from overheating and experiencing a catastrophic failure. 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. Over-Current Protection When the SC615A is in 2X charge pump mode, the input current will be approximately double 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. Capacitor Selection The SC615A 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. 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. Thermal Resistance The SC615A 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 SC615A 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 critical to maintain adequate ground plane around the device to maximize heat transfer and avoid over-temperature shutdown. 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 SC615A’s maximum current and select the package size necessary for the power dissipation required in Flash mode. The typical application © 2008 Semtech Corp. www.semtech.com 7 SC615A POWER MANAGEMENT Typical Characteristics Flash Current at 500ms, RISET = 500mΩ, VOUT = 3.38V Flash Duration, RISET=500mΩ, VOUT = 3.52V(start) to 3.38V (LED heated 500ms) 540 510 520 VIN = 4.2V Current [mA] LED Current [mA] 505 500 VIN = 3.7V 500 VIN = 3.3V 480 495 460 3.30 490 0 100 200 300 400 500 3.45 3.60 3.75 3.90 4.05 4.20 VIN [V] Pulse Duration [ms] Flash Duration, RISET = 350mΩ, VOUT = 3.62V (start) to 3.40V (LED heated 500ms) Flash Current at 100ms, RISET = 500mΩ, VOUT = 3.46V 755 540 VIN = 4.2V 520 Current [mA] Current [mA] 735 715 VIN = 3.7V VIN = 3.3V 695 500 480 675 0 100 200 300 400 460 3.30 500 3.45 3.60 Time [ms] 3.90 4.05 4.20 Flash Current at 10ms, RISET = 500mΩ, VOUT = 3.52V 200mA Spotlight Current, RISET = 500mΩ, VOUT = 3.0V 212.5 540 207.5 520 202.5 Current [mA] Current [mA] 3.75 VIN [V] 197.5 500 480 192.5 187.5 3.00 3.45 3.90 4.35 4.80 460 3.30 5.25 VIN [V] 3.45 3.60 3.75 3.90 4.05 4.20 VIN [V] © 2008 Semtech Corp. www.semtech.com 8 SC615A POWER MANAGEMENT Typical Characteristics (Cont.) Flash Current at 350ms, RISET = 350mΩ, VOUT = 3.45V Flash Mode VISET Ripple 755 Current [mA] 735 715 695 675 3.30 3.45 3.60 3.75 3.90 4.05 Ch1 100mV/div Ch2 2V/div Ch3 2V/div 4us/div 4.20 VIN [V] 755 Flash Current at 100ms, RISET = 350mΩ, VOUT = 3.53V Startup Flash Mode 500mA Current [mA] 735 715 695 675 3.30 3.45 3.60 3.75 3.90 4.05 Ch1 100mV/div Ch2 2V/div Ch3 2V/div 40us/div 4.20 VIN [V] 755 Flash Current at 10ms, RISET = 350mΩ, VOUT = 3.62V Current [mA] 735 715 695 675 3.30 3.45 3.60 3.75 3.90 4.05 4.20 VIN [V] © 2008 Semtech Corp. www.semtech.com 9 SC615A 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 SC615A VOUT pin. C4 is the input decoupling capacitor placed near the SC615A 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 Top Copper © 2008 Semtech Corp. www.semtech.com 10 SC615A POWER MANAGEMENT Outline Drawing -MLPD-10 3x3 A E B DIM A A1 A2 b C D E e L N aaa bbb E PIN 1 INDICATOR (LASER MARK) A aaa C A1 C 1 DIMENSIONS INCHES MILLIMETERS MIN NOM MAX MIN NOM MAX .031 .039 .000 .002 (.008) .007 .009 .011 .074 .079 .083 .042 .048 .052 .114 .118 .122 .020 BSC .012 .016 .020 10 .003 .004 1.00 0.80 0.05 0.00 (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 615A yyww xxxx yyww = Datecode (Example = 0552) xxxx = Semtech Lot Number © 2008 Semtech Corp. www.semtech.com 11 SC615A POWER MANAGEMENT Land Pattern -MLPD-10 3x3 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 www.semtech.com © 2008 Semtech Corp. www.semtech.com 12