SC635 Charge Pump Flash LED Driver POWER MANAGEMENT Description Features The SC635 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. Two selectable modes - Flash and Spotlight 200mA max output - Flash Mode Spotlight mode set to 40% of Flash Current 3.0V to 5.25V Input Range External pins for control of flash and spotlight modes for synchronization to a camera module or graphics controller u Short circuit, over-voltage, and over-temperature protection u Soft-start functionality u Micro Lead Package MLPD-10, 3mm x 3mm u u u u u The SC635 has two modes of operation: Flash mode and Spotlight mode. In Flash mode, the SC635 is capable of delivering 200mA to a high-intensity LED during image capture. In Spotlight mode the SC635 outputs 40% of the Flash mode current for general purpose lighting or status indication. An external resistor is connected in series with the LED to set the current. In Flash mode, this resistor can dissipate up to 50mW, reducing the power dissipation requirement of the SC635. The flash input (FLASH) overrides the control input (CTRL) to make sure the flash function is activated when called for. Applications u Mobile Camera Phones u Digital Cameras u PDAs with Built-in Cameras The thermally efficient MLPD-10 package and ceramic bypass and bucket capacitors make the SC635 a high output current driver that requires minimal PCB area. Typical Application Circuit Typical Application Circuit 1 VBAT 10µF 8 1µF 4 10 1µF 2 VIN SC635 VOUT C1+ GND C1- ISET C2+ CTRL C2- FLASH 9 3 white LED 1µF 6 7 5 RSET FLASH CTRL December 2, 2005 www.semtech.com SC635 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 Input Supply Voltage Output Voltage Symbol Maximum Units VVIN -0.3 to +6.5 V VVOUT -0.3 to +6.5 V -0.3 to VVIN + 0.3 V -0.3 to VVOUT + 0.3 V Pin Voltage - FLASH, CTRL, ISET, C1-, C2Pin Voltage - C1+, C2+ Thermal Resistance, Junction to Ambient (JESD51 Standard Method)(1) qJA 49 °C/W VOUT Short Circuit Duration SC Indefinite s Operating Ambient Temperature Range TA -40 to +85 °C Junction Temperature Range TJ -40 to +150 °C Storage Temperature Range TSTG -60 to +150 °C Peak IR Flow Temperature TLEAD 260 °C ESD Protection Level(2) VESD 2 kV (1) Calculated from package in still air, mounted to 3” x 4.5”, 4 layer FR4 PCB with thermal vias under the exposed pad as 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; VVIN = 3.0V to 5.25V; VVOUT = 2.8V to 4.25V; RSET = 0.5Ω (0.1%). Parameter Output Current ISET Reference Voltage Quiescent Current 2005 Semtech Corp. Symbol IOUT VISET IQ Conditions Min Typ Max FLASH high, RISET = 1.25W 3.3V < VVIN < 4.2V 2.8V < VVOUT = 4.25V 184 200 216 FLASH low, CTRL high, RISET = 1.25W 3.0V < VVIN < 4.5V 2.8V < VVOUT < 4.5V 68 80 92 FLASH high, RISET = 1.25W 3.3V < VVIN < 4.2V 2.8V < VVOUT < 4.25V 230 250 270 FLASH low, CTRL high, RISET = 1.25W 3.0V < VVIN < 4.5V 2.8V < VVOUT < 4.5V 85 Units mA mV 100 115 FLASH high 3.4 5.0 mA FLASH low, CTRL high 2.0 4.5 mA FLASH low, CTRL low 0.1 2.0 µA www.semtech.com SC635 POWER MANAGEMENT Electrical Characteristics (Cont.) Parameter Symbol Conditions Flash Mode Start-up Time(1) tF-SU t = 0 when FLASH goes high to IOUT = 90% of final value Flash Mode Pulse Duration tFLASH 3.3V < VVIN < 4.2V IOUT = 200mA, VVOUT > 2.8V Spotlight Mode Start-up Time(1) tS-SU t = 0 when CTRL goes high to IOUT = 90% of final value Oscillator Frequency fOSC Device enabled Oscillator Frequency Accuracy Short-circuit Output Current Limit Min VOUT shorted to GND Input Current Limit ILIMIT 3.3V < VVIN < 4.2V Over-temperature Protection(1) TOT Logic Input High Threshold Units 1 ms s 1 250 1.0 10 VIH FLASH, CTRL 1.5 Logic Input Low Threshold VIL FLASH, CTRL Logic Input High Current IIH Logic Input High Current IIL ms kHz 15 % 465 mA 2.1 A 150 Hysteresis VISET(P-P) Max indefinite -15 DfOSC ISC ISET Ripple Voltage(1) Typ °C V 0.4 FLASH 1 20 35 CTRL 2 40 70 FLASH, CTRL 0.1 2.0 Spotlight mode - IOUT = 80mA 25 FLASH mode - IOUT = 200mA 100 V µA µA mV Notes: (1) Guaranteed by design - not tested in production. 2005 Semtech Corp. www.semtech.com SC635 POWER MANAGEMENT Pin Configuration Ordering Information DEVICE PACKAGE SC635MLTRT(1)(2) MLPD-10 3x3 SC635EVB Evaluation Board (2)(1) VIN 1 10 C2+ C2- 2 9 VOUT GND 3 8 C1+ C1- 4 7 CTRL FLASH 5 6 ISET TOPVIEW T (1) Notes: (1) Available in tape and reel only. A reel contains 3,000 devices. (2) Available in lead-free package only. Device is WEEE and RoHS compliant. MLP10:3X310LEAD 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 2005 Semtech Corp. 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. www.semtech.com SC635 POWER MANAGEMENT Pin Configuration Applications Information the output current being set too low. General Operation The SC635 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. Protection Circuitry The SC635 also provides protection circuitry that prevents the device from operating in an unspecified state. These functions include Input Over-Voltage Protection (IOVP), Output Over-Voltage Protection (OVP), Over-Temperature (OT) Protection, Over-Current Protection (OCP), and ShortCircuit Current Protection (SCCP). In Flash mode the SC635 output can drive 200mA at 4.25V into an LED for an unlimited duration under all temperature and input conditions. The FLASH pin is used to trigger this mode (active high). In Spotlight mode the SC635 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. Input Over-Voltage Protection Input over-voltage protection is included to prevent operation at high input voltages that could damage the device. The IOVP circuit senses the input voltage and determines when the supply exceeds 6V. Hysteresis is included in this circuit to avoid chattering between states. When the voltage rises above this threshold, the device is disabled until the input voltage drops to a level within the specified range. Output current is regulated by attaching the ISET pin to the cathode(s) of the LED package and a low resistance sense resistor (typically 1.25Ω). 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. Output Over-Voltage Protection Output over-voltage protection is included to prevent the SC635 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 Flash Mode Flash mode is enabled whenever the FLASH pin is pulled decreases to a level within the acceptable range. This high and remains active until the FLASH pin is released. circuit allows the device to drive LEDs with high forward This mode has higher priority than Spotlight mode, so the voltages at a reduced level without exceeding the output state of the CTRL pin is overridden whenever the FLASH voltage limits specified for the device. Note, however, that pin is activated. While in Flash mode the reference volt- this effect is a consequence of the OVP circuit and is not its intended purpose. age on the ISET pin is set to 250mV. 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. Output currents other than the rated maximum of 200mA can be set by changing the RISET value. In Flash mode, IOUT = 250mV/RISET. Spotlight Mode Spotlight mode is enabled by setting the CTRL pin high and keeping the FLASH pin low. When in Spotlight mode, the SC635 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 80mA when a 1.25Ω resistor is used. Spotlight current is always 40% of flash current for any given value of RISET. In spotlight mode, IOUT = 100mV/RISET. The resistor value should not exceed 2Ω, however, to ensure the SC635 does not become unstable while in Spotlight mode due to 2005 Semtech Corp. Over-Current Protection When the SC635 is in 2X 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. www.semtech.com SC635 POWER MANAGEMENT Applications Information (Cont.) 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. 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 SC635. 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. 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 resistance. It is recommended that the resistor be selected to match the desired LED current for Flash mode. This allows the designer to set the SC635’s maximum current and select the resistor package size necessary for the power dissipation required in Flash mode. The typical application shown on page 1 uses a 1.25Ω resistor to set a flash mode current of 200mA and spotlight mode current of 80mA. A high precision resistor should be used to ensure the specified accuracy for LED current. Capacitor Selection The SC635 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. Thermal Resistance The SC635 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 SC635 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. It is critical to maintain adequate ground plane around the device to maximize heat transfer and avoid over-temperature shutdown. 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 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 2005 Semtech Corp. www.semtech.com SC635 POWER MANAGEMENT Typical Characteristics 200mA Flash Duration, RISET = 1.25W, VOUT = 3.30V(start) to 3.25V(LED heated 500ms) Flash Current at 500ms, RISET = 1.25W, VOUT = 3.25V 203.0 203.0 201.0 LED Current [mA] 205.0 LED Current [mA] 205.0 201.0 VIN = 4.2V VIN = 3.7V 199.0 199.0 VIN = 3.3V 197.0 197.0 195.0 195.0 0 100 200 300 Pulse Duration [ms] 400 3.3 500 Flash Current at 100ms, RISET = 1.25W, VOUT = 3.28V 3.45 3.6 3.75 VIN [V] 3.9 4.05 4.2 Flash Current at 10ms, RISET = 1.25W, VOUT = 3.30V 205.0 203.0 203.0 LED Current [mA] LED Current [mA] 205.0 201.0 201.0 199.0 199.0 197.0 197.0 195.0 195.0 3.3 3.45 3.6 3.75 3.9 VIN [V] 4.05 4.2 3.3 3.45 3.6 3.75 VIN [V] 3.9 4.05 4.2 80mA Spotlight Current, RISET = 1.25W, VOUT = 2.96V 85.0 LED Current [mA] 83.0 81.0 79.0 77.0 75.0 3 3.45 2005 Semtech Corp. 3.9 VIN [V] 4.35 4.8 5.25 www.semtech.com SC635 POWER MANAGEMENT Typical Characteristics (Cont.) Flash Mode Ripple, RISET = 1.25W Spotlight Mode Ripple, RISET = 1.25W Ch1 50mV/div Ch2 200mV/div Ch3 200mV/div 4us/div Ch1 50mV/div Ch2 100mV/div Ch3 100mV/div 4us/div Startup Flash Mode 200mA Ch1 100mV/div Ch2 2V/div Ch3 2V/div Ch4 2V/div 40us/div 2005 Semtech Corp. www.semtech.com SC635 POWER MANAGEMENT Suggested Layout 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 200mA pulsed for one half clock cycle. C3 is the output decoupling capacitor placed near the SC635 VOUT pin. C4 is the input decoupling capacitor placed near the SC635 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 2005 Semtech Corp. www.semtech.com SC635 POWER MANAGEMENT Block Diagram VIN 1 LDO 250kHz 8 C+ 4 C- 10 C2+ CTRL 7 FLASH 5 LogicControl CHARGE PUMP Reference Voltage Generator 2005 Semtech Corp. 10 2 C2- 9 VOUT 3 GND 6 ISET www.semtech.com SC635 POWER MANAGEMENT Outline Drawing - MLPD-10 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 A2 .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 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 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 Information Top Mark 635 yyww xxxx yyww = Datecode (Example = 0552) xxxx = Semtech Lot Number 2005 Semtech Corp. 11 www.semtech.com SC635 POWER MANAGEMENT Land Pattern - MLPD-10 K (C) H DIM G Y X P Z C G H K P X Y Z 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 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 2005 Semtech Corp. 12 www.semtech.com