SC104 Micro Power Constant-Current DC-DC Converter POWER MANAGEMENT Description Features The SC104 is a micro power dc-dc step-up converter which converts an input voltage, in the range of 1.55V to 10V, to a constant current. The part features a range of user programmable voltages and currents including dynamic adjustment of the “constant” current. The converter is capable of generating output voltages as low as the input supply voltage and up to 38V. During shutdown, the part draws a typical 500nA standby current. Adjustable output current using pulse width The output current is set by the external resistor R1. Dynamic adjustment of the output current can be made by the application of an analog voltage to the ADJ input, or by PWMing this pin. modulation or analog voltage input 38V output capability supports up to 10 white LEDs Wide range of input voltages 1.55V to 10V Low quiescent current 0.5µA standby current in shutdown Programmable cycle by cycle current limit Surface mount packaging (3x3mm 8pin MLP) Output voltage and over-temperature protection Applications The peak switch current is programmable through the external resistor RLIM enabling the use of a wide range of inductors and battery technologies. White LED supplies Color LED supplies Cellular phones PDAs Electronic books Handheld computers Wireless web appliances Typical Application Circuit - 6 LEDs VIN = 3V to 5V 1 IOUT ADJUST 2 IOUT = 15mA LED4 LED5 3 LED6 4 LED3 LED2 LED1 RSET 23.2R March 22, 2005 U1 SC104 ADJ EN FB LIM GND IN OUT LX CIN 4.7uF 8 ENABLE 7 6 5 L1 12uH RLIM 7.50k COUT 0.47uF D1 1 www.semtech.com SC104 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 Input Supply Voltage VIN -0.3 to 12 V LX Pin Voltage (Power switch OFF) V LX -0.3 to 55 V FB Pin Voltage V FB -0.3 to 6 V EN Pin Voltage V EN -0.3 to 6 V LIM Pin Voltage VLIM -0.3 to 6 V ADJ Pin Voltage V AD J -0.3 to 2 V OUT Pin Voltage VOUT -0.3 to 55 V Thermal Impedance Junction to Ambient θJ A 84 °C/W Operating Ambient Temperature Range TA -40 to +85 °C Operating Junction Temperature Range TJ -40 to +125 °C Storage Temperature Range TSTG -65 to +150 °C Lead Temperature SC104IMLTR (Soldering) 10s - 30s SC104IMLTRT (Soldering) 20s - 40s TLEAD 240 260 °C ESD Rating (Human Body Model) V ESD 2 kV Electrical Characteristics Unless specified: VIN = VEN = 2V, -40 ≤ TA ≤ 85°C, typical values are at room temperature. Parameter Input Supply Voltage Symbol Test Conditions Min VIN TA = 25oC 1.55 10 V 1.75 10 3 µA 340 350 360 mV 200 700 1115 nA 150 250 mV 140 150 160 Test current = 10µA 36 38 44 V IADJ= 0A 0.97 1.00 1.03 V 100 mV IQ(OFF) Feedback Voltage V FB Feedback Input Current IFB VFB < 350mV Power Switch Saturation Voltage VCE(SAT) ILX = 300mA Junction Temperature at Thermal Shutdown(1) TTSD Over-Voltage Protection VOVP Adjust Voltage V AD J 2005 Semtech Corp. Units 0.5 Shutdown Current Adjust Voltage Switching Inhibit Threshold Max V E N = 0V Typ VTH(ADJ) 2 o C www.semtech.com SC104 POWER MANAGEMENT Electrical Characteristics (Cont.) Unless specified: VIN = VEN = 2V, -40 ≤ TA ≤ 85°C, typical values are at room temperature. Parameter Adjust Input Current Symbol Test Conditions Min Typ Max Units IADJ V A D J = 0V 6 10 20 µA V A D J = 1V -500 0 500 nA VADJ = 1.25V -1.3 -2.3 -3.8 µA Maximum Switch Current ILX ILI M= 150µA -920 Switch Off Time tOFF VFB = 300mV 0.60 0.76 1.00 V FB = 0V 1.00 1.25 1.60 excludes current limited conditions 1.8 2.25 2.7 Switch On Time tON Maximum Duty Cycle %DC Switch Leakage Voltage Reference for Current Limit Setting Resistor ILX to ILIM Ratio mA 70 ILX switch off, VLX = 5V VLIM ILIM = 50µA ILX / ILIM VIH µs µs % -0.01 -1.0 µA 385 400 410 mV ILIM = 50µA 7100 8150 8800 A/A IEN > 300nA 1.5 Logic Inputs Enable Input Voltage 0.2 VIL Enable Input Bias Current V IIL VEN = 0.3V 0.3 IIH VEN = 1.3V 0.7 µA Note: (1) Guaranteed by design. 2005 Semtech Corp. 3 www.semtech.com SC104 POWER MANAGEMENT Pin Configuration Ordering Information Top View Part Number P ackag e SC104IMLTR(1) MLP-8 SC104IMLTRT(2) S C 104E V B Evaluation Board Notes: (1) Only available in tape and reel packaging. A reel contains 3000 devices. (2) Lead free product. This product is fully WEEE and RoHS compliant. MLP-8 Block Diagram 2005 Semtech Corp. 4 www.semtech.com SC104 POWER MANAGEMENT Pin Descriptions Pin Pin Name Pin Function 1 AD J 2 FB 3 GND Ground pin. 4 OUT Connect to the boost output at the cathode of the schottky diode. This pin is the input for the over-voltage protection circuit. 5 LX Internal switch connection. Connect the inductor and the anode of the schottky diode to this pin. 6 IN Input supply pin. Connect to a battery or power supply. 7 LIM Current limit set pin. A resistor (RLIM) connected from LIM to GND sets the peak inductor current limit threshold. 8 EN Digital input for enable. Connect this pin to ground for shutdown or connect a voltage between 1.2V to 5.0V for enable. A 1MΩ pull-up resistor connecting to IN is also acceptable, provided 10µA > IEN > 300nA. Apply a PWM or analog voltage to this pin for dynamic output current adjustment. Connects to the resistor in the ground leg of the series LEDs (feedback for the constant load current). Marking Information 104 yyww Marking for the MLP 8 Lead package: yyww = Date Code (Example: 0012) 2005 Semtech Corp. 5 www.semtech.com SC104 POWER MANAGEMENT Applications Information Component Selection - Introduction Vf = 0.35V VCE(SAT) = 0.25V Referring to the 6 LED typical schematic below, there are three components that depend upon the application that need to be determined: RSET - this resistor sets the output current for the device RLIM - this resistor sets the peak inductor current L - the output inductor All the other components can be mostly generalized and are addressed below the following design steps. thus DC = 0.87 Since this value is greater than the guaranteed minimum value for maximum duty cycle, the device will be operating in discontinuous mode to provide the desired output. Note that the duty cycle does not depend upon the output current, and that unless the output to input ratio is low, the device will usually need to be in discontinuous mode, so we will cover that first (Step 1 through Step 5). Continuous mode calculations start at Step 6. VIN = 3V to 5V 1 IOUT ADJUST 2 IOUT = 15mA LED4 LED5 3 LED6 4 LED3 LED2 LED1 RSET 23.2R U1 SC104 ADJ EN FB LIM GND IN OUT LX CIN 4.7uF 8 Step 2: Calculating the Inductor for Discontinuous Mode ENABLE 7 6 5 L1 12uH Having determined that we need to be operating in discontinuous mode, we next need to calculate the maximum inductor value allowed that will permit the part to output the correct power. The maximum discontinuous inductor value, L(D) is given by: RLIM 7.50k COUT 0.47uF D1 Step 1: Continuous or Discontinuous? t ON(MIN ) • VIN • (VIN − VCE ( SAT ) ) 2 L(D ) = The first thing to do when designing with the SC104 is to determine whether the output inductor will be operating in continuous mode (where the inductor current does not drop to zero while the device is switching) or discontinuous mode (where the inductor current drops to zero while switching). This determination can be made simply by calculating the required duty cycle needed for the target output voltage, and comparing it to the guaranteed minimum value for the maximum duty cycle from the Electrical Characteristics on Page 3. %DC(MIN) = 70% (or 0.7 duty). If DC is greater than 0.7 then discontinuous mode is required. The required duty cycle is calculated as follows: DC = OUT (V OUT − VCE ( SAT ) + Vf ) (VOUT − VIN + Vf ) Using our 6 LED example: IOUT = 15mA thus L(D) = 14.4µH Selecting the next lower standard value gives us L(D) = 12µH. Of course a lower value inductor may be used if desired, but may not necessarily be the most efficient choice. − VCE( SAT ) + Vf ) Where: VOUT = output voltage, the sum of the total LED (max.) forward voltage drop at the required output voltage plus the feedback voltage, 0.35V. VIN = minimum input voltage Vf = Schottky diode (D1) forward voltage drop VCE(SAT) = power switch saturation voltage Step 3: Calculating the Current Limit Required with this Inductor for Discontinuous Mode Having determined the inductor value we are going to use, we next need to calculate the current limit required to meet the necessary output power. The discontinuous mode current limit, ILIM(D), is given by: Using the 6 LED example above: VOUT = (6 * 3.475) + 0.35 = 21.2V VIN = 3V 2005 Semtech Corp. • Where: tON(MIN) = minimum switch on-time = 1.8µs IOUT = required output current tOFF(MIN) = minimum switch off-time = 0.6µs (VOUT − VIN + Vf ) (V 2 • 1.4 • VOUT • IOUT • (t ON(MIN ) + t OFF(MIN ) ) ILIM(D ) = 6 (V IN − VCE( SAT ) ) • t ON(MIN) L (D ) www.semtech.com SC104 POWER MANAGEMENT Applications Information (Cont.) Step 3: (Cont.) equation: Using our 6 LED example: L(D) = 12µH R SET = thus ILIM(D) = 412mA Using our 6 LED example: IOUT = 15mA Step 4: Calculating the Current Limit Resistor for Discontinuous Mode thus RSET = 23.3Ω We will select the 1% resistor value 23.2Ω. The current limit resistor value is calculated based upon the minimum ratio of the switch current to the current out of the LIM pin. It also takes into account the fact that there is a propagation delay during which time the inductor current ramps beyond the current limit trip point. Since ILIM increases as RLIM decreases, this value is a maximum. The maximum current limit resistor, RLIM(D), for discontinuous mode is therefore: RLIM(D ) = Note: this calculation is applicable to both continuous and discontinuous modes. Step 6: Calculating the Inductor for Continuous Mode Having determined that we need to be operating in continuous mode, we next need to calculate the maximum inductor value allowed that will permit the part to output the correct power. The maximum continuous inductor value, L(C) is given by: VLIM(MIN) • Ratio (MIN) t • (VIN − VCE(SAT ) ) ILIM(D ) − plh L ( D ) Where: VLIM(MIN) = the minimum value of the current limit voltage reference = 385mV Ratio (MIN) = the minimum value of the I LX to I LIM ratio = 7100 A/A tplh = propagation delay from reaching the current limit trip point to the power switch turning off = 200ns L(C) = 2 • VIN • t OFF(MIN) • (VOUT + Vf − VIN ) 1.4 • VOUT • IOUT Where: IOUT = required output current tOFF(MIN) = minimum switch off-time = 0.6µs Selecting the next lower standard value gives us a safe value for this inductor. Using our 6 LED example: ILIM(D) = 412mA Step 7: Calculating the Current Limit Required with this Inductor for Continuous Mode thus RLIM(D) = 7.5kΩ Having determined the inductor value we are going to use, we next need to calculate the current limit required to meet the necessary output power. The continuous mode current limit, ILIM(C), is given by: Selecting this value or the next lower standard value in this case gives us 7.5kΩ. Of course a lower value resistor may be used if desired, but may not necessarily be the most efficient choice. ILIM( C ) = Step 5: Calculating the Current Set Resistor (VOUT + Vf − VIN ) • t OFF(MIN) 0.4 • L( C ) Step 8: Calculating the Current Limit Resistor for Continuous Mode The current set resistor is in series with the series LED string. Thus the voltage developed across it is proportional to the current flowing through the LEDs. The device will regulate this voltage so that its average value equals the feedback voltage, VFB, which is typically 350mV. Thus the current set resistor value is given by the following 2005 Semtech Corp. VFB IOUT The current limit resistor value is calculated based upon the minimum ratio of the switch current to the current out of the LIM pin. It also takes into account the fact that there is a propagation delay during which time the 7 www.semtech.com SC104 POWER MANAGEMENT Applications Information (Cont.) Step 8: (Cont.) Schottky diode: any schottky diode rated for the average and peak currents being seen in the circuit will suffice. However a higher current rated schottky diode will result in lower forward voltage drops and hence higher efficiency. The selection of the schottky will depend upon the optimum choice between efficiency, board space, and cost. inductor current ramps beyond the current limit trip point. Since ILIM increases as RLIM decreases, this value is a maximum. The maximum current limit resistor, RLIM(C), for continuous mode is therefore: RLIM( C ) = VLIM(MIN ) • Ratio (MIN) t • (VIN − VCE(SAT ) ) ILIM( C ) − plh L(C) Inductor: similarly, any inductor rated for the average and peak currents required by the design and capable of operating at the fixed off-time of 760ns will suffice, but inductors with lower series resistance will result in lower losses. The selection of the inductor will depend upon the optimum choice between efficiency, board space, component height, and cost. Toko D62LCB and D63LCB series work very well. Where: VLIM(MIN) = the minimum value of the current limit voltage reference = 385mV Ratio (MIN) = the minimum value of the I LX to I LIM ratio = 7100 A/A tplh = propagation delay from reaching the current limit trip point to the power switch turning off = 200ns LED Dimming Selecting the calculated value or the next lower standard value is recommended. Dimming the LEDs (i.e. reducing the output current from the set level to reduce brightness) can be achieved a couple of ways: 1) PWMing the ADJ pin using an open drain or open collector (with no pull-up). Using a PWM signal at this pin will reduce the output current by alternating between OFF (ADJ < 100mV) and switching normally. The lower the duty cycle, the lower the output current. A PWM frequency of 1kHz maximum is recommended. 2) analog voltage applied to the ADJ pin: apply a DC voltage between 0V to 0.1V (OFF) and 1V (full current) to the ADJ pin. This pin should not be pulled above 1V under normal operation, and should never exceed the absolute maximum rating. Using a DC voltage will result in the modulation frequency of the inductor current ramp reducing and care must be taken to ensure that this does not become audible in sensitive applications. Component Selection - General Capacitor Selection: the SC104 has been designed to be used with ceramic input and output capacitors. The input to the device should be bypassed using a 4.7µF ceramic capacitor rated for the maximum input voltage. The output capacitor should be a ceramic capacitor in the range of 0.22µF to 1µF. Care should be taken that the voltage rating of this capacitor meets the output voltage requriements, and if the part is going to be run open circuit during assembly testing using the OVP feature, then the capacitor should be rated 50V. 2005 Semtech Corp. 8 www.semtech.com SC104 POWER MANAGEMENT Typical Characteristics Shutdown Current vs. Junction Temperature Average Feedback Voltage vs. Junction vs. Input Voltage Temperature vs. Input Voltage 360 2.0 VEN = 0V 358 1.6 356 1.4 354 1.2 352 VFB (mV) IQ(OFF) (µA) 1.8 VIN = 10V 1.0 VIN = 5V 0.8 V IN = 10V V IN = 5V 350 348 V IN = 2V 346 0.6 344 V IN = 2V 0.4 342 0.2 340 0.0 -50 -25 0 25 50 75 -50 100 -25 0 25 TA (°C) Current Limit Reference Voltage vs. Junction Temperature vs. Junction Temperature 100 125 100 125 410.0 VIN = 2V ILX = 300mA VIN = 2V ILIM = 50µA 407.5 200 405.0 175 402.5 150 VLIM (mV) VCE(SAT) (mV) 75 Power Switch Saturation Voltage 250 225 50 TJ (C) 125 100 75 400.0 397.5 395.0 392.5 50 390.0 25 387.5 0 -50 -25 0 25 50 75 100 385.0 125 -50 TJ (°C) -25 0 25 50 75 TJ (°C) ILX to ILIM Ratio vs. Junction Temperature 9000 VIN = 2V ILIM = 50µA 8800 8600 ILX/ILIM (A/A) 8400 8200 8000 7800 7600 7400 7200 7000 -50 -25 0 25 50 75 100 125 TJ (C) 2005 Semtech Corp. 9 www.semtech.com SC104 POWER MANAGEMENT Typical Application Circuit - 3 LEDs VIN = 3V to 5V U1 1 IOUT ADJUST 2 IOUT = 15mA 3 LED3 4 LED2 LED1 CIN 4.7uF SC104 ADJ EN FB LIM GND IN OUT LX 8 ENABLE 7 6 5 L1 27uH RLIM 15k COUT 1uF RSET 23.2R D1 Typical Application Circuit - 10 LEDs VIN = 3V to 5V 1 IOUT ADJUST 2 IOUT = 15mA LED6 LED7 LED8 LED9 3 LED10 4 LED5 LED4 LED3 LED2 LED1 SC104 ADJ EN FB LIM GND IN OUT LX 8 ENABLE 7 6 5 L1 6.2uH RLIM 3.9k COUT 0.22uF RSET 23.2R 2005 Semtech Corp. U1 CIN 4.7uF D1 10 www.semtech.com SC104 POWER MANAGEMENT Outline Drawing - MLP-8 D A B N DIM E PIN 1 INDICATOR (LASER MARK) 1 2 01 SEATING PLANE A3 A2 A aaa C C bxN bbb A1 A A1 A2 A3 b b2 D E e L L1 L2 N 01 aaa bbb DIMENSIONS MILLIMETERS INCHES MIN NOM MAX MIN NOM MAX .031 .039 .000 .002 .026 .030 (.008) .011 .012 .015 .007 .012 .114 .118 .122 .114 .118 .122 .026 BSC .008 .011 .018 .008 .011 .018 .005 8 0° 12° .003 .004 1.00 0.80 0.00 0.05 0.65 0.75 (0.20) 0.29 0.31 0.39 0.17 0.30 2.90 3.00 3.10 2.90 3.00 3.10 0.65 BSC 0.20 0.29 0.45 0.20 0.29 0.45 0.13 8 0° 12° 0.08 0.10 C A B e L2 e/2 L b2 L1 L2 NOTES: 1. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). 2. DIMENSIONS "D" AND "E" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. 2005 Semtech Corp. 11 www.semtech.com SC104 POWER MANAGEMENT Land Pattern - MLP-8 X DIM (C) G Z Y P DIMENSIONS INCHES MILLIMETERS (.114) .079 .026 .015 .035 .150 C G P X Y Z (2.90) 2.00 0.65 0.38 0.90 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 Visit us at: www.semtech.com 2005 Semtech Corp. 12 www.semtech.com