SC104 SEMTECH | Alldatasheet
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1 www.semtech.com SC104 Micro Power Constant-Current DC-DC Converter March 22, 2005 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. 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. The peak switch current is programmable through the external resistor R LIM 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 Adjustable output current using pulse width 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 Description Features
Applications
Typical Application Circuit - 6 LEDs ENABLE RSET 23.2R LED2 IOUT = 15mA U1 SC104 4 5 ADJ FB GND OUT LX IN LIM EN LED1 LED3 VIN = 3V to 5V LED5 RLIM 7.50k LED4 CIN 4.7uF IOUT ADJUST 12uH LED6 COUT 0.47uF
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Electrical Characteristics
Exceeding the specifications below may result in permanent damage to the device, or device malfunction. Operation outside of th e parameters specified in the Electrical Characteristics section is not implied.
3 2005 Semtech Corp. www.semtech.com SC104 POWER MANAGEMENT retemaraPl obmySs noitidnoCtseTn iMp yTx aMs tinU tnerruCtupnItsujdAI JDA V JDA V0=6 0 10 2A µ V JDA V1=0 05-0 0 05A n tnerruChctiwSmumixaMI XL I MIL Aµ051=0 29-m A emiTffOhctiwSt FFO V BF Vm003=0 6.06 7.00 0.1s µ V BF V0=0 0.15 2.10 6.1 emiTnOhctiwSt NO snoitidnocdetimiltnerrucsedulcxe8 .15 2.27 .2s µ elcyCytuDmumixaM% CD 07% egakaeLhctiwSI XL V,ffohctiws XL V5=1 0.0-0 .1-A µ timiLtnerruCrofecnerefeRegatloV rotsiseRgnitteS V MIL I MIL Aµ05=5 830 040 14V m I XL Iot MIL oitaRI XL I/ MIL I MIL Aµ05=0 0170 5180 088A /A stupnIcigoL egatloVtupnIelbanEV HI I NE An003>5 .1V VLI 2.0 tnerruCsaiBtupnIelbanEI LI V NE V3.0=3 .0A µ IHI V NE V3.1=7 .0 Electrical Characteristics (Cont.) Note: (1) Guaranteed by design. Unless specified: VIN = VEN = 2V, -40 ≤ TA ≤ 85°C, typical values are at room temperature.
4 2005 Semtech Corp. www.semtech.com SC104 POWER MANAGEMENT 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. rebmuNtraPe gakcaP RTLMI401CS )1( 8-PLM TRTLMI401CS )2( BVE401CSd raoBnoitaulavE Pin Configuration Ordering Information Block Diagram Top View MLP-8
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6 2005 Semtech Corp. www.semtech.com SC104 POWER MANAGEMENT Applications Information Component Selection - Introduction 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. ENABLE RSET 23.2R LED2 IOUT = 15mA U1 SC104 4 5 ADJ FB GND OUT LX IN LIM EN LED1 LED3 VIN = 3V to 5V LED5 RLIM 7.50k LED4 CIN 4.7uF IOUT ADJUST 12uH LED6 COUT 0.47uF Step 1: Continuous or Discontinuous? 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: () f)SAT(CEOUT fINOUT VVV VVVDC +− +−= 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. V IN = minimum input voltage Vf = Schottky diode (D1) forward voltage drop VCE(SAT) = power switch saturation voltage Using the 6 LED example above: VIN = 3V Vf = 0.35V VCE(SAT) = 0.25V 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. Step 2: Calculating the Inductor for Discontinuous Mode 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: () fINOUT f)SAT(CEOUT )MIN(OFF)MIN(ONOUTOUT )SAT(CEININ )MIN(ON )D( VVV VVV ttIV4.12 VVVtL +− −••= Where: tON(MIN) = minimum switch on-time = 1.8µs IOUT = required output current tOFF(MIN) = minimum switch off-time = 0.6µs 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. 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, I LIM(D), is given by: ( ) )D( )MIN(ON)SAT(CEIN )D(LIM L tVVI •−=
7 2005 Semtech Corp. www.semtech.com SC104 POWER MANAGEMENT Step 3: (Cont.) Using our 6 LED example: L(D) = 12µH thus ILIM(D) = 412mA Step 4: Calculating the Current Limit Resistor for Discontinuous Mode 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 I LIM increases as R LIM decreases, this value is a maximum. The maximum current limit resistor, RLIM(D), for discontinuous mode is therefore: −•− )D( )SAT(CEINplh )D(LIM )MIN()MIN(LIM )D(LIM L VVtI RatioVR 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 t plh = propagation delay from reaching the current limit trip point to the power switch turning off = 200ns Using our 6 LED example: ILIM(D) = 412mA thus RLIM(D) = 7.5kΩ 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. Step 5: Calculating the Current Set Resistor 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, V FB, which is typically 350mV. Thus the current set resistor value is given by the following Applications Information (Cont.) equation: OUT FB SET I VR = Using our 6 LED example: IOUT = 15mA thus RSET = 23.3Ω We will select the 1% resistor value 23.2Ω . 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: OUTOUT INfOUT)MIN(OFFIN )C( IV4.1 VVVtV2L •• −+•••= 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. Step 7: Calculating the Current Limit Required with this Inductor for Continuous 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 continuous mode current limit, I LIM(C), is given by: )C( )MIN(OFFINfOUT )C(LIM L4.0 tVVVI •
- −+= Step 8: Calculating the Current Limit Resistor for Continuous Mode 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
8 2005 Semtech Corp. www.semtech.com SC104 POWER MANAGEMENT Applications Information (Cont.) Step 8: (Cont.) inductor current ramps beyond the current limit trip point. Since I LIM increases as R LIM decreases, this value is a maximum. The maximum current limit resistor, RLIM(C), for continuous mode is therefore: −•− )C( )SAT(CEINplh )C(LIM )MIN()MIN(LIM )C(LIM L VVtI RatioVR 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 t plh = propagation delay from reaching the current limit trip point to the power switch turning off = 200ns Selecting the calculated value or the next lower standard value is recommended. 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. 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: 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, com- ponent height, and cost. Toko D62LCB and D63LCB se- ries work very well. LED Dimming 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.
9 2005 Semtech Corp. www.semtech.com SC104 POWER MANAGEMENT Shutdown Current vs. Junction Temperature vs. Input Voltage Average Feedback Voltage vs. Junction Temperature vs. Input Voltage Typical Characteristics Power Switch Saturation Voltage vs. Junction Temperature Current Limit Reference Voltage vs. Junction Temperature ILX to ILIM Ratio vs. Junction Temperature 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 -50 -25 0 25 50 75 100 T A (°C) IQ(OFF) (µA) VEN = 0V VIN = 5V VIN = 2V VIN = 10V 100 125 150 175 200 225 250 -50 -25 0 25 50 75 100 125 T J (°C) VCE(SAT) (mV) VIN = 2V ILX = 300mA 7000 7200 7400 7600 7800 8000 8200 8400 8600 8800 9000 -50 -25 0 25 50 75 100 125 T J (C) ILX/ILIM (A/A) VIN = 2V ILIM = 50µA 340 342 344 346 348 350 352 354 356 358 360 -50 -25 0 25 50 75 100 125 T J (C) VFB (mV) VIN = 2V VIN = 5V VIN = 10V 385.0 387.5 390.0 392.5 395.0 397.5 400.0 402.5 405.0 407.5 410.0 -50 -25 0 25 50 75 100 125 T J (°C) VLIM (mV) VIN = 2V ILIM = 50µA
10 2005 Semtech Corp. www.semtech.com SC104 POWER MANAGEMENT Typical Application Circuit - 3 LEDs RSET 23.2R IOUT = 15mA ENABLE 27uH CIN 4.7uF VIN = 3V to 5V LED1 IOUT ADJUST LED2 COUT 1uF LED3 U1 SC104 4 5 ADJ FB GND OUT LX IN LIM EN RLIM 15k ENABLEIOUT ADJUST RLIM 3.9k LED9 6.2uH LED4 COUT 0.22uF LED10 CIN 4.7uF LED8 LED1 LED2 LED7 U1 SC104 4 5 ADJ FB GND OUT LX IN LIM EN RSET 23.2R LED3 LED6 IOUT = 15mA VIN = 3V to 5V LED5 Typical Application Circuit - 10 LEDs
11 2005 Semtech Corp. www.semtech.com SC104 POWER MANAGEMENT Outline Drawing - MLP-8 e D E A B aaa C L 0.08.003 .118 3.00 01 0.450.20 0.29 .005-- 0.13-- .018.011.008 0.31.012 (LASER MARK) INDICATOR PIN 1 N 2 1 bbb DIMENSIONS e N aaa L b D E NOM INCHES A DIM MIN MAX MILLIMETERS MAXNOMMIN 3.10 3.10 2.90 2.90 .026 BSC .118 .004 .011 0.10
0.65 BSC
3.00 .015 0.29 0.39 bxN A bbb C A B .011 .008 .026 .000 .031 12° 0° - 12° 0.20 0.65 0.00 .018 .039 .030 .002 0.80 0.29 0.45 - 1.00 0.75 0.05 e/2 2. DIMENSIONS "D" AND "E" DO NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. CONTROLLING DIMENSIONS ARE IN MILLIMETERS (ANGLES IN DEGREES). NOTES: - (.008) (0.20) - PLANE SEATING C .122 .122 .114 .114
12 2005 Semtech Corp. www.semtech.com SC104 POWER MANAGEMENT Land Pattern - MLP-8 Semtech Corporation Power Management Products Division
200 Flynn Road, Camarillo, CA 93012
Phone: (805) 498-2111 FAX (805)498-3804 Contact Information Visit us at: www.semtech.com THIS LAND PATTERN IS FOR REFERENCE PURPOSES ONLY. CONSULT YOUR MANUFACTURING GROUP TO ENSURE YOUR COMPANY'S MANUFACTURING GUIDELINES ARE MET. NOTES: (C) Y G INCHES DIMENSIONS Z P Y X DIM C G MILLIMETERS (.114) (2.90) Z P 2.00.079 0.65.026 0.38.015 0.90.035 3.80.150 X