SD3314A

SD3314A HIGH EFFICIENCY 1A STEP-DOWN CONSTANT CURRENT LED DRIVER Description Features The SD3314A is a step-down constant current LED driver. When the • Efficiency up to 93% input voltage down to lower than LED forward voltage, then SD3314A • 180µA(typ) Quiescent Current run into LDO mode. • Output Current: Up to 1A • Internal Synchronous Rectifier • 1.5MHz Switching Frequency • Soft-Start • Under-Voltage Lockout • Short LED Protection • Open LED Protection SD3314A employ internal power switch and synchronous rectifier to • Thermal Shutdown minimize external part count and realize high efficiency. • 5-Pin Small TSOT25 Packages • Pb-Free Package The SD3314A supports a range of input voltages from 2.5V to 6.0V, allowing the use of a single Li+/Li-polymer cell, 3AA or 4AA cell, USB, and other standard power sources. The FB voltage is only 0.1V to achieve high efficiency. During shutdown, the input is disconnected from the output and the shutdown current is less than 1µA. Other key features include undervoltage lockout to prevent deep battery discharge of the Li+ battery. Pin Assignments Applications • 3AA or 4AA Batteries Powered Flashlight • 1 Cell Li-Ion Battery Powered Flashlight Marking Information Top View TSOT25 EEVYW EE: Product Code of SD3314A V: Internal Code Y: Year W: Week Typical Applications Circuit ILED = 0.1/RS 1 www.sdw-tw.com Oct 2012 Rev1.0 SD3314A Pin Description Pin Number Pin Name 1 EN 2 3 4 GND 5 Function Enable control input. Force this pin voltage above 1.5V, enables the chip, and below 0.3V shuts down the device. Ground SW The drains of the internal main and synchronous power MOSFET. VIN Chip main power supply pin. FB Feedback voltage to internal error amplifier, the threshold voltage is 0.1V. Block Diagram Absolute Maximum Ratings (@TA = +25°C, unless otherwise specified.) These are stress ratings only and functional operation is not implied. Exposure to absolute maximum ratings for prolonged time periods may affect device reliability. All voltages are with respect to ground. Parameter Input Pin Voltage EN, FB Pin Voltage SW Pin Voltage Junction Temperature Range Storage Temperature Range Soldering Temperature Rating -0.3 to +6.5 Unit -0.3 to VIN V -0.3 to (VIN +0.3) 150 -65 to +150 300, 5sec °C 2 www.sdw-tw.com Oct 2012 Rev1.0 SD3314A Recommended Operating Conditions (@TA = +25°C, unless otherwise specified.) Parameter Rating Supply Voltage Unit 2.5 to 6.0 Operation Temperature Range -40 to +85 Junction Temperature Range -40 to +125 °C Thermal Information Symbol Package Max Thermal Resistance (Junction to Case) Parameter θJC TSOT25 (Note 1) 130 Thermal Resistance (Junction to Ambient) θJA TSOT25 250 Internal Power Dissipation PD TSOT25 400 Note: Unit °C/W mW 1. The maximum output current for TSOT25 package is limited by internal power dissipation capacity as described in Application Information herein after. Electrical Characteristics (@TA = +25°C, VIN = 4.2V, Real WLED load, L = 4.7µH, CIN = 10µF, CO = 10µF, unless otherwise specified.) Parameter Symbol Test Conditions Min Input Voltage Range VIN 2.5 Regulated Feedback Voltage VFB 0.095 Peak Inductor Current IPK Quiescent Current IQ VIN = 5V No Load Shutdown Current ISD VEN = 0V Oscillator Frequency fOSC VO = 100% Drain-Source On-State Resistance SW Leakage Current RDS(ON) High Efficiency ILSW η EN Threshold High VEH EN Threshold Low VEL EN Leakage Current Over Temperature Protection OTP Hysteresis 1.2 P MOSFET N MOSFET IDS = 100mA Typ 0.100 Max Units 6.0 V 0.105 A 180 µA 1 µA 1.5 1.8 MHz 0.30 0.35 0.45 0.50 Ω Ω ±0.01 1 µA 93 % 1.5 V 0.3 IEN OTP OTH V 1.5 V ±0.01 µA 150 30 °C °C 3 www.sdw-tw.com Oct 2012 Rev1.0 SD3314A Typical Performance Characteristics (@TA = +25°C, L = 4.7µF, CIN = 10µF, CO = 10µF, unless otherwise specified.) 4 www.sdw-tw.com Oct 2012 Rev1.0 SD3314A Typical Performance Characteristics (cont.) @TA = +25°C, L = 4.7µF, CIN = 10µF, CO = 10µF, unless otherwise specified.) 5 www.sdw-tw.com Oct 2012 Rev1.0 SD3314A Application Information The basic SD3314A application circui t is shown in Page 1. External component selection is determined by the load requirement, selecting L first and then CIN and COUT. Inductor Selection For most applications, the value of the inductor will fall in the range of 1μH to 4.7μH. Its value is chosen based on the desired ripple current. Large value inductors lower ripple current and small value inductors result in higher ripple currents. Higher VIN or VOUT also increases the ripple current as shown in equation 1. A reasonable starting point for setting ripple current is ΔIL = 400mA (40% of 1A). ΔIL = ⎛ 1 V OUT ⎞⎟ V OUT ⎜⎜1 − ⎟ (f )(L ) VIN ⎠ ⎝ Equation (1) The DC current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. Thus, a 1.4A rated inductor should be enough for most applications (1A + 400mA). For better efficiency, choose a low DC-resistance inductor. Using Ceramic Input Output Capacitors Higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. Their high ripple current, high voltage rating and low ESR make them ideal for switching regulator applications. Using ceramic capacitors can achieve very low output ripple and small circuit size. When choosing the input and output ceramic capacitors, choose the X5R or X7R dielectric formulations. These dielectrics have the best temperature and voltage characteristics of all the ceramics for a given value and size. Thermal Consideration Thermal protection limits power dissipation in the SD3314A. When t he junction temperature exceeds +150°C, the OTP (Over Temperature Protection) starts the thermal shutdown and turns the pass transistor off. The pass transistor resumes operation after the junction temperature drops below +120°C. For continuous operation, the junction temperature should be maintained below +125°C. The power dissipation is defined as: PD = IO2 V O RDS(ON)H + (VIN − V O )RDS(ON)L VIN + (tSW FSIO + IQ ) VIN IQ is the step-down converter quiescent current. The term tsw is used to estimate the full load step-down converter switching losses. For the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: PD = IO2 RDS(ON)H + IQ VIN Since RDS(ON), quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete input voltage range. The maximum power dissipation depends on the thermal resistance of IC package, PCB layout, the rate of surrounding airflow and temperature difference between junction and ambient. The maximum power dissipation can be calculated by the following formula: PD = T J(MAX ) − T A θJA Where TJ(MAX) is the maximum allowable junction temperature +125°C. TA is the ambient temperature and θJA is the thermal resistance from the junction to the ambient. Based on the standard JEDEC for a two layers thermal test board, the thermal resistance θJA of TSOT25 package is 250°C/W. The maximum power dissipation at TA = +25°C can be calculated by following formula: PD = (125°C − 25°C ) / 250°C / W = 0.4 W 6 www.sdw-tw.com Oct 2012 Rev1.0 SD3314A Application Information Setting the Output Current The internal feedback(FB) voltage is 0.1V (Typical). The output current is calculated as below: ILED = 0.1 / RS The output Current is given by the following table. ILED(mA) RS(Ω) 0.286 350 0.143 700 0.1 1000 As the input voltage approaches the LED forward voltage, the SD3314A turns the P-Chan nel transistor continuously on. In this mode the Voltage drop on LED is equal to the input voltage minus the voltage drop across the P-Channel transistor, Inductor and current resistor: ( VLEDDROP = VIN − ILED RDS(ON) + RL + RS ) where RDS(ON) = P-Channel switch ON resistance, ILED = LED current, RL = Inductor DC Resistance, RS = Inductor DC Resistance. Thermal Shutdown When the die temperature exceeds +150°C, a reset occurs and the reset remains until the temperature decrease to +120°C, at which time the circuit can be restarted. PCB Layout Check List When laying out the printed circuit board, the following checklist should be used to ensure proper operation of the SD3314A. Th ese items are also illustrated graphically in Figure 1. Check the following in your layout: 1. The power traces, consisting of the GND trace, the SW trace and the VIN trace should be kept short, direct and wide. 2. Does the VFB pin connect directly to the current sense resistor? The current sense resistor to GND trace should be kept short, direct and wide. 3. Does the (+) plate of CIN connect to VIN as closely as possible? This capacitor provides the AC current to the internal power MOSFETs. 4. Keep the switching node, SW, away from the sensitive VFB node. 5. Keep the (–) plates of CIN and COUT as close as possible. 7 www.sdw-tw.com Oct 2012 Rev1.0 SD3314A Ordering Information Part Number SD3314A Marking Refer to Marking Information Below Package Type Standard Package TSOT25 3000 Units/Tape&Reel Package Outline Dimensions (All dimensions in mm.) TSOT25 8 www.sdw-tw.com Oct 2012 Rev1.0