STI3508

STI3508 28V High Efficiency 1MHz, 2A Step Up Regulator FEATURES            GENERAL DESCRIPTION Integrated 80mΩ Power MOSFET 2V to 24V Input Voltage 1MHz Fixed Switching Frequency Internal 4A Switch Current Limit Adjustable Output Voltage Internal Compensation Up to 28V Output Voltage Automatic Pulse Frequency Modulation Mode at Light Loads up to 97% Efficiency Available in a 6-Pin SOT23-6 Package APPLICATIONS      Battery-Powered Equipment Set-Top Boxed White LED Driver Power Bank DSL and Cable Modems and Routers The STI3508 is a constant frequency, 6-pin SOT23 current mode step-up converter intended for small, low power applications. The STI3508 switches at 1MHz and allows the use of tiny, low cost capacitors and inductors 2mm or less in height. Internal soft-start results in small inrush current and extends battery life. The STI3508 features automatic shifting to pulse frequency modulation mode at light loads. The STI3508 includes under-voltage lockout, current limiting, and thermal overload protection to prevent damage in the event of an output overload. The STI3508 is available in a small 6-pin SOT-23 package. APPILCATIONS Figure 1. Basic Application Circuit TMI and SUNTO are the brands of TOLL microelectronic STI3508 V2.1 2013.05 www.toll-semi.com www.suntosemi.com 1 STI3508 ABSOLUTE MAXIMUM RATINGS (Note 1) Parameter Value Unit Input Supply Voltage , 2~24 V LX Voltages 28 V EN,FB Voltage 24 V Junction Temperature(Note2) 155 °C Power Dissipation 500 mW Lead Temperature(Soldering,10s) 260 °C PACKAGE/ORDER INFORMATION SOT23-6 Top Mark: S35XXX (S35: Device Code, XXX: Inside Code) www.toll-semi.com 2 Part Number Package Top mark Quantity/ Reel STI3508 SOT23-6 S35XXX 3000 www.suntosemi.com TMI and SUNTO are the brands of TOLL microelectronic STI3508 V2.1 2013.05 STI3508 PIN DESCRIPTIONS Pin Name Function 1 LX 2 GND 3 FB 4 EN 5 IN Input Supply Pin. Must be locally bypassed. 6 NC Not Connection Power Switch Output. LX is the drain of the internal MOSFET switch. Connect the power inductor and output rectifier to LX. LX can swing between GND and 28V. Ground Pin Feedback Input. The FB voltage is 0.6V. Connect a resistor divider to FB. Regulator On/Off Control Input. A high input at EN turns on the converter, and a low input turns it off. When not used, connect EN to the input supply for automatic startup. ESD RATING Items Description Value Unit VESD Human Body Model for all pins ±2000 V JEDEC specification JS-001 RECOMMENDED OPERATING CONDITIONS Items Description Voltage Range IN 2 24 V TA Operating Temperature Range -40 85 °C TMI and SUNTO are the brands of TOLL microelectronic STI3508 V2.1 2013.05 Min www.toll-semi.com Max Unit www.suntosemi.com 3 STI3508 ELECTRICAL CHARACTERISTICS (Note 3) ( VIN=VEN=5V , TA = 25°C, unless otherwise noted.) Parameter Conditions Operating Input Voltage Min Typ 2 Under Voltage Lockout Under Voltage Lockout Hysteresis Current (Shutdown) Max Unit 24 V 1.98 V 100 mV VEN = 0V 0.1 1 Quiescent Current (PFM) VFB=1.2V，No switch 100 200 µA Quiescent Current (PWM) VFB=1.2V，switch 1.6 2.2 mA Switching Frequency Maximum Duty Cycle 1 VFB = 0V EN Input High Voltage FB Input Bias Current VFB = 1.2V LX On Resistance (1) LX Current Limit (1) VIN= 5V, Duty cycle=50% LX Leakage VLX = 12V Thermal Shutdown MHz 90 % 1.5 V EN Input Low Voltage FB Voltage µA 0.4 V 0.612 V 0.588 0.6 -50 -10 nA 80 mΩ 3.5 A 1 μA ℃ 155 Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ = TA + (PD) x (250°C/W). Note3: 100% production test at +25°C. Specifications over the temperature range are guaranteed by design and characterization. Note 4: Dynamic supply current is higher due to the gate charge being delivered at the switching frequency www.toll-semi.com 4 www.suntosemi.com TMI and SUNTO are the brands of TOLL microelectronic STI3508 V2.1 2013.05 STI3508 OPERATION The STI3508 uses a fixed frequency, peak current mode boost regulator architecture to regulate voltage at the feedback pin. The operation of the STI3508 can be understood by referring to the block diagram of Figure 3. At the start of each oscillator cycle the MOSFET is turned on through the control circuitry. To prevent sub-harmonic oscillations at duty cycles greater than 50 percent, a stabilizing ramp is added to the output of the current sense amplifier and the result is fed into the negative input of the PWM comparator. When this voltage equals the output voltage of the error amplifier the power MOSFET is turned off. The voltage at the output of the error amplifier is an amplified version of the difference between the 1.2V band gap reference voltage and the feedback voltage. In this way the peak current level keeps the output in regulation. If the feedback voltage starts to drop, the output of the error amplifier increases. These results in more current to flow through the power MOSFET, thus increasing the power delivered to the output. The STI3508 has internal soft start to limit the amount of input current at startup and to also limit the amount of overshoot on the output. FUNCTIONAL BLOCK DIAGRAM Figure 2.STI3508 Block Diagram TMI and SUNTO are the brands of TOLL microelectronic STI3508 V2.1 2013.05 www.toll-semi.com www.suntosemi.com 5 STI3508 APPLICATION INFORMATION Setting the Output Voltage The internal reference VREF is 0.6V (Typical).The output voltage is divided by a resistor divider,R1 and R2 to the FB pin. The output voltage is given by VOUT  VREF  (1  R1 ) R2 Inductor Selection The recommended values of inductor are 4.7 to 22μH. Small size and better efficiency are the major concerns for portable device, such as STI3508 used for mobile phone. The inductor should have low core loss at 1MHz and low DCR for better efficiency. To avoid inductor saturation current rating should be considered. Capacitor Selection Input and output ceramic capacitors of 22μF are recommended for STI3508 applications. For better voltage filtering, ceramic capacitors with low ESR are recommended. X5R and X7R types are suitable because of their wider voltage and temperature ranges. Diode Selection Schottky diode is a good choice for STI3508 because of its low forward voltage drop and fast reverses recovery. Using Schottky diode can get better efficiency. The high speed rectification is also a good characteristic of Schottky diode for high switching frequency. Current rating of the diode must meet the root mean square of the peak current and output average current multiplication as following: I D ( RMS )  I OUT  I PEAK The diode’s reverse breakdown voltage should be larger than the output voltage. Layout Consideration For best performance of the STI3508, the following guidelines must be strictly followed.  Input and Output capacitors should be placed close to the IC and connected to ground plane to reduce noise coupling.  The GND should be connected to a strong ground plane for heat sinking and noise protection.  Keep the main current traces as possible as short and wide.  LX node of DC-DC converter is with high frequency voltage swing. It should be kept at a small area.  Place the feedback components as close as possible to the IC and keep away from the noisy devices. www.toll-semi.com 6 www.suntosemi.com TMI and SUNTO are the brands of TOLL microelectronic STI3508 V2.1 2013.05 STI3508 PACKAGE INFORMATION SOT23-6 Note: 1) All dimensions are in millimeters. 2) Package length does not include mold flash, protrusion or gate burr. 3) Package width does not include inter lead flash or protrusion. 4) Lead popularity (bottom of leads after forming) shall be 0.10 millimeters max. 5) Pin 1 is lower left pin when reading top mark from left to right, TMI and SUNTO are the brands of TOLL microelectronic STI3508 V2.1 2013.05 www.toll-semi.com www.suntosemi.com 7