SX1308

SX1308 85T High Efficiency 1.2MHz 2A Step Up Converter 85T FEATURES GENERAL DESCRIPTION • Integrated 80mΩ Power MOSFET • 2V to 24V Input Voltage • 1.2MHz 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 96% Efficiency • Available in a 6-Pin SOT23-6 Package The SX1 308 is a constant frequency, 6-pin SOT23 current mode step-up converter intended for small, low power applications. The SX1308 switches at 1.2MHz 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 SX1308 features automatic shifting to pulse frequency modulation mode at light loads. The SX1308 includes under-voltage lockout, current limiting, and thermal overload protection to prevent damage in the event of an output overload. The SX1308 is available in a small 6-pin SOT-23 package. APPLICATIONS • Battery-Powered Equipment • Set-Top Boxed • LCD Bais Supply • DSL and Cable Modems and Routers • Networking cards powered from PCI or PCI express slots TYPICAL APPLICATION Efficiency (%) Efficiency Iout (mA) Figure 1. Basic Application Circuit Copyright ©2010 by Suosemi Corporation Figure 2. Efficiency Curve 1 SX1308 ABSOLUTE MAXIMUM RATINGS IN, EN voltages ………..….…… -0.3V to 26V Operating Temperature….... -40°C to +85°C FB Voltages ................................-0.3V to 6V Junction Temperature ………………...160°C SW Voltage ……………………..-0.3V to 30V Storage Temperature Range -65°C to 150°C Peak SW Sink and Source Current ………4A Lead Temperature (Soldering, 10s) ...+300°C PACKAGE/ORDER INFORMATION SW 1 6 NC GND 2 5 IN FB 3 4 EN SOT23-5 SOT23-6 (MT3540) (SX1308) PIN DESCRIPTION PIN NAME FUNCTION 1 SW Power Switch Output. SW is the drain of the internal MOSFET switch. Connect the power inductor and output rectifier to SW. SW can swing between GND and 28V. 2 GND Ground Pin 3 FB Feedback Input. The FB voltage is 0.6V. Connect a resistor divider to FB. 4 EN 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. 5 IN 6 NC Input Supply Pin. Must be locally bypassed. NC Copyright ©2010 by Suosemi Corporation 2 SX1308 ELECTRICAL CHARACTERISTICS (VIN=VEN=5V, TA = 25°C, unless otherwise noted.) Parameter Conditions Operating Input Voltage MIN TYP 2 Under Voltage Lockout Under Voltage Lockout Hysteresis MAX unit 24 V 1.98 V 100 mV Current (Shutdown) VEN= 0V 0.1 1 µA Quiescent Current (PFM) VFB=0.7V，No switch 100 200 µA Quiescent Current (PWM) VFB=0.5V，switch 1.6 2.2 mA Switching Frequency Maximum Duty Cycle 1.2 VFB = 0V EN Input High Voltage 90 % 1.5 V EN Input Low Voltage FB Voltage FB Input Bias Current VFB = 0.6V SW On Resistance (1) 0.588 0.6 -50 -10 80 SW Current Limit (1) VIN= 5V, Duty cycle=50% SW Leakage VSW = 20V Thermal Shutdown MHz 0.4 V 0.612 V nA 150 4 A 1 155 mΩ μA ℃ Note: 1) Guaranteed by design, not tested. Copyright ©2010 by Suosemi Corporation 3 SX1308 OPERATION The SX1308 uses a fixed frequency, peak current mode boost regulator architecture to regulate voltage at the feedback pin. The operation of the SX1308 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 0.6V bandgap 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 SX1308 has internal soft start to limit the amount of input current at startup and to also limit the amount of overshoot on the output. Figure 3. Functional Block Diagram Copyright ©2010 by Suosemi Corporation 4 SX1308 TYPICAL OPERATING CHARACTERISTICS Efficiency Curve Efficiency Current limit(A) Efficiency Curve Iout (mA) Iout(mA) Load regualation Vout(V) Vout(V) line Regulation Vin (V) Freq VS Vin Copyright ©2010 by Suosemi Corporation Iout (mA) Efficiency VS Vin 5 SX1308 APPLICATION INFORMATION Setting the Output Voltage Layout Consideration 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 For best performance of the SX1308, 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.  SW 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. 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 SX1308 used for mobile phone. The inductor should have low core loss at 1.2MHz 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 SX1308 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 SX1308 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. Copyright ©2010 by Suosemi Corporation 6 SX1308 PACKAGE DESCRIPTION TOP VIEW RECOMMENDED LAND PATTERN FRONT VIEW SIDE VIEW DETAIL “A” Figure 4. TSOT23-6/SOT23-6 Physical Dimensions 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 INTERLEAD FLASH OR PROTRUSION. 4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.10 MILLIMETERS MAX. 5) DRAWING CONFORMS TO JEDEC MO-193, VARIATION AB. 6) DRAWING IS NOT TO SCALE. 7) PIN 1 IS LOWER LEFT PIN WHEN READING TOP MARK FROM LEFT TO RIGHT, (SEE EXAMPLE TOP MARK) Copyright ©2010 by Suosemi Corporation 7