SY8290ABC

Application Note: AN_SY8290 High Efficiency, 2MHz, 40V Input, 200mA Asynchronous Step Down Regulator Preliminary Specification General Description Features The SY8290 is a high efficiency 2MHz, adaptive constant OFF time controlled asynchronous step-down DC-DC regulator capable of delivering 200mA output current. The SY8290 operates over a wide input voltage range from 5V to 40V. • • • • • • • Low output voltage ripple and small external inductor and capacitor sizes are achieved with 2MHz switching frequency. Ordering Information Applications SY8290 □(□□)□ • • • • • • Temperature Code Package Code Optional Spec Code Temperature Range: -40°C to 85°C Ordering Number SY8290ABC 5-40V input voltage range 2MHz switching frequency Adaptive constant OFF time control Internal softstart limits the inrush current 2% 0.6V reference RoHS Compliant and Halogen Free Compact package: SOT23-6 Package type SOT23-6 Note -- Smart meter Set Top Box Portable TV Access Point Router DSL Modem LCD TV Typical Applications VIN IN CBS 100nF BS CIN 2.2uF L = 10uH VOUT=12V LX D R1 100kΩ COUT 4.7uF FB EN R2 5.62kΩ OFF/ON GND Figure 1. Schematic Diagram AN_SY8290 Rev. 0.1 Figure2. Efficiency Figure Silergy Corp. Confidential- Prepared for Customer Use Only 1 AN_SY8290 Pinout (top view) BS 1 6 LX GND 2 5 IN FB 3 4 EN (SOT23-6) Top Mark: TExyz (Device code: TE, x=year code, y=week code, z= lot number code) Pin Name BS Pin Number 1 GND FB 2 3 EN IN LX 4 5 6 Pin Description Boot-Strap Pin. Supply high side gate driver. Decouple this pin to LX pin with 0.1uF ceramic cap. Ground pin Output Feedback Pin. Connect this pin to the center point of the output resistor divider (as shown in Figure 1) to program the output voltage: VOUT=0.6*(1+R1/R2) Enable control. Pull high to turn on. Do not float. Input pin. Decouple this pin to GND pin with at least 1uF ceramic cap Inductor pin. Connect this pin to the switching node of inductor Absolute Maximum Ratings (Note 1) Supply Input Voltage ----------------------------------------------------------------------------------------------------------- 42V Enable Voltage------------------------------------------------------------------------------------------------------------V IN + 0.6V FB Voltage----------------------------------------------------------------------------------------------------------------------- 3.6V BS to LX Voltage--------------------------------------------------------------------------------------------------------------- 3.6V Power Dissipation, PD @ TA = 25°C, SOT23-6-------------------------------------------------------------------------- 0.4W Package Thermal Resistance (Note 2) θ JA -------------------------------------------------------------------------------------------------------------- 250°C/W θ JC -------------------------------------------------------------------------------------------------------------- 130°C/W Junction Temperature Range ------------------------------------------------------------------------------------- ---------- 150°C Lead Temperature (Soldering, 10 sec.) ----------------------------------------------------------------------- ------------ 260°C Storage Temperature Range ------------------------------------------------------------------------------------- -65°C to 150°C Recommended Operating Conditions (Note 3) Supply Input Voltage -------------------------------------------------------------------------------------------------- 5V to 40V BS to LX Voltage ---------------------------------------------------------------------------------------------------------------3.3V Junction Temperature Range ------------------------------------------------------------------------------------- -40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------- -40°C to 85°C AN_SY8290 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 2 AN_SY8290 Electrical Characteristics (VIN = 20V, VOUT = 12V, L=10uH, COUT =4.7uF, TA = 25°C, IOUT = 100mA unless otherwise specified) Parameter Input Voltage Range Input UVLO Threshold Symbol VIN VUVLO Input UVLO Hysteresis Quiescent Current VUVLO_HYS IQ Shutdown Current Feedback Reference Voltage FB Input Current Power FET RON Power FET Current Limit EN Rising Threshold EN Falling Threshold Minimum OFF Time Minimum ON Time Soft Start Time Switching Frequency Thermal Shutdown Temperature Thermal Recovery Hysteresis ISHDN VREF IFB RDS(ON)1 ILIM VENH VENL TOFF TOFF Tss FSW TSD Test Conditions Min 5 Rising IOUT=0, VFB=VREF×105% EN=0 VFB=VIN THYS 0.588 -50 Typ 4.9 Unit V V 200 160 mV µA 0.6 10 2 Max 40 10 0.612 50 450 1.5 0.4 100 100 1.6 400 2 150 2.4 15 µA V nA Ω mA V V ns ns us MHz °C °C Note 1: Stresses beyond the “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only. Functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specification is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Note 2: θ JA is measured in the natural convection at TA = 25°C on a low effective single layer thermal conductivity test board of JEDEC 51-3 thermal measurement standard. Note 3: The device is not guaranteed to function outside its operating conditions AN_SY8290 Rev. 0.1 Silergy Corp. Confidential- Prepared for Customer Use Only 3 AN_SY8290 Typical Performance Characteristics AN_SY8290 Rev.0.1 Silergy Corp. Confidential-prepared for Internal Use Only 4 AN_SY8290 AN_SY8290 Rev.0.1 Silergy Corp. Confidential-prepared for Internal Use Only 5 AN_SY8290 Operation SY8290 is an asynchronous buck regulator IC that integrates the PWM control, main switch on the same die. High switch frequency minimizes the external inductor and capacitor size, thus minimizes the PCB area and cost. It features low output voltage ripple, cycle by cycle current limit, output short circuit protection and thermal shutdown protection. Output inductor L: There are several considerations in choosing this inductor. 1) Choose the inductance to provide the desired ripple current. It is suggested to choose the ripple current to be about 40% of the maximum output current. The inductance is calculated as: Applications Information L= VOUT (1 − VOUT /VIN, MAX ) FSW × IOUT, MAX × 40% Because of the high integration in the SY8290 IC, the application circuit based on this regulator IC is rather simple. Only input capacitor CIN, output capacitor COUT, output inductor L and feedback resistors (R1 and R2) need to be selected for the targeted applications. Where FSW is the switching frequency and IOUT,MAX is the maximum load current. Feedback resistor dividers R1 and R2: The SY8290 regulator IC is quite tolerant of different ripple current amplitude. Consequently, the final choice of inductance can be slightly off the calculation value without significantly impacting the performance. Choose R1 and R2 to program the proper output voltage. To minimize the power consumption under light loads, it is desirable to choose large resistance values for both R1 and R2. A value of between 10kΩ and 1MΩ is highly recommended for both resistors. If Vout is 5V, R1=100k is chosen, then using following equation, R2 can be calculated to be 13.7k: 2) The saturation current rating of the inductor must be selected to be greater than the peak inductor current under full load conditions. ISAT, MIN > IOUT, MAX + VOUT R2 = 0.6V R1 . VOUT − 0.6V R1 0.6VFB GND R2 Input capacitor CIN: The ripple current through input capacitor is calculated as： I CIN _ RMS = I OUT ⋅ D(1 − D) . To minimize the potential noise problem, place a typical X5R or better grade ceramic capacitor really close to the IN pin and the negative end of rectifier. A low ESR ceramic capacitor is recommended with greater than 1uF capacitance. Output capacitor COUT: The output capacitor is selected to handle the output ripple noise requirements. Both steady state ripple and transient requirements must be taken into consideration when selecting this capacitor. For the best performance, it is recommended to use X5R or better grade ceramic capacitor with greater than 4.7uF capacitance. AN_SY8290 Rev.0.1 3) VOUT(1-VOUT/VIN,MAX) 2 ⋅ FSW ⋅ L The DCR of the inductor and the core loss at the switching frequency must be low enough to achieve the desired efficiency requirement. It is desirable to choose an inductor with DCR