SY8291ABC

Application Note: AN_SY8291 High Efficiency, 800kHz, 40V Input, 1.2A Asynchronous Step Down Regulator General Description Features The SY8291 is a high efficiency 800 kHz, adaptive constant OFF time controlled asynchronous step-down DC-DC regulator capable of delivering 1.2A output current respectively. The SY8291 can operate over a wide input voltage range from 5V to 40V and integrate the main switch with very low Rds(on) to minimize the conduction loss. Low output voltage ripple and small external inductor and capacitor sizes are achieved with 800 kHz switching frequency. • 5-40V input voltage range • Low Rds(on) for internal N-channel Power FET: 180 mΩ • 800kHz 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 fo r Ordering Information Tempera ture Code Packa ge Code Optiona l Spec Code Package type SOT23-6 Note -- .C on fid en Typical Applications Set Top Box Portable TV Access Point Router DSL Modem LCD TV tia l-P re p Ordering Number SY8291ABC • • • • • ar ed Applications SY8291□(□□)□ IN CIN 4.7uF CBS 100nF Co rp VIN BS L 10uH VOUT=5V LX er gy D EN Sil OFF/ON R1 100kΩ CFF 22pF COUT 22uF FB R2 13.7kΩ GND Figure 1. Schematic Diagram SY8291 Rev. 0.9A Figure2. Efficiency Figure Silergy Corp. Confidential- Prepared for Customer Use Only 1 SY8291 Pinout (top view) BS 1 6 LX GND 2 5 IN FB 3 4 EN (SOT23-6) Top Mark: YMxyz (Device code: YM, x=year code, y=week code, z= lot number code) 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 tia l-P re p ar ed fo r Pin Name BS er gy Co rp .C on fid en (Note 1) Supply Input Voltage ----------------------------------------------------------------------------------------------------------- 42V Enable Voltage------------------------------------------------------------------------------------------------------ -----VIN + 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) Sil 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 SY8291 Rev. 0.9A Silergy Corp. Confidential- Prepared for Customer Use Only 2 SY8291 Electrical Characteristics (VIN = 12V, VOUT = 5V, L=10uH, COUT =22uF, TA = 25°C, IOUT = 0.5A unless otherwise specified) ISHDN VREF IFB RDS(ON)1 ILIM VENH VENL TOFF TOFF TON FOSC TSD Rising Falling Typ Max 40 Unit V V V mV µA 10 0.612 50 2 800 150 µA V nA mΩ A V V ns ns us kHz °C 15 °C 4.5 4.3 200 160 IOUT=0, VFB=VREF×105% EN=0 0.588 -50 VFB=VIN 0.6 180 2 1.5 tia l-P re p 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 Maximum ON Time Oscillator Frequency Thermal Shutdown Temperature Thermal Shutdown Recovery Hysteresis Min 5 0.4 100 100 r VUVLO_HYS IQ Test Conditions fo Symbol VIN VUVLO ar ed Parameter Input Voltage Range Input UVLO Threshold Input UVLO Threshold Input UVLO Hysteresis Quiescent Current THYS .C on fid en 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. Sil er gy Co rp Note 3: The device is not guaranteed to function outside its operating conditions SY8291 Rev. 0.9A Silergy Corp. Confidential- Prepared for Customer Use Only 3 SY8291 Sil er gy Co rp .C on fid en tia l-P re p ar ed fo r Typical Performance Characteristics AN_SY8291 Rev.0.9A Silergy Corp. Confidential-prepared for Internal Use Only 4 .C on fid en tia l-P re p ar ed fo r SY8291 Co rp Shutdown From Enable (VIN=12V, VOUT=5V, ILOAD=1.2A) er gy EN Startup From Enable (VIN=12V, VOUT=5V, ILOAD=1.2A) Sil VOUT 5V/div EN 5V/div VOUT 5V/div 5V/div VLX 10V/div VLX 10V/div IL 1A/div IL 1A/div Time (2ms/div) AN_SY8291 Rev.0.9A Time (2ms/div) Silergy Corp. Confidential-prepared for Internal Use Only 5 AN_SY8291 Applications Information Because of the high integration in the SY8291 IC, the application circuit based on this regulator IC is rather simple. Only input capacitor CIN, output capacitor COUT, output inductor L, rectifier diode D and feedback resistors (R1 and R2) need to be selected for the targeted applications. .C on 0.6V R1 . VOUT − 0.6V fid en 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: R2 = 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 + R1 3) Co rp R2 er gy The ripple current through input capacitor is calculated as： I CIN _ RMS = I OUT ⋅ D(1 − D) . Sil The SY8291 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. VOUT Input capacitor CIN: 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 4.7uF capacitance. AN_SY8291 Rev.0.9A Where FSW is the switching frequency and IOUT,MAX is the maximum load current. VOUT(1-VOUT/VIN,MAX) 2 ⋅ FSW ⋅ L 0.6VFB GND Output capacitor COUT: VOUT (1 − VOUT /VIN, MAX ) FSW × IOUT, MAX × 40% tia l-P re p Feedback resistor dividers R1 and R2: L= r 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: fo SY8291 is an asynchronous buck regulator IC that integrates the PWM control, main switch on the same die. With ultra low Rds(on) power switch and proprietary PWM control, this regulator IC can achieve high efficiency and fast transient response. High switch frequency minimizes the external inductor and capacitor size, thus minimize the PCB area and cost. SY8291 also features cycle by cycle current limit, 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 22uF capacitance. ar ed Operation 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