SY8401ABC

Application Note: SY8401 High Efficiency, 1.2MHz, 50V Input, 0.8A Asynchronous Step Down Regulator Preliminary Specification General Description Features The SY8401 develops a high efficiency asynchronous step-down DC-DC converter which is capable of delivering 0.8A output current. The device adopts current mode adaptive constant off time control. The SY8401 operates over a wide input voltage range from 4.5V to 50V and integrates main switch with very low RDS(ON) to minimize the conduction loss. • Low RDS(ON) for internal N-channel power FET:700mΩ • 4.5-50V input voltage range • 0.8A output current capability • 1.2MHz pseudo constant switching frequency • Internal soft-start limits the inrush current • Hic-cup mode output short circuit protection • EN ON/OFF control with accurate threshold • Cycle by cycle peak current limit • 0.6V±1 % reference voltage • SOT23-6 package Low output voltage ripple and small external inductor and capacitor sizes are achieved with 1.2MHz switching frequency. Ordering Information SY8401 □(□□)□ Tempera ture Code Packa ge Code Optiona l Spec Code Ordering Number SY8401ABC Package type SOT23-6 Note -- Applications • Non-Isolated Telecommunication Buck Regulator • Secondary High Voltage Post Regulator • Automotive Systems Typical Applications Figure 1. Schematic Diagram AN_SY8401 Rev. 0.1C Figure 2. Efficiency Silergy Corp. Confidential- Prepared for Customer Use Only 1 SY8401 Pinout (top view) (SOT23-6) Top Mark: My xyz(Device code: My, x=year code, y=week code, z= lot number code) Pin Name Pin Number BS 1 GND 2 FB 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 leave it floating. 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 ------------------------------------------------------------------------------------------------------ 55 V BS-LX --------------------------------------------------------------------------------------------------------------------------4V All other pins -------------------------------------------------------------------------------------------------------- VIN + 0.3V Power Dissipation, PD @ TA = 25°C SOT23-6, ------------------------------------------------------------------------- 1W Package Thermal Resistance (Note 2) θ JA ----------------------------------------------------------------------------------------------------------- 100°C/W θ JC ------------------------------------------------------------------------------------------------------------- 25°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 --------------------------------------------------------------------------------------------- 4.5V to 50V Junction Temperature Range --------------------------------------------------------------------------------- -40°C to 125°C Ambient Temperature Range --------------------------------------------------------------------------------- -40°C to 85°C AN_SY8401 Rev. 0.1C Silergy Corp. Confidential- Prepared for Customer Use Only 2 SY8401 Electrical Characteristics (VIN = 20V, VOUT = 12V, L = 6.8uH, COUT = 10uF, TA = 25°C, IOUT =0.1A unless otherwise specified) Parameter Input Voltage Range Quiescent Current Shutdown Current Feedback Reference Voltage FB Input Current Power FET RON Power FET Peak Current Limit EN Rising Threshold EN Falling Threshold Input UVLO Threshold Switching Frequency Switching Frequency Accuracy Min ON Time Min Off Time Soft-start Time Thermal Shutdown Temperature Thermal Shutdown Hysteresis Symbol VIN IQ ISHDN Test Conditions LX not switching EN=0 0.594 VREF IFB RDS(ON)1 Min 4.5 VFB=VIN Typ 150 5 0.6 -50 1.05 VENH VENL VUVLO FSW 1.14 0.94 50 1.2 1 THYS Unit V µA µA V nA mΩ 1.65 A 1.26 1.06 4.5 V V V MHz %FSW 1.2 -20 TSD 10 0.606 700 ILIM,TOP tSS Max 50 20 100 80 1.4 150 ns ns ms °C 15 °C Note 1: Stresses beyond “Absolute Maximum Ratings” may cause permanent damage to the device. These are for stress ratings. Functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions may affect device reliability. Note 2: θ JA is measured in the natural convection at TA = 25°C on a high effective thermal conductivity four-layer test board per JESD51-7. Pin 2 of SOT-23-6 packages is the case position for θ JC measurement. Note 3: The device is not guaranteed to function outside its operating conditions. AN_SY8401 Rev. 0.1C Silergy Corp. Confidential- Prepared for Customer Use Only 3 SY8401 Typical Performance Characteristics Efficiency vs. Output Current Efficiency vs. Output Current 100 100 90 90 80 80 70 70 60 60 50 50 40 VIN=12V,VOUT=5V VIN=24V,VOUT=5V VIN=40V,VOUT=5V 30 20 10 0.001 40 VIN=24V,VOUT=12V VIN=36V,VOUT=12V VIN=50V,VOUT=12V 30 20 0.01 0.1 1 0.001 Output Current (A) ∆VOUT IL Load Transient Load Transient (VIN=24V, VOUT=12V, IOUT=0A~0.4A) (VIN=24V, VOUT=12V, IOUT=0.08A~0.8A) IL 1 100mV/div ∆VOUT 500mV/div IL 500mA/div 200mA/div Time (200µs/div) Output Ripple Output Ripple (VIN=24V, VOUT=12V, IOUT=0A) (VIN=24V, VOUT=12V, IOUT=0.08A) ∆VOUT VLX 0.1 Output Current (A) Time (200µs/div) ∆VOUT 0.01 20mV/div 20mV/div VLX 10V/div IL 0.5A/div 10V/div 0.5A/div Time (4µs/div) AN_SY8401 Rev. 0.1C Time (4µs/div) Silergy Corp. Confidential- Prepared for Customer Use Only 4 SY8401 ∆VOUT Output Ripple Output Ripple (VIN=24V, VOUT=12V, IOUT=0.4A) (VIN=24V, VOUT=12V, IOUT=0.8A) 10mV/div ∆VOUT VLX 10V/div IL 0.5A/div Time (1µs/div) 10mV/div VLX 10V/div IL 1A/div Time (1µs/div) Startup from VIN Shutdown from VIN (VIN=24V, VOUT=12V, IOUT=0.8A) (VIN=24V, VOUT=12V, IOUT=0.8A) VIN 20V/div VIN 20V/div VOUT 10V/div VOUT 10V/div VLX 20V/div VLX 20V/div IL 0.5A/div IL 0.5A/div Time (10ms/div) VEN Time (4ms/div) Startup from Enable Shutdown from VIN (VIN=24V, VOUT=12V, IOUT=0.8A) (VIN=24V, VOUT=12V, IOUT=0.8A) VEN 5V/div 5V/div VOUT 10V/div VOUT 10V/div VLX 20V/div VLX 20V/div IL 0.5A/div IL 0.5A/div Time (4ms/div) AN_SY8401 Rev. 0.1C Time (4ms/div) Silergy Corp. Confidential- Prepared for Customer Use Only 5 SY8401 Short Circuit Protection Short Circuit Protection (VIN=24V, VOUT=12V, IOUT=0A~Short) (VIN=24V, VOUT=12V, IOUT=0.8A~Short) VOUT IL 10V/div 500mA/div Time (20ms/div) AN_SY8401 Rev. 0.1C VOUT IL 10V/div 500mA/div Time (20ms/div) Silergy Corp. Confidential- Prepared for Customer Use Only 6 SY8401 IN/GND pins. In this case, a 10uF low ESR ceramic capacitor is recommended. Operation The SY8401 develops a high efficiency asynchronous step-down DC-DC converter which is capable of delivering 0.8A output current. The device adopts current mode adaptive constant off time control. The SY8401 operates over a wide input voltage range from 4.5V to 50V and integrates 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 1.2MHz switching frequency. Applications Information Because of the high integration in the SY8401 IC, the application circuit based on this regulator IC is rather simple. Only input capacitor CIN, output capacitor COUT, output inductor L1 and feedback resistors (R1 and R2) need to be selected for the targeted applications specifications. Feedback Resistor Dividers R1 and R2: 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 1.2V, R1=100k is chosen, then using following equation, R2 can be calculated to be 100kΩ: 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 most applications, an X5R or better grade ceramic capacitor greater than 22uF capacitance can work well. The capacitance derating with DC voltage must be considered. Output Inductor L1: 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: L= VOUT (1 − VOUT /VIN, MAX ) FSW × IOUT, MAX × 40% where Fsw is the switching frequency and IOUT,MAX is the maximum load current. The SY8401 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 R1 R2 = 0.6V R1 . VOUT − 0.6V 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 and GND pins. Care should be taken to minimize the loop area formed by CIN, and AN_SY8401 Rev. 0.1C 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 + 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