SY8121BABC

Application Note: SY8121B High Efficiency Fast Response, 2A, 18V Input 1.2MHz Synchronous Step Down Regulator General Description Features SY8121B develops high efficiency synchronous stepdown DC-DC converter capable of delivering 2A load current. SY8121B operates over a wide input voltage range from 4.5V to 18V and integrates main switch and synchronous switch with very low RDS(ON) to minimize the conduction loss. • Low RDS(ON) for internal switches (top/bottom):170/160 mΩ • 4.5-18V input voltage range • 2A load current capability • Instant PWM architecture to achieve fast transient responses • Internal softstart limits the inrush current • 2% 0.6V reference • RoHS Compliant and Halogen Free • Compact package: SOT23-6 SY8121B always operates under continuous condition mode, low output ripple and small inductor and capacitor size are achieved with 1.2MHz switching frequency. fo r Ordering Information Note -- re re Package type SOT23-6 Set Top Box Portable TV Access Point Router DSL Modem LCD TV tia l-P Ordering Number SY8121BABC • • • • • pa Temperature Code Package Code Optional Spec Code d Applications SY8121 □(□□)□ Sil Efficiency (%) er gy Co rp .C on f id en Typical Applications Figure 1. Schematic Diagram AN_SY8121B Rev.0.9 Figure 2. Efficiency Figure Silergy Corp. Confidential-prepared for Internal Use Only 1 SY8121B Pinout (top view) (SOT23-6) Top Mark: TVxyz for SY8121BABC, (Device code: TV, x=year code, y=week code, z= lot number code) SOT23-6 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 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 l-P re pa re d fo r Pin Name tia Absolute Maximum Ratings (Note 1) Co rp .C on f id en Supply Input Voltage -------------------------------------------------------------------------------------------------------- 21V LX, EN Voltage------------------------------------------------------------------------------------------------------- VIN + 0.3V FB, BS-LX Voltage------------------------------------------------------------------------------------------------------------- 4V 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 gy Recommended Operating Conditions (Note 3) Sil er Supply Input Voltage --------------------------------------------------------------------------------------------- 4.5V to 18V Junction Temperature Range --------------------------------------------------------------------------------- -40°C to 125°C Ambient Temperature Range ---------------------------------------------------------------------------------- -40°C to 85°C AN_SY8121B Rev.0.9 Silergy Corp. Confidential-prepared for Internal Use Only 殷先生：１３３８０３６８９３９　　　　　ＱＱ：７１９３０７６１０ 2 SY8121B Block Diagram IN BS Input UVLO 4.5V Internal Power LX FB fo 1.5V r PWM Control & Protect Logic EN d Current Sense 0.6V pa re Internal SST GND Sil er gy Co rp .C on f id en tia l-P re Thermal Protection AN_SY8121B Rev.0.9 Silergy Corp. Confidential-prepared for Internal Use Only 殷先生：１３３８０３６８９３９　　　　　ＱＱ：７１９３０７６１０ 3 SY8121B Electrical Characteristics (VIN = 12V, VOUT = 1.2V, L = 2.2uH, COUT = 10uF, TA = 25°C, IOUT = 1A unless otherwise specified) Parameter Input Voltage Range Shutdown Current Feedback Reference Voltage FB Input Current Top FET RON Bottom FET RON Bottom FET Valley Current Limit EN Rising Threshold EN Falling Threshold Input UVLO Threshold Switching Frequency Min ON Time Min Off Time Thermal Shutdown Temperature Thermal Shutdown Hysteresis Symbol VIN ISHDN Test Conditions Min 4.5 EN=0 0.588 VREF IFB RDS(ON)1 RDS(ON)2 VFB=VIN Typ 5 0.6 -50 Max 18 10 0.612 Unit V µA V 50 nA Ω Ω 3.45 A 0.17 0.16 ILIM 2 VENH VENL VUVLO FSW 1.5 1.2 50 100 150 V V V MHz ns ns °C 15 °C re d fo r 0.4 4.5 pa TSD l-P re THYS id en tia 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. on f 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 JEDEC 51-7. Pin 2 of SOT-23-6 packages is the case position for θ JC measurement. Sil er gy Co rp .C Note 3: The device is not guaranteed to function outside its operating conditions. AN_SY8121B Rev.0.9 Silergy Corp. Confidential-prepared for Internal Use Only 殷先生：１３３８０３６８９３９　　　　　ＱＱ：７１９３０７６１０ 4 SY8121B Typical Performance Characteristics Efficiency vs. Load Current Efficiency vs. Load Current 100 100 Efficiency (%) 90 90 80 80 70 70 60 60 50 VIN=5.0V,VOUT=1.2V VIN=12V,VOUT=1.2V VIN=18V,VOUT=1.2V 40 VIN=5.0V,VOUT=3.3V VIN=12V,VOUT=3.3V VIN=18V,VOUT=3.3V 50 30 40 0 0.5 1 1.5 2 0 2.5 0.5 1 2 2.5 Load Current (A) fo r Load Current (A) 1.5 Output Ripple Efficiency vs. Load Current d (VIN=12V, VOUT=3.3V, ILOAD=2A) re 100 pa ∆VOUT re 90 l-P 80 60 tia 70 40 0.5 1 1.5 2 on f 0 2A/div id 50 IL 10V/div en VIN=7.0V,VOUT=5V VIN=12V,VOUT=5V VIN=18V,VOUT=5V VLX 10mV/div 2.5 Time (1µs/div) .C Load Current (A) Load Transient (VIN=12V, VOUT=3.3V, ILOAD=0.2 ~2A) Co rp Load Transient (VIN=12V, VOUT=3.3V, ILOAD=Null ~1A) 50mV/div ∆VOUT 100mV/div Sil er gy ∆VOUT IL IL 1A/div Time (200µs/div) AN_SY8121B Rev.0.9 1A/div Time (200µs/div) Silergy Corp. Confidential-prepared for Internal Use Only 殷先生：１３３８０３６８９３９　　　　　ＱＱ：７１９３０７６１０ 5 SY8121B Startup from VIN (VIN=12V, VOUT=3.3V, ILOAD=2A) VIN 5V/div VOUT 2V/div VLX 10V/div IL 2A/div r Time (2ms/div) fo Startup from Enable 5V/div VLX 10V/div VOUT 2V/div 1A/div Sil er gy Co rp .C on Time (400µs/div) fid en IL tia l-P re p EN ar ed (VIN=12V, VOUT=3.3V, ILOAD=2A) AN_SY8121B Rev.0.9 Silergy Corp. Confidential-prepared for Internal Use Only 6 SY8121B SY8121B is a synchronous buck regulator IC that integrates the PWM control, top and bottom switches on the same die to minimize the switching loss and conduction loss. With ultra low RDS(ON) power switches 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, and thus achieving the minimum solution footprint. SY8121B also features cycle by cycle current limiting, output short circuit protection and thermal shutdown protection. Co rp .C on fo 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 3.3V, R1=100k is chosen, then using following equation, R2 can be calculated to be 22.1k: VOUT R1 Sil The ripple current through input capacitor is calculated as： I CIN _ RMS = I OUT ⋅ D(1 − D) . AN_SY8121B Rev.0.9 ar ed The SY8121B 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. 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) Input capacitor CIN: VOUT (1 − VOUT /VIN, MAX ) FSW × IOUT, MAX × 40% where Fsw is the switching frequency and IOUT,MAX is the maximum load current. R2 er gy GND 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= Feedback resistor dividers R1 and R2: 0.6V R1 . VOUT − 0.6V 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 greater than 22uF capacitance. tia l-P re p Because of the high integration in the SY8121B 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 specifications. R2 = Output capacitor COUT: Output inductor L: Applications Information 0.6VFB 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 IN/GND pins. In this case, a 4.7uF low ESR ceramic capacitor is recommended. r Operation 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