SY8121ABC

Application Note: SY8121 High Efficiency Fast Response, 2A, 18V Input 1MHz Synchronous Step Down Regulator Features SY8121 develops high efficiency synchronous stepdown DC-DC converter capable of delivering 2A load current. SY8121 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):140/130 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/ DFN2x2-6 w fo r re re pa Set Top Box Portable TV Access Point Router DSL Modem LCD TV l-P id en t Package type SOT23-6 DFN2x2-6      Note --- on f Ordering Number SY8121ABC SY8121DEC Applications ia SY8121 □(□□)□ Temperature Code Package Code Optional Spec Code d SY8121 adopts the instant PWM architecture to achieve fast transient responses for high step down applications and high efficiency at light loads. In addition, it operates at pseudo-constant frequency of 1 MHz under heavy load conditions to minimize the size of inductor and capacitor. Ordering Information oo ko o General Description Co rp .C Typical Applications Efficiency vs. Load Current 96 CIN 4.7uF Si ON/ OFF BS 91 L1 3.3uH R1 100k SY8121 EN VOUT 3.3V LX C4 (opt.) COUT 22uF Efficiency (%) IN le rg VIN 4.5~18V y C1 100nF 86 81 76 5VIN,3.3VOUT 12VIN,3.3VOUT FB 71 16VIN,3.3VOUT GND R2 22.1k 66 0 0.5 1 1.5 2 Load Current (A) Figure 1. Schematic Diagram AN_SY8121 Rev.0.9B © 2018 Silergy Corp. Figure 2. Efficiency Figure Silergy Corp. Confidential-prepared for Customer Use Only 1 All Rights Reserved. AN_SY8121 BS 1 6 LX GND 2 5 FB 3 4 1 6 BS IN IN 2 5 GND EN EN 3 4 FB (DFN2x2-6) fo r (SOT23-6) GND w LX oo ko o Pinout (top view) DFN2x2-6 BS 1 6 GND 2 5 FB 3 4 EN IN LX 4 5 6 3 2 1 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 re SOT23-6 id en t ia l-P re pa Pin Name d Top Mark: JWxyz for SY8121ABC, (Device code: JW, x=year code, y=week code, z= lot number code) PTxyz for SY8121DEC, (Device code: PT, x=year code, y=week code, z= lot number code) on f Absolute Maximum Ratings (Note 1) Si le rg y Co rp .C 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 Recommended Operating Conditions (Note 3) Supply Input Voltage --------------------------------------------------------------------------------------------- 4.5V to 18V Junction Temperature Range --------------------------------------------------------------------------------- -40°C to 125°C Ambient Temperature Range ---------------------------------------------------------------------------------- -40°C to 85°C AN_SY8121 Rev.0.9B © 2018 Silergy Corp. Silergy Corp. Confidential-prepared for Customer Use Only 2 All Rights Reserved. AN_SY8121 Block Diagram oo ko o IN BS FB Current Sense ia GND Si le rg y Co rp .C on f Thermal Protection l-P Internal SST id en t 0.6V re 1.5V re pa PWM Control & Protect Logic EN LX d fo r w Input UVLO 4.5V Internal Power AN_SY8121 Rev.0.9B © 2018 Silergy Corp. Silergy Corp. Confidential-prepared for Customer Use Only 3 All Rights Reserved. AN_SY8121 Electrical Characteristics (VIN = 12V, VOUT = 1.2V, L = 2.2uH, COUT = 10uF, TA = 25°C, IOUT = 1A unless otherwise specified) Min 4.5 IOUT=0, VFB=VREF×105% EN=0 0.588 VREF VFB=VIN -50 2.7 d 2 re ITOP VENH VENL VUVLO 10 0.612 re pa VUVP VFB Falling TON Tss VIN = 12V ,VOUT=1.2V, IOUT = 1A id en t ia l-P VFB Rising nA Ω Ω 3.4 A 5.0 A V V V on f Shutdown Temperature(Note4) Hysteresis(Note4) 0.4 4.5 105 120 33 100 400 50 100 90 150 15 Unit V µA µA V 50 1.5 VOVP TSDN Max 18 0.14 0.13 ILIM DMAX 400 5 0.6 fo r IFB RDS(ON)1 RDS(ON)2 Typ oo ko o Test Conditions w Symbol VIN IQ ISHDN %VREF %VREF ns us ns ns % °C .C Parameter Input Voltage Range Quiescent Current Shutdown Current Feedback Reference Voltage FB Input Current Top FET RON Bottom FET RON Bottom FET Valley Current Limit Top FET Current Rating EN Rising Threshold EN Falling Threshold Input UVLO Threshold Output Over Voltage Protection Threshold Output Under Voltage Protection Threshold On Time Soft-start Time Min ON Time Min Off Time Maximum Duty Cycle Thermal Shutdown Threshold y Co rp 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. Si le rg Note 2: θ JA is measured in the natural convection at T A = 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. Note 3: The device is not guaranteed to function outside its operating conditions. Note4: Specified by design (not production tested) AN_SY8121 Rev.0.9B © 2018 Silergy Corp. Silergy Corp. Confidential-prepared for Customer Use Only 4 All Rights Reserved. AN_SY8121 Typical Performance Characteristics Efficiency vs. Load Current 95 91 85 7VIN,5VOUT 80 86 81 w 90 oo ko o 96 Efficiency (%) Efficiency (%) Efficiency vs. Load Current 100 76 5VIN,3.3VOUT 12VIN,5VOUT 71 16VIN,5VOUT 75 16VIN,3.3VOUT 0.5 1 1.5 0 2 re pa Load Current (A) Efficiency vs. Load Current 90 l-P 85 80 ia 75 65 5VIN,1.2VOUT 55 16VIN,1.2VOUT 45 0.5 1 1.5 .C 0 on f 12VIN,1.2VOUT 50 1 1.5 Co rp Load Current (A) Load Current (A) Load Transient (VIN=12V, VOUT=3.3V, ILOAD=0.2-1A) VOUT(AC) 100mV/div IL 0.5A/div 2 Time (40μs/div) Load Transient Output Ripple (VIN=12V, VOUT=3.3V, ILOAD=1-2A) (VIN=12V,VOUT=3.3V, ILOAD=2A) le rg Time (40μs/div) AN_SY8121 Rev.0.9B © 2018 Silergy Corp. 10mV/div VLX 5V/div IL 2A/div 1A/div Si IL VOUT(AC) 100mV/div y VOUT(AC) 2 id en t 70 60 0.5 re 0 d 66 70 Efficiency (%) fo r 12VIN,3.3VOUT Time (1μs/div) Silergy Corp. Confidential-prepared for Customer Use Only 5 All Rights Reserved. AN_SY8121 Startup Shutdown (VIN=12V, VOUT=3.3V, ILOAD=2A) (VIN=12V, VOUT=3.3V, ILOAD=2A) EN 5V/div EN VLX 10V/div VLX 2V/div VOUT 2V/div IL 2A/div 2A/div oo ko o fo r IL 10V/div w VOUT 5V/div Time (200μs/div) re d Time (200μs/div) Short Circuit Protection Short Circuit Protection (VIN=12V, VOUT=3.3V, 2A to Short) IL 1A/div re pa 2V/div VOUT 2V/div on f id en t ia l-P VOUT (VIN=12V, VOUT=3.3V, Open to Short) 1A/div Time (2ms/div) Si le rg y Co rp .C Time (2ms/div) IL AN_SY8121 Rev.0.9B © 2018 Silergy Corp. Silergy Corp. Confidential-prepared for Customer Use Only 6 All Rights Reserved. AN_SY8121 SY8121 is a synchronous buck regulator IC that integrates the PWM control, top and bottom switches on the same die to minimize the switching transition loss and conduction loss. With ultra low RDS(ON) power switches and proprietary PWM control, this regulator IC can achieve the highest efficiency and the highest switch frequency simultaneously to minimize the external inductor and capacitor size, and thus achieving the minimum solution footprint. w Output capacitor COUT: fo r 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. re d SY8121 provides protection functions such as cycle by cycle current limiting and thermal shutdown protection. SY8121 will sense the output voltage conditions for the fault protection. re pa 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: on f Feedback resistor dividers R1 and R2: id en t ia l-P Applications Information Because of the high integration in the SY8121 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. oo ko o 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. Operation Co rp .C 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: y 0.6V R1 . VOUT  0.6V Si le rg R2  VOUT R1 GND ISAT, MIN  IOUT, MAX  R2 3) The ripple current through input capacitor is calculated as： AN_SY8121 Rev.0.9B © 2018 Silergy Corp. VOUT (1  VOUT /VIN, MAX ) FSW  IOUT, MAX  40% where Fsw is the switching frequency and I OUT,MAX is the maximum load current. The SY8121 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. 0.6VFB Input capacitor CIN: I CIN _ RMS  I OUT  D(1  D) . L 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