SY8105IADC

Applications Note:AN_SY8105 High Efficiency, 500kHz, 5A, 18V Input Synchronous Step Down Regulator General Description Features The SY8105 is a high efficiency 500 kHz synchronous step-down DC-DC converter capable of delivering 5.0A current. The SY8105 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): 40mΩ/26mΩ 4.5-18V input voltage range 5.0A output current capability 500 kHz switching frequency Instant PWM architecture to achieve fast transient responses. Internal softstart limits the inrush current Cycle-by-cycle peak current limitation 1.5% 0.6V reference TSOT23-6 package Low output voltage ripple and small external inductor and capacitor sizes are achieved with 500 kHz switching frequency. It adopts the instant PWM architecture to achieve fast transient responses for high step down applications • • • • Ordering Information Applications SY8105 □(□□)□ Temperature Code Package Code Optional Spec Code Ordering Number SY8105ADC Package type TSOT23-6 Note -- • • • • • Set Top Box Portable TV Access Point Router DSL Modem LCD TV Typical Applications Efficiency vs. Load Current 100 90 80 Ef fic ie nc y ( % ) 70 60 50 VIN=5V,VOUT=3.3V 40 VIN=12V,VOUT=3.3V 30 VIN=16V,VOUT=3.3V 20 10 0 0.001 0.01 0.1 1 10 Load Current (A) Figure 1. Schematic Diagram AN_SY8105 Rev. 0.9 Figure 2. Schematic Diagram Silergy Corp. Confidential- Prepared for Customer Use Only 1 AN_SY8105 Pinout (top view) FB BS EN LX GND IN TSOT23-6(FC) Top Mark: NYxyz, (Device code: NY, x=year code, y=week code, z= lot number code) Pin Name Pin Number FB 1 Pin Description EN 2 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. GND 3 Ground pin IN LX BS 4 5 6 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 Boot-Strap Pin. Supply high side gate driver. Decouple this pin to LX pin with 0.1uF ceramic cap. Absolute Maximum Ratings (No e 1) Supply Input Voltage -----------------------------------------------------------------------------------------------------19V Enable Voltage----------------------------------------------------------------------------------------------------- VIN + 0.3V FB Voltage ------------------------------------------------------------------------------------------------------------------4V Power Dissipation, PD @ TA = 25°C, TSOT23-6（FC）-------------------------------------------------------1.75W Package Thermal Resistance (Note 2) θJA -------------------------------------------------------------------------------------------------------------56°C /W θJC -------------------------------------------------------------------------------------------------------------6.3°C /W Junction Temperature Range -----------------------------------------------------------------------------------------125°C Lead Temperature (Solde ing, 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_SY8105 Rev. 0.9 Silergy Corp. Confidential- Prepared for Customer Use Only 2 AN_SY8105 Block Diagram AN_SY8105 Rev. 0.9 Silergy Corp. Confidential- Prepared for Customer Use Only 3 AN_SY8105 Electrical Characteristics (VIN = 12V, VOUT = 1.2V, L = 2.2uH, COUT = 47uF, TA = 25°C, IOUT = 1A unless otherwise specified) Parameter Input Voltage Range Quiescent Current Shutdown Current Feedback Reference Voltage FB Input Current Top FET RON Bottom FET RON TOP FET Peak Current Limit Bottom FET Valley Current Limit EN Rising Threshold EN Falling Threshold Input UVLO Threshold UVLO Hysteresis Min ON Time Min OFF Time Switching Frequency Thermal Shutdown Temperature Thermal Shutdown Hysteresis Symbol V Test Conditions IN IQ ISHDN V IOUT=0, VFB=VREF*105% EN=0 0.591 REF I FB R DS(ON)1 R I Min 4.5 VFB=3.3V Typ 100 5 0.6 -50 DS(ON)2 LIM,BOTTOM V ENH V ENL V UVLO V T Unit V µA µA V 50 nA mΩ mΩ 10 A 5.0 A SD 0.3 80 160 500 150 V V V V ns ns kHz °C HYS 15 °C HYS T 10 0.609 40 20 LIM,TOP I Max 18 1.5 0.4 4.5 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 specificati n is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Note 2: θJA is measured in the natural convection at TA = 25°C on a two-layer Silergy Evaluation Board.. Note 3: The device is not guaranteed to function outside its operating conditions AN_SY8105 Rev. 0.9 Silergy Corp. Confidential- Prepared for Customer Use Only 4 AN_SY8105 Typical Performance Characteristics Ef fic ie nc y ( % ) Efficiency (%) Ef fic ie nc y ( % ) AN_SY8105 Rev. 0.9 Silergy Corp. Confidential- Prepared for Customer Use Only 5 AN_SY8105 VIN Shutdown (VIN=12V, VOUT=5V, ILOAD=5A) VIN 10V/div VLX 10V/div VOUT 2V/div IL 2A/div Time (800µs/div) EN Shutdown (VIN=12V, VOUT=5V, ILOAD=5A) EN 5V/div VLX 10V/div VOUT 2V/div IL 2A/div Time (200µs/div) Short Circuit Protection (VIN=12V, VOUT=5V, Open to Short) VOUT 2V/div IL 2A/div Time (800us/div) AN_SY8105 Rev. 0.9 Short Circuit Protection (VIN=12V, VOUT=5V, 5A to Short) VOUT 2V/div IL 2A/div Time (1ms/div) Silergy Corp. Confidential- Prepared for Customer Use Only 6 AN_SY8105 Operation SY8105 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 high efficiency and fast transient response. The high switching frequency allows using of small profile inductor and capacitor and the highest switch frequency simultaneously to minimize the external inductor and capacitor size, and thus achieving the minimum solution footprint. Applications Information Because of the high integration in the SY8105 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. 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 s highly recommended for both resistors. If Vout is 3.3V, R1=100k is chosen, then using following equatio , R2 can be calculated to be 22.1k: 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 greater than 47uF capacitance. 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: L= 0.6V R . VOUT − 0.6V 1 FB GND Input capacitor CIN: The ripple current through input capacitor is calculated as： ICIN _ RMS = IOUT ⋅ 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 IN/GND pins. For most applications, a 10uF ceramic capacitor in parallel with 100nF 0603 size ceramic capacitor are recommended. And place the 100nF/0603 capacitor close to IC to attenuate high frequency noise. AN_SY8105 Rev. 0.9 /V OUT F ×I ) IN,MAX × 40% OUT,MAX where Fsw is the switching frequency and IOUT,MAX is the maximum load current. The SY8105 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 + R1 R2 (1− V OUT SW VOUT R2 = V 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