SY8703ABC

Application Note: AN_SY8703 High Efficiency, 1MHz, 1A, 30V Step Down White LED Driver Preliminary Specification General Description Features SY8703 is a high efficiency step down regulator capable of driving 1.0A white LED from up to 30V input. It integrates the low RON MOSFET and internal compensation. The 1MHz switching frequency allows the use of very small inductor. This, along with the small SOT23-6 package, achieves an extremely small LED driver design. • • • • • • • Ordering Information Applications SY8703□(□□)□ • Flash light Temperature Code Package Code Optional Spec Code Ordering Number SY8703ABC Package type SOT23-6 Wide input range: 2.5-30 V 1 MHz switching frequency Very low RON: 200mΩ Enable and dimming control available 20kHz~1MHz wide dimming frequency range Compact 6 pin SOT23 package RoHS Compliant and Halogen Free • Display cabinet lamp • LED sign Note 1A Typical Applications Figure 1. Schematic diagram AN_SY8703 Rev. 0.9C Silergy Corp. Confidential- Prepared for Internal Use Only 1 AN_SY8703 Pinout (top view) SOT23-6 Top Mark:EFxyz (device code: EF, x=year code, y=week code, z= lot number code) Pin Name Pin Number IN 5 SEN GND LX 6 2 1 EN 4 TM 3 Pin Description Input pin. Decouple this pin to GND pin with 1uF ceramic cap. Also used as the positive current sense pin. Negative Current Sense Pin. Ground pin Inductor node. Enable and dimming control. Pull high to turn on IC. When used as dimming input, the first pulse should be longer than 100ns to turn on IC, and then shorter than 40nS to turn off IC. The recommend dimming frequency range is 20kHz~1MHz. Test mode pin. Ground this pin in the real application. Absolute Maximum Ratings (Note 1) LX, IN, EN------------------------------------------------------------------------------------------------------------------------ 33V SEN ----------------------------------------------------------------------------------------------------------------------- VIN ± 0.7V All other pins-------------------------- -------------------------------------------------------------------------------------------- 4V Power Dissipation, PD @ TA = 25°C SOT-23-6, ------------------------------------------------------------------------- 0.6W Package Thermal Resistance (Note 2) θ JA --------------------------------------------------------------------------------------------------------------- 200°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) IN, LX, EN ------------------------------------------------------------------------------------------------------------- 2.5V to 30V SEN ----------------------------------------------------------------------------------------------------------------------- VIN ± 0.5V All other pins ------------------------------------------------------------------------------------------------------------------ 0-3.6V Junction Temperature Range ------------------------------------------------------------------------------------- -40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------- -40°C to 85°C AN_SY8703 Rev. 0.9C Silergy Corp. Confidential- Prepared for Internal Use Only 2 AN_SY8703 Electrical Characteristics (VIN = 5V, IOUT=100mA, TA = 25°C unless otherwise specified) Parameter Input Voltage Range Shutdown Current Low Side Main FET RON Main FET Current Limit Switching Frequency Current Sense Limit EN Rising Threshold EN Falling Threshold Symbol VIN ISHDN RDS(ON)1 ILIM1 FSW VIN-SEN VENH VENL Test Conditions Min 2.5 IN UVLO Rising Threshold VIN,UVLO UVLO Hysteresis Thermal Shutdown Temperature Max Duty Cycle Min Duty Cycle VUVLO,HYS 0.1 V TSD 150 C EN=0 Typ 5 200 1.3 0.8 96 1.5 1 100 Max 30 10 1.2 104 Unit V µA mΩ A MHz mV 0.4 2.5 10 100 12 V % % Note 1: Stresses listed as the above “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 for extended periods may remain possibility to 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. Note 3. The device is not guaranteed to function outside its operating conditions Block Diagram AN_SY8703 Rev. 0.9C Silergy Corp. Confidential- Prepared for Internal Use Only 3 AN_SY8703 Typical Operation Characteristics 1 0.9 0.8 0.7 ILED/A 0.6 0.5 0.4 0.3 0.2 20kHz Dimming 200kHz Dimming 0.1 1MHz Dimming 0 0% 10% 20% 30% 40% 50% 60% 70% 80% 90% 100% PWM Duty Cycle Startup (VIN=25V, IOUT=1A, 5pcs LED Series) VIN 5V/div VLX 10V/div ILED 0.5A/div Fre.(kHz) Time (2ms/div) AN_SY8703 Rev. 0.9C Silergy Corp. Confidential- Prepared for Internal Use Only 4 AN_SY8703 Operation SY8703 is a floating buck regulator IC that integrates the PWM control, power MOSFET 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 the high 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 SY8703 IC , the application circuit based on this regulator IC is rather simple. Only input capacitor CIN, output capacitor COUT, output inductor L and current sense resistor RSEN need to be selected for the targeted applications specifications. Current sense resistor RSEN: Choose RSEN to program the proper output Current: ILED(A) = 0.1(V ) R SEN (Ω) Input capacitor CIN: The ripple current through input capacitor is calculated as: ICIN_RMS = IOUT ⋅ D(1 - D) A typical X7R or better grade ceramic capacitor with suitable capacitance should be choosen to handle this ripple current well. To minimize the potential noise problem, place this 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. Output capacitor COUT: The output capacitor is selected to handle the output current ripple noise requirements. For the best performance, it is recommended to use X7R or better grade ceramic capacitor greater than 1uF 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= VOUT (1 − VOUT /VIN,MAX ) FSW × I OUT,MAX × 40% where Fsw is the switching frequency and IOUT,MAX is the LED current. The SY8703 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 + AN_SY8703 Rev. 0.9C VOUT(1-VOUT/VIN,MAX) 2 ⋅ FSW ⋅ L Silergy Corp. Confidential- Prepared for Internal Use Only 5 AN_SY8703 Dimming Control Fig.2 shows the internal block diagram of the dimming circuit of SY8703. The PWM signal changes the regulation voltage by change the duty cycle. The relationship between the duty cycle and internal reference voltage is calculated as: VIN-SEN =Duty*100mV Figure 2 Internal block diagram of the dimming circuit Since the cut-off frequency of the internal low pass filter is near 5kHz, it is recommended selecting the PWM signal frequency to be higher than 20kHz. Layout Design: The layout design of SY8703 regulator is relatively simple. For the best efficiency and minimum noise problems, we should place the following components close to the IC: CIN, L, COUT and RSEN. 1) It is desirable to maximize the PCB copper area connecting to GND pin to achieve the best thermal and noise performance. If the board space allowed, a ground plane is highly desirable. 2) CIN must be close to Pins IN and GND. The loop area formed by CIN and GND must be minimized. 3) The PCB copper area associated with LX pin must be minimized to avoid the potential noise problem. AN_SY8703 Rev. 0.9C Silergy Corp. Confidential- Prepared for Internal Use Only 6 AN_SY8703 SOT23-6 Package Outline & PCB layout 1.90 1.50 - 1.70 1.00 2.70 - 3.00 2.40 2.80 - 3.10 0.95 0.60 0.30 - 0.50 0.1 - 0.15 0.01 - 0.1 Top View 0.25 REF Recommended Pad Layout 1.0 - 1.3 0.95 TYP 0.3 - 0.6 1.90 TYP Notes: All dimensions are in millimeters. All dimensions don’t include mold flash & metal burr. AN_SY8703 Rev. 0.9C Silergy Corp. Confidential- Prepared for Internal Use Only 7