SY8707ABC

Application Note: AN_SY8707 High Efficiency, 1MHz, 1.5A, 30V Step Down White LED Driver Preliminary Specification General Description Features SY8707 is a high efficiency step down regulator capable of driving 1.5A 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. The LED current is programmable through the external resistor. It incorporates both analog and PWM dimming onto a single control pin. • • • • • • • Ordering Information Applications SY8707 □(□□)□ • IP camera and CCD camera Temperature Code Package Code Optional Spec Code • Flash light • Display cabinet lamp • LED sign Temperature Range: -40°C to 85°C Ordering Number SY8707ABC Package type SOT23-6 Wide input range: 2.5-30 V 1 MHz switching frequency Very low RON: 100mΩ 100Hz-1kHz wide PWM dimming frequency range 0.65-1.2V analog dimming Compact package: SOT23-6 RoHS Compliant and Halogen Free Note 1.5A Typical Applications Figure1. Schematic diagram AN_SY8707 Rev. 0.9 Silergy Corp. Confidential- Prepared for Internal Use Only 1 AN_SY8707 Pinout (top view) SOT23-6 Top Mark: TWxyz (device code: TW, x=year code, y=week code, z= lot number code) Pin Number Pin Description Pin Name LX 1 Inductor node. Connect an inductor between IN pin to LX pin. GND 2 Ground pin TM 3 Test mode pin. Ground this pin in the real application. On/Off Control Input and Dimming Command Input. A voltage greater than 0.65V will turn on the chip. When the EN/ADIM pin voltage rises from 0.65V to 1.2V, the LED current will change from EN/ADIM 4 0% to 100% of the maximum LED current. To use PWM dimming, apply a 100Hz to 1kHz square wave signal with amplitude greater than 1.2V to this pin. Input pin. Decouple this pin to GND pin with 1uF ceramic cap. Also IN 5 used as the positive current sense pin. SEN 6 Negative Current Sense Pin. 100% ILED 50% 0% 0.65V 0.925V 1.2V EN/ADIM Figure2. Analog Dimming Curve Absolute Maximum Ratings (Note 1) LX, IN, EN/ADIM--------------------------------------------------------------------------------------------------------------- 33V SEN------------------------------------------------------------------------------------------------------------------------ VIN ± 0.7V All other pins-------------------------- -------------------------------------------------------------------------------------------- 4V Power Dissipation, PD @ TA = 25°C SOT23-6, ------------------------------------------------------------------------- 0.55W Package Thermal Resistance (Note 2) θ JA --------------------------------------------------------------------------------------------------------------- 180°C/W θ JC --------------------------------------------------------------------------------------------------------------- 140°C/W AN_SY8707 Rev. 0.9 Silergy Corp. Confidential- Prepared for Internal Use Only 2 AN_SY8707 Junction Temperature Range ------------------------------------------------------------------------------------------------ 125°C Lead Temperature (Soldering, 10 sec.) ------------------------------------------------------------------------------------ 260°C Storage Temperature Range -------------------------------------------------------------------------------------- -65°C to 150°C Recommended Operating Conditions (Note 3) IN, LX, EN/ADIM----------------------------------------------------------------------------------------------------- 2.5V to 30V Junction Temperature Range ------------------------------------------------------------------------------------- -40°C to 125°C Ambient Temperature Range -------------------------------------------------------------------------------------- -40°C to 85°C Electrical Characteristics (VIN = 5V, IOUT=100mA, TA = 25°C unless otherwise specified) Parameter Input Voltage Range Quiescent Current Shutdown Current Internal Reference Voltage Low Side Main FET RON Main FET Current Limit ADIM Linear Dimming Range ADIM Dimming Accuracy Symbol VIN IQ ISHDN VREF RDS(ON) ILIM1 VADIM ILED,ACC EN Rising Threshold EN Falling Threshold IN UVLO Rising Threshold UVLO Hysteresis Switching Frequency Minimum ON Time Maximum Duty Cycle Thermal Shutdown Temperature Thermal Hysteresis VENH VENL VIN,UVLO UVLO,HYS FSW TON,MIN DMAX Test Conditions VIN-SEN=0.3V EN=0 EN=3V Min 2.5 96 Typ 100 10 100 100 2 0.65 VADIM = 0.65V VADIM = 1.2V Max 30 200 15 104 1.2 TBD 100 0.65 0.3 2.5 0.8 0.2 1 100 90 1.2 Unit V µA µA mV mΩ A V % % V V V V MHz nS % TSD 150 C THYS 20 C Note 1: Stresses listed 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 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 AN_SY8707 Rev. 0.9 Silergy Corp. Confidential- Prepared for Internal Use Only 3 AN_SY8707 Block Diagram AN_SY8707 Rev. 0.9 Silergy Corp. Confidential- Prepared for Internal Use Only 4 AN_SY8707 Typical Operation Characteristics 98 1.2 Frequency(MHz) Efficiency(%) 96 94 92 90 3PCS LED 88 5PCS LED 86 0 5 10 15 20 25 1.15 1.1 1.05 1 30 0 5 10 15 20 25 30 35 Input Voltage(V) 1.2 1.2 1 1 0.8 0.8 ILED(A) ILED(A) Input Voltage(V) 0.6 0.4 0.2 0.6 0.4 0.2 0 0 10 20 30 40 50 60 PWM Duty(%) AN_SY8707 Rev. 0.9 70 80 90 100 0 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 1.8 2.0 EN/ADIM Voltage(V) Silergy Corp. Confidential- Prepared for Internal Use Only 5 AN_SY8707 AN_SY8707 Rev. 0.9 Silergy Corp. Confidential- Prepared for Internal Use Only 6 AN_SY8707 Operation performance, it is recommended to use X7R or better grade ceramic capacitor greater than 1uF capacitance. SY8707 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. Output inductor L: There are several considerations in choosing this inductor. Applications Information Because of the high integration in the SY8707 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) 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 SY8707 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 + 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 chosen 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 AN_SY8707 Rev. 0.9 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: VOUT(1-VOUT/VIN,MAX) 2 ⋅ FSW ⋅ L Layout Design: The layout design of SY8707 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. Silergy Corp. Confidential- Prepared for Internal Use Only 7 AN_SY8707 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_SY8707 Rev. 0.9 Silergy Corp. Confidential- Prepared for Internal Use Only 8