UNISONIC TECHNOLOGIES CO., LTD USL3531 Advance LINEAR INTEGRATED CIRCUIT NON-ISOLATED BUCK OFFLINE LED DRIVER DESCRIPTION The UTC USL3531 is a high performance, high precision and low cost constant current LED driver for non-isolated buck application. The device operates in critical conduction mode and is suitable for 85V~265V universal input offline LED lighting. It operates in critical conduction mode, the output current does not change with the inductance and LED output voltage. The UTC USL3531 integrates a 500V power MOSFET. It can achieve excellent constant current performance with very few external components, so the system cost and size are minimized. The UTC USL3531 offers rich protection functions to improve the system reliability, including LED open circuit protection, LED short circuit protection, VCC under voltage protection, CS resistor short circuit protection and thermal regulation function. SOP-8 FEATURES * Critical conduction mode operation * Internal 500V Power MOSFET * Ultra low operating current * No auxiliary winding * ±5% LED output current accuracy * LED short protection * LED open protection * VCC under voltage protection * Current sensing resistor short protection * Thermal regulation function ORDERING INFORMATION Ordering Number USL3531G-S08-R USL3531G-S08-R Package SOP-8 (1)Packing Type (1) R: Tape Reel (2)Package Type (2) S08: SOP-8 (3)Green Package (3) G: Halogen Free and Lead Free Packing Tape Reel MARKING www.unisonic.com.tw Copyright © 2015 Unisonic Technologies Co., Ltd 1 of 6 QW-R103-101.a USL3531 Advance PIN CONFIGURATION PIN DESCRIPTION PIN NO. 1 2 3 4 5, 6 7, 8 PIN NAME GND ROVP NC VCC DRAIN CS LINEAR INTEGRATED CIRCUIT DESCRIPTION Ground Over voltage protection setting pn. Connect a resistor to GND No connection. Should be connected to GND(Pin1) Power supply pin Internal HV Power MOSFET Drain. Current sense pin. Connect a sense resistor between this pin and GND pin. BLOCK DIAGRAM UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 2 of 6 QW-R103-101.a USL3531 Advance LINEAR INTEGRATED CIRCUIT ABSOLUTE MAXIMUM RATING PARAMETER SYMBOL RATINGS UNIT VCC Pin Maximum Sink Current ICC_MAX 5 mA Internal HV MOSFET Drain Voltage DRAIN -0.3~500 V Current Sense Pin Input Voltage CS -0.3~6 V Over-Voltage Setting Pin Voltage ROVP -0.3~6 V Power Dissipation PD 0.45 W Junction Temperature TJ -40~+150 °C Storage Temperature TSTG -55~+150 °C Note: Absolute maximum ratings are those values beyond which the device could be permanently damaged. Absolute maximum ratings are stress ratings only and functional device operation is not implied. RECOMMENDED OPERATION CONDITIONS PARAMETER Output LED Current @ VOUT=72V (Input Voltage 176V~265V) Output LED Current @ VOUT=36V (Input Voltage 176V~265V) Minimum LED Loading Voltage RATINGS UNIT ILED1 160 mA ILED2 220 mA VLED min >15 V RATING 150 UNIT °C/W THERMAL RESISTANCES CHARACTERISTICS PARAMETER Junction to Ambient SYMBOL SYMBOL θJA ELECTRICAL CHARACTERISTICS (Notes 1, 2) (Unless otherwise specified, VCC=14V and TA=25°C) PARAMETER SYMBOL TEST CONDITIONS MIN TYP MAX UNIT Supply Voltage Section VCC Clamp Voltage VCC_CLAMP 1mA 16.8 V VCC Turn On Threshold VCC_ON VCC Rising 13.8 V VCC Turn Off Threshold VCC_UVLO VCC Falling 9 V VCC Startup Current IST VCC= VCC-ON - 1V 180 280 µA VCC Operating Current IOP FOP=70KHz 200 300 µA Current Sense Section Threshold Voltage for Peak Current Limit VCS_peak 390 400 410 mV Threshold Voltage for Peak Current Limit When VCS_SHORT Output Short 200 mV Output Short Leading Edge Blanking Time for Current Sense TLEB 300 ns Switch Off Delay Time TDELAY 200 ns Internal Time Control Section Minimum OFF Time TOFF_MIN 4.5 µs Maximum OFF Time TOFF_MAX 220 µs Maximum On Time TON_MAX 35 µs ROVP Pin Voltage VROVP 0.5 V MOSFET Section Static Drain-source On-resistance RDS_ON VGS=15V/IDS=0.4A 14 Ω Drain-Source Breakdown Voltage BVDSS VGS=0V/IDS=250µA 500 V Power MOSFET Drain Leakage Current IDSS VGS=0V/VDS=500V 1 µA Thermal Regulation Section Thermal Regulation Temperature TREG 150 °C Notes: 1. Production testing of the chip is performed at 25°C. 2. The maximum and minimum parameters specified are guaranteed by test, the typical value are guaranteed by design, characterization and statistical analysis. UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 3 of 6 QW-R103-101.a USL3531 Advance LINEAR INTEGRATED CIRCUIT APPLICATION INFORMATION The UTC USL3531 is a high performance non-isolated Buck converter specially designed for LED lighting. The device integrates a 500V power MOSFET. With very few external components, the converter achieves excellent constant current control. And it does not need auxiliary winding for powering the IC or voltage sensing, thus the system size and cost is greatly reduced. Start Up When system powered up, the VCC pin capacitor is charged up by the start up resistor. When the VCC pin voltage reaches the start up threshold, the internal circuits start operating. The UTC USL3531 integrates a 17V zener diode to clamp the VCC voltage. Constant Current Control Cycle by Cycle current sense is adjusted in UTC USL3531, the CS pin is connected to the current sense comparator, and the voltage on CS pin is compared with the internal 400mV reference voltage. The MOSFET will be switched off when the voltage on CS pin reaches the Peak Current threshold. The CS comparator includes a 350ns leading edge blanking time. After the MOSFET switched off, the OFF time controller would open the MOSFET again at time up. At that moment, CS pin voltage is 0mV usually. The Delta inductor current is given by: IPK = 400 (mA） RCS Where, RCS is the current sense resistor value. The current in LED can be calculated by the equation: ILED = IPK 200 = (mA） 2 RCS Where, IPK is the Peak current of the inductor. Inductor Selection The UTC USL3531 works under inductor current critical conduction mode. When the power MOFET is switched on, the current in the inductor rises up from zero, the on time of the MOSFET can be calculated by the equation: ton L I PK V IN - V LED Where, L is the inductance value VIN is the DC bus voltage after the rectifier bridge VLED is the voltage on the LED After the power MOSFET is switched off, the current in the inductor decreases. When the inductor current reaches zero, the power MOSFET is turned on again by IC internal logic. The off time of the MOSFET is given by: toff L I PK V LED The inductance can be calculated by the equation: L V LED (V IN - V LED ) freq I PK V IN The freq is the system switching frequency, which is proportional to the input voltage. So the minimum switching frequency is set at lowest input voltage, and the maximum switching frequency is set at highest input voltage. The minimum and maximum off time of UTC USL3531 is set at 4.5µs and 240µs, respectively. Referring to the equation of tOFF calculation, if the inductance is too small, the tOFF may be smaller than the minimum off time, system will operate in discontinuous conduction mode and the output current will be smaller than the designed value. If the inductance is too large, the tOFF may be larger than the maximum off time, the outputt current will not be constant follow design value. So it is important to choose a proper inductance, we recommend user to regulate the inductance value for 70KHz application. UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 4 of 6 QW-R103-101.a USL3531 Advance LINEAR INTEGRATED CIRCUIT APPLICATION INFORMATION(Cont.) Over Voltage Protection The over voltage protection can be programmed by the ROVP pin resistor. The ROVP pin voltage is 0.5V. When the LED is open circuit, the output voltage increases gradually, and the demagnetization time gets shorter. The demagnetization time at OVP---- Tovp can be calculated by the open circuit protection voltage: TOVP ≈ L I PK VOVP Where， Vovp is the open circuit protection voltage And then the Rovp resistor value can be calculated by the equation: ROVP ≈ 19 Top 10 6 (kΩ) Protection Function The UTC USL3531 offers rich protection functions to improve the system reliability, including LED open/short protection, CS resistor short protection, VCC under voltage protection, thermal regulation. When the LED is open circuit, the system will trigger the over voltage protection and stop switching. When the LED short circuit is detected, the system works at low frequency (about 5kHz), and the CS pin turn off threshold is reduced to 200mV. So the system power consumption is very low. At some catastrophic fault condition, such as CS resistor shorted or inductor saturated, the internal fast fault detection circuit will be triggered, the system stops switching immediately. After the system enters into fault condition, the VCC voltage will decrease until it reaches the UVLO threshold, then the system will re-start again. If the fault condition is removed, the system will recover to normal operation. Thermal Regulation The UTC USL3531 integrates thermal regulation function. When the system is over temperature, the output current is gradually reduced; the output power and thermal dissipation are also reduced. The system temperature is regulated and the system reliability is improved. The thermal regulation temperature is set to 150°C internally. PCB Layout The following rules should be followed in UTC USL3531 PCB layout: Bypass Capacitor The bypass capacitor on VCC pin should be as close as possible to the VCC Pin and GND pin. ROVP Pin The ROVP resistor should be as close as possible to the ROVP Pin. Ground Path The power ground path for current sense should be short, and the power ground path should be separated from small signal ground path before connecting to the negative node of the bulk capacitor. The Area of Power Loop The area of main current loop should be as small as possible to reduce EMI radiation, such as the inductor, the power MOSFET, the output diode and the bus capacitor loop. NC pin The NC pin should be connected to GND (pin1). Drain Pin To increase the copper area of DRAIN pin for better thermal dissipation. However too large copper area may compromise EMI performance. UNISONIC TECHNOLOGIES CO., LTD www.unisonic.com.tw 5 of 6 QW-R103-101.a USL3531 Advance LINEAR INTEGRATED CIRCUIT TYPICAL APPLICATION CIRCUIT AC UTC USL3531 VCC DRAIN ROVP DRAIN NC CS GND CS UTC assumes no responsibility for equipment failures that result from using products at values that exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or other parameters) listed in products specifications of any and all UTC products described or contained herein. UTC products are not designed for use in life support appliances, devices or systems where malfunction of these products can be reasonably expected to result in personal injury. Reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. The information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice. 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