WS3252

WS3252 WS3252 High Precision CC/CV Primary-Side PWM Controller Features ■ 5uA ultra-low startup current ■ 2mA Low operating current ■±5% Constant Voltage Regulation at Universal AC input ■ Primary-side Sensing and Regulation Without TL431 and Opto-coupler ■ Programmable CV and CC Regulation ■ Built-in Primary winding inductance compensation ■ Programmable cable drop compensation ■ Built-in soft start ■ Built-in Leading-edge blanking ■ Cycle by cycle over current protection (OCP) ■ VCC over voltage clamp & under voltage lockout( UVLO) ■ Maximum Gate output voltage clamped at 12V ■ Frequency jittering General Description WS3252 is a high-integrated offline PWM controller, optemized for high poformance low power AC/DC charger and adapter adapter application. WS3252 operates in primary-side sensing and regulation. Consequently, opto-coupler and TL431 could be eliminated, thus reduce the cost. It can achieve ± 5% constant voltage precision in full input voltage range. CC/CV Control as shown in fig.1.In CC Control, the current and output power setting can be adjusted externally by the sense resistor Rs at CS pin. In CV control, multi-mode operations are utilized to achieve high performance and high efficiency. In addition, good load regulation is achieved by the built-in cable drop compensation. Device operates in PFM in CC mode as well at large load condition and it operates in PWM with frequency reduction at light/medium load. Vo 5% Applications Low power AC/DC offline SMPS for ■ Cell Phone Charger ■ Digital Cameras Charger ■ Small Power Adapter ■ Auxiliary Power for PC, TV etc. ■ Linear Regulator/RCC Replacement Io WS3252 offers power on soft start control and protection coverage with auto-recovery features including Cycle-by-Cycle current limiting, VCC OVP,VCC clamp and UVLO. The gate-driven output is clamped to maximum 12V to protect the internal MOSFET. Excellent EMI performance is achieved by using the soft-switching and frequency jittering at the totem-pole-gate-drive output. The WS3252 is the ideal substitute of the linear power supply or the RCC-mod e power, for a better performance of the whole switch power system and a lower cost. WS3252 is available in SOT23-6 package. Icc Typical Application Circuit Rev.A Sep.2011 Copyright@W insemi Microelectronics Co., Ltd., All right reserved. WS3252 WS3252 Pin Definition and Device Marking 1 GND VCC 6 52: WS3252 Y: Year Code(0-9) WW: Week Code (1-52) 2 GATE CO M P 5 3CS IN V 4 SOT 23-6 Pin Function Description Pin Name GND GATE CS Pin Number 1 2 3 Pin Type GND Gate-driven output Current Monitoring Ground. Function Description Totem-pole gate driver output for power MOSFET. Current sense input. The voltage feedback from auxiliary winding. Connected to resistor divider from auxiliary winding reflecting output voltage. PWM duty cycle is determined by EA output and current sense signal at pin3. Loop Compensation for CV Stability Power supply INV 4 Feedback Input COMP VCC 5 6 Loop Compensation Power Block Diagram GND 1 V c c _O V P regulator Inter supply UVLO PO R 6 VCC G ate 2 Driver Logic CLK Generation CC Controller LEB OCP PW M +& S S Drop Com p 5 COM P CS 3 EA 2V + Sampler Sa m pling Controller 4 IN V 2/8 Steady, keep you advance WS3252 WS3252 Ordering Information Package 6-Pin SOT23-6, Pb-free IC Marking Information WS3252TP Purchasing Device Name WS3252TP Recommended Operating Condition Symbol VCC TA Parameter VCC supply voltage Operating temperature Value 10~30 -20~85 Unit V ℃ Absolute Maximum Ratings Symbol VCC VINV VCS VCOMP TJ TSTG ICC Parameter DC supply voltage INV input voltage CS input voltage COMP input voltage Max. Operating junction temperature Min./Max. Storage temperature VCC Clamp Continuous Current Value 30 -0.3~7 -0.3~7 -0.3~7 150 -55~150 10 Unit V V V V ℃ ℃ mA Note: Stresses above those listed under 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 Recommended Operating Conditions section are not implied. Exposure to absolute maximum-rated conditions for extended periods may affect device reliability. 3/8 Steady, keep you advance WS3252 WS3252 Electrical Characteristics (TA=25℃，VCC=16V, if not otherwise noted) Supply Voltage (VCC) symbol I_VCC_ST I_VCC_OP UVLO_ON UVLO_OFF VCC_Clamp OVP Threshold parameter Start up current Operation Current Turn on threshold Voltage Turn-off threshold Voltage VCC Zener Clamp Voltage Over voltage protection Test condition VCC=13V VCC=18V,INV=2V,CS=0V VCC falling VCC rising IVCC=10mA Ramp VCC until gate shut down Min Typ 5 2 Max 20 3 10.5 16.0 31 30 Unit uA mA V V V V 8.2 13.5 28 27 9.0 14.8 29 28.3 Error Amplifier Section Vref_EA Gain I_comp_max current Reference voltage for EA DC gain of EA Max. Cable compensation INV=2V,COMP=0V 37.5 uA 1.97 2 60 2.03 V dB Current Sense Section TLEB Zsense TD_OC VTH_OC T_ss Leading edge Blanking Time Input impedance OCP control delay OCP threshold Soft start time 0.88 50 110 0.91 17 0.94 625 ns kΩ ns V ms Oscillator Section Freq_Max1 Freq_Nom frequency Freq_startup ∆f/Freq Frequency shuffling range INV=0V,COMP=5V 14 ±6 khz % IC Maximum frequency System nominal switch 50 khz 55 60 65 khz Gate Driver Output Section VOL VOH V_clamp T_r T_f Output Low Level Output High Level Output Clamp Voltage Level Output Rising Time Output Falling Time CL=0.5nF CL=0.5nF Io=20mA Io=20mA 6 12 650 40 1 V V V ns ns Note: 1. Freq_Max indicates IC internal maximum clock frequency. In system application, the maximum operation frequency of 60kHz nominal occurs at maximum output power or the transition point from CV to CC. 4/8 Steady, keep you advance WS3252 WS3252 Typical Operating Characteristics 5/8 Steady, keep you advance WS3252 WS3252 Function Description WS3252 is a high-integrated offline PWM controller, optemized for high poformance low power AC/DC charger and adapter adapter application. WS3252 operates in primary-side opto-coupler sensing and and regulation. could be Consequently, TL431 winding. During MOSFET turn-on time, the load current is supplied from the output filter capacitor Co. The current in the primary winding ramps up. When MOSFET turns off, the primary current transfers to the secondary at the amplitude of eliminated, thus reduce the cost. High presicion CC/CV control can meet most adapter and charger application requirements. Is = NP *Ip Ns The auxiliary voltage reflects the output voltage, given by V AUX = Startup Current and Startup Control Startup current of WS3252 is designed to be extremely low at 5uA, so that VCC could be charged up above UVLO threshold level and device starts up quickly. A large value startup resistor can therefore be used to minimize the power loss, predigest the design of startup circuit and provides reliable startup in application. N AUX * (Vo + ∆V ) NS Where △ V indicates the drop voltage of the output Diode. Via a resistor divider connectrd between the auxiliary winding and INV, the auxiliary voltage is sampled at the end of the demagnetization and it is hold until the next sampling. The sampled voltage is compared with Vref(2V) and the error is amplified. The error amplifier output COMP reflects the load condition and controls the PWM switching frequency to regulate the output voltage, thus the constant output current can be achieved. When sampled voltage is below Vref and error amplifier output COMP reaches its maximum, the switching frequency is controlled by the sampled voltage thus the output voltage to regulate the output current, thus the constant output current can be achieved. Operating Current The operating current of WS3252 is low at 2mA. Excellent efficiency is achieved with low operating current together and multi-mode control circuit. CC/CV Operation WS3252 is designed to produce good CC/CV control characteristic as shown in the fig.1. In charger applications, a discharged battery charging starts in the CC portion of the curve until it is nearly full charged and smoothly switches to operate in CV portion of the curve. In an AC/DC adapter, the normal operation occurs only on the CV portion of the curve. The CC portion provides output current limiting. In CV operation, the output voltage is regulated through the primary side control. In CC operation mode, WS3252 will regulate the output current constant regardless of the output voltage drop. Adjustable CC point and Output Power In WS3252, the CC point and maximum output power can be externally adjusted by eaternal current sense resistor Rs at CS pin. The output power is adjusted through CC point change. The larger Rs, the smaller CC point is, and the smaller output power becomes, and vice versa. Vo Large R s Sm all R s Principle of Operation To achieve high precision CC/CV control, system needs to be designed in DCM mode for flyback system. In DCM mode, the output voltage can be sensed via the auxiliary Fig.2 Adjustable output power by changing Rs 6/8 Io Steady, keep you advance WS3252 WS3252 Operation switching frequency The switching frequency of WS3252 is adaptively controlled according to the load conditions and the operation modes. The operation switching frequency at maximum output power is set to 60KHz internally. In DCM mode, the maximum output power is given by Programmable Cable Drop Compensation Cable drop compensation is implemented to achieve good load regulation inWS3252. An offset voltage is generated at INV by an internal current flowing into the resister divider. The current is inversely proportional to the voltage across pin COMP, as a result, it is inversely proportional to the output load current, thus the drop due to the cable loss can be compensated. As the load current decreases from full-load to no-load, the offset voltage at INV will increase. It can also be programmed by adjusting the resistance of the divider to compensate the drop for various cable lines used. PoMAX 1 2 = LP FSW I P 2 Where Lp indicate the inductance of primary winding and Ip is peak current of primary winding. The change of the primary winding inductance results in the change of the maximum output power and constant output current in CC mode. To compensate the change from viariations of primary winding inductance, the switching frequency is locked by an internal loop such that the switching frequency is Gate Drive The gate drive strength which is too weak leads to over switch loss of MOSFET while too strong gate drive output compromises in the over EMI. A good tradeoff between output strength and dead time control is FSW = Since TDemag is 1 2TDemag proportional to the inversely achieved through the design of the built-in totem pole gate. The low standby dissipation and good EMI system design is easier to achieve through this dedicated devise. For MOSFET gate protection, an internal 12V clamp is added at higher than expected VCC input. inductance, as a result, the product Lp and Fsw is constant, thus the maximum output power and constant current in CC mode will not change as primary winding inductance changes. Up to ±10% variation of the primary winding inductance can be compensation. Protection Controls Frequency Shuffling Excellent EMI performance is achieved by using frequency jittering in WS3252 Excellent system stability is of achieved WS3252. by the comprehensive protection Including Cycle-by-Cycle current limiting (OCP), VCC Clamp, Under Voltage Lockout on VCC (UVLO). Device restarts when VCC voltage drops below UVLO limit. It is clamped when VCC is higher than threshold Current Sensing and Leading Edge Blanking Cycle-by-Cycle current limiting is offered in WS3252. The switch current is detected by a sense resistor into the sense pin. An internal leading edge blanking circuit chops off the sense voltage spike at initial MOSFET on state due to snubber diode reverse recovery so that the external RC filtering on sense input is no longer required. The current limit comparator is disabled and thus cannot turn off the internal MOSFET during the blanking period. PWM duty cycle is determined by the current sense input voltage and the EA output voltage. value. The power MOSFET is shut down when VCC drops below UVLO limit and device enters power on start-up sequence thereafter. 7/8 Steady, keep you advance WS3252 WS3252 SOT23-6 Package Outline Dimensions Symbol A A1 A2 b c D E E1 e e1 L θ Dimensions In Milimeters Min Max 1.000 1.300 0.000 0.150 1.000 1.200 0.300 0.500 0.100 0.200 2.800 3.020 1.500 1.700 2.600 3.000 0.950(BSC) 1.800 2.000 0.300 0.600 0° 8° Dimensions In Inches Min Max 0.039 0.051 0.000 0.006 0.039 0.047 0.012 0.020 0.004 0.008 0.110 0.119 0.059 0.067 0.102 0.118 0.037(BSC) 0.071 0.079 0.012 0.024 0° 8° 8/8 Steady, keep you advance