BL8835 High Precision CC/CV Primary-Side PWM Power Switch GENERAL DESCRIPTION FEATURES BL8835 is a high performance offline PWM Power switch for low power AC/DC charger and adapter applications. It operates in primary-side sensing and regulation. Consequently, opto-coupler and TL431 could be eliminated. Proprietary Constant Voltage (CV) and Constant Current (CC) control is integrated as shown in the figure below. ■ ±5% Constant Voltage Regulation at Universal AC input ■ High Precision Constant Current Regulation at Universal AC input ■ Primary-side Sensing and Regulation Without TL431 and Opto-coupler ■ Programmable CV and CC Regulation ■ Adjustable Constant Current and Output Power Setting ■ Built-in Secondary Constant Current Control with Primary Side Feedback ■ Built-in Adaptive Current Peak Regulation ■ Built-in Primary winding inductance compensation ■ Programmable Cable drop Compensation ■ Power on Soft-start ■ Built-in Leading Edge Blanking (LEB) ■ Cycle-by-Cycle Current Limiting ■ VDD Under Voltage Lockout with Hysteresis (UVLO) ■ VDD OVP ■ VDD Clamp Fig.1. Typical CC/CV Curve 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. BL8835 offers power on soft start control and protection coverage with auto-recovery features including Cycle-by-Cycle current limiting, VDD OVP, VDD clamp and UVLO. High precision constant voltage (CV) and constant current (CC) can be achieved by BL8835. 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 BL8835 is offered in SOP8 package. TYPICAL APPLICATION www.belling.com.cn 1/8 v1.0 BL8835 High Precision CC/CV Primary-Side PWM Power Switch GENERAL INFORMATION Pin Configuration The pin map is shown as below for SOP8. VDD 1 8 GND COMP 2 7 GND INV 3 6 DRAIN CS 4 5 DRAIN Absolute Maximum Ratings Parameter Value Drain Voltage (off state) -0.3V to Bvdss VDD Voltage -0.3 to VDD_clamp VDD Zener Clamp 10mA Continuous Current COMP Voltage -0.3 to 7V CS input Voltage -0.3 to 7V INV input Voltage -0.3 to 7V Max Operation Junction 150℃ Temperature Tj Min/Max storage -55 to 150℃ Temperature T-stg Lead Temperature 260℃ (Soldering,10secs) TERMINAL ASSIGNMENTS Pin Num. 1 2 3 4 5/6 7/8 Pin Name VDD COMP I/O P I INV I CS I DRAIN O GND P www.belling.com.cn Description Power Supply Loop Compensation for CV Stability 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 pin 4. Current sense input HV MOSFET Drain pin. The Drain pin is connected to the primary lead of the transformer Ground 2/8 v1.0 BL8835 High Precision CC/CV Primary-Side PWM Power Switch OUTPUT POWER TABLE Product BL8835 Universal Voltage Adapter 6W 10W Package Test Condition SOP-8 DIP-8 Indoor temperature 40℃ BLOCK DIAGRAM www.belling.com.cn 3/8 v1.0 BL8835 High Precision CC/CV Primary-Side PWM Power Switch ELECTRICAL CHARACTERISTICS (TA=25℃ if not otherwise noted) Symbol Parameter Supply Voltage (VDD) Standby Current IDD _ST Operation Current VDD Under Voltage Lockout Enter VDD Under Voltage Lockout Exit Maximum VDD Clamp Voltage Over Voltage Protection Threshold Current Sense Input LEB Time Over Current Threshold OCP Propagation Delay Input Impedance Soft Start Time Frequency Section IC Maximum Frequency System Nominal Switch Frequency System Start-up Frequency Frequency Shuffling Range IDD_Op Test Conditions Min VDD=13V Operation Supply Current INV=1.96V, CS=0V, VDD=18V Typ Max Unit 5 20 uA 2 3 mA UVLO(ON) VDD falling 8.2 9.0 10.5 V UVLO(OFF) VDD rising 13.5 14.8 16.0 V VDD_Clamp IDD=10mA 33.5 35.0 36.5 V OVP Ramp VDD until gate shut down 28.0 29.5 31.0 V 880 625 910 110 940 T_LEB Vth_OC Td _OC ZSENSE_IN T_SS 50 17 Freq_MaxNote1 55 Freq_Nom Freq_startup Δf/Freq INV=0V, Comp=+5V 60 65 ns mV ns KΩ mS KHz 50 KHz 14 KHz ±3% Error Amplifier Reference Voltage for EA DC Gain of EA Max. Cable Compensation Current Vref_EA Gain I_COMP_MAX 1.97 INV=+2V, Comp=0V 2.00 60 2.03 V dB uA 37.5 Power MOSFET Section MOSFET Drain Source Breakdown Voltage ON Resistance 600 BVdss Rdson Static, Id=0.4A 7 V 9 11 Ω 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. www.belling.com.cn 4/8 v1.0 BL8835 High Precision CC/CV Primary-Side PWM Power Switch CHARACTERIZATION PLOTS www.belling.com.cn 5/8 v1.0 BL8835 High Precision CC/CV Primary-Side PWM Power Switch OPERATION DESCRIPTION BL8835 is a cost effective PWM power switch optimized for off-line low power AC/DC applications including battery chargers and adapters. It operates in primary side sensing and regulation, thus Opto -coupler and TL431 are not required. Proprietary built-in CV and CC control can achieve high precision CC/CV control meeting most adapter and charger application requirements. • Startup Current and Start up Control Startup current of BL8835 is designed to be very low so that VDD could be charged up above UVLO threshold and starts up quickly. A large value startup resistor can therefore be used to minimize the power loss in application. When MOSFET turns off, the primary current transfers to the secondary at the amplitude of IS NP IP NS (1) The auxiliary voltage reflects the output voltage as shown in fig.2 and it is given by VAUX N AUX VO V NS (2) Where △V indicates the drop voltage of the output Diode. • Operating Current The Operating current of BL8835 is as low as 2.5mA. Good efficiency is achieved with the low operating current together with ‘Muti-mode’ control features. • Soft Start BL8835 features an internal soft start to minimize the component electrical over-stress during power on startup. As soon as VDD reaches UVLO (OFF), the control algorithm will ramp peak current voltage threshold gradually from nearly zero to normal setting of 0.90V. Every restart is a soft start. • CC/CV Operation BL8835 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, BL8835 will regulate the output current constant regardless of the output voltage drop. • Principle of Operation To support BL8835 proprietary CC/CV control, system needs to be designed in DCM mode for flyback system (Refer to Typical Application Diagram on page1). In the DCM flyback converter, the output voltage can be sensed via the auxiliary 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. www.belling.com.cn Fig.2. Auxiliary voltage waveform Via a resistor divider connected between the auxiliary winding and INV (PIN 3), 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 (2.0V) 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 constant output voltage can be achieved. When sampled voltage is below Vref and the 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. • Adjustable CC point and output Power In BL8835, the CC point and maximum output power can be externally adjusted by external current sense resistor Rs at CS pin as illustrated in Typical Application Diagram. The output power is adjusted through CC point change. The large Rs, the smaller CC point is, and the smaller output power becomes, and vice versa as shown in Fig.3. 6/8 v1.0 BL8835 High Precision CC/CV Primary-Side PWM Power Switch •Current Sensing and Leading Edge Blanking Cycle-by-Cycle current limiting is offered in BL8835 current mode PWM control. The switch current is detected by a sense resistor into the CS pin. An internal leading edge blanking circuit chops off the sensed voltage spike at initial internal power MOSFET on state so that the external RC filtering on sense input is no longer needed. The PWM duty cycle is determined by the current sense input voltage and the EA output voltage. • Gate Drive Fig.3 Adjustable output power by changing Rs • Operation switching frequency The switching frequency of BL8835 is adaptively controlled according to the load conditions and the operation modes. No external frequency setting components are required. The operation switching frequency at maximum output power is set to 60KHz internally. For flyback operating in DCM, The maximum output power is given by 1 PO _ MAX LP FSW I P2 2 Where Lp indicate the inductance of primary winding and Lp is the peak current of primary winding. Refer to the equation 3, the change of the primary winding inductance results in the change of the maximum output power and the constant output current in CC mode. To compensate the change from variations of primary winding inductance, the switching frequency is locked by an internal loop such that the switching frequency is FSW The internal power MOSFET in BL8835 is driven by a dedicated gate driver for power switch control. Too weak the gate drives strength results in higher conduction and switch loss of MOSFET while too strong gate drive compromises EMI. A good tradeoff is achieved through the built-in totem pole gate design with right output strength control. • Programmable Cable drop Compensation In BL8835, cable drop compensation is implemented to achieve good load regulation. 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. 1 2TDemag Since T-Demage is inversely proportional to the 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 compensated. • Frequency shuffling for EMI improvement The frequency shuffling (switching frequency modulation) is implemented in BL8835. The oscillation frequency is modulated so that the tone energy is spread out. The spread spectrum minimizes the conduction band EMI and therefore eases the system design. www.belling.com.cn • Protection Control Good power supply system reliability is achieved with its rich protection features including Cycle-by-Cycle current limiting (OCP), VDD clamp, Power on Soft Start, and Under Voltage Lockout on VDD (UVLO). VDD is supplied by transformer auxiliary winding output. The output of BL8835 is shut down when VDD drops below UVLO (ON) limit and Switcher enters power on start-up sequence thereafter. 7/8 v1.0 BL8835 High Precision CC/CV Primary-Side PWM Power Switch SOP8 PACKAGE OUTLINE DIMENSIONS PACKAGE MECHANICAL DATA Symbol Dimensions In Millimeters Dimensions In Inches Min Max Min Max A 1.350 1.750 0.053 0.069 A1 0.050 0.250 0.002 0.010 A2 1.250 1.650 0.049 0.065 B 0.310 0.510 0.012 0.020 C 0.170 0.250 0.006 0.010 D 4.700 5.150 0.185 0.203 E 3.800 4.000 0.150 0.157 E1 5.800 6.200 0.228 0.244 e 1.270(BSC) 0.05(BSC) L 0.400 1.270 0.016 0.050 θ 0° 8° 0° 8° www.belling.com.cn 8/8 v1.0