OB2279_DataSheet_Raiser_081211

©On-Bright Electronics Confidential - 1 - OB_DOC_DS_79A1 OB2279 Current Mode PWM ControllerFreq Shuffling with Latch Shutdown GENERAL DESCRIPTION OB2279 is a highly integrated current mode PWM control IC optimized for high performance, low standby power and cost effective offline flyback converter applications. PWM switching frequency at normal operation is externally programmable and trimmed to tight range. At no load or light load condition, the IC operates in extended ‘burst mode’ to minimize switching loss. Lower standby power and higher conversion efficiency is thus achieved. VDD low startup current and low operating current contribute to a reliable power on startup design with OB2279. A large value resistor could thus be used in the startup circuit for reduced power loss. The internal slope compensation improves system large signal stability and reduces the possible sub- harmonic oscillation at high PWM duty cycle output. Leading-edge blanking on current sense input removes the signal glitch due to snubber circuit diode reverse recovery and greatly reduces the external component count and system cost in the design. OB2279 offers comprehensive protection coverage including Cycle-by-Cycle current limiting(OCP), VDD Under Voltage Lockout(UVLO), VDD Over Voltage Protection(OVP), VDD Clamp, Gate Clamp, Over Load protection(OLP) and Over Temperature protection (OTP), etc. Different latch shutdown options are offered on OB2279 in different device version. V version has OVP Latch shutdown. T version supports both OVP and OTP latch shutdown. L version provides all OVP, OTP and OLP latch shutdown control. Excellent EMI performance is achieved with On- Bright proprietary frequency shuffling technique together with soft switching control at the totem pole gate drive output. OB2279 is offered in SOP-8 and DIP-8 packages. FEATURES ■ On-Bright Proprietary Frequency Shuffling Technology for Improved EMI Performance ■ Power On Soft Start ■ Extended Burst Mode Control For Improved Efficiency and Minimum Standby Power Design ■ Audio Noise Free Operation ■ External Programmable PWM Switching Frequency ■ Internal Synchronized Slope Compensation ■ Low VIN/VDD Startup Current(3uA) and Low Operating Current (2.3mA) ■ Leading Edge Blanking on Current Sense Input ■ Complete Protection Coverage with selective protections for Latch Shutdown o VDD Over Voltage Protection(OVP) – Latch Shutdown o Over Temperature Protection(OTP) – Auto recovery or Latch Shutdown o Over Load Protection. (OLP) – Auto recovery or Latch Shutdown o VDD Under Voltage Lockout with Hysteresis (UVLO) o Gate Output Voltage Clamp (16.5V) o Built-in OCP Compensation to Achieve Minimum OPP Variation over Universal AC Input Range. APPLICATIONS Offline AC/DC flyback converter for ■ Adaptor ■ Notebook Adaptor ■ LCD Monitor/TV/PC/Set-Top Box Power Supplies ■ Open-frame SMPS ■ Printer Power TYPICAL APPLICATION On -B rig ht C on fid en tia l to Ra ise r ©On-Bright Electronics Confidential - 2 - OB_DOC_DS_79A1 OB2279 Current Mode PWM ControllerFreq Shuffling with Latch Shutdown GENERAL INFORMATION Pin Configuration The pin map of OB2279 in DIP8 and SOP8 package is shown as below. Ordering Information Part Number Description OB2279AP-V DIP8, tube package, V version with OVP Latch OB2279AP-T DIP8, tube package, T version with OVP/OTP latch OB2279AP-L DIP8, tube package, L version with OVP/OTP/OLP latch OB2279CP-V SOP8, tube package, V version with OVP latch OB2279CPA-V SOP8, taping package, V version with OVP latch OB2279CP-T SOP8, tube package, T version with OVP/OTP latch OB2279CPA-T SOP8, taping package, T version with OVP/OTP latch OB2279CP-L SOP8, tube package, L version with OVP/OTP/OLP latch OB2279CPA-L SOP8, taping package, L version with OVP/OTP/OLP latch Note: All Devices are offered in Pb-free Package if not otherwise noted. Package Dissipation Rating Package RθJA (°C/W) DIP8 90 SOP8 150 Absolute Maximum Ratings Parameter Value VDD Clamp Voltage (Vclamp) 35 V VDD Clamp Continuous Current 10 mA VIN / VDD Input Voltage -0.3V to Vclamp FB Input Voltage -0.3 to 7V Sense Input Voltage -0.3 to 7V RT Input Voltage -0.3 to 7V RI Input Voltage -0.3 to 7V Min/Max Operating Junction Temperature TJ -20 to 150 oC Min/Max Storage Temperature Tstg -55 to 150 oC Lead Temperature (Soldering, 10 seconds) 260 oC Note: Stresses beyond 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 under “recommended operating conditions” is not implied. Exposure to absolute maximum-rated conditions for extended periods may affect device reliability. On -B rig ht C on fid en tia l to Ra ise r ©On-Bright Electronics Confidential - 3 - OB_DOC_DS_79A1 OB2279 Current Mode PWM ControllerFreq Shuffling with Latch Shutdown Marking Information TERMINAL ASSIGNMENTS Pin Num Pin Name I/O Description 1 GND P Ground 2 FB I Feedback input pin. PWM duty cycle is determined by voltage level into this pin and current-sense signal level at Pin 6. 3 VIN I Connected through a large value resistor to rectified line input for startup and line voltage sensing. 4 RI I Internal oscillator frequency setting pin. A resistor connected between RI and GND sets the PWM frequency. 5 RT I Dual function pin. Either connected through a NTC resistor to GND for over temperature shutdown control or used as latch shutdown control input. 6 SENSE I Current sense input pin. Connected to MOSFET current sensing resistor node. 7 VDD P DC power supply pin. 8 GATE O Totem-pole gate drive output for power MOSFET. On -B rig ht C on fid en tia l to Ra ise r ©On-Bright Electronics Confidential - 4 - OB_DOC_DS_79A1 OB2279 Current Mode PWM ControllerFreq Shuffling with Latch Shutdown BLOCK DIAGRAM RECOMMENDED OPERATING CONDITION Symbol Parameter Min Max Unit VDD VDD Supply Voltage 11.5 25 V TA Operating Ambient Temperature -20 85 oC On -B rig ht C on fid en tia l to Ra ise r ©On-Bright Electronics Confidential - 5 - OB_DOC_DS_79A1 OB2279 Current Mode PWM ControllerFreq Shuffling with Latch Shutdown ELECTRICAL CHARACTERISTICS (TA = 25℃, RI=100K ohm, VDD=16V, if not otherwise noted) Symbol Parameter Test Conditions Min Typ Max Unit Supply Voltage (VDD) I_VDD_Startup VDD Start up Current VDD =15VMeasure current into VDD 3 20 uA I_VDD_Ops Operation Current VFB=3V 2.3 mA UVLO(Enter) VDD Under Voltage Lockout Enter 8.8 9.8 10.8 V UVLO(Exit) VDD Under Voltage Lockout Exit (Startup) 15.5 16.5 17.5 V OVP(Latch) VDD Over Voltage Latch Trigger 26.5 28 29.5 V OVP(De-Latch) VDD Latch Release Voltage Threshold 7.5 V I(Vdd)_latch VDD bleeding current at latch shutdown when VDD = 9V 45 uA TD_OVP VDD OVP Debounce time 80 uSec VDD_Clamp VDD Zener Clamp Voltage I(VDD ) = 5 mA 35 V T_Softstart Soft Start Time 3 mSec Feedback Input Section(FB Pin) AVCS PWM Input Gain ΔVFB /ΔVcs 2.8 V/V VFB_Open VFB Open Voltage 6.2 V IFB_Short FB pin short circuit current Short FB pin to GND, measure current 0.75 mA VTH_0D Zero Duty Cycle FB Threshold Voltage 0.95 V VTH_BM Burst Mode FB Threshold Voltage 1.6 V VTH_PL Power Limiting FB Threshold Voltage 4.4 V TD_PL Power limiting Debounce Time 80 mSec ZFB_IN Input Impedance 9.0 Kohm Current Sense Input(Sense Pin) T_blanking Sense Input Leading Edge Blanking Time 300 nSec ZSENSE_IN Sense Input Impedance 30 Kohm TD_OC Over Current Detection and Control Delay CL=1nf at GATE, 70 nSec VTH_OC_0 Current Limiting Threshold at No Compensation I(VIN) = 0uA 0.85 0.90 0.95 V On -B rig ht C on fid en tia l to Ra ise r ©On-Bright Electronics Confidential - 6 - OB_DOC_DS_79A1 OB2279 Current Mode PWM ControllerFreq Shuffling with Latch Shutdown VTH_OC_1 Current Limiting Threshold at Compensation I(VIN) = 150uA, 0.80 V Oscillator FOSC Normal Oscillation Frequency 60 65 70 KHZ ∆f_Temp Central Frequency Temperature Stability -20oC to 100 oC 3 % ∆f_VDD Central Frequency Voltage Stability VDD = 12-28V, 3 % RI_range Operating RI Range 50 100 250 Kohm V_RI_open RI open voltage 2.0 V F_BM Burst Mode Base Frequency 20 KHZ Gate Drive Output VOL Output Low Level Io = 20 mA 0.3 V VOH Output High Level Io = 20 mA 11 V VG_Clamp Output Clamp Voltage Level 16.5 V T_r Output Rising Time CL = 1nf 120 nSec T_f Output Falling Time CL = 1nf 50 nSec Over Temperature Protection I_RT Output Current of RT pin 70 uA VTH_OTP OTP Threshold Voltage 1.015 1.065 1.115 V VTH_OTP_off (Version V Only) OTP Recovery Threshold Voltage 1.165 V VTH_RT_latch (Version V Only) RT Input Latch Threshold Voltage 0.6 V TD_OTP OTP De-bounce Time 100 uSec V_RT_Open RT Pin Open Voltage 3.7 V Frequency Shuffling ∆f_OSC Frequency Modulation range /Base frequency -3 3 % Freq_Shuffling Shuffling Frequency 32 HZ On -B rig ht C on fid en tia l to Ra ise r ©On-Bright Electronics Confidential - 7 - OB_DOC_DS_79A1 OB2279 Current Mode PWM ControllerFreq Shuffling with Latch Shutdown CHARACTERIZATION PLOTS VDD Startup Current vs. VDD 0 2 4 6 8 10 12 14 16 18 20 0 2 4 6 8 10 12 14 16 VDD(V) I_ vd d( uA ) I_vdd Startup vs. Temperature 0 2 4 6 8 -20 0 20 40 60 80 100 120 Temp (C) I_ vd d (u A) VDD UVLO and Ops Current 0 0.5 1 1.5 2 2.5 3 0 4 8 12 16 20 24 28 VDD (V) I_ VD D (m A) VDD Operation Current vs. Load 1 2 3 4 5 6 0 500 1000 1500 2000 Gatedrive Loading (pf) I( VD D) ( mA ) Fosc 50Khz Fosc 65Khz Fosc 100Khz UVLO(enter) vs. Temp 9.3 9.4 9.5 9.6 9.7 9.8 9.9 -20 0 20 40 60 80 100 120 Temp (C) UV LO (e nt er ) (V ) UVLO(exit) vs. Temp 15.8 15.9 16 16.1 16.2 16.3 16.4 16.5 16.6 -20 0 20 40 60 80 100 120 Temp (C) UV LO (e xi t) ( V) On -B rig ht C on fid en tia l to Ra ise r ©On-Bright Electronics Confidential - 8 - OB_DOC_DS_79A1 OB2279 Current Mode PWM ControllerFreq Shuffling with Latch Shutdown Fosc vs. RI 0 20 40 60 80 100 120 140 50 70 90 110 130 150 170 190 210 230 250 RI (Kohm) Fo sc ( Kh z) Fosc vs. Temperature 64 64.5 65 65.5 66 66.5 67 67.5 -20 0 20 40 60 80 100 120 Temp (C) Fo sc ( Kh z) Vth_OC(V) vs Ivin(uA) 0.6 0.7 0.8 0.9 1.0 0 50 100 150 200 250 300 Ivin(uA) V th _O C (V ) I_RT vs. Temp 69 69.2 69.4 69.6 69.8 70 70.2 70.4 70.6 -20 0 20 40 60 80 100 120 Temp (C) I_ RT ( uA ) w/ RI =1 00 Ko hm Ivdd_lacth(uA) vs Vdd(V) 30.0 35.0 40.0 45.0 50.0 7.5 7.8 8.1 8.4 8.7 9.0 Vdd(V) Iv dd _l ac th (u m A On -B rig ht C on fid en tia l to Ra ise r ©On-Bright Electronics Confidential - 9 - OB_DOC_DS_79A1 OB2279 Current Mode PWM ControllerFreq Shuffling with Latch Shutdown OPERATION DESCRIPTION OB2279 is a highly integrated PWM controller IC optimized for offline flyback converter applications with requirement in latch shutdown or auto recovery. The extended burst mode control greatly reduces the standby power consumption and helps the design easily meet the international power conservation requirements. z Startup Current and Start up Control Startup current of OB2279 is designed to be very low so that VDD could be charged up above UVLO(exit) threshold level and device starts up quickly. A large value startup resistor can therefore be used to minimize the power loss yet reliable startup in application. For a typical AC/DC adaptor with universal input range design, a 2 MΩ, 1/8 W startup resistor could be used together with a VDD capacitor to provide a fast startup and yet low power dissipation design solution. z Operating Current The Operating current of OB2279 is low at 2.3mA. Good efficiency is achieved with OB2279 low operating current together with extended burst mode control schemes. z Frequency shuffling for EMI improvement The frequency Shuffling/jittering (switching frequency modulation) is implemented in OB2279. The oscillation frequency is modulated with a internally generated random source so that the tone energy is evenly spread out. The spread spectrum minimizes the conduction band EMI and therefore eases the system design in meeting stringent EMI requirement. z Burst Mode Operation At zero load or light load condition, most of the power dissipation in a switching mode power supply is from switching loss of the MOSFET transistor, the core loss of the transformer and the loss in the snubber circuit. The magnitude of power loss is in proportion to the number of switching events within a fixed period of time. Reducing switching events leads to the reduction on the power loss and thus conserves the energy. OB2279 self adjusts the switching mode according to the loading condition. At no load or light load condition, the FB input drops below burst mode threshold level. Device enters Burst Mode control. The Gate drive output switches only when VDD voltage drops below a preset level and FB input is actived to output an on state. Otherwise the gate drive remains at off state to minimize the switching loss thus reduce the standby power consumption to the greatest extend. The nature of high frequency switching also reduces the audio noise at any loading conditions. z Oscillator Operation A resistor connected between RI and GND sets the constant current source to charge/discharge the internal cap and thus the PWM oscillator frequency is determined. The relationship between RI and switching frequency follows the below equation within the specified RI in Kohm range at nominal loading operational condition. )( )( 6500 Khz KohmRI FOSC = z Current Sensing and Leading Edge Blanking (LEB) Cycle-by-Cycle current limiting is offered in OB2279 current mode PWM control. 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 needed. The current limit comparator is disabled and cannot turn off the external MOSFET during the blanking period. The PWM duty cycle is determined by the current sense input voltage and the FB input voltage. z Internal Synchronized Slope Compensation Built-in slope compensation circuit adds voltage ramp onto the current sense input voltage for PWM generation. This greatly improves the close loop stability at CCM and prevents the sub-harmonic oscillation and thus reduces the output ripple voltage. z Over Temperature Protection with Latch Shutdown(Only to T and L version) A NTC resistor in series with a regular resistor should be connected between RT and GND for temperature sensing and protection. NTC resistor value becomes lower when the ambient temperature rises. With the fixed internal current IRT flowing through the resistors, the voltage at RT pin becomes lower at high temperature. The internal OTP circuit is triggered and shutdown the MOSFET when the sensed input voltage is lower than VTH_OTP. OTP is a latched shutdown. On -B rig ht C on fid en tia l to Ra ise r ©On-Bright Electronics Confidential - 10 - OB_DOC_DS_79A1 OB2279 Current Mode PWM ControllerFreq Shuffling with Latch Shutdown z RT Pin Used as Latch Shutdown Input Control RT pin could also be used as a control input to implement system latch shutdown function. An example is to implement system OVP protection with a latch shutdown function through a photo coupler and affiliated circuits. When OVP detection signal connected to RT is lower than VTH_OTP for Version T/L device, (or VTH_OT_Latch for Version V), OB2279 controls system into latch shutdown. The recovery of the AC/DC system could only start by resetting internal latch when VDD voltage drops below VDD_De-latch value. This could be achieved by unplugging/re-plugging of AC source in AC start- up configuration. z Gate Drive OB2279 Gate is connected to the Gate of an external MOSFET for power switch control. Too weak the gate drive strength results in higher conduction and switch loss of MOSFET while too strong gate drive output compromises the EMI. Good tradeoff is achieved through the built-in totem pole gate drive design with right output strength and dead time control. The low idle loss and good EMI system design is easier to achieve with this dedicated control scheme. An internal 16.5V clamp is added for MOSFET gate protection at higher than expected VDD input. z Protection Controls Good system reliability is achieved with OB2279’s rich protection features including Cycle-by-Cycle current limiting (OCP), Over Load Protection (OLP) with auto-recovery(V and T version) or latch shutdown(L version), over temperature protection (OTP) with auto-recovery(V version) or latch shutdown(T and L version), on-chip VDD over voltage protection (OVP) with latch shutdown and under voltage lockout (UVLO). VDD OVP protection is a latched shutdown in OB2279. The OCP threshold value is self adjusted lower at higher current into VIN pin. This OCP threshold