SW2273A High Performance Current Mode PWM Controller GENERAL DESCRIPTION FEATURES SW2273A 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 internally fixed and is 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 and low standby design with SW2273A. SW2273A offers complete protection coverage with auto-recovery including Cycle-by-Cycle current limiting (OCP), over load protection (OLP), and VDD under voltage lockout (UVLO). It also provides the protections with latched shut down including over temperature protection (OTP), and over voltage (fixed or adjustable) protection (OVP). Excellent EMI performance is achieved with OnBright proprietary frequency shuffling technique. The tone energy at below 20KHZ is minimized in the design and audio noise is eliminated during operation. ■ SW2273A is offered in SOT23-6 package. TYPICAL APPLICATION -1- ■ ■ ■ ■ ■ Power on Soft Start Reducing MOSFET Vds Stress Frequency shuffling for EMI Extended Burst Mode Control For Improved Efficiency and Minimum Standby Power Design Audio Noise Free Operation Fixed 65KHZ Switching Frequency Comprehensive Protection Coverage o VDD Under Voltage Lockout with Hysteresis (UVLO) o Cycle-by-cycle over current threshold setting for constant output power limiting over universal input voltage range o Overload Protection (OLP) with autorecovery o Over Temperature Protection (OTP) with latch shut down o VDD Over voltage Protection(OVP) with latch shut down o Adjustable OVP through external Zener APPLICATIONS Offline AC/DC flyback converter for ■ Battery Charger ■ Power Adapter ■ Set-Top Box Power Supplies ■ Open-frame SMPS SW2273A High Performance Current Mode PWM Controller Package Dissipation Rating Package RθJA(℃/W) SOT23-6 200 GENERAL INFORMATION Pin Configuration The SW2273A is offered in SOT23-6 package, shown as below. Absolute Maximum Ratings Parameter Value VDD DC Supply Voltage 30 V VDD Zener Clamp VDD_Clamp+0.1V VoltageNote VDD DC Clamp Current 10 mA FB Input Voltage -0.3 to 7V Sense Input Voltage -0.3 to 7V RT Input Voltage -0.3 to 7V Min/Max Operating -40 to 150 ℃ Junction Temperature TJ Min/Max Storage -55 to 160 ℃ Temperature Tstg Lead Temperature 260 ℃ (Soldering, 10secs) Note: VDD_Clamp has a nominal value of 32V. Ordering Information Part Number Description SW2273A SOT23-6, Pb-free in T&R 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. -2- SW2273A High Performance Current Mode PWM Controller TERMINAL ASSIGNMENTS Pin Name GND I/O P FB I RT I CS VDD Gate I P O Description Ground Feedback input pin. The PWM duty cycle is determined by voltage level into this pin and the current-sense signal at Pin 4. Dual function pin. Either connected through a NTC resistor to ground for over temperature shutdown/latch control or connected through Zener to VDD for adjustable over voltage protection Current sense input Power Supply Totem-pole gate driver output for power Mosfet RECOMMENDED OPERATING CONDITION Symbol VDD TA Parameter VDD Supply Voltage Operating Ambient Temperature BLOCK DIAGRAM -3- Min/Max 12 to 25 -40 to 85 Unit V ℃ SW2273A High Performance Current Mode PWM Controller ELECTRICAL CHARACTERISTICS (TA = 25℃, VDD=18V, unless otherwise noted) Symbol Parameter Supply Voltage (VDD) Istartup VDD Start up Current I_VDD_Operation Operation Current UVLO(ON) UVLO(OFF) Vpull-up Vdd_clamp OVP(ON) Test Conditions protection Ivdd=10mA CS=0V,FB=3V Ramp up VDD until gate clock is off Vlatch_release Latch release voltage Feedback Input Section(FB Pin) VFB_Open VFB Open Loop Voltage PWM input gain Δ VFB/ Δ Avcs VCS Maximum duty Max duty cycle @ cycle VDD=18V,VFB=3V,VCS=0V The threshold enter green Vref_green mode Vref_burst_H The threshold exit burst mode The threshold enter burst Vref_burst_L mode IFB_Short FB pin short circuit current Typ Max Unit 5 20 uA 1.8 2.5 mA 8 9 10 V 14.3 15.3 16.3 V 30 13 32 34 V V 26 28 30 V VDD=UVLO(OFF)1V, measure leakage current into VDD VDD=18V,VFB=3V, CS=0V,Cgate=1nF VDD Under Voltage Lockout Enter VDD Under Voltage Lockout Exit (Recovery) Pull-up PMOS active Over voltage voltage Min 3.9 75 Short FB pin to GND and measure current Power Limiting FB Threshold Voltage Power limiting Debounce TD_PL Time ZFB_IN Input Impedance Current Sense Input(CS Pin) SST Soft start time T_blanking Leading edge blanking time ZSENSE_IN Input Impedance VTH_PL TD_OC VTH_OC Vocp_clamping Oscillator Over Current Detection and Control Delay 80 From Over Current Occurs till the Gatedrive output start to turn off Internal Current Limiting Threshold Voltage with zero duty cycle CS voltage clamper FOSC Normal Oscillation Frequency △f_OSC F_shuffling Frequency jittering Shuffling frequency VDD=18V, CS=0V FB=3V, 60 5 V 4.2 V 2 V/V 80 % 2 V 1.275 V 1.175 V 0.4 mA 3.7 V 88 96 mSec 16 Kohm 4 220 40 ms ns Kohm 120 nSec 0.75 V 0.9 V 65 +/-4 32 -4- 85 70 KHZ % Hz SW2273A High Performance Current Mode PWM Controller △f_Temp △f_VDD F_Burst Gate driver Frequency Temperature Stability Frequency Voltage Stability Burst Mode Switch Frequency Output low level @ VDD=18V, Io=5mA Output high level @ VOH VDD=18V, Io=20mA V_clamping Output clamp voltage Output rising time 1V ~ 12V T_r @ CL=1000pF Output falling time 12V ~ 1V T_f @ CL=1000pF Over temperature protection IRT Output current of RT pin VOTP Threshold voltage for OTP Td_OTP OTP debounce time VRT_FL Float voltage at RT pin External OVP threshold Vth_OVP voltage 1 % 1 22 % KHZ VOL 1 6 95 0.95 V 12 V 175 nS 85 nS 100 1 32 2.3 4 -5- V 105 1.05 uA V Cycle V V SW2273A High Performance Current Mode PWM Controller CHARACTERIZATION PLOTS VDD = 18V, TA = 25℃ condition applies if not otherwise noted. Istartup(uA) vs Temperature(℃ ) Vth_otp(V) vs Temperature(℃ ) 1.02 4.5 Vth_otp(V) Istartup(uA) 5.0 4.0 3.5 1.01 1.00 0.99 0.98 3.0 -40 0 40 80 -40 120 UVLO(on)(V) vs Temperature(℃ ) UVLO(off)(V) UVLO(on)(V) 9.4 9.2 9 8.8 40 80 120 15.4 15.2 15 14.8 14.6 14.4 120 -40 0 Temperature(℃ ) 40 80 120 Temperature(℃ ) Vth_OC(V)vs duty(%) Fosc(KHz) vs Temperature(℃ ) 0.95 64.0 0.90 63.8 Fosc(KHz) Vth_OC(V) 80 UVLO(off)(V) vs Temperature(℃ ) 9.6 0 40 Temperature(℃) Temperature(℃) -40 0 0.85 0.80 63.5 63.3 63.0 0.75 0 14 28 42 Duty(%) 56 -40 70 0 40 80 Temperature(℃) 6 120 SW2273A High Performance Current Mode PWM Controller OPERATION DESCRIPTION SW2273A is a highly integrated current mode PWM control IC optimized for high performance, low standby power and cost effective offline flyback converter applications. The ‘Extended burst mode’ control greatly reduces the standby power consumption and helps the design easily to meet the international power conservation requirements. • Startup Current and Start up Control Startup current of SW2273A is designed to be very low so that VDD 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 yet achieve a reliable startup in application. • Operating Current The Operating current of SW2273A is low at 1.8mA. Good efficiency is achieved with SW2273A low operating current together with the ‘Extended burst mode’ control features. Vref_burst_L (the threshold enter burst mode) and device enters Burst Mode control. The Gate drive output switches when FB input rises back to Vref_burst_H (the threshold exit burst mode). Otherwise the gate drive remains at off state to minimize the switching loss and reduces the standby power consumption to the greatest extend. The switching frequency control also eliminates the audio noise at any loading conditions. • Oscillator Operation The switching frequency is internally fixed at 65KHZ. No external frequency setting components are required for PCB design simplification. • Soft Start SW2273A features an internal 4ms soft start to soften the electrical stress occurring in the power supply during startup. It is activated during the power on sequence. As soon as VDD reaches UVLO(OFF), the CS peak voltage is gradually increased from 0.05V to the maximum level. Every restart up is followed by a soft start. • Current Sensing and Leading Edge Blanking Cycle-by-Cycle current limiting is offered in SW2273A 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 due to snubber diode reverse recovery and surge gate current of power MOSFET. The current limiting comparator is disabled and cannot turn off the internal power MOSFET during the blanking period. The PWM duty cycle is determined by the current sense input voltage and the FB input voltage. • Frequency shuffling for EMI improvement The frequency Shuffling (switching frequency modulation) is implemented in SW2273A. 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. • 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 subharmonic oscillation and thus reduces the output ripple voltage. • Extended Burst Mode Operation At light load or zero load condition, most of the power dissipation in a switching mode power supply is from switching loss on the MOSFET, the core loss of the transformer and the loss on the snubber circuit. The magnitude of power loss is in proportion to the switching frequency. Lower switching frequency leads to the reduction on the power loss and thus conserves the energy. The switching frequency is internally adjusted at no load or light load condition. The switch frequency reduces at light/no load condition to improve the conversion efficiency. At light load or no load condition, the FB input drops below • Drive The power MOSFET is driven by a dedicated gate driver for power switch control. Too weak the gate drive strength results in higher conduction and switch loss of MOSFET while too strong gate drive results the compromise of EMI. A good tradeoff is achieved through the built-in totem pole gate 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. • 7 Protection Controls SW2273A High Performance Current Mode PWM Controller Good power supply system reliability is achieved with auto-recovery protection features including Cycle-by-Cycle current limiting (OCP), Over Load Protection (OLP), and Under Voltage Lockout on VDD (UVLO), and latch shutdown features including over temperature protection (OTP), fixed or adjustable VDD over voltage protection (OVP). With On-Bright Proprietary technology, the OCP is line voltage compensated to achieve constant output power limit over the universal input voltage range. At overload condition when FB input voltage exceeds power limit threshold value for more than TD_PL, control circuit reacts to shut down the converter. It restarts when VDD voltage drops below UVLO limit. For protection with latch shut down mode, control circuit shutdowns (latch) the power MOSFET when an Over Temperature condition or Over Voltage condition is detected until VDD drops below 5V (Latch release voltage) , and device enters power on restart-up sequence thereafter. -8- SW2273A High Performance Current Mode PWM Controller PACKAGE MECHANICAL DATA Symbol A A1 A2 b c D E E1 e e1 L θ Dimensions In Millimeters 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 0º 8º -9- 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 0º 8º