FAN7602B

FAN7602B — Green Current-Mode PWM Controller March 2007 FAN7602B Green Current-Mode PWM Controller Features Green Current-Mode PWM Control Fixed 65kHz Operation Internal High-Voltage Start-up Switch Burst-Mode Operation Line Voltage Feedforward to Limit Maximum Power Line Under-Voltage Protection Latch Protection & Internal Soft-Start (10ms) Function Overload Protection Over-Voltage Protection Low Operation Current: 1mA Typical 8-pin DIP/SOP Description The FAN7602B is a green current-mode PWM controller. It is specially designed for off-line adapter applications; DVDP, VCR, LCD monitor applications; and auxiliary power supplies. The internal high-voltage start-up switch and the burstmode operation reduce the power loss in standby mode. As a result, it is possible to supply 0.5W load, limiting the input power under 1W when the input line voltage is 265VAC. On no-load condition, input power is under 0.3W. The maximum power can be limited constantly, regardless of the line voltage change, using the power limit function. The switching frequency is internally fixed at 65kHz. The FAN7602B includes various protections for the system reliability and the internal soft-start prevents the output voltage over-shoot at start-up. Applications Adapter LCD Monitor Power Auxiliary Power Supply Related Application Notes AN6014 - Green Current Mode PWM Controller FAN7602 Ordering Information Part Number FAN7602BN FAN7602BM FAN7602BMX -25°C to +125°C Yes Operating Temp. Range Pb-Free Package 8-DIP 8-SOP Packing Method Rail Rail Tape & Reel Marking Code FAN7602B FAN7602B FAN7602B © 2007 Fairchild Semiconductor Corporation FAN7602B Rev. 1.0.0 www.fairchildsemi.com FAN7602B — Green Current-Mode PWM Controller Typical Application Diagram FAN7602B Figure 1. Typical Flyback Application Internal Block Diagram VSTR 8 6 VCC LUVP 1 2V/1.5V LUVP OLP OVP Latch Auto Restart Protection Latch Protection Reset Circuit VCC OVP SS End 19V 5V Ref UVLO 12V/8V 10ms Soft Start SS End PWM Block 65kHz clock Delay Circuit Latch/ Plimit 0.95V/0.88V 2 4V Plimit Offset Generator Plimit Offset Soft Start Latch PWM+ OLP Soft Start Driver Circuit Plimit Offset 5 OUT 3 CS/FB Power Limit Plimit Offset OLP 4 GND Figure 2. Functional Block Diagram of FAN7602B © 2007 Fairchild Semiconductor Corporation FAN7602B Rev. 1.0.0 2 www.fairchildsemi.com FAN7602B — Green Current-Mode PWM Controller Pin Assignments VSTR 8 NC 7 VCC 6 Out 5 FAN7602B YWW 1 LUVP 2 Latch/ Plimit 3 CS/FB 4 GND Figure 3. Pin Configuration (Top View) Pin Definitions Pin # 1 2 Name LUVP Latch/Plimit Description Line Under-Voltage Protection Pin. This pin is used to protect the set when the input voltage is lower than the rated input voltage range. Latch Protection and Power Limit Pin. When the pin voltage exceeds 4V, the latch protection works; the latch protection is reset when the VCC voltage is lower than 5V. For the power limit function, the OCP level decreases as the pin voltage increases. Current Sense and Feedback Pin. This pin is used to sense the MOSFET current for the current mode PWM and OCP. The output voltage feedback information and the current sense information are added using an external RC filter. Ground Pin. This pin is used for the ground potential of all the pins. For proper operation, the signal ground and the power ground should be separated. Gate Drive Output Pin. This pin is an output pin to drive an external MOSFET. The peak sourcing current is 450mA and the peak sinking current is 600mA. For proper operation, the stray inductance in the gate driving path must be minimized. Supply Voltage Pin. IC operating current and MOSFET driving current are supplied using this pin. No Connection. Start-up Pin. This pin is used to supply IC operating current during IC start-up. After start-up, the internal JFET is turned off to reduce power loss. 3 4 5 6 7 8 CS/FB GND OUT VCC NC VSTR © 2007 Fairchild Semiconductor Corporation FAN7602B Rev. 1.0.0 3 www.fairchildsemi.com FAN7602B — Green Current-Mode PWM Controller Absolute Maximum Ratings Stresses exceeding the absolute maximum ratings may damage the device. The device may not function or be operable above the recommended operating conditions and stressing the parts to these levels is not recommended. In addition, extended exposure to stresses above the recommended operating conditions may affect device reliability. The absolute maximum ratings are stress ratings only. Symbol VCC IOH, IOL VCS/FB VLUVP VLatch VSTR TJ TA TSTG PD VESD_HBM VESD_MM VESD_CDM Supply Voltage Parameter Peak Drive Output Current CS/FB Input Voltage LUVP Input Voltage Latch/Plimit Input Voltage VSTR Input Voltage Operating Junction Temperature Operating Temperature Range Storage Temperature Range Power Dissipation ESD Capability, Human Body Model ESD Capability, Machine Model ESD Capability, Charged Device Model Value 20 +450/-600 -0.3 to 20 -0.3 to 10 -0.3 to 10 600 150 -25 to 125 -55 to 150 1.2 2.0 200 500 Unit V mA V V V V °C °C °C W kV V V Thermal Impedance Symbol θJA Note: 1. Regarding the test environment and PCB type, please refer to JESD51-2 and JESD51-10. Parameter Thermal Resistance, Junction-to-Ambient 8-DIP Value 100 Unit °C/W © 2007 Fairchild Semiconductor Corporation FAN7602B Rev. 1.0.0 4 www.fairchildsemi.com FAN7602B — Green Current-Mode PWM Controller Electrical Characteristics VCC = 14V, TA = -25°C~125°C, unless otherwise specified Symbol START UP SECTION ISTR Vth(start) Vth(stop) HY(uvlo) ISTR ICC tSS fOSC VCS/FB1 tD DMAX DMIN VCS/FB2 VCS/FB3 KPlimit VOH VOL tR tF VLatch tOLP tOLP_ST VOLP VLUVPoff VLUVPon VOVP Note: Parameter VSTR Start-up Current Start Threshold Voltage Stop Threshold Voltage UVLO Hysteresis Start-up Supply Current Operating Supply Current Soft-Start Time(1) Operating Frequency CS/FB Threshold Voltage Propagation Delay to Maximum Duty Cycle Minimum Duty Cycle Burst On Threshold Voltage Burst Off Threshold Voltage Offset Gain Output Voltage High Output Voltage Low Rising Falling Time(1) Time(1) Output(1) Condition VSTR = 30V, TA = 25°C VCC increasing VCC decreasing Min. 0.7 11 7 3.6 Typ. 1.0 12 8 4.0 250 1.0 Max. 1.4 13 9 4.4 320 1.5 15 73 1.1 150 80 0 Unit mA V V V μA mA ms kHz V ns % % V V UNDER VOLTAGE LOCK OUT SECTION SUPPLY CURRENT SECTION TA = 25°C Output no switching 5 VCS/FB = 0.2V, TA = 25°C TA = 25°C 59 0.9 70 SOFT-START SECTION 10 65 1.0 100 75 PWM SECTION BURST MODE SECTION TA = 25°C TA = 25°C VLatch/Plimit = 2V, TA = 25°C TA = 25°C, Isource = 100mA TA = 25°C, Isink = 100mA TA = 25°C, CL = 1nF TA = 25°C, CL= 1nF 3.6 (1) 0.84 0.77 0.12 11.5 0.95 0.88 0.16 12.0 1.0 45 35 4.0 22 37 0 1.06 0.99 0.20 14.0 2.5 150 150 4.4 24 44 0.1 2.1 1.6 20 POWER LIMIT SECTION OUTPUT SECTION V V ns ns V ms ms V V V V PROTECTION SECTION Latch Voltage Overload Protection Time Overload Protection Time at Startup Overload Protection Level Line Under-Voltage Protection On to Off Line Under-Voltage Protection Off to On Over-Voltage Protection TA = 25°C TA = 25°C TA = 25°C 1.9 1.4 18 20 30 2.0 1.5 19 1. These parameters, although guaranteed by design, are not tested in production. © 2007 Fairchild Semiconductor Corporation FAN7602B Rev. 1.0.0 5 www.fairchildsemi.com FAN7602B — Green Current-Mode PWM Controller Typical Performance Characteristics 12.8 12.4 8.8 8.4 VTH[V] VTL[V] 12.0 11.6 11.2 -25 0 25 50 75 100 125 8.0 7.6 7.2 -25 0 25 50 75 100 125 Temperature [°C] Temperature [°C] Figure 4. Start Threshold Voltage vs. Temp. Figure 5. Stop Threshold Voltage vs. Temp. 4.4 4.3 350 UVLO Hysteresis [V] 4.2 300 4.0 3.9 3.8 3.7 3.6 -25 0 25 50 75 100 125 Ist [μA] 4.1 250 200 150 -25 0 25 50 75 100 125 Temperature [°C] Temperature [°C] Figure 6. UVLO Hysteresis vs. Temp. Figure 7. Start-up Supply Current vs. Temp. 1.5 1.4 1.3 1.3 1.2 Iop [mA] Istr [mA] 0 25 50 75 100 125 1.2 1.1 1.0 0.9 0.8 -25 1.1 1.0 0.9 0.8 -25 0 25 50 75 100 125 Temperature [°C] Temperature [°C] Figure 8. Operating Supply Current vs. Temp. Figure 9. VSTR Star-up Current vs. Temp. © 2007 Fairchild Semiconductor Corporation FAN7602B Rev. 1.0.0 6 www.fairchildsemi.com FAN7602B — Green Current-Mode PWM Controller Typical Performance Characteristics (Continued) 1.10 1.05 CSFB2 CSFB3 70 68 CS/FB Threshold [V] 1.00 0.95 0.90 0.85 0.80 0.75 0.70 -25 0 25 50 75 100 125 Fosc [kHz] 66 64 62 60 -25 0 25 50 75 100 125 Temperature [°C] Temperature [°C] Figure 10. Burst On/Off Voltage vs. Temp. Figure 11. Operating Frequency vs. Temp. 0.20 0.18 0.16 0.14 0.12 0.10 -25 80 78 Dmax [%] 0 25 50 75 100 125 Kplimit 76 74 72 70 -25 0 25 50 75 100 125 Temperature [°C] Temperature [°C] Figure 12. Offset Gain vs. Temp. Figure 13. Maximum Duty Cycle vs. Temp. 20.0 19.6 19.2 18.8 18.4 18.0 -25 4.4 4.2 VLATCH [V] 0 25 50 75 100 125 VOVP [V] 4.0 3.8 3.6 -25 0 25 50 75 100 125 Temperature [°C] Temperature [°C] Figure 14. OVP Voltage vs. Temp. Figure 15. Latch Voltage vs. Temp. © 2007 Fairchild Semiconductor Corporation FAN7602B Rev. 1.0.0 7 www.fairchildsemi.com FAN7602B — Green Current-Mode PWM Controller Typical Performance Characteristics (Continued) 2.10 1.70 1.65 2.05 VLUVPoff [V] VLUVPon [V] 0 25 50 75 100 125 1.60 1.55 1.50 2.00 1.95 1.45 1.90 -25 1.40 -25 0 25 50 75 100 125 Temperature [°C] Temperature [°C] Figure 16. LUVP On-to-Off Voltage vs. Temp. Figure 17. LUVP Off-to-On Voltage vs. Temp. CSFB1 Threshold voltage [V] 1.08 1.04 1.00 0.96 0.92 -25 0 25 50 75 100 125 Temperature [°C] Figure 18. CS/FB Threshold Voltage vs. Temp. © 2007 Fairchild Semiconductor Corporation FAN7602B Rev. 1.0.0 8 www.fairchildsemi.com FAN7602B — Green Current-Mode PWM Controller Applications Information 1. Start-up Circuit and Soft Start Block The FAN7602B contains a start-up switch to reduce the power loss of the external start-up circuit of the conventional PWM converters. The internal start-up circuit charges the VCC capacitor with 0.9mA current source if the AC line is connected. The start-up switch is turned off 15ms after IC starts up, as shown in Figure 19. The softstart function starts when the VCC voltage reaches the start threshold voltage of 12V and ends when the internal soft-start voltage reaches 1V. The internal start-up circuit starts charging the VCC capacitor again if the Vcc voltage is lowered to the minimum operating voltage, 8V. The UVLO block shuts down the output drive circuit and some blocks to reduce the IC operating current and the internal soft-start voltage drops to zero. If the VCC voltage reaches the start threshold voltage, the IC starts switching again and the soft-start block works as well. During the soft-start, the pulse-width modulated (PWM) comparator compares the CS/FB pin voltage with the soft-start voltage. The soft-start voltage starts from 0.5V and the soft-start ends when it reaches 1V and the softstart time is 10ms. The start-up switch is turned off when the soft-start voltage reaches 1.5V. 12V 8V Start-up Current 1.5V 1V 0.5V Soft Start Voltage Soft Start Time (10ms) t 5ms PWM Comparator PWM+ Soft Start Plimit Offset Power Limit 3 RFB CS/FB CF RS IFB RF Isw charging CF to adjust the offset voltage. If IFB is zero, CF is discharged through RF and RS to lower offset voltage. Figure 21 shows typical voltage waveforms of the CS/FB pin. The current-sense waveform is added to the offset voltage, as shown in Figure 21. The CS/FB pin voltage is compared with PWM+ that is 1V - Plimit offset. If the CS/ FB voltage meets PWM+, the output drive is shut off. If the feedback offset voltage is low, the switch on time is increased. If the feedback offset voltage is high, the switch on time is decreased. In this way, the duty cycle is controlled according to the output load condition. In general, the maximum output power increases as the input voltage increases because the current slope during switch on-time increases. To limit the output power of the converter constantly, a power-limit function is included. Sensing the converter input voltage through the Latch/Plimit pin, the Plimit offset voltage is subtracted from 1V. As shown in Figure 21, the Plimit offset voltage is subtracted from 1V and the switch on-time decreases as the Plimit offset voltage increases. If the converter input voltage increases, the switch on-time decreases, keeping the output power constant. The offset voltage is proportional to the Latch/ Plimit pin voltage and the gain is 0.16; if the Latch/Plimit voltage is 1V, the offset voltage is 0.16V. Vcc VCC Figure 19. Start-up Current and VCC Voltage Figure 20. Current-Sense and Feedback Circuits 1V PWM+ CS/FB Power Limit Offset 2. Oscillator Block The oscillator frequency is set internally. The switching frequency is 65kHz. FB Offset 3. Current Sense and Feedback Block The FAN7602B performs the current sensing for the current-mode PWM and the output voltage feedback with only one pin, pin3. To achieve the two functions with one pin, an internal leading edge blanking (LEB) circuit to filter the current-sense noise is not included because the external RC filter is necessary to add the output voltage feedback information and the current-sense information. Figure 20 shows the current-sense and feedback circuits. RS is the current-sense resistor to sense the switch current. The current-sense information is filtered by an RC filter composed of RF and CF. According to the output voltage feedback information, IFB charges or stops GND On Time (a) Low-Power Limit Offset Case 1V PWM+ CS/FB Power Limit Offset FB Offset GND On Time (b) High-Power Limit Offset Case Figure 21. CS/FB Pin Voltage Waveforms © 2007 Fairchild Semiconductor Corporation FAN7602B Rev. 1.0.0 9 www.fairchildsemi.com FAN7602B — Green Current-Mode PWM Controller 4. Burst-Mode Block The FAN7602B contains the burst-mode block to reduce the power loss at a light load and no load. A hysteresis comparator senses the offset voltage of the Burst+ for the burst mode, as shown in Figure 22. The Burst+ is the sum of the CS/FB voltage and Plimit offset voltage. The FAN7602B enters burst mode when the offset voltage of the Burst+ is higher than 0.95V and exits the burst mode when the offset voltage is lower than 0.88V. The offset voltage is sensed during the switch off time. O ffs e t D e la y C irc u it voltage feedback loop is saturated, and the OLP initiates if the LUVP condition persists more than 22ms. Vin 1 − + 2V/1.5V LUVP Figure 24. Line UVP Circuit 5.3 Latch Protection The latch protection is provided to protect the system against abnormal conditions using the Latch/Plimit pin. The Latch/Plimit pin can be used for the output overvoltage protection and/or other protections. If the Latch/ Plimit pin voltage is made higher than 4V by an external circuit, the IC is shut down. The latch protection is reset when the VCC voltage is lower than 5V. 5.4 Over-Voltage Protection (OVP) If the VCC voltage reaches 19V, the IC shuts down and the OVP protection is reset when the VCC voltage is lower than 5V. + − B u rs t+ 3 C S /F B 0 .9 5 V /0 .8 8 V Figure 22. Burst-Mode Block 5. Protection Block The FAN7602B contains several protection functions to improve system reliability. 5.1 Overload Protection (OLP) The FAN7602B contains the overload protection function. If the output load is higher than the rated output current, the output voltage drops and the feedback error amplifier is saturated. The offset of the CS/FB voltage representing the feedback information is almost zero. As shown in Figure 23, the CS/FB voltage is compared with 50mV reference when the internal clock signal is high and, if the voltage is lower than 50mV, the OLP timer starts counting. If the OLP condition persists for 22ms, the timer generates the OLP signal. This protection is reset by the UVLO. The OLP block is enabled after the soft-start finishes. Clock OLP 22ms Timer Soft-Start 50mV 3 CS/FB 6. Output Drive Block The FAN7602B contains a single totem-pole output stage to drive a power MOSFET. The drive output is capable of up to 450mA sourcing current and 600mA sinking current with typical rise and fall time of 45ns and 35ns, respectively, with a 1nF load. Figure 23. Overload Protection Circuit 5.2 Line Under-Voltage Protection If the input voltage of the converter is lower than the minimum operating voltage, the converter input current increases too much, causing component failure. Therefore, if the input voltage is low, the converter should be protected. In the FAN7602B, the LUVP circuit senses the input voltage using the LUVP pin and, if this voltage is lower than 2V, the LUVP signal is generated. The comparator has 0.5V hysteresis. If the LUVP signal is generated, the output drive block is shut down, the output © 2007 Fairchild Semiconductor Corporation FAN7602B Rev. 1.0.0 10 www.fairchildsemi.com FAN7602B — Green Current-Mode PWM Controller Typical Application Circuit Application Adapter Output Power 48W Input Voltage Universal input (85~265VAC) Output Voltage 12V Features Low stand-by power (