FA5626

FA5626 Fuji Switching Power Supply Control IC Green Mode PWM IC FA5626 Application Note April.-2011 Fuji Electric Co., Ltd. Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 1 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 Caution 1. The contents of this note (Product Specification, Characteristics, Data, Materials, and Structure etc.) were prepared in April 2011 The contents will subject to change without notice due to product specification change or some other reasons. In case of using the products stated in this document, the latest product specification shall be provided and the data shall be checked. 2. The application examples in this note show the typical examples of using Fuji products and this note shall neither assure to enforce the industrial property including some other rights nor grant the license. 3. Fuji Electric Co.,Ltd. is always enhancing the product quality and reliability. However, semiconductor products may get out of order in a certain probability. Measures for ensuring safety, such as redundant design, spreading fire protection design, malfunction protection design shall be taken, so that Fuji Electric semiconductor product may not cause physical injury, property damage by fire and social damage as a result. 4. Products described in this note are manufactured and intended to be used in the following electronic devices and electric devices in which ordinary reliability is required: - Computer - OA equipment - Communication equipment (Pin) - Measuring equipment - Machine tool - Audio Visual equipment - Home appliance - Personal equipment - Industrial robot etc. 5. Customers who are going to use our products in the following high reliable equipments shall contact us surely and obtain our consent in advance. In case when our products are used in the following equipment, suitable measures for keeping safety such as a back-up-system for malfunction of the equipment shall be taken even if Fuji Electric semiconductor products break down: - Transportation equipment (in-vehicle, in-ship etc.) - Communication equipment for trunk line - Traffic signal equipment - Gas leak detector and gas shutoff equipment - Disaster prevention/Security equipment - Various equipment for the safety. 6. Products described in this note shall not be used in the following equipments that require extremely high reliability: - Space equipment - Aircraft equipment - Atomic energy control equipment - Undersea communication equipment - Medical equipment. 7. When reprinting or copying all or a part of this note, our company’s acceptance in writing shall be obtained. 8. If obscure parts are found in the contents of this note, contact Fuji Electric Co.,Ltd. or a sales agent before using our products. Fuji Electric Co.,Ltd. and its sales agents shall not be liable for any damage that is caused by a customer who does not follow the instructions in this cautionary statement. Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 2 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 Contents 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. Overview Features Outline drawing Block diagram Functional description of pins Rating & Characteristics Characteristics Operation of each block Advice for designing Application circuit example ・ ・ ・・ ・・ ・・ ・・ ・・ ・・ ・ ・・ ・ ・ ・・ ・・ ・・ ・・ ・・ ・・ ・ ・・ ・ ・ ・・ ・・ ・・ ・・ ・・ ・・ ・ ・・ ・ ・ ・・ ・・ ・・ ・・ ・・ ・・ ・ ・・ ・ ・ ・・ ・・ ・・ ・・ ・・ ・・ ・ ・・ ・ ・ ・・ ・・ ・・ ・・ ・・ ・・ ・ ・・ ・ ・ ・・ ・・ ・・ ・・ ・・ ・・ ・ ・・ ・ ・ ・・ ・・ ・・ ・・ ・・ ・・ ・ ・・ ・ ・ ・・ ・・ ・・ ・・ ・・ ・・ ・ ・・ ・ ・ ・・ ・・ ・・ ・・ ・・ ・・ ・ ・・ 4 4 4 5 6 7～ 11 12～ 14 15～ 21 22～ 26 27 Caution) ・ The contents of this note subject to change without notice due to improvement. ・ The application examples or the parts constants in this note are shown to help your design. Variation of parts and service condition are not fully taken into account. Before use, a design with due consideration for these variations and conditions shall be conducted. Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 3 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 1. Overview FA5626 is a current mode type switching power supply control IC possible to drive a power MOSFET directly. Despite of a small package with 8 pins, it has a lot of functions and it is best suited for power saving at the light load and decreasing external parts. Moreover it enables to realize a reduced space and a high cost-performance power supply. 2. Features  Excellent  Low Power Saving by lowering the oscillation frequency depending on the load at light load. protection function with a few numbers of external components. Function without additional external components. power consumption by a built-in startup circuit.  Overload  Brown-In/Out  Current  Latch Minus detection. Power Saving of the revision of the input voltage of OLP MOSFET driving suitable for Power Supply up to 200W: -1.0A(sink),/+0.5A(source) pin for an external signal: Over Temperature Protection, Over Voltage Protection etc.  External  VCC  Low Under-Voltage Lock-Out function (UVLO). EMI by Frequency diffusion function 3. Outline drawing SOP-8 Unit:（mm） Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 4 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 4. Block diagram FA5626 (Overload protection : Auto recovery type) Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 5 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 5. Functional description of pins Pin No. 1 2 3 4 5 6 7 8 Pin Name LAT FB IS GND OUT VCC （NC） VH I/O I I I － O － － I Pin function External latch signal input. (Connect capacitor LAT and GND) Feedback control signal input Current Limiter Input (Negative voltage sense) IC Ground Output Power Supply (Connect capacitor between VCC and GND) No Connection High Voltage input, Brown-out (Series connection of diode and resistance between VH and the bulk capacitor or the rectified AC line) PIN CONNECTION VH （NC) VCC OUT 8 7 6 5 1 2 3 4 LAT FB IS GND Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 6 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 6. Rating & characteristics ・”+”shows sink and “-“ shows source in current prescription. (1)Absolute Maximum Ratings Stress exceeding absolute maximum ratings may malfunction or damage the device. Item LAT pin voltage LAT pin current FB pin voltage FB pin current IS pin voltage IS pin current Voltage at OUT pin Symbol VLAT ILAT VFB IFB VIS IIS VOUT IOH Rating -0.3 to 5.0 -100 to 100 -0.3 to 5.0 -500 to 100 -2.0 to 5.0 -100 to 100 -0.3 to VCC+0.3 -0.5 +1.0 (The period that excee ds +1.0A is 100ns or l ess.) -0.3 to 28 -30 to 4 -0.1 to 0 -0.3 to 750 -0.1 to 30 400 -30 to +125 -40 to +150 Unit V uA V uA V uA V A Peak current at OUT pin *1 IOL A VCC pin voltage VCCpin current *1 (Ta=25°C) VVCC At input plus voltage At input minus voltage IVCC VVH IVH Pd Tj Tstg V mA V mA mW °C °C VH pin voltage VH pin current *1 (Ta=25°C) Power dissipation (Ta=25°C) Maximum junction temperature in operation Storage temperature *1 Never exceed power dissipation Pd. ○Maximum dissipation curve(SOP) Maximum dissipation Pd [mW] 400mW Package thermal resistor θj-a= 250°C／W 0 -30 25 Ambiance temperature 85 Ta [°C] 125 Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 7 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 (2)Recommended Operating Conditions Item Supply voltage (after VCCon) VH pin voltage VH pin resistance LAT pin capacitor VCC pin capacitor Ambiance temperature in operation Symbol VCC VVH RVH CLAT CVCC Ta MIN. 12 100 2.2 0.22 22 -30 TYP. 18 － － 1.0 33 － MAX. 24 650 10 2.2 56 85 Unit V V kΩ uF uF °C (3)Electrical Characteristics Tj=25degree, VCC=18V(after VCCon), VH=120V,VFB=2.5V, VIS=0V, no load , unless otherwise specified. Voltage described in condition is DC input. Notes) *1： This parameter is not 100% tested in production but guaranteed by design. It doesn’t guarantee the column of ‘－’ to have been specified. Over temperature protection and external latch-off section. (LAT pin) Item Source current of LAT pin Latch-off level Equivalent resistance of LAT pin for Latch-off Latch-off delay timer *1 Soft-start section (LAT pin) Symbol Vss1 Vss2 Vdss Vss Vss3 VssL VssH Condition *2-1 *2-1 *2-1 *2-1 *2-1 *2-1 MIN. 1.9 2.3 440 1.8 1.45 1.45 1.9 TYP. 2.1 2.5 490 2.0 1.6 1.6 2.1 MAX. 2.3 2.7 540 2.2 1.75 1.75 2.3 Unit V V us V V V Symbol ILAT VthLAT RLAT TdLAT Condition LAT=1.15V,FB=0V VLAT=Decreasing VthLAT / -llat VLAT=VthLAT MIN. -80 1.00 1 3 .5 50 TYP. -70 1.05 15 65 MAX. -60 1.10 1 6 .5 80 Unit uA V kΩ us Item Output minimum ON pulse LAT pin voltage Keep minimum ON pulse LAT pin voltage Operating time of minimum ON pulse *1 Start soft-start LAT pin voltage *1 Finish soft-start LAT pin voltage After soft-start LAT pin voltage *2-1：Start and Re-start of after VCCon or Brown-in Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 8 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 Switching oscillator section Item Center oscillation frequency Voltage stability Temperature stability *1 Frequency modulation width *1 Frequency modulation period *1 FB pin threshold voltage for stop frequency modulation *1 FB pin threshold voltage for light load mode FB pin voltage at minimum frequency Oscillation reduction ratio Minimum frequency frequency oscillation (FB pin) Symbol Fosc Fdv ⊿Fdt Fm Tfmodu Vfbmst Vfbm Vfmin Kf Fmin VFB=2V VCC=12 to 24V VFB=2V Tj=-30 to 125°C VFB=2V VFB=2V VFB=2V VFB=Decreasing VLAT=1.8V *3-1 VFB=Decreasing VLAT=1.8V *3-1 VFB=Decreasing ⊿f/⊿VFB VLAT=1.8V *3-1 ⊿VFB=Vfbm-Vfmin VLAT=1.8V *3-1 VFB=0.5V Condition MIN. 60 -2 TYP. 65 － MAX. 70 +2 Unit kHz % % % ms V V V kHz/V kHz -5 ±5 7.0 1.45 1.7 1.1 80 0.25 － ±7 8.0 1.55 1.8 1.2 110 0.45 +5 ±9 9.0 1.65 1.9 1.3 140 0.65 *3-1 After IC starts, the voltage at LAT pin rises to Vss1. Pulse width modulation section Item Maximum duty cycle Minimum duty cycle Input threshold voltage FB pin source current (FB pin) Symbol Dmax Dmin VthFB0 Ifb0 VFB=0V VFB=Decreasing DUTY=0% VFB=0V, VLAT=1.8V Full & Half-wave Steady rectification VVH< VHVTH1 DC *1 Full & Half-wave Steady rectification VVH>= VHVTH1 DC *1 Start (Restart) / over load *4-1 Condition VFB=4.5V MIN. 75 － 340 -320 TYP. 85 － 400 -260 MAX. 95 0 460 -200 Unit % % mV uA Tmin1 Minimum ON pulse width *4-1 1200 1700 2200 ns Tmin2 Tmin3 900 1200 180 120 1250 1700 280 210 1600 2200 380 260 ns ns V VH voltage detected change VHVTH1 Minimum ON pulse width *1 *4-1：When input voltage at VH pin is DC, this function doesn’t operate. Over load protection and auto-restart circuit section Item Over load detection threshold voltage *1 Over load detection Delay time *1 Waiting time of auto restart *1 Symbol VthOLP TdOLP TdOLP2 (FB pin) Condition VFB=Increasing VFB=VthOLP VFB=VthOLP MIN. 3.5 60 1300 TYP. 4.2 70 1530 MAX. 5.0 80 1760 Unit V ms ms Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 9 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 Current sense section (IS pin) Item Voltage gain ⊿VFB/⊿VIS Symbol AvIS Condition VFB=2V to 1.5V VFB= Full & Half-wave VthOLP, rectification VVH>= DC *1 VHVTH2 VFB= Full & Half-wave VthOLP, rectification VVH< VHVTH2 DC *1 MIN. -4.6 -0.525 -0.552 TYP. -3.8 -0.500 -0.525 MAX. -3.0 -0.475 V -0.498 Unit V/V Maximum threshold voltage *6-1 VthIS1 -0.552 -0.525 -0.498 V VH voltage detected change VHVTH2 Maximum threshold voltage Input bias current Delay to output *1 IIS TpdIS *6-1 VIS=0V,VFB=0V Tj=25°C 138 -50 100 148 -40 200 158 -30 300 V uA ns *6-1：When input voltage at VH pin is DC, this function doesn’t operate. Output circuit section Item Low output voltage High output voltage Rise time Fall time (OUT pin) Symbol VOL VOH tr tf Condition IOL=+100mA VFB=0V IOH=-100mA, VFB=2V VCC=24V,VFB=3V, CL=1nF, Tj=25°C VCC=24V,VFB=3V, CL=1nF, Tj=25°C MIN. 0.4 14.5 30 20 TYP. 0.8 16 60 40 MAX. 1.6 18 100 70 Unit V V ns ns VCC circuit section Item (VCC pin) Symbol VCCon VCCoff Vhys Vthovp TdOVP Vthshort TdSCP Condition VCC=Increasing VCC=Decreasing VCCon-VCCoff VCC=Increasing VCC=Vthovp VFB=VthOLP, VCC=Decreasing VFB=VthOLP, VCC=Vthshort MIN. 16 8.0 7.0 25 50 10 50 TYP. 18 9.0 9.0 26 65 11 65 MAX. 20 10.0 11.0 27 80 12 80 Unit V V V V us V us Start-up threshold voltage Shutdown threshold voltage Hysteresis width VCC over-voltage protection threshold voltage(OVP) OVP delay timer *1 Short current protection threshold voltage (SCP) SCP delay timer *1 Power supply current Item (VCC pin) Symbol ICCop1 Condition Duty=Dmax,FB=2V, OUT=no load Duty=0%,FB=0V OUT=no load VH=0V,VFB=0V, VCC=14.5V VH=0V,VFB=0V, VCC=11V MIN. 1.0 0.95 0.6 0.6 TYP. 1.4 1.35 0.8 0.9 MAX. 1.7 1.65 1.1 1.1 Unit mA mA mA mA Operating-state supply current ICCop2 Supply current at Brownout or OLP Latch mode supply current ICCbo ICClat Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 10 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 High-voltage input section Item (VH pin、VCC pin) Symbol IHrun Condition VH=450V,VFB=0V VH=120V, VCC=0V,VFB=0V VH=120V,VCC=2 to 8V, VFB=0V VH=120V,VCC=11V, VFB=0V VH=120V,VCC=16V, VFB=0V VCC=16V, VH=120V,VFB=0V VCC=11V, VH=120V,VFB=0V at Latch VH pin = Decreasing MIN. 60 3.5 11 6 3.5 -14 TYP. 100 6.5 17 12 8 -8 MAX. 140 9.5 23 mA 18 14 -3.5 mA Unit uA Input Current of VH pin IHstb Ipre1 Charge current for VCC pin Ipre2 Threshold voltage level at Brown-out (VH pin) Threshold voltage level at Brown-in (VH pin) Brown-out delay time *1 -18 -12 -6 mA VthBO 89 99 109 V VthBI TpdBO VH pin = Increasing VH=VthBO 95 30 14 12 13 12 11 105 50 15.5 13.5 14.5 13 12 115 70 17 15 16 14 13 V ms V V V V V VCC voltage at Brown-out VCC voltage at Latch VH=80V,VFB=2V VCCBH Upper level VH=80V,VFB=2V VCCBL Lower level VH=120V,VFB=2V VCCLHH 1time clamp VH=120V,VFB=2V VCCLH Upper level VH=120V,VFB=2V VCCLL Lower level Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 11 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 7. Characteristic Curves (DC Characteristics) ・Unless otherwise specified, Ta=25 degree, Vcc=18V ・”+”shows sink and “-“ shows source in current prescription. ・ The data stated in this chapter are intended for giving typical IC characteristics and not for guaranteeing performance. Oscilation Frequency (Fosc) vs. Junction Temparature(Tj) 71 69 -255 Fo sc (kHz) 67 65 63 -265 61 59 -50 0 50 100 Junction Temparature Tj ( ℃) 150 -270 -50 0 50 100 Junction Temparature Tj ( ℃) 150 I fb0 (uA) -260 -250 FB pin source current (Ifb0) vs. Junction Temparature(Tj) 3 2 1 Oscillation Frequency changing rate(Fdt) vs. Junction Temparature(Tj) 320 310 300 Tmin (ns ) 290 280 270 Minimum ON width (Tmin3) vs. Junction Temparature(Tj) Fdt (% ) 0 -1 -2 -3 -50 0 50 100 Junction Temparature Tj (℃) 150 260 250 -50 0 50 100 Junction Temparature Tj (℃) 150 FB pin voltage at frequency drop started (Vfbm) vs. Junction Temparature(Tj) 2.1 2 1.9 V fbm (V ) 1.8 1.7 1.6 1.5 -50 0 50 100 Junction Temparature Tj [ ℃] 150 20 UVLO ON threshold voltage(VCCon) vs. Junction Temparature(Tj) 19 V CCon (V ) 18 17 16 15 -50 0 50 100 Junction Temparature Tj (℃) 150 Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 12 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 11 UVLO OFF threshold voltage(VCCoff) vs. Junction Temparature(Tj) -10 VCC pin charge current (Ipre2) vs. Junction Temparature(Tj) 10 V CCoff (V ) Ipre2 (mA ) -11 9 -12 8 -13 7 -50 0 50 100 Junction Temparature Tj (℃) 150 -14 -50 0 50 100 Junction Temparature Tj (℃) 150 27.0 Overvoltage thoreshold voltage(Vthovp) vs. Junction Temparature(Tj) 120 VH pin input current (IHrun) vs. Junction Temparature(Tj) 26.5 V thov p (V) IHrun (uA ) 110 26.0 100 25.5 90 25.0 -50 0 50 100 Junction Temparature Tj (℃) 150 80 -50 0 50 100 Junction Temparature Tj (℃) 150 8 VH pin input current (IHstb) vs. Junction Temparature(Tj) 20 18 VH pin input current (IHstb) vs. VCC pin voltage 7 IHs tb (mA ) IHs tb [ mA ] 16 14 6 12 10 8 6 5 4 4 2 3 -50 0 50 100 Junction Temparature Tj (℃) 150 0 0 5 10 VCC [V] 15 Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 13 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 1.6 Operating-state supply current (ICCop1) vs. Junction Temparature(Tj) FB=2V 1.6 Operating-state supply current (ICCop2) vs. Junction Temparature(Tj) FB=0V 1.5 I CCop1 (mA ) ICCop2 (mA) -50 0 50 100 Junction Temparature Tj (℃) 150 1.5 1.4 1.4 1.3 1.3 1.2 1.2 1.1 1.1 -50 0 50 100 Junction Temparature Tj (℃) 150 90 Maximum duty cycle (Dmax) vs. Junction Temparature(Tj) -0.47 -0.48 -0.49 Vt hIS 1 [V ] IS pin maximum input threshold voltage (VthIS1) vs. Junction Temparature(Tj) 88 Dmax (% ) 86 -0.5 -0.51 -0.52 -0.53 84 82 80 -50 0 50 100 Junction Temparature Tj (℃) 150 -50 0 50 100 Junction Temparature Tj ( ℃) 150 108 107 Brown-in threshold voltage (VthBI) vs. Junction Temparature(Tj) 101 Brown-out threshold voltage (VthBO) vs. Junction Temparature(Tj) 100 V thB O (V) 106 Vt hB I (V ) 105 104 103 102 -50 0 50 100 Junction Temparature Tj (℃) 150 97 99 98 96 -50 0 50 100 Junction Temparature Tj (℃) 150 Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 14 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 8. Operation of each block (1)Startup circuit The IC integrates a startup circuit having withstood voltage of 750V to achieve low power consumption. Fig.1 to Fig.3 shows connections. Turning on the power, capacitor C2 connected to the VCC pin is charged and the voltage increases due to the current fed from the startup circuit to the VCC pin. If the ON threshold voltage (Vcc = 18V typ.) of the under-voltage lockout circuit (UVLO) is exceeded, the power for internal operation is turned on, and the IC starts operating. If the VCC pin voltage exceeds the ON threshold voltage(VCCon=18V (typ)) and the IC starts operating, the startup circuit is shut down and the VH pin current decreases to several 10 to several 100uA. RVH is connected in series to the VH pin to prevent the IC from being damaged by the surge voltage of the AC line. Fig.1 shows a typical connection where the VH pin is connected to the half-wave rectifier circuit of AC input voltage. The startup time of this connection is the longest in 3 types of connection. Fig.2 shows the connection where the VH pin is connected to the full-wave rectifier circuit of AC input voltage. The startup time of this connection is approximately half of the connection shown in Fig.1. C1 Startup circuit current Startup circuit control signal RVH VH 8 6 VCC C2 start Fig.1 Startup circuit 1 (Half-wave) Fig.2 Startup circuit 2 (Full-wave) Fig.3 shows the connection where the VH pin is connected to the back of rectification and smoothing of AC input voltage. The startup time of this connection is the shortest in 3 types. In this connection, however, even if the AC input voltage is shut down after the IC enters the latch mode, the voltage charged in C1 is kept impressed to the VH pin, requiring much time for the latch mode to be reset. It takes approximately several minutes to reset the latch mode, although the time varies depending on conditions. If the overvoltage protection is actuated, causing the IC to enter the latch mode, then the startup circuit is subjected to ON/OFF control to maintain the VCC voltage within the 12V to 13V (typ) range. (P.19 8-(7) over voltage protection) Fig.3 Startup circuit 3 (Rectification) Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 15 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 (2)Oscillator This oscillator is used to determine the switching frequency. The switching frequency in the normal operation mode is set to 65kHz (typ) within the IC. To minimize the loss of power in the standby state, this IC is equipped with a function of automatically decreasing the switching frequency under light load. When the FB pin voltage decreases down to 1.8V (typ) or lower under light load, the frequency decreases almost linearly proportional to the FB pin voltage.( See Fig.4) The minimum frequency, Fmin, has been set to 0.45kHz (typ). When the load further decreases and thus the FB pin voltage decreases down to 0.4V (typ) or lower, the switching is stopped. (See one-shot circuit.) In addition to trigger signals for determining switching frequency, the oscillator generates pulse signals for determining the maximum duty cycle and ramp signals for performing slope compensation. Fig.4 Oscillation frequency Frequency diffusion（Spread spectrum） FA5626 perform frequency modulation of ± 4.5 kHz for switching frequency 65 kHz (during the operation in which the FB pin voltage is higher than 1.55 V.). This function enables more noise energy of the switching to disperse compared to the case with fixed frequency and obtains a conduction EMI reduction effect. While the reduction effect depends on the filter parts mounted on the power supply board, effective use of this function allows the reduction of the number of the filter parts and the constants. (3) Current comparator & PWM circuit The IC performs current mode control. Fig.5 shows a circuit block for basic operations, and Fig.6 shows a timing chart. The polarity of the current detection voltage of the IS pin is negative. The GND of the IC is connected between the current detection resistor Rs and the MOSFET. (See Fig.5) A trigger signal having the switching frequency that is output from the oscillator is input to the PWM (F.F.) through the one-shot circuit as a set signal. Then the output of the PWM as well as the OUT pin voltage reaches the High state. On the other hand, the current comparator (IS comp.) monitors the MOSFET current, and if the threshold voltage is reached, a reset signal is output. When a reset signal is input, the output of PWM (F.F.) as well as the OUT pin voltage reaches the Low state. The ON pulse width of the OUT pin is thus controlled with the threshold voltage of the current comparator (IS comp.). The output is controlled by changing the threshold voltage of this IS comp. with feedback signals. As shown in Fig.7, the FB pin voltage is level-shifted by a reverse amplifier and input into the current comparator (IS comp.) as the threshold voltage. In addition, -0.5V (typ) reference voltage is input inside the IC to regulate the maximum input threshold voltage of the IS pin, VthIS1 (over current control threshold). Fig.5 Current mode basic operation circuit block Fig.6 Current mode basic operation timing chart Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 16 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 The reverse amplifier output or the maximum IS pin input threshold voltage, VthIS1, whichever is higher, is given precedence as the IS pin threshold voltage. (Example: When the output of the reverse amplifier is -0.2V in a product whose maximum threshold voltage of the IS pin, VthIS1, is -0.5V, the output of the reverse amplifier is given precedence and thus the current comparator is reversed when the IS pin voltage reaches -0.2V.) In normal operation, the output voltage of the power supply is maintained constant by changing the threshold voltage of the current comparator via the FB pin voltage. When the output voltage decreases, the feedback circuit increases the FB voltage to allow the threshold voltage of the current comparator to scale out to Low, thus increasing the MOSFET current. The maximum input threshold voltage of the IS pin, VthIS1 (-0.5V typ) controls the maximum current of the MOSFET. If the FB pin voltage increases under overload, the output of the reverse amplifier scales out to Low, decreasing down to lower than VthIS1. The threshold voltage of the IS pin is thus controlled not to exceed VthIS1. The oscillator outputs pulses for determining the maximum duty cycle. Using these pulses, the maximum duty cycle has been set to 85% (typ). Reduction of dependency of OCP on input voltage This IC has an improved OCP function which changes the maximum input threshold voltage (the current limit threshold voltage) so that OCP dependency on the input voltage will be compensated. The maximum input threshold voltage is lowers by 5% when VH pin voltage (VVH) is over 148Vdc (approx. 105Vac) if VH pin is connected to AC line. VthIS1 = –0.525V typ. when VVH < VHVTH2 VthIS1 = –0.500V typ. when VVH ≥ VHVTH2 (See p. 24 "9-(7) Reduction of dependency of overload detection level on input voltage".) noise filter for the IS pin in principle. The minimum ON width is usually set to 1250ns or 1700ns (typ) in normal operations, and to 280ns (typ) at startup or rebooting to prevent the transient MOSFET drain voltage from surging. In addition, an exclusive comparator is integrated to keep the output pulse at zero under no load. (See Fig.9) This comparator reverses its output when the FB pin voltage decreases down to 400mV (typ), preventing a set pulse to be input to the PWM latch (F.F.). The output is thus maintained in Low state and switching is stopped. 5V INV AMP FB 2 IS comp. A A=1/AvIS VthIS1 4 GND 3 IS Fig.7 Current comparator (4) One shot circuit (minimum ON width) When the MOSFET is turned on, a surge current is generated due to discharge corresponding to the capacitance of the main circuit and gate drive current. If this surge current reaches the IS pin threshold voltage, the current comparator output is reversed, and consequently normal pulses may not be generated from the OUT pin. To avoid this phenomenon, a minimum ON width of OUT pin output is set within the one-shot circuit block of the IC. If a trigger signal having the switching frequency is input from the oscillator, a pulse having a specific width is output as a PWM latch (F.F.) set signal. Since the set signal has priority over the input signal of the PWM latch, the output of the PWM latch (F.F.) is not reversed while the set signal from the one-shot circuit is being input, even if a reset signal is input from the current comparator (IS comp.) (See Fig.5) As a result, the input to the IS pin is kept invalid for the specified period of time immediately after the output pulse is generated from the OUT pin (minimum ON width), and made not to respond to the surge current at turn-on. (See Fig.8) This minimum ON width function eliminates the need of a Fig.8 Minimum ON width Fig.9 Output shutdown function of FB pin Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 17 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 (5) Overload protection circuit FA5626 integrates auto-restart mode overload protection function. Fig. 10 shows the circuit block diagram and Fig. 11 shows the protection timing chart. When output current increases by the overload, MOSFET current is limited by the maximum threshold voltage (-0.5V typ.) of IS pin. The output voltage is drops because of current limit and FB pin voltage rises. When FB pin voltage is over the threshold voltage (VthOLP), overload is detected. After the overload is detected, internal OLP timer starts counting for the delay time. When OLP delay time (70 msec typ.) has elapsed, the IC stops switching operation and MOSFET is kept off state. When the self-return wait time (1530 ms typ.) has elapsed thereafter, IC re-starts switching operation automatically. IC repeats stop and restart switching operation until overload condition is removed. Vcc voltage is maintained at between 12V and 13V by ON/OFF control of startup circuit when IC stops switching operation at overload. Fig.10 Overload protection circuit (auto recovery) Fig.11 Overload protection timing chart (auto recovery) Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 18 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 (6) Short circuit detection FA5626 has a protection function for output short-circuit without delay time. If output of PSU is shorted, FB pin voltage goes high. In addition, Vcc voltage drops because auxiliary winding voltage almost zero. IC stops switching operation at the instance when IC detects that FB pin voltage exceeds overload detection voltage and Vcc drops below Vthshort (11V typ.). As in the case of overload, IC restart switching operation after 1600ms and repeats it until short circuit condition is removed. (8) Latch shutdown circuit by an external signal The LAT pin is equipped with a latch shutdown function. (See Fig.13) By decreasing the LAT pin voltage to 1.05V or lower, the IC enters the latch mode. To cancel the latch mode, interrupt the input voltage,thus decreasing the VCC voltage to the OFF threshold voltage (9.0V typ.) or lower. LAT function operates after LAT pin voltage rises to more than 2.1V once. If the external latch shutdown function by the LAT pin is not to be used, connect a capacitor only. (7)Over voltage protection circuit The IC integrates an overvoltage protection circuit for monitoring the VCC pin voltage. (See Fig.12) If the VCC voltage increases and exceeds 26V typ, which is the reference voltage of the comparator (OVP), the comparator output is reversed to High level, setting the latch circuit to perform latch shutdown. At this time, the startup circuit is subjected to ON/OFF control to maintain the latch mode, thus keeping the VCC voltage within the 12V or 13V (typ) range. To cancel the latch mode, shut down the input voltage to cause brownout, as in the case of the overload protection.(latch type) Since 65s (typ) delay time has been set to the set input of the latch circuit, the latch mode is not entered even if the VCC pin exceeds the detection voltage temporarily. -Overheat protectionConnect an NTC thermistor to the LAT pin to use the overheat protective function. (See Fig.13, P23 9-(4) Lat pin) 5V LAT 1 CLAT UVLO LAT Latch Set Reset TH Fig.13 Overheat protection function using a thermistor (9) Under voltage lockout circuit (VCC pin) The IC integrates an under voltage lockout (UVLO) function to prevent circuit malfunction that might occur when power supply voltage decreases. When the VCC voltage increases from 0V and reaches 18V (typ), the circuit starts operating. When the VCC decreases down to 9V (typ), the circuit stops operating. In a state in which the under voltage lockout function is actuated to stop IC operation, the OUT pin is forcibly made to enter the Low state. The latch mode of the protection circuit is also reset. Fig.14 Overvoltage protection circuit (10)Output circuit The push/pull structure output circuit drives the MOSFET directly. The peak output current of the OUT pin is 0.5A (source) and 1.0A (sink) in the maximum absolute ratings. In a state in which the IC is stopped in the under voltage lockout circuit or operation is suspended in the latch mode, or in an auto reset wait state by overload protection function, the OUT pin is brought into the Low level, and the MOSFET is interrupted. Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 19 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 (11)Brown-out FA5626 has a brown-out function that stops switching operation when the AC input voltage drops below normal operating voltage.Fig.14 shows input voltage waveform of VH pin. When VH pin voltage reached brown-in threshold voltage (DC 105V typ.), switching operation is started. When VH pin voltage drops below brown-out threshold voltage for longer than delay timer, brown-out function stops switching operation. In case of half wave input, the brownout timer is counted because VH pin voltage drops until 0 V at every period. But brown-out function doesn’t operate because brown-out delay time longer than the half wave period. Brown-out delay time depends on the oscillation frequency as shown in Fig.15. Vcc voltage is maintained at between 12V and 13V by ON/OFF control of startup circuit when IC stops switching operation at brown-out function, and IC restarts after VH pin voltage reached brown-in threshold voltage . Fig.14 Brown-out operation 500 400 Br o w n o u t de la y t ime [ ms ] 300 200 100 0 0 10 20 30 40 50 60 70 Oscillation frequency [kHz] Fig.15 Brown-out delay time Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 20 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 (12)Soft-start This IC has an adjustable soft start function by LAT pin capacitor. Fig. 16 shows the soft-start timing chart at start up. (1)(2)(3) are soft start period in Fig.16. When VCC voltage reaches uvlo on threshold voltage , LAT pin voltage rises gradually, and switching starts at LAT pin voltage 2.1 V. In period (1), a minimum ON width pulse are output 32 times after switching has started. The minimum ON width pulses avoids Vds surge voltage of power MOSFET at start up. In period (2), LAT pin voltage is discharged from 2.5 V to 2.0 V by constant current (70uA). In this period, the minimum ON width pluses are output continuously. Period (3) is effective soft-start period. In period (3), the pulse width gradually widen from minimum ON width. The soft-start time can be adjusted by capacitor connected to LAT pin. Approximate effective soft start time (period(3)) can be calculated using the following expression. Tss = 0.4×CLAT / Ilat Tss :Soft-start time [sec] CLAT: Capacitor connected to LAT pin [uF] Ilat :LAT pin source current [uA] (70uA typ.) (4) PWM operation start Fig.16 Soft-start operation Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 21 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 9. Advice for designing (1)Start up To properly start or stop the power supply, a capacitor having appropriate capacitance must be selected. Fig.17 shows the VCC voltage at the time of startup when an appropriate capacitor is connected. When the power is turned on, the capacitor of the VCC is charged with the current supplied from the startup circuit, and the voltage increases. When the VCC reaches the ON threshold voltage, the IC starts operating. The IC is operated based on the voltage supplied from the auxiliary winding. Note that during the period immediately after startup until the voltage of the auxiliary winding starts up, the VCC decreases. Select a capacitor for the VCC that does not allow the VCC to decrease down to the OFF threshold voltage. Specifically, a VCC pin capacitor whose OFF threshold voltage is 11V or higher is recommended. If the capacitance of the VCC pin is too small, VCC decreases to lower than the OFF threshold voltage before the voltage of the auxiliary winding starts up as shown by Fig.18. In this case, the VCC repeats up/down operation between ON and OFF threshold voltages, and consequently the power supply cannot be turned on. (2) VCC hold time To prevent the VCC pin voltage from decreasing to lower than the UVLO OFF threshold voltage due to sudden load change and other reasons, it may be desirable that the capacitance of the capacitor to be connected to the VCC pin be made larger. However, if the capacitance of the capacitor of the VCC pin is increased, the startup time is made longer. In such cases, the circuit shown in Fig.19 can balance the capacitance and the startup time. By setting C1 to less than C2, the startup time can be kept short. Since current is supplied via C2 after startup, the VCC pin voltage hold time can be kept long even under sudden change conditions. Fig.19 VCC circuit (3) Gate drive circuit To adjust switching speed and prevent vibration of the gate pin, a resistor is connected between the MOSFET gate pin and the OUT pin of the IC in general. In some cases, driving current for turning on the MOSFET Select a capacitor whose and that for turning it off are required to be determined capacitance does not allow VCC separately. voltage to decrease down to In this case, connect a gate drive circuit shown in Fig.20 or VCCoff. 21 between the gate pin of the MOSFET and the OUT pin. Auxiliary winding voltage In Fig.20, the current is limited by R1 and R2 when the power is turned on, while the current is limited only by R2 when it is turned off. In Fig.21, the current is limited only by R1 when the power is turned on, while the current is limited by R1 and R2 connected in parallel when the power is turned off. Fig.17 VCC pin voltage at startup Fig.20 Gate drive circuit (1) Time t Fig.18 VCC pin voltage at startup (when capacitance is too small) Fig.21Gate drive circuit (2) Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 22 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 (4)LAT pin • To perform overheat protection using an NTC thermistor As shown in Fig.22, thermistor TH1 is connected to the LAT pin to perform overheat protection (latch shutdown). Since the LAT pin source current is 70A (Typ.), select TH1 whose resistor Rth satisfies the following expression at the desired overheat protection temperature. If temperature setting for overheat protection is not feasible with TH1 only, connect an additional resistor (R5) in series for adjustment. Rth @ LAT+R5  1.05V / 70A  15.0k (6) Current sensing unit As described in 8-(4) One-shot circuit, the minimum ON width is set for this IC to minimize malfunction due to surge current that occurs when the power MOSFET is turned on. However, if the surge current that occurs at the time of power ON is large, or noise is applied externally at the time of power ON, malfunction might occur. In such cases, add RC filters C6 and R7 as shown in Fig.25. Determine the CR filter constants according to the cutoff frequency and time constant. The cutoff frequency is given by: fc = 1/(2    C6  R7) This frequency must be greater than IC operation frequency of 65 kHz. Set the RC time constant to 500 nsec or smaller. Note that, by the input bias current at IS pin, R7 is subjected to offset with respect to the overload detection threshold voltage. Do not connect an excessive value. Otherwise, the overload detection value may vary considerably. Recommendations: R7 = 1 k. 100pF C6  470pF. To obtain an optimum effect in function, position capacitor C6 as near IC as possible, and minimize the wiring length. Fig.22 Overheat protection function using a thermistor • To perform latch shutdown using independent abnormality detection signal As shown in Fig. 23, NPN transistor Tr1 is connected to LAT pin, and a detection signal is inputted to the base of Tr1. The polarity of the input signal must be such that the level will go high at an error. Note that, because a constant current flows from LAT pin, there is no need of a circuit for clamping LAT pin voltage to above latch shutoff threshold voltage when normal. Fig. 23 Latch shutdown function by an external signal CLAT (5) Feedback Fig.24 shows the circuit configuration of the FB pin. A photo-coupler PC is connected as a feedback circuit that monitors the output voltage and performs PWM control. This signal gives threshold voltage for the current comparator. Consequently, if noise is added to this signal, the output pulses are disturbed. Capacitor C3 is generally connected for protection against noise. Fig.25 IS pin filter 2 FB PC C3 Fig.24 FB pin circuit configuration Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 23 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 (7) Reduction of overload detection level on input voltage Output current at overload depends on the input voltage because of propagation delay of current limit by IS pin. (Fig.26) The dependency will be compensated by connecting resistor R9 between the auxiliary winding and IS pin. (Fig. 27) A negative voltage of the auxiliary winding is proportional to the input voltage. Current sense of this IC is negative voltage; therefore line compensation for overload can be achieved by negative auxiliary voltage. This design can reduce the power loss of the compensation resistor. For example, in case of 1kΩ of resistor R7,100 k to 1 M is recommended for resistor R9. Line compensation becomes large as R9 is decreased. (Fig.28) Fig.28 Overload detection level on input voltage (2) High Line voltage Vds Low Line voltage (8) Input power improvement at light load FA5626 can reduce the standby power by lowering the oscillation frequency at light load. However, in some case internal function of IC may not reduce standby power enough. In such a case, connect resistor R8 between OUT pin and IS pin. If resistor R7 is 1 k for example, select resistance R8 between several hundred k and 1 M. Current Limit Difference of High Line and Low Line Id tpdls tpdls Fig.26 Overload detection level of input voltage (1) Fig.29 Compensation circuit of Input power improvement at light load Fig.27 Input voltage compensation circuit of overload detection level Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 24 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 (9) Approximation of over current detection intensity The expression here explains how to calculate the over current detection as below. Case where only RC filter is connected (See Fig. 25) On IS pin voltage, offset voltage Voffset1 by IS pin input bias current of 45 A (IS = –0.5 V) appears at resistor R7. In this case, the current limit voltage at resistor Rs is as follows, Rs voltage at OCP = VthIS1 + Voffset1 Case where input voltage dependency reducing resistor R9 is connected (as in Fig. 27) If an input voltage dependency reducing resistor is connected, IS pin voltage changes as shown in Fig. 31. In this case, the overload detection voltage level that appears at IS pin is as follows, Rs voltage at OCP =VthIS1 - Voffset2 Example 1)R7=1kΩ、R9=330kΩ、Vaux2=-20V Voffset2=Voffset1-((Vaux2/R9)×R7) =(-45uA×1k) - ((-20V/330k)×1k)= 15.6mV Rs voltage at OCP= -0.5V - (15.6mV)= -0.516V Example 2)R7=1kΩ、R9=680kΩ、Vaux2=-20V Voffset2=(-45uA×1k) - ((-20V/680k)×1k)= -15.6mV Rs voltage at OCP =- 0.5V –(-15.6mV)= -0.484V Fig.30 IS pin voltage when RC filter only is connected. Example) When AC input voltage Vin is a minimum, the primary current will be a maximum. Np  Vo Np Ns  Vo  2  Vin  D 2  Lp  fsw D Ns 2  Vin  Fig. 31 IS pin voltage when correction resistor R9 is connected. Case where R8 for input power improvement at light load is connected (See Fig. 29) If an input power improvement at light load is applied, the waveform of IS pin voltage changes as shown in Fig. 32. In this case, the current limit voltage at Rs is as follows, Rs voltage at OCP =VthIS1 + Voffset1 + Voffset3 Example)R7=1kΩ、R8=1.0MΩ、VCC=18V Voffset1=-45mV Voffset3=-(18/1.0MΩ)×1k=-0.018V Rs voltage at OCP = -0.5V - 45mV - 0.018V = -0.563V ILp  Po 2  Vin  D   D : Duty , Vin :AC Input voltage (rms) Np : Turn Number of primary winding Ns : Turn Number of secondary winding Vo : Output voltage Po : Output power (overload detection power) η : Efficiency Fsw : Switching frequency Lp: Primary side inductance Example)Vin=85V,Np=28T,Ns=5T,Lp=340uH,fsw=65kHz, η=0.9,Vo=19V,Po=100W,R7=1kΩ 28  19 28 5 ILp  100 2  85  0.47  0.9  2  85  0.47 2  340u  65k  3.24  0.47  19 D 5 2  85  Rs  VthIS1  Voffset1 / ILp   0.5  ( 45u  1k ) / 3.24  0.168 Rs = 0.17  W has to be connected. However, in actual circuit, output current at OLP shows tendency to be slightly larger than calculated current because of the propagation delay in IC, etc. Please decide Rs value after test in the actual circuit. Fig. 32 IS pin voltage when correcting resistor R8 is connected. Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 25 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 (10) Prevention of malfunction due to negative potential of the pin If large negative voltage is applied to each pin of the IC, the parasitic element within the IC may be actuated, thus causing malfunction to occur. Be sure to maintain the voltage to be applied to each pin within the maximum absolute ratings. (11) Loss calculation To use the IC within its ratings, the loss of the IC may have to be found. However, it is not feasible to measure loss directly. The following is an example of finding a rough value of loss by calculation. The rough value of the total loss of the IC, Pd, can be calculated using the following expression: Pd≒VCC × (ICCop1 + Qg × fsw) + VVH × IHrun where, VVH: voltage to be applied to the VH pin, IHrun: current fed to the VH pin during operation, VCC: power voltage, ICCop1: Consumption current of the IC Qg: electrical charge to be input to the MOSFET gate used, and Fsw: switching frequency. A rough value can be found using the above expression, and the total loss found by the calculation, Pd, is slightly larger than the actual value. Be sure to take into consideration that each characteristic value varies depending on temperatures and other factors. Example: When the VH pin is connected to a half-wave rectifier circuit with 100VAC input, the average voltage to be applied to the VH pin is calculated to be approximately 45V, and the average current to be fed to the VH pin is approximately 130A;. Furthermore, assuming that Tj = 25C, VCC = 18V, and Qg = 80nC, and based on IHrun=100uA (typ.) ICCop1=1.4mA (typ.) fsw=65kHz (typ.) the loss of the IC having standard characteristics can be calculated as follows: Pd≒18V × (1.4mA + 80nC × 65kHz) + 45V × 100uA ≒ 123 mW Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 26 http://www.fujielectric.co.jp/products/semiconductor/ FA5626 10．Application circuit example C6 R16 C13 F1 R1 NF1 NF2 C1 DS1 T1 NF3 C5 C4 D1 R3 DS2 C14 C15 C16 19V/3.4A AC90 to 264V R2 FB1 HS1 C3 R17 HS1 R19 TR1 D3 D2 R7 R6 R18 R20 C18 R21 PC1A R9 R5 R8 D4 R13 IC2 R22 R14 GND 4 8 VH 7 (NC) 6 VCC 5 OUT IC1 LAT 1 FA5626 FB 2 IS 3 C11 C12 R15 TH1 R10 C8 C9 PC1B C10 Caution） 1) This application circuit example shows typical directions for use of this IC for reference and does not guarantee the operation and characteristics. 2) VH Pin is connected to near by diode bridge (DS1) to avoid VH Pin’s surge voltage it happens by change of startup current when startup circuit repeats on-off operating. 3) Please connect the diode and resistance with the series between the bulk capacitor or the rectified AC line so that VH Pin must not become a negative voltage. Fuji Electric Co., Ltd. AN-071E Rev.1.2 April-2011 27 http://www.fujielectric.co.jp/products/semiconductor/