Application Information STR-W6200D Series PWM Off-Line Switching Regulator ICs General Description The STR-W6200D series are power ICs for switching power supplies, incorporating a power MOSFET and a current mode PWM controller IC in one package. Including a startup circuit and a standby function in the controller, the product achieves low power consumption, low standby power, and high cost-effectiveness in power supply systems, while reducing external components. Features and Benefits ▪ TO-220 fully-molded package with 6 pins ▪ Current mode PWM control ▪ PWM and frequency modulation functions: reduces EMI noise, simplifies EMI filters, and cuts cost by external part reduction ▪ Built-in Slope Compensation circuit: avoids subharmonic oscillation ▪ Automatic Standby Mode function (Input Power < 40 mW at no load) ▫ Normal operation: PWM mode ▫ Light load operation: Standby mode (burst oscillation) ▪ Built-in Audible Noise Suppression function during Standby mode ▪ Built-in startup circuit: reduces power consumption in standby operation, and eliminates external components ▪ Bias-Assist function: improves startup operation, suppresses VCC pin voltage drop in operation, and allows use of smaller VCC capacitor ▪ Built-in Leading Edge Blanking function ▪ Protection Functions: ▫ Overcurrent Protection function (OCP); pulse-by-pulse, built-in compensation circuit to minimize OCP point variation on AC input voltage ▫ Overload Protection function (OLP); auto restart, built-in timer, reduces heat during overload condition, and few external components required ▫ External Latch Protection function (ELP): latched shutdown by external signal ▫ Overvoltage Protection function (OVP): latched shutdown ▫ Thermal Shutdown function (TSD); latched shutdown STRW6200D-AN Rev.2.0 Figure 1. STR-W6200 series packages are fully molded TO-220 package types. Pin 2 is deleted for greater isolation. A flange is provided for heatsink mounting. Applications Switching power supplies for electronic devices such as: • White goods • Consumer electronics • Office automation • Industrial equipment • Communications equipment The product lineup for the STR-W6200D series provides the following options: Part Number fOSC (kHz) MOSFET VDSS(min) (V) STR-W6251D STR-W6252D STR-W6253D 67 650 POUT* (W) RDS(on) (max) (Ω) 230 VAC 85 to 265 VAC 3.95 45 30 2.8 60 40 1.9 90 60 *The listed output power is based on the thermal ratings, and the peak output power can be 120% to 140% of the value stated here. At low output voltage and short duty cycle, the output power may be less than the value stated here. SANKEN ELECTRIC CO., LTD. http://www.sanken-ele.co.jp/en/ STARTUP VCC D/ST 7.1 V UVLO REG VREG 28.5 V OVP 7.1 V R SQ ELP TSD RQ S Dmax 75% PWM OSC DRV SQ R S2 Frequency Modulation FM /ELP Istartup =1.6 mA RESET 15.5 V / 8.9 V OLP Q Drain Peak Current Compensation CK S1 tDLY = tFM ×16 R OCP 7.8 V 160 μA Feedback Control FB LEB Slope Compensation S/OCP GND Pin List Table Number Name Function 1 D/ST 2 – 3 S/OCP 4 VCC Power supply voltage input for Control Part and input of Overvoltage Protection (OVP) signal 5 GND Ground 6 FB 7 FM/ELP MOSFET drain and input of the startup current (Pin removed) MOSFET source and input of Overcurrent Protection (OCP) signal Input for constant voltage control signal Capacitor connection pin for frequency modulation and input of External Latch Protection Table of Contents General Description 1 Product Lineup 1 Functional Block Diagram 2 Package Diagram 3 Electrical Characteristics 4 Typical Application Circuit 6 Functional Description 7 Startup Operation Frequency Modulation Function Automatic Standby Mode Function STRW6200D-AN Rev.2.0 7 9 10 Constant Output Voltage Control Fault Latch External Latch Protection Function (ELP) Overload Protection Function (OLP) Overvoltage Protection Function (OVP) Overcurrent Protection Function (OCP) Thermal Shutdown Function (TSD) Design Notes 10 11 11 12 12 12 13 14 Peripheral Components 14 Phase Compensation 14 Capacitance of External Capacitor at FM/ELP Pin14 Secondary Diode EMI Measure 15 PCB Trace Layout and Component Placement 15 SANKEN ELECTRIC CO., LTD. 2 Package Diagram TO-220F-6L package Leadform: 2003 10.0 ±0.2 4.2 ±0.2 Gate Burr Ø3.2 ±0.2 16.9 ±0.3 7.9 ±0.2 4.0 ±2 0.5 2.8 ±0.2 +0.2 End of bend (2 R1 ) (5.4) 6X0.65 –0.1 10.4 ±0.5 6X0.74 ±0.15 5.0 ±0.5 2.8 2.6 ±0.1 (At base of pin) View B View A 1.27 ±0.15 6×1.27 ±0.15 = 7.62 ±0.15 +0.2 0.45 –0.1 (At base of pin) 3 5 5.08 ±0.6 7 (At tip of pin) 1 2 4 6 0.5 0.5 View A Bottom View 0.5 0.5 View B Unit: mm Dashed line at Gate Burr indicates protrusion of 0.3 mm (max) STR W62xx YMDDR Part Number Lot Number Y is the last digit of the year (0 to 9) M is the month (1 to 9, O, N, or D) DD is a period of day (01 to 31) R is the Sanken Registration Number Pin treatment Pb-free. Device composition compliant with the RoHS directive. STRW6200D-AN Rev.2.0 SANKEN ELECTRIC CO., LTD. 3 Electrical Characteristics • This section provides separate sets of electrical characteristic data for each product. • The polarity value for current specifies a sink as "+ ," and a source as “−,” referencing the IC. Absolute Maximum Ratings Unless specifically noted, valid at TA = 25°C Characteristic Symbol Note Pin STR-W6251D Drain Peak Current Maximum Switching Current Avalanche Energy IDPEAK IDMAX EAS Rating Unit 2.6 A 3.2 A STR-W6253D 10 A STR-W6251D 2.6 A 3.2 A STR-W6252D Single Pulse STR-W6252D TA = –20°C to 125°C 1-3 1-3 STR-W6253D 10 A STR-W6251D ILPEAK = 2 A 47 mJ 62 mJ 86 mJ Single Pulse, STR-W6252D ILPEAK = 2.3 A VDD = 99 V, STR-W6253D ILPEAK = 2.7 A L = 20 mH 1-3 S/OCP Pin Voltage VOCP 3-5 –6 to 6 V FM/ELP Pin Voltage VFM 7-5 –0.3 to 12 V FM/ELP Pin Sink Current IFM FB Pin Voltage VFB Controller Part Input Voltage VCC FB pin is open 7-5 3 mA 6-5 –0.3 to 9 V 4-5 0 to 32 V 25 W STR-W6251D MOSFET Power Dissipation PD1 STR-W6252D With infinite heatsink STR-W6253D 26 W 27.5 W 1.3 W 4-5 0.8 W – –20 to 115 °C 1-3 Without heatsink Controller Part Power Dissipation Internal Frame Temperature in Operation PD2 TF Recommended operating temperature is TF = 105°C (max) Operating Ambient Temperature Top – –20 to 115 °C Storage Temperature Tstg – –40 to 125 °C Channel Temperature Tch – 150 °C STRW6200D-AN Rev.2.0 SANKEN ELECTRIC CO., LTD. 4 Electrical Characteristics of Control Part Unless specifically noted, TA is 25°C, VCC = 18 V Characteristic Symbol Pin Min. Typ. Max Unit Operation Start Voltage VCC(ON) 4-5 13.9 15.5 17.1 V Operation Stop Voltage VCC(OFF) 4-5 8.0 8.9 9.8 V ICC(ON) 4-5 – 1.4 2.8 mA Circuit Current in Non-Oscillation ICC(STOP) 4-5 – 0.8 1.3 mA Circuit Current in Non-Operation ICC(OFF) 4-5 – 5 20 μA Startup Current ISTARTUP 4-5 –0.9 –1.6 –2.3 mA Bias Assist Voltage VCC(BIAS) 4-5 13.6 15.2 16.8 V FM/ELP Pin High Threshold Voltage VFM(H) 7-5 4.0 4.5 5.0 V FM/ELP Pin Low Threshold Voltage VFM(L) 7-5 2.4 2.8 3.2 V Power Supply Startup Operation Circuit Current in Operation Normal Operation FM/ELP Pin Voltage Difference ∆VFM 7-5 1.4 1.7 1.8 V IFM(SRC) 7-5 –17.4 –13 –8.6 μA FM/ELP Pin Sink Current IFM(SNK) 7-5 8.6 13 17.4 μA Average Switching Frequency fOSC(AVG) 1-5 60 67 74 kHz FM/ELP Pin Source Current Frequency Modulation Deviation ∆f 1-5 4.8 6.9 9 kHz Maximum Duty Cycle (On-duty) DMAX 1-5 71 75 79 % FB Pin Maximum Feedback Current IFB(MAX) 6-5 –220 –160 –100 μA Standby Operation Startup Voltage VSTBY 6-5 0.99 1.10 1.21 V Slope Compensation Startup Duty Cycle DSLP 6-5 – 27 – % Slope Compensation Rate SLP 6-5 –22 –17 –12 mV/μs VOCP1 3-5 0.71 0.78 0.86 V DPC – 1.5 1.9 2.3 mV/D% VOCP2 3-5 0.82 0.93 1.04 V tBW 1-5 280 400 520 ns Protection Operation OCP Threshold Voltage at Zero Duty Cycle (0% On-duty) Drain Peak Current Compensation Coefficient OCP Threshold Voltage After Compensation LEB Time tDLY 1-5 – 200 – ms Circuit Current in OLP-Operation ICC(OLP) 4-5 – 410 700 μA OVP Threshold Voltage VCC(OVP) 4-5 27 28.5 30 V Latch Circuit Holding Current ICC(La.H) 4-5 – 140 220 μA Latch Circuit Release Voltage VCC(La.OFF) 4-5 6.4 7.1 7.8 V ELP Threshold Voltage VELP 7-5 6.4 7.1 7.8 V Sink Current in ELP Operation IELP 7-5 – 55 100 μA TJ(TSD) – 135 – – °C OLP Delay Time* Thermal Shutdown Activating Temperature *Reference value of 47 nF capacitor between FM/ELP and GND Pins. STRW6200D-AN Rev.2.0 SANKEN ELECTRIC CO., LTD. 5 Electrical Characteristics of MOSFET Unless specifically noted, TA is 25°C Characteristic Symbol Drain-to-Source Breakdown Voltage VDSS Drain Leakage Current IDSS Note Pin Min. Typ. Max. Unit 1-3 650 – – V 1-3 – – 300 μA – – 3.95 Ω 1-3 – – 2.8 Ω – – 1.9 Ω 1-3 – – 400 ns – – 2.23 °C/W – – 2.04 °C/W – – 1.75 °C/W STR-W6251D On-Resistance RDS(ON) Switching Time tr STR-W6252D STR-W6253D STR-W6251D Thermal Resistance Between channel and internal frame STR-W6252D Rθch-F STR-W6253D – Typical Application Circuit Clamp Snubber Circuit T1 VAC C10 R9 V OUT PC1 R3 P R6 R4 D4 C1 L2 D3 S U1 R7 C6 C5 R5 U2 C7 R8 GND D1 R2 D/ST S/OCP VCC GND FB FM/ELP STR-W6200D 1 3 4 5 6 7 CV ROCP C2 D External Latch Circuit (Optional) C4 PC1 C3 C8 Damper Snubber The following design feature should be observed: In applications having a power supply specified such that VDS has large transient surge voltages, a clamp snubber circuit of a capacitor-resistor-diode (CRD) combination should be added on the primary winding, P, or a damper snubber circuit of a capacitor (C) or a resistor-capacitor (CR) combination should be added between the D/ST pins and the S/OCP pin. STRW6200D-AN Rev.2.0 SANKEN ELECTRIC CO., LTD. 6 Functional Description With regard to current direction, "+" indicates sink current (toward the IC) and "–" indicates source current (from the IC). Startup Operation Figure 2 shows the VCC pin peripheral circuit. The built-in startup circuit is connected to the D/ST pin, and it generates a constant current, ISTARTUP (–1.6 mA typical) to charge capacitor C2 connected to the VCC pin. During this process, when the VCC pin voltage reaches VCC(ON) (15.5 V typical), the control circuit starts operation. After that, the startup circuit stops automatically, in order to eliminate its own power consumption. The startup time is determined by the C2 capacitance, and a value of 10 to 47 μF is generally recommended. The approximate startup time, tSTART , can be calculated as follows: tSTARTUP (s) = C2 (µF) × VCC(ON) (V) – VCC(INT) (V) |ISTARTUP |(mA) where VCC(INT) is the initial voltage on the VCC pin. C1 P D1 VCC 4 R2 C2 STR-W6200D The rectified voltage from the auxiliary winding, D (figure 2), becomes a power source to the control circuit after the operation start. The VCC pin voltage should become as follows within the specification of input voltage range and the output load range of power supply, taking account of the winding turns of the D winding; the target voltage of the VCC pin voltage is about 15 to 20 V: VCC(OFF) = 9.8 V (max) < VCC < VCC(OVP) = 27.0 V (min) (2) Figure 4 shows the VCC pin voltage behavior during the startup period. When the VCC pin voltage reaches VCC(ON) , the control circuit starts operation, the circuit current, ICC , increases, and thus the VCC pin voltage begins dropping. At the same time, the auxiliary winding voltage, VD , increases in proportion to the output voltage rise. Thus, the VCC pin voltage is set by the balance between dropping by the increase of ICC and rising by the increase of the auxiliary winding voltage, VD . Just at the turning-off of the power MOSFET, a surge voltage occurs at the output winding. If the feedback control is activated by the surge voltage on light load condition at startup, and the VCC pin voltage decreases to VCC(OFF) , a startup failure can occur, because the output power is restricted and the output voltage decreases. 1 D/ST (1) Figure 3 shows the relationship of VCC and ICC. When the VCC pin voltage increases to VCC(ON), the control circuit starts operation and the circuit current, ICC , increases. In operation, when the VCC pin voltage decreases to VCC(OFF) (8.9 V typical), the control circuit stops operation, by the UVLO (Undervoltage Lockout) circuit, and reverts to the state before startup. D GND 5 In order to prevent this, when the VCC pin voltage falls to the Bias Assist Voltage, VCC(BIAS) (15.2 V typical), the Bias Figure 2. VCC pin peripheral circuit VCC (V) ICC Bias Assist Period Target Operation Voltage 1.4 mA (Typ.) 15.5 (typ) 15.2 (typ) Stop Bias Assist Voltage 8.9 (typ) Star t Operation Stop Voltage Startup Failure Event 5 μA (Typ.) 8. 9 V (Typ.) Figure 3. VCC versus ICC STRW6200D-AN Rev.2.0 13.8 V (Typ.) 15. 5 V (Typ.) VCC VIN(AC) turn on Start of normal operation time Figure 4. VCC during startup period SANKEN ELECTRIC CO., LTD. 7 Assist function is activated. While this function is operating, the decrease of the VCC pin voltage is suppressed by providing the startup current, ISTARTUP , from the startup circuit. By this function, the use of a small value C2 capacitor is allowed, resulting in shortened startup time. Also, because the increase of VCC pin voltage becomes faster when the output runs with excess voltage, the response time of the OVP function can also be shortened. After the IC starts switching operation, the Bias Assist function is available until the FM/ELP pin voltage reaches the FM/ELP pin High Threshold Voltage, VFM(H) (4.5 V typical), and at this voltage, this function stops. In actual power supply circuits, there are cases in which the VCC pin voltage fluctuates in proportion to the output of the SMPS (see figure 5), and the Overvoltage Protection (OVP) on the VCC pin may be activated. This happens because C2 is charged to a peak voltage on the auxiliary winding D, which is caused by the transient surge voltage coupled from the primary winding when the power MOSFET turns off. For alleviating C2 peak charging, it is effective to add some value R2, of several tenths of ohms to several ohms, in series with D1 (see figure 6). The optimal value of R2 should be determined using a transformer matching what will be used in the actual application, because the variation of the auxiliary winding voltage is affected by the transformer structural design. Bobbin Barrier VCC P1 S1 2 out R With P2 S2 D Barrier With R2 P1 ,P2 S1 IOUT S2 D Figure 5. VCC versus IOUT with and without resistor R2 Primary winding Secondary output winding controlled to constant voltage Secondary output winding Auxiliary winding for VCC Figure 7. Winding structural example (a) Bobbin D1 4 VCC STR-W6200D Added Barrier R2 P1 D C2 S1 D S2 S1 P2 Barrier GND 5 P1 ,P2 S1 S2 D Figure 6. VCC pin peripheral circuit with R2 STRW6200D-AN Rev.2.0 Primary winding Secondary output winding controlled to constant voltage Secondary output winding Auxiliary winding for VCC Figure 8. Winding structural example (b) SANKEN ELECTRIC CO., LTD. 8 The variation of VCC pin voltage becomes worse if: • The coupling between the primary and secondary windings of the transformer gets worse and the surge voltage increases (low output voltage, large current load specification, for example). • The coupling of the auxiliary winding, D, and the secondary side stabilization output winding (winding of the output line which is controlling constant voltage) gets worse and it is subject to surge voltage. In order to reduce the influence of surge voltages on the VCC pin, alternative structures of the auxiliary winding, D, can be used; as examples of transformer structural designs see figures 7 and 8. • Winding structural example (a): Separating the auxiliary winding D from the primary side windings P1 and P2. The primary side winding is divided into two windings, P1 and P2. • Winding structural example (b): Placing the auxiliary winding D within the secondary winding S1 in order to improve the coupling of those windings. The output winding S1 is a stabilized output winding, controlled to constant voltage. Frequency Modulation Function The frequency modulation is superposed on the PWM frequency, helping to reduce the conductive EMI noise, and simplify noise filtering on input lines. Figure 9 shows the VDS and ID waveforms at an average frequency of 67 kHz and an internally-fixed fluctuation width, Δf, of 6.9 kHz typical. Figure 10 shows the relationship between the FM/ELP pin voltage and the frequency modulation period. The C3 connected to the FM/ELP pin is charged by the constant source current, IFM(SRC) (–13 μA typical), until its voltage increases to about 4.5 V. After that, it is discharged by the Frequency modulation signal FM/ELP Voltage 2.8 V (typ) ∆f = 6.9 kHz VDS 4.5 V (typ) Drain Current, ID ID f(min) ≈ 63.55 kHz f(max) ≈ 70.45 kHz tFM = (2 × C3 × 1.7) /13 μA (s) Figure 9. VDS and ID waveforms in frequency modulation Figure 10. FM/ELP pin voltage and frequency modulation period Burst Oscillation Mode Output Current, IOUT Less than a few kilohertz Drain Current, ID Normal Load Standby Load Normal Load Figure 11. Automatic-Standby mode operation STRW6200D-AN Rev.2.0 SANKEN ELECTRIC CO., LTD. 9 constant sink current, IFM(SNK) (13 μA typical), until its voltage decreases to about 2.8 V, and then the mode is reverted to the constant charge by IFM(SRC). The repetition of this makes the frequency modulation signal a triangle waveform on the FM/ELP pin. By inputting this signal to the PWM oscillation circuit, the frequency modulation occurs. The frequency modulation period, tFM , can be adjusted by the value of C3. The tFM can be calculated as follows. tFM (s) = 2 × C3 × ∆VFM 13 (μA) where ∆VFM is 1.7 V typical. (3) In general, a C3 value in the range of 0.01 to 0.047 μF is recommended, and should be determined based on actual operation in the application. VROCP GND FB 5 6 RROCP PC1 The operation mode becomes burst oscillation, as shown in figure 11. Burst oscillation reduces switching losses and improves power supply efficiency because of periodic non-switching intervals. Generally, to improve efficiency under light load conditions, the frequency of the burst oscillation becomes just a few kilohertz. When the burst oscillation frequency is in the human audible range (20 Hz to 20 kHz), audible noise may occur from the transformer. This IC keeps the peak drain current low during burst oscillation mode, and suppresses the audible noise of the transformer. Constant Output Voltage Control The constant output voltage control function uses current-mode control (peak current mode), which enhances response speed and provides stable operation. This IC compares the voltage, VROCP , of the current detection resistor with the target voltage, VSC , by the internal FB comparator, and controls the peak value of VROCP so that it gets close to VSC. VSC is internally generated by inputting the FB pin voltage to the feedback control (see the Functional Block diagram) and adding the slope compensation value (refer to figures 12 and 13). STR-W6200D S/OCP 3 Automatic Standby Mode Function The Automatic Standby mode is activated automatically when the drain current, ID , reduces under light load conditions, at which ID is less than 15% of the maximum drain current (it is in the Overcurrent Protection state). IFB C4 • Light load conditions When load conditions become lighter, the output voltage, VOUT, rises, and the feedback current from the error amplifier on the secondary side also increases. The feedback current is sunk at the FB pin, transferred through a Figure 12. FB pin peripheral circuit – + VSC Target voltage without Slope Compensation Target voltage including Slope Compensation VROCP S/OCP signal voltage across ROCP FB Comparator ton1 Drain Current, ID T Figure 13. Drain current, ID, and FB comparator operation in steady operation STRW6200D-AN Rev.2.0 ton2 T T Figure 14. Drain current, ID, waveform in subharmonic oscillation SANKEN ELECTRIC CO., LTD. 10 photo-coupler, PC1, and the FB pin voltage decreases. Thus, VSC decreases, the peak value of VROCP is controlled to be low, and the peak drain current of ID decreases. This control prevents the output voltage from increasing. • Heavy load conditions When load conditions become greater, the control circuit performs the inverse operation to that described above. Thus, VSC increases and the peak drain current of ID increases. This control prevents the output voltage from decreasing. In the current-mode control method, when the drain current waveform becomes trapezoidal in continuous operating mode, even if the peak current level set by the target voltage is constant, the on-time fluctuates based on the initial value of the drain current. This results in the on-time fluctuating in multiples of the fundamental operating frequency as shown in figure 14. This is called the subharmonics phenomenon. In order to avoid this, the IC incorporates the Slope Compensation function. Because the target voltage is added, a down-slope compensation signal that reduces the peak drain current as the on-duty gets wider relative to the FB pin signal to compensate VSC , the subharmonics phenomenon is suppressed. Even if subharmonic oscillations occur when the IC has some excess supply being out of feedback control, such as during startup and load shorted, this does not affect performance during normal operation. In the current-mode control method, the FB comparator and/or the OCP comparator may respond to the surge voltage resulting from the drain surge current in turning-on the power MOSFET, and may turn off the power MOSFET irregularly. Leading Edge Blanking, tBW (400 ns typical), is built-in to prevent malfunc- Vcc tions caused by surge voltage in turning-on the power MOSFET. Fault Latch When the OVP, ELP, and TSD functions are activated, the latch circuit is also activated, and then the IC stops switching operation, in latch mode. After that, the VCC pin voltage decreases to VCC(OFF) (8.9 V typical), and then the startup circuit is activated. When the VCC pin voltage increases to VCC(ON) (15.5 V typical), the circuit current increases, and the VCC pin voltage decreases again. As a result, the VCC pin voltage fluctuates between 8.9 V typical and 15.5 V typical as shown in figure 15, and it prevents the VCC pin voltage from increasing. Releasing the latched state is done by turning off the input voltage and allowing the VCC pin voltage to drop below VCC(La.OFF) (7.1 V typical). External Latch Protection Function (ELP) This function forces a latched shutdown if more than the ELP Threshold Voltage, VELP (7.1 V typical), is applied between the FM/ELP and the GND pins. The applied voltage should be within –0.3 to 12 V (the Absolute Maximum Rating of the FM/ELP pin voltage). The Typical Application Circuit shows an example, whereby a current limitation resistor and a latch trigger switch (that is, a photocoupler), are inserted between the VCC and FM/ELP pins. Because the FM/ELP pin has a built-in Zener diode, the current limitation resistor value should be such that the current going into the FM/ELP pin would be below the Absolute Maximum Rating of 3 mA for IFM . 8.9 V (typ) Circuit current is small Circuit current is large 7 C3 time Figure 15. VCC pin voltage at fault latch STRW6200D-AN Rev.2.0 5 FB FM/ELP 15.5 V (typ) GND STR-W6200D 6 PC1 C4 IFB Figure 16. FB pin and FM/ELP pin peripheral circuit SANKEN ELECTRIC CO., LTD. 11 Overload Protection Function (OLP) When the peak drain current of ID is limited by OCP operation, the output voltage, VOUT , decreases and the feedback current from the secondary photo-coupler, IFB (see figure 16), becomes zero. When this state remains for the OLP Delay Time, tDLY , the OLP function is activated, and the IC stops switching operation. When the VCC pin voltage decreases to VCC(OFF) , the control circuit stops its operation by the UVLO circuit, and reverts to the state before startup. After that, the VCC pin voltage increases to VCC(ON) because the startup circuit is activated. As a result, the operation becomes the intermittent oscillation mode by UVLO as shown in figure 17, during OLP operation. This operation reduces stresses on the power MOSFET and on the secondary rectifier diode, furthermore, it reduces power consumption because it reduces the frequency of the intermittent oscillation and the ratio of the switching period, by lowering the circuit current to ICC(OLP) (410 μA typical) during OLP operation. The approximate value of tDLY is equal to 16 times the charge-discharge cycle of C3, connected to the FM/ELP pin (see figure 16), and its equation is: tDLY (s) = tFM × 16 = 2 × C3 (µF) × 1.7 (V) × 16 13 (µA) (typ) (4) where tFM is determined by equation 3. The Delay Time, tDLY , should be longer than the period from a point where the VCC pin voltage increases to VCC(ON) , to other where the output voltage reaches its target value, in order to prevent startup failure caused by OLP operation. In general, a C3 value is recommended to be about 0.01 to 0.047 μF, and the optimal value should be determined based on actual operation in the application. Switching stopped interval VCC pin voltage Swtiching turns off Overvoltage Protection Function (OVP) When the voltage between the VCC pin and the GND pin increases to VCC(OVP) (28.5 V typical) or more, the OVP function is activated and stops switching operation. When the auxiliary winding supplies the VCC pin voltage, the OVP function is able to detect an excessive output voltage, such as when the detection circuit for output control is open on the secondary side, because the VCC pin voltage is proportional to the output voltage. The secondary side output voltage, which initiates OVP operation, is calculated approximately as follows: V (normal operation) × 28.5 (V) (typ.) VOUT(OVP) = OUT (5) VCC(normal operation) Overcurrent Protection Function (OCP) The OCP function detects each peak drain current level of a power MOSFET on a pulse-by-pulse basis, by monitoring the voltage across the current detection resistor ROCP between the S/ OCP pin and the GND pin, and limits the output power accordingly. When the voltage drop on both sides of ROCP increases to the OCP threshold voltage, the power MOSFET is turned off. ICs with PWM control usually have some detection delay time on OCP detection. The steeper the slope of the actual drain current at a high AC input voltage is, the later the actual detection point is, compared to the internal OCP threshold voltage, VOCP. Thus, the actual OCP point limiting the output current usually has some variation depending on the AC input voltage, as shown in figure 18. The IC incorporates a built-in AC Input Compensation function that superposes a signal with a defined slope into the detection signal from the S/OCP pin as shown in figures 19 and 20. When the AC input voltage is lower and the duty cycle is higher, the OCP compensation level of this function is increased. Therefore, the OCP point in low AC input voltage is increased to minimize the difference of OCP points between low AC input voltage and high AC input voltage, without additional external components. VOUT VCC(OFF)= 8.9 V typical Variance resulting from propagation delay t npu Ci A t Low npu Ci A h Hig FM/ELP pin voltage Delay Time, tDLY Drain Current, ID Figure 17. Waveforms during OLP operation STRW6200D-AN Rev.2.0 IOUT Figure 18. Output current at OCP without input compensation SANKEN ELECTRIC CO., LTD. 12 Because the compensation signal level is designed to depend upon the duty cycle, the OCP threshold voltage after compensation, VOCP(D%) , is calculated as follows: VOCP(D%) (V) = VOCP1 (V) + DPC (mV/duty%) × D (%) where VOCP1 is the OCP threshold voltage at zero duty cycle (V), 0.78Vtypical, (6) DPC is the OCP compensation coefficient (mV/D%), 1.9 mV/D% typical, and D is the duty cycle. Assuming an AC input voltage of 85 V, if the transformer is designed so the duty cycle, D, at a maximum load is 50%, then, according to equation 6, VOCP(50%) = 0.875 V typical. Thermal Shutdown Function (TSD) When the controller chip temperature increases to 135°C (min) or more, the IC stops switching operation, in latch mode. 1.05 0. 95 Max. Typ. Min. 0.95 ≈ 0.875 0. 85 VOCP2(D%) Typical (V) VOCP(D%) (V) 1.00 ≈ 0.923 0. 90 0.90 0.85 0.80 ≈ 0.809 0. 80 0. 75 0. 70 0. 60 0. 50 0.75 0.70 0 10 20 30 40 50 60 70 80 0 0 Duty Cycle, D (%) 15. 5 50 75 Duty Cycle, D (%) Figure 19. Duty Cycle versus OCP Threshold Voltage After Compensation STRW6200D-AN Rev.2.0 85 VAC (as an example) 265 VAC (as an example) Figure 20. Duty Cycle versus typical value of OCP Threshold Voltage After Compensation relative to input voltage, for examaple SANKEN ELECTRIC CO., LTD. 13 Design Notes Peripheral Components Take care to use the proper rating and proper type of components. • Input and output electrolytic capacitors ▫ Apply proper design margin to accommodate ripple current, voltage, and temperature rise. ▫ Use of high ripple current and low impedance types, designed for switch-mode power supplies, is recommended, depending on their purposes. • Transformer ▫ Apply proper design margin to core temperature rise by core loss and copper loss. ▫ Because the switching circuits contain high frequency currents, the skin effect may become a consideration. ▫ In consideration of the skin effect, choose a suitable wire gauge in consideration of the rms current and a current density of about 3 to 4 A/mm2. ▫ If measures to further reduce temperature are still necessary, use paralleled wires or litz wires to increase the total surface area of the wiring. L2 D3 Frequency of Frequency Modulation versus C3 Value 10.00 C6 C5 Capacitance of External Capacitor at FM/ELP Pin The capacitor C3 at the FM/ELP pin determines the frequency of frequency modulation, fFM , and the OLP delay time tDLY . Figure 23 shows the relationship between them and the C3 value. A C3 value of 0.01 to 0.047 μF is recommended, and should be selected based on actual operation in the application. R6 R4 S Place C4 between the FB pin and the GND pin, as shown in figure 22, to perform high frequency noise reduction and phase compensation. The value for C4 is recommended to be about 2200 pF to 0.01 μF, and should be selected based on actual operation in the application. OUTPUT PC1 R3 Phase Compensation A typical phase compensation circuit with a secondary shunt regulator (U2) is shown in figure 21. The value for C6 is recommended to be about 0.047 to 0.47 μF, and should be selected based on actual operation in the application. R7 C7 R5 U2 fFM (kHz) T1 • Current detection resistor, ROCP ▫ A high frequency switching current flows to ROCP , and may cause poor operation if a high inductance resistor is used. ▫ Choose a low inductance and high surge tolerant type. R8 1.00 0..10 GND 0.01 0.001 Figure 21. Peripheral circuit around secondary shunt regulator (U2) D1 C2 S/OCP VCC GND FB FM/ELP D/ST 1 3 4 5 6 7 R1 PC1 STRW6200D-AN Rev.2.0 1000 D 0.1 OLP Delay Time versus C3 Value 100 10 1 0.001 C4 Figure 22. FB pin peripheral circuit T1 tDLY (ms) STR-W6200D R2 0.01 C3 (μF) C3 0.01 C3 (μF) 0.1 Figure 23. The relationship between tFM, tDLY , and C3 (calculated values) SANKEN ELECTRIC CO., LTD. 14 Secondary Diode EMI Measure A ceramic capacitor, CDI , parallel to the secondary rectifier as shown in figure 24, may become necessary in some cases to reduce EMI noise reduction. If ringing occurs on the drain current, it is recommended to connect a damper resistor, RDI , in series with CDI , as shown in figure 25, in order to reduce ringing waveforms, and to stabilize switching operation. Note: The values chosen for RDI and CDI should take those temperature rises into consideration, based on actual operation in the application. PCB Trace Layout and Component Placement PCB circuit trace design and component layout significantly affect operation, EMI noise, and power dissipation. Therefore, pay extra attention to these designs. In general, where high frequency current traces form a loop, as shown in figure 26, wide, short traces, and small circuit loops are important to reduce line impedance. In addition, earth ground traces affect radiated EMI noise, and the same measures should be taken into account. Switch-mode power supplies consist of current traces with high frequency and high voltage, and thus trace design and compo- nent layouts should be done to comply with all safety guidelines. Furthermore, because the incorporated power MOSFET has a positive thermal coefficient of RDS(ON) , consider it when preparing a thermal design. Figure 27 shows a circuit layout design example for the IC peripheral circuit and secondary smoothing circuit. • S/OCP Trace Layout: S/OCP pin to ROCP to C1 to T1 (winding P) to D/ST pin. This is the main trace containing switching currents, and thus it should be as wide and short as possible. If C1 and the IC are distant from each other, an electrolytic capacitor or film capacitor (about 0.1 μF and with proper voltage rating) near the IC or the transformer is recommended to reduce impedance of the high frequency current loop. • GND Trace Layout: GND pin to C2 (negative pin) to T1 (winding D) to R2 to D1 to C2 (positive pin) to VCC pin. This trace also must be as wide and short as possible. If C2 and the IC are distant from each other, placing a capacitor (approximately 0.1 to 1.0 μF film capacitor) close to the VCC pin and the GND pin is recommended. CDI T1 D3 ID P C2 S C5 D1 R2 D Figure 24. Rectifier measure example RDI CDI T1 D3 ID P C2 S C5 Figure 26. High-frequency current loops (hatched areas) D1 R2 D Figure 25. Damper resistor example STRW6200D-AN Rev.2.0 SANKEN ELECTRIC CO., LTD. 15 • ROCP Trace Layout: ROCP should be placed as close as possible to the S/OCP pin. The connection between the power ground of the main trace and the control circuit ground should be at a single point ground (A in figure 27) to remove common impedance, and to avoid interference from switching currents to the control circuit. • Secondary Smoothing Circuit Trace Layout: T1 (winding S) to D3 to C5. This trace should be as wide and short as possible. If the loop distance is lengthy, leakage inductance resulting from the long loop may increase surge voltage at turning off the incorporated power MOSFET. Proper secondary trace layout helps to increase margin against the power MOSFET breakdown voltage, and reduces stress on the clamp snubber circuit and losses in it. T1 C10 D3 R9 P D4 C1 S C5 D1 R2 D/ST S/OCP VCC GND FB FM/ELP U1 STR-W6200D 1 3 4 5 6 7 CV C2 D Main power circuit trace GND trace for the IC C4 ROCP PC1 A C3 C8 Figure 27. Peripheral circuit example around the IC STRW6200D-AN Rev.2.0 SANKEN ELECTRIC CO., LTD. 16 • The contents in this document are subject to changes, for improvement and other purposes, without notice. Make sure that this is the latest revision of the document before use. • Application and operation examples described in this document are quoted for the sole purpose of reference for the use of the products herein and Sanken can assume no responsibility for any infringement of industrial property rights, intellectual property rights or any other rights of Sanken or any third party which may result from its use. • Although Sanken undertakes to enhance the quality and reliability of its products, the occurrence of failure and defect of semiconductor products at a certain rate is inevitable. Users of Sanken products are requested to take, at their own risk, preventative measures including safety design of the equipment or systems against any possible injury, death, fires or damages to the society due to device failure or malfunction. • Sanken products listed in this document are designed and intended for the use as components in general purpose electronic equipment or apparatus (home appliances, office equipment, telecommunication equipment, measuring equipment, etc.). When considering the use of Sanken products in the applications where higher reliability is required (transportation equipment and its control systems, traffic signal control systems or equipment, fire/crime alarm systems, various safety devices, etc.), and whenever long life expectancy is required even in general purpose electronic equipment or apparatus, please contact your nearest Sanken sales representative to discuss, prior to the use of the products herein. The use of Sanken products without the written consent of Sanken in the applications where extremely high reliability is required (aerospace equipment, nuclear power control systems, life support systems, etc.) is strictly prohibited. • In the case that you use Sanken products or design your products by using Sanken products, the reliability largely depends on the degree of derating to be made to the rated values. Derating may be interpreted as a case that an operation range is set by derating the load from each rated value or surge voltage or noise is considered for derating in order to assure or improve the reliability. In general, derating factors include electric stresses such as electric voltage, electric current, electric power etc., environmental stresses such as ambient temperature, humidity etc. and thermal stress caused due to self-heating of semiconductor products. For these stresses, instantaneous values, maximum values and minimum values must be taken into consideration. In addition, it should be noted that since power devices or IC's including power devices have large self-heating value, the degree of derating of junction temperature affects the reliability significantly. • When using the products specified herein by either (i) combining other products or materials therewith or (ii) physically, chemically or otherwise processing or treating the products, please duly consider all possible risks that may result from all such uses in advance and proceed therewith at your own responsibility. • Anti radioactive ray design is not considered for the products listed herein. • Sanken assumes no responsibility for any troubles, such as dropping products caused during transportation out of Sanken's distribution network. • The contents in this document must not be transcribed or copied without Sanken's written consent. STRW6200D-AN Rev.2.0 SANKEN ELECTRIC CO., LTD. 17