STR-V600 APPLICATION NOTE STR-V600 Application Note Rev.1.1 SANKEN ELECTRIC CO., LTD. http/www.sanken-ele.co.jp/en/ Copy Right: SANKEN ELECTRIC CO., LTD. Page.1 Rev.1.1 STR-V600 APPLICATION NOTE Contents General Descriptions ----------------------------------------------------------------------- 3 1. Absolute Maximum Ratings --------------------------------------------------------- 4 2. Electrical Characteristics ------------------------------------------------------------ 4 2.1 Electrical Characteristics of Control Part --------------------------------- 4 2.2 Electrical Characteristics of MOSFET ------------------------------------- 5 3. Functional Block Diagram ----------------------------------------------------------- 6 4. Pin List Table --------------------------------------------------------------------------- 6 5. Typical Application Circuit --------------------------------------------------------- 7 6. Package Diagram ---------------------------------------------------------------------- 8 7. Marking Diagram --------------------------------------------------------------------- 8 8. Functional Description --------------------------------------------------------------- 9 8.1 Startup Operation --------------------------------------------------------------- 9 8.2 Undervoltage Lockout (UVLO) Circuit ------------------------------------ 9 8.3 Bias Assist Function ------------------------------------------------------------- 9 8.4 Constant Voltage Control Operation --------------------------------------- 10 8.5 Auto Standby Mode Function ----------------------------------------------- 11 8.6 Random Switching Function ------------------------------------------------- 11 8.7 Brown-In and Brown-Out Function ---------------------------------------- 12 8.8 Overcurrent Protection Function (OCP) ---------------------------------- 14 8.9 Overvoltage Protection Function (OVP) ---------------------------------- 14 8.10 Overload Protection Function (OLP) -------------------------------------- 15 8.11 Thermal Shutdown Function (TSD) ---------------------------------------- 15 9. Design Notes --------------------------------------------------------------------------- 16 9.1 Peripheral Components ------------------------------------------------------- 16 9.2 PCB trace layout and Component placement ------------------------------- 17 IMPORTANT NOTES ------------------------------------------------------------------- 19 Copy Right: SANKEN ELECTRIC CO., LTD. Page.2 Rev.1.1 STR-V600 APPLICATION NOTE Rev.1.1 General Descriptions Package The STR-V600 series is a power IC for switching power supplies, incorporating a power MOSFET and a current mode PWM controller IC in one package. The SIP8L full mold package features low height and creeping distance of 4mm or longer between high and low voltage pin bases. To achieve low power consumption, the product includes a startup circuit and a standby function in the controller. The switching modes are automatically changed according to load conditions so that the PWM mode is in normal operation and the burst mode is in light load condition. The rich set of protection features helps to realize low component counts, and high performance-to-cost power supply. SIP8L Features Applications SIP8L package (2.54 pitch, straight lead): Creeping distance of 4mm or longer between high voltage and low voltage pin bases. Low height of less than 12 mm from PCB (Printed Circuit Board) Current mode PWM control Auto Standby function: improves efficiency by burst mode operation in light load ▫ Normal operation: PWM mode ▫ Light load operation: Burst mode No load power consumption < 25 mW Brown-In and Brown-Out function: auto-restart, prevents excess input current and heat rise at low input voltage Random Switching function: reduces EMI noise, and simplifies EMI filters Slope Compensation function: avoids subharmonic oscillation Leading Edge Blanking function High Speed Latch Release function Protection features ▫ Overcurrent Protection function (OCP): pulse-by-pulse, with input compensation function ▫ Overvoltage Protection function (OVP): latched shutdown ▫ Overload Protection function (OLP): auto-restart, with timer ▫ Thermal Shutdown function (TSD): latched shutdown Standby power supply Home appliances Digital appliances Office automation (OA) equipment Industrial apparatus Communication facilities Product Lineup Power MOSFET Output Power, POUT * (W) Part Number fOSC (kHz) VDSS (min) (V) RDS(ON) (max) (Ω) 230VAC 85 to 265VAC STR-V653 67 650 1.9 30 23 * 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. Copy Right: SANKEN ELECTRIC CO., LTD. Page.3 STR-V600 APPLICATION NOTE Rev.1.1 1. Absolute Maximum Ratings Refer to the datasheet of each product for these details. The polarity value for current specifies a sink as "+," and a source as "−," referencing the IC. Unless otherwise specified, Ta is 25 °C Characteristic Pins Symbol Rating Unit Drain Peak Current 1−3 IDPEAK 6.7 A Single pulse Avalanche Energy 1−3 EAS 99 mJ ILPEAK 2.9 A Single pulse VDD=99V,L=20mH S/OCP Pin Voltage 3−5 VOCP Control Part Input Voltage 8−5 VCC 32 V FB/OLP Pin Voltage 6−5 VFB −0.3 to 14 V FB/OLP Pin Sink Current 6−5 IFB 1.0 mA BR Pin Voltage 4−5 VBR −0.3 to 7 V BR Pin Sink Current 4−5 IBR 1.0 mA 1−3 PD1 10.8 W With infinite heat sink Power Dissipation of MOSFET 1.6 W Without heat sink −2 to 6 Notes V Power Dissipation of Control Part 8−5 PD2 1.2 W Operating Ambient Temperature − Top −30 to +125 °C Storage Temperature − Tstg −40 to +125 °C Channel Temperature − Tch +150 °C 2. Electrical Characteristics Refer to the datasheet of each product for these details. The polarity value for current specifies a sink as "+," and a source as "−," referencing the IC. 2.1 Electrical Characteristics of Control Part Unless otherwise specified, Ta is 25 °C, VCC is 18 V Characteristic Pins Symbol Min. Typ. Max. Unit 8−5 VCC(ON) 13.8 15.3 16.8 V 8−5 VCC(OFF) 7.3 8.1 8.9 V Circuit Current in Operation 8−5 ICC(ON) − − 4 mA Minimum Startup Voltage 8−5 VST(ON) − 38 − V Startup Current Startup Current Supply Threshold Biasing Voltage Frequency Modulation Deviation Oscillation Frequency Fluctuation Range Maximum Duty Cycle 8−5 I STARTUP −3.7 −2.5 −1.5 mA 8−5 VCC(BIAS) 8.5 9.5 10.5 V 1−5 fOSC(AVE) 60 67 74 kHz 1−5 Δf − 5 − kHz 1−5 DMAX 77 83 89 % Minimum On-time − tON(MIN) − 550 − ns Leading Edge Blanking Time − tBW − 330 − ns OCP Compensation Coefficient − DPC − 20 − mV/µs OCP Compensation Duty Cycle Limit − DDPC − 36 − % Operation Start Voltage Operation Stop Voltage (1) (1) Copy Right: SANKEN ELECTRIC CO., LTD. Page.4 Notes VCC=12V STR-V600 APPLICATION NOTE Characteristic OCP Threshold Voltage at Zero Duty Cycle OCP Threshold Voltage at 36% Duty Cycle Maximum Feedback Current Rev.1.1 Pins Symbol Min. Typ. Max. Unit 3−5 VOCP(L) 0.70 0.78 0.86 V 3−5 VOCP(H) 0.81 0.90 0.99 V 6−5 IFB(MAX) −340 −230 −150 µA Minimum Feedback Current FB/OLP Pin Oscillation Stop Threshold Voltage OLP Threshold Voltage 6−5 IFB(MIN) −30 −15 −7 µA 6−5 VFB(OFF) 0.85 0.95 1.05 V 6−5 VFB(OLP) 7.3 8.1 8.9 V OLP Delay Time 6−5 tOLP 54 68 82 ms OLP Operation Current 8−5 ICC(OLP) − 300 600 µA FB/OLP Pin Clamp Voltage 6−5 VFB(CLAMP) 11 12.8 14 V Brown-In Threshold Voltage 4−5 VBR(IN) 5.2 5.6 6 V Brown-Out Threshold Voltage 4−5 VBR(OUT) 4.45 4.8 5.15 V BR Pin Clamp Voltage BR Function Disable Threshold Voltage VCC Pin OVP Threshold Voltage 4−5 VBR(CLAMP) 6 6.4 7 V 4−5 VBR(DIS) 0.3 0.48 0.7 V 8−5 VCC(OVP) 26 29 32 V 8−5 ICC(LATCH) − 700 − µA − Tj(TSD) 135 − − °C Latch Circuit Holding Current (2) Thermal Shutdown Temperature (1) (2) Notes VCC(BIAS) > VCC(OFF) always. A latch circuit is a circuit operated with Overvoltage Protection (OVP) and/or Thermal Shutdown Protection (TSD) in operation. 2.2 Electrical Characteristics of MOSFET Unless otherwise specified, Ta is 25 °C Characteristic Pins Symbol Min. Typ. Max. Unit Drain-to-Source Breakdown Voltage 1–3 VDSS 650 − − V Drain Leakage Current 1–3 IDSS − − 300 μA On-Resistance 1–3 RDS(ON) − − 1.9 Ω Switching Time 1–3 tf − − 250 ns − θch−F − − 3.0 °C/W Thermal Resistance * * The thermal resistance between the channels of the MOSFET and the internal frame Copy Right: SANKEN ELECTRIC CO., LTD. Page.5 Notes STR-V600 APPLICATION NOTE Rev.1.1 3. Functional Block Diagram D/ST VCC 8 VCC STRATUP UVLO REG OVP VREG 1 D/ST TSD BR 4 BR Brown-in/Out 6.4V DRV PWM OSC SQ R OCP Drain Peak current Compensation OLP VCC 7V S/OCP Feedback Control FB/OLP 6 FB LEB Slope Compensation 12.8V GND 3 S/OCP GND 5 4. Pin List Table 1 VCC FB/OLP GND BR S/OCP D/ST 8 Number Name 1 D/ST 2 − 3 S/OCP 4 BR 5 GND 6 FB/OLP 7 − 8 VCC Copy Right: SANKEN ELECTRIC CO., LTD. Page.6 Function MOSFET drain pin and input of the startup current (Pin removed) MOSFET source and input of Overcurrent Protection (OCP) signal Input of Brown-In and Brown-Out detection voltage Ground Feedback signal input for constant voltage control signal and input of Overload Protection (OLP) signal (Pin removed) Power supply voltage input for Control Part and input of Overvoltage Protection (OVP) signal STR-V600 APPLICATION NOTE Rev.1.1 5. Typical Application Circuit The following drawings show circuits enabled and disabled the Brown-In/Brown-Out function. The following design features should be observed: The PCB traces from the D/ST pin (pin 1) should be as wide as possible, in order to enhance thermal dissipation. In applications having a power supply specified such that V DS has large transient surge voltages, a clamp snubber circuit of a capacitor-resistor-diode (CRD) combination should be added on the primary-side winding P, or a damper snubber circuit of a capacitor (C) or a resistor-capacitor (RC) combination should be added between the D/ST pin and the S/OCP pin. CRD clamp snubber BR1 VAC VOUT R54 R1 C5 RA L51 D51 T1 PC1 C1 R51 P R55 C51 D1 RB D2 D/ST NC C53 C52 R53 R2 U51 8 1 C4 R52 S VCC R56 D C2 U1 GND STR-V600 S/OCP BR GND FB/OLP 3 C, CR damper snubber RC 4 5 6 C10 C3 PC1 ROCP C9 Figure 5-1 Typical application circuit instance, enabled Brown-In/Brown-Out function (DC line detection) CRD clamp snubber BR1 L51 D51 T1 VAC VOUT R54 R1 C5 PC1 C1 P R55 C51 D1 S D2 D/ST C4 NC R52 U51 VCC C2 U1 GND S/OCP BR GND FB/OLP 3 4 5 6 C3 PC1 C9 ROCP Figure 5-2 Typical application circuit example, disabled Brown-In/Brown-Out function Copy Right: SANKEN ELECTRIC CO., LTD. R56 D STR-V600 C, CR damper snubber C53 C52 R53 R2 8 1 R51 Page.7 STR-V600 APPLICATION NOTE Rev.1.1 6. Package Diagram SIP8L package (2.54 pitch, straight lead) The pin 2 removed to provide greater creepage and clearance isolation between the high voltage pins (pins 1: D/ST) and the low voltage pin (pin 3: S/OCP). Creeping distance of 4mm or longer between high voltage and low voltage pin bases. Low height of less than 12 mm from PCB (Printed Circuit Board) 4±0.2 9 ±0.2 1.2±0.1 （At base of pin） 7.2 ±0.5 2.3 ±0.2 Gate burr 1.15 +0.2 -0.1 0.55 +0.2 -0.1 0.55 +0.2 -0.1 7xP2.54±0.1=(17.78) （At base of pin） C1.5 ±0.5 0.7 20.15 ±0.3 0.7 Front view 1 2 3 4 5 6 7 0.7 0.7 Side view 8 NOTES: Unit: mm Gate burr indicates protrusion of 0.3 mm (max). Pin treatment Pb-free. Device composition compliant with the RoHS directive. 7. Marking Diagram YMDD Lot Number Y is the last digit of year (0 to 9) M is the month (1 to 9, N or D) DD is a period of days (01 to 31) STRV6xx Part Number Copy Right: SANKEN ELECTRIC CO., LTD. Page.8 STR-V600 APPLICATION NOTE Rev.1.1 8. Functional Description All of the parameter values used in these descriptions are typical values, unless they are specified as minimum or maximum. With regard to current direction, "+" indicates sink current (toward the IC) and "–" indicates source current (from the IC). 8.1 Startup Operation Figure 8-1 shows the VCC pin peripheral circuit, disabled the Brown-In/Brown-Out function by connecting the BR pin trace to the GND pin trace. In Figure 8-1, the Startup Current, ISTARTUP, which is a constant current of –2.5 mA, is provided from the IC to capacitor C2 connected to the VCC pin, and it charges C2. When the VCC pin voltage increases to VCC(ON) = 15.3 V, the IC starts operation. After that, the startup circuit stops automatically, in order to eliminate its own power consumption. During the IC operation, the rectified voltage from the auxiliary winding voltage, VD, of Figure 8-1 becomes a power source to the VCC pin. The winding turns of the winding D should be adjusted so that the VCC pin voltage is applied to equation (1) within the specification of the input voltage range and output load range of the power supply. The target voltage of the winding D is about 18 V. VCC(ON ) VCC( INT ) ISTARTUP C1 P 1 D/ST VCC D2 8 U1 BR 4 C2 GND R2 VD D 5 Figure 8-1 VCC pin peripheral circuit (1) The startup time, tSTART, is determined by the value of C2, and it is approximately given as below: t START C2 T1 (2) ICC(ON) = 4mA(max) Stop where: tSTART is the startup time in s, and VCC(INT) is the initial voltage of the VCC pin in V. ICC Start VCC(BIAS) (max) VCC VCC(OVP) (min) ⇒ 10.5(V) VCC 26.0(V) BR1 VAC 8.2 Undervoltage Lockout (UVLO) Circuit Figure 8-2 shows the relationship of VCC and ICC. After the IC starts operation, when the VCC pin voltage decreases to VCC(OFF) = 8.1 V, the IC stops switching operation by the UVLO (Undervoltage Lockout) circuit and reverts to the state before startup again. 8.1V VCC(OFF) 15.3V VCC(ON) Figure 8-2 VCC versus ICC 8.3 Bias Assist Function Figure 8-3 shows the VCC pin voltage behavior during the startup period. When the VCC pin voltage increases to VCC(ON) = 15.3 V, the IC starts operation. Thus, the circuit current, ICC, increases, and the VCC pin voltage begins dropping. At the same time, the auxiliary winding voltage, V D, increases in proportion to the output voltage rise. Thus, the VCC pin voltage is set by the balance between dropping due to the increase of ICC and rising due to the increase of the auxiliary winding voltage, VD. VCC pin voltage IC startup VCC(ON) VCC(BIAS) Startup success Target operating voltage Increasing by output voltage rising Bias Assist period VCC(OFF) Just at the turning-off of the power MOSFET, a surge voltage occurs at the output winding. If the feedback control is Startup failure activated by the surge voltage on light load condition at startup, the output power is restricted and the output voltage decreases. Time When the VCC pin voltage decreases to VCC(OFF) = 8.1 V, the IC stops switching operation and a startup failure occurs. Figure 8-3 VCC pin voltage during startup period In order to prevent this, the Bias Assist function is activated when the VCC pin voltage decreases to the Startup Current Threshold Biasing Voltage, VCC(BIAS) = 9.5 V, during a state of operating feedback control. While the Bias Assist function is activated, any decrease of the VCC pin voltage is counteracted by providing the Startup Current, ISTARTUP, from the startup circuit. Thus, the VCC pin voltage is kept almost constant. By the Bias Assist function, the value of C2 is allowed to be small and the startup time becomes shorter. Furthermore, Copy Right: SANKEN ELECTRIC CO., LTD. Page.9 STR-V600 APPLICATION NOTE Rev.1.1 because the increase of VCC pin voltage becomes faster when the output runs with excess voltage, the response time of the OVP function becomes shorter. It is necessary to check and adjust the startup process based on actual operation in the application, so that the startup failure does not occur. 8.4 Constant Voltage Control Operation The constant output voltage control function uses current mode control (peak current mode), which enhances response speed and provides stable operation. The FB/OLP pin voltage is internally added the slope compensation at the feedback control (refer to Section 3 Functional Block Diagram), and the target voltage, VSC, is generated. The IC compares the voltage, VROCP, of a current detection resistor with the target voltage, V SC, by the internal FB comparator, and controls the peak value of VROCP so that it gets close to VSC, as shown in Figure 8-4 and Figure 8-5. Light load conditions When load conditions become lighter, the output voltage, V OUT, increases. Thus, the feedback current from the error amplifier on the secondary-side also increases. The feedback current is sunk at the FB/OLP pin, transferred through a photocoupler, PC1, and the FB/OLP pin voltage decreases. Thus, VSC decreases, and the peak value of VROCP is controlled to be low, and the peak drain current of I D decreases. This control prevents the output voltage from increasing. Heavy load conditions When load conditions become greater, the IC performs the inverse operation to that described above. Thus, V SC increases and the peak drain current of I D 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 8-6. 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, which reduces the peak drain current as the on-duty gets wider relative to the FB/OLP 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 of 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. As a result, the power MOSFET may turn off irregularly. In order to prevent this response to the surge voltage in turning-on the power MOSFET, Leading Edge Blanking, tBW = 330 ns, is built-in. Copy Right: SANKEN ELECTRIC CO., LTD. Page.10 U1 S/OCP 3 GND 5 FB/OLP 6 PC1 ROCP VROCP C3 IFB Figure 8-4 FB/OLP pin peripheral circuit Target voltage including Slope Compensation − VSC + VROCP ROCP voltage FB comparator Drain current, ID Figure 8-5 Drain current, ID, and FB comparator operation in steady operation Target voltage without Slope Compensation tON1 t tON2 t t Figure 8-6 Drain current, ID, waveform in subharmonic oscillation STR-V600 APPLICATION NOTE Rev.1.1 8.5 Auto Standby Mode Function Auto standby mode is activated automatically when the drain current, ID, reduces under light load conditions, at which ID is less than 15% to 20% of the maximum drain current (it is in the Overcurrent Protection state). The operation mode becomes burst oscillation, as shown in Figure 8-7. Burst mode reduces switching losses and improves power supply efficiency because of periodic non-switching intervals. Generally, in order to improve efficiency under light load conditions, the frequency of the burst mode becomes just a few kilohertz. Because the IC suppresses the peak drain current well during burst mode, audible noises can be reduced. Output current, IOUT Burst oscillation Below several kHz Drain current, ID Normal operation Standby operation Normal operation Figure 8-7 Auto Standby mode timing If the VCC pin voltage decreases to VCC(BIAS) = 9.5 V during the transition to the burst mode, the Bias Assist function is activated and stabilizes the standby mode operation, because ISTARTUP is provided to the VCC pin so that the VCC pin voltage does not decrease to VCC(OFF). However, if the Bias Assist function is always activated during steady-state operation including standby mode, the power loss increases. Therefore, the VCC pin voltage should be more than VCC(BIAS), for example, by adjusting the turns ratio of the auxiliary winding and secondary-side winding and/or reducing the value of R2 in Figure 9-2 (refer to Section 9.1 Peripheral Components for a detail of R2). 8.6 Random Switching Function The IC modulates its switching frequency randomly within Δf = ± 5 kHz superposed on the average operation frequency, fOSC(AVG) = 67 kHz. The conduction noise with this function is smaller than that without this function, and this function can simplify noise filtering of the input lines of power supply. Copy Right: SANKEN ELECTRIC CO., LTD. Page.11 STR-V600 APPLICATION NOTE Rev.1.1 8.7 Brown-In and Brown-Out Function This function stops switching operation when it detects low input line voltage, and thus prevents excessive input current and overheating. During Auto Standby mode, this function is disabled. 8.7.1 Disabled Brown-In and Brown-Out Function When the Brown-In and Brown-Out function is unnecessary, connect the BR pin trace to the GND pin trace so that the BR pin voltage is VBR(DIS) = 0.48 V or less, as shown in Figure 8-8. C1 8 1 D/ST 8.7.2 Brown-In and Brown-Out Function by DC Line Detection The BR pin detects a voltage proportional to the DC input voltage (C1 voltage), with the resistive voltage divider R A, RB, and RC connected between the DC input and GND, plus C10 connected to the BR pin, as shown in Figure 8-9. This method detects peaks of the ripple voltage of the rectified AC input voltage, and thus it minimizes the influence of load conditions on the detecting voltage. During the input voltage rising from the stopped state of power supply, when the BR pin voltage increases to VBR(DIS) = 0.48 V or more, this function is enabled. After that, when the BR pin voltage increases to VBR(IN) = 5.6 V or more and the VCC pin voltage increases to VCC(ON) or more, the IC starts switching operation. During the input voltage falling from the operated state of power supply, when the BR pin voltage decreases to VBR(OUT) = 4.8 V or less for about 68 ms, the IC stops switching operation. NC VCC U1 S/OCP BR GND FB/OLP 3 4 5 6 C3 PC1 ROCP BR pin is connected to GND Figure 8-8 The circuit used to disable Brown-In and Brown-Out function Component values of the BR pin peripheral circuit: ▫ RA, RB : A few megohms. Because of high DC voltage applied and high resistance, it is recommended to select a resistor designed against electromigration or use a combination of resistors in series for that to reduce each applied voltage, according to the requirement of the application. ▫ RC : A few hundred kilohms ▫ C10: 100 p to 1000 pF for high frequency noise rejection EIN ID RA C1 EIN RB VCC pin voltage VCC(ON) VCC(OFF) 8 1 D/ST NC VCC U1 BR pin voltage VBR(IN)= 5.6V S/OCP BR GND FB/OLP 3 4 5 6 VBR(OUT)= 4.8V VBR(DIS)= 0.48V RC C10 C3 PC1 Drain current, ID ROCP 68ms Figure 8-9 Brown-In and Brown-Out function controlled by DC line detection Copy Right: SANKEN ELECTRIC CO., LTD. Page.12 STR-V600 APPLICATION NOTE Rev.1.1 8.7.3 Brown-In and Brown-Out Function by AC Line Detection The BR pin detects a voltage proportional to the AC input voltage, with the resistive voltage divider R A, RB, and RC connected between one side of the AC line and GND, plus C10 connected to the BR pin and R9 connected between the BR pin and the VCC pin, as shonw in Figure 8-10. This method detects the AC input voltage, and thus it minimizes the influence from C1 charging and discharging time, or load conditions, on the detecting voltage. This method is set together with the High-Speed Latch Release function. During the input voltage rising from the stopped state of power supply, when the BR pin voltage increases to VBR(DIS) = 0.48 V or more, this function is enabled. After that, when the BR pin voltage increases to VBR(IN) = 5.6 V or more and the VCC pin voltage increases to VCC(ON) or more, the IC starts switching operation. During the input voltage falling from the operated state of power supply, when the BR pin voltage decreases to VBR(OUT) = 4.8 V or less for about 68 ms, the IC stops switching operation. Component values of the BR pin peripheral circuit: ▫ RA, RB : A few megohms. Because of high DC voltage applied and high resistance, it is recommended to select a resistor designed against electromigration or use a combination of resistors in series for that to reduce each applied voltage, according to the requirement of the application. ▫ RC : A few hundred kilohms ▫ C10: 0.047 μ to 0.47 μF for AC ripple rejection. This should be adjusted according to values of RA, RB, and RC. ▫ R9: In order to enable the Brown-In and Brown-Out function, this value must be adjusted so that the BR pin voltage is more than VBR(DIS) = 0.48 V when the VCC pin voltage decreases to VCC(OFF) = 8.1 V. High-Speed Latch Release The Brown-In and Brown-Out function by AC line detection shown in Figure 8-10 can quickly release the latch mode when the AC input, VAC, is turned off. When the Overvoltage Protection function (OVP) or Thermal Shutdown function (TSD) are activated, the IC stops switching operation in latch mode. Releasing the latch mode is done by decreasing the VCC pin voltage below VCC(OFF) = 8.1 V after unplugging the AC input, or by decreasing the BR pin voltage below VBR(OUT) = 4.8 V. The method of unplugging the AC input will spend much time until the VCC pin voltage decreases below VCC(OFF) = 8.1 V, because the release time is determined by the discharge time of C1. In contrast, the configuration of the BR pin peripheral circuit of Figure 8-10 makes the releasing process faster. Because the BR pin voltage immediately decreases to VBR(OUT) = 4.8 V or less when the AC input, VAC, is turned off, and thus the latch mode is quickly released. BR1 VAC VAC ID C1 RA R9 1 VCC pin voltage VCC(ON) VCC(OFF) 8 D/ST NC VCC U1 RB BR pin voltage VBR(IN)= 5.6V S/OCP BR GND FB/OLP 3 4 5 6 VBR(OUT)= 4.8V VBR(DIS)= 0.48V RC C10 C3 PC1 Drain current, ID ROCP 68ms Figure 8-10 Brown-In and Brown-Out function controlled by AC line detection Copy Right: SANKEN ELECTRIC CO., LTD. Page.13 STR-V600 APPLICATION NOTE Rev.1.1 8.8 Overcurrent Protection Function (OCP) Variance resulting from propagation delay Output voltage, VOUT (V) The OCP function detects each peak drain current level of the power MOSFT by the current detection resistor, ROCP. When the OCP pin voltage increases to the internal OCP threshold voltage, the IC turns off the power MOSFET on pulse-by-pulse basis, and limits the output power. 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. Thus, the actual OCP point limiting the output current usually has some variation depending on the AC input voltage, as shown in Figure 8-11. w Lo AC p in ut gh Hi A np Ci ut Output current, IOUT （A） The IC incorporates a built-in Input Compensation function that superposes a signal with a defined slope into the detection signal on the OCP pin as shown in Figure 8-12. When AC input voltage is lower and the duty cycle is longer, the OCP compensation level increases more than that in high AC input voltage. Thus, the OCP point in low AC input voltage increases to minimize the difference of OCP points between low AC input voltage and high AC input voltage, without any additional components. Figure 8-11 Output current at OCP without input compensation AC265V (as an example) AC85V (as an example) 1.0V VOCP(H) About 0.83V VOCP(L) VOCP(ONTime) Because the compensation signal level is designed to depend upon the on-time of the duty cycle, the OCP threshold voltage after compensation, VOCP(ONTime), is given as below. However, when the duty cycle becomes 36 % or more, the OCP threshold voltage after compensation remains at VOCP(H) = 0.9 V, constantly. VOCP(ONTime) (V) (3) VOCP(L) (V) DPC(mV / s) ONTime(s) where: VOCP(L) is the OCP threshold voltage at zero duty cycle (V), 0.78 V DPC is the OCP compensation coefficient (mV/μs), 20 mV/µs, and ONTime is the on-time of the duty cycle (μs): ONDuty ONTime f OSC( AVG ) 0.5V 0 0 15 36 50 80 ON Duty (%) Figure 8-12 Relationship of duty cycle and OCP threshold voltage after compensation 8.9 Overvoltage Protection Function (OVP) When the voltage between the VCC pin and the GND pin is applied to the OVP threshold voltage, VCC(OVP) = 29 V or more, the Overvoltage Protection function (OVP) is activated and the IC stops switching operation. When the VCC pin voltage decreases to VCC(BIAS) = 9.5 V, the startup circuit provides the Startup Current, ISTARTUP, to the VCC pin, in order to prevent the VCC pin voltage from decreasing to V CC(OFF) = 8.1 V or less. Thus, the IC maintains latch mode. Releasing the latch mode is done by decreasing the VCC pin voltage below VCC(OFF) = 8.1 V after unplugging the AC input. In the Brown-In and Brown-Out function by AC line detection of Section 8.7.3, releasing the latch mode is done by the High-Speed Latch Release decreasing the BR pin voltage below VBR(OUT) = 4.8 V. 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 output voltage of the secondary-side at OVP operation, VOUT(OVP), is approximately given as below: VOUT (OVP ) VOUT (normal operation ) 29V VCC (normal operation ) Copy Right: SANKEN ELECTRIC CO., LTD. (4) Page.14 STR-V600 APPLICATION NOTE Rev.1.1 8.10 Overload Protection Function (OLP) Figure 8-13 shows the FB/OLP pin peripheral circuit, and Figure 8-14 shows each waveform for OLP operation. When the peak drain current of ID is limited by OCP operation, the output voltage, VOUT, decreases and the feedback current flowing to the photocoupler becomes zero. Thus, the feedback current, IFB, charges C3 connected to the FB/OLP pin, and the FB/OLP pin voltage increases. U1 GND 5 VCC 8 FB/OLP 6 IFB PC1 When the FB/OLP pin voltage increases to VFB(OLP) = 8.1 V or more for the OLP Delay Time, tOLP = 68 ms or more, the OLP function is activated and the IC stops switching operation. When the OLP function is activated, the Bias Assist function is disabled and the VCC pin voltage decreases to VCC(OFF) = 8.1 V. Thus, the IC stops switching operation by the UVLO (Undervoltage Lockout) circuit and reverts to the state before startup. After that, the startup circuit is activated, the VCC pin voltage increases to VCC(ON) = 15.3 V, and the IC starts switching operation again. In this way, the intermittent operation by UVLO is repeated during OLP state. This operation reduces power stress on the power MOSFET and secondary-side rectifier diode. Furthermore, this reduces power consumption, because the switching period in this intermittent operation is shorter than non-switching interval. When the fault condition is removed, the IC returns to normal operation automatically. C2 D Figure 8-13 FB/OLP pin peripheral circuit VCC pin voltage VCC(ON) VCC(OFF) FB/OLP pin voltage VFB(OLP) Non-switching interval tOLP Drain current, ID 8.11 Thermal Shutdown Function (TSD) If the temperature of the control part in the IC increases to more than Tj(TSD) = 135 °C (min), the Thermal Shutdown function (TSD) is activated and the IC stops switching operation in latch mode, in the same way as Section 8.9 Overvoltage Protection Function (OVP). Releasing the latch mode is done by decreasing the VCC pin voltage below VCC(OFF) = 8.1 V after unplugging the AC input. In the Brown-In and Brown-Out function by AC line detection of Section 8.7.3, releasing the latch mode is done by High-Speed Latch Release decreasing the BR pin voltage below VBR(OUT) = 4.8 V. Copy Right: SANKEN ELECTRIC CO., LTD. C3 D2 R2 Page.15 Figure 8-14 OLP operation waveforms tOLP STR-V600 APPLICATION NOTE Rev.1.1 9. Design Notes 9.1 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. A low ESR type for output smoothing capacitor, designed for switch-mode power supplies, is recommended to reduce output ripple voltage. T1 C1 P 1 D/ST D C2 U1 FB/ S/ OCP BR GND OLP 3 4 5 6 BR pin peripheral circuit The Brown-In and Brown-Out function has two types of detection method: AC line or DC line. Refer to Section 8.7 Brown-In and Brown-Out Function. RC ROCP C10 PC1 C3 Figure 9-1 IC peripheral circuit FB/OLP pin peripheral circuit C3, located between the FB/OLP pin and the GND pin in Figure 9-1, performs high frequency noise rejection and phase compensation. C3 should be connected close to these pins. The reference value of C3 is about 2200p to 0.01µF, and should be adjusted based on actual operation in the application. Phase Compensation A typical phase compensation circuit with a secondary-side shunt regulator (U51) is shown in Figure 9-4. The reference value of C52 for phase compensation is about 0.047µ to 0.47μF, and should be adjusted based on actual operation in the application. 8 NC VCC RB Current detection resistor, ROCP Choose a low inductance and high surge-tolerant type. Because a high frequency switching current flows to ROCP in Figure 9-1, a high inductance resistor may cause poor operation. VCC pin peripheral circuit Figure 9-2 shows the VCC pin peripheral circuit. The reference value of C2 is generally 10µ to 47μF (refer to Section 8.1 Startup Operation, because the startup time is determined by the value of C2). In actual power supply circuits, there are cases in which the VCC pin voltage fluctuates in proportion to the output current, IOUT (see Figure 9-3), and the Overvoltage Protection function (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-side 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 D2 (see Figure 9-2). 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. D2 R2 RA D2 8 VCC R2 Added D C2 U1 GND 5 Figure 9-2 VCC pin peripheral circuit VCC pin voltage Without R2 With R2 Output current, IOUT Figure 9-3 VCC versus IOUT with and without resistor R2 L51 D51 T1 VOUT R54 PC1 R55 C51 S R51 R52 C53 C52 R53 U51 R56 GND Figure 9-4 Peripheral circuit around secondary-side shunt regulator (U51) Copy Right: SANKEN ELECTRIC CO., LTD. Page.16 STR-V600 APPLICATION NOTE Rev.1.1 Transformer Apply proper design margin to core temperature rise due to core loss and copper loss. Because the switching currents contain high frequency currents, the skin effect may become a consideration. 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, the following should be considered to increase the total surface area of the wiring: ▫ Increase the number of wires in parallel. ▫ Use litz wire. ▫ Thicken the wire gauge Fluctuation of the VCC pin voltage by IOUT worsens in the following cases, requiring a transformer designer to pay close attention to the placement of the auxiliary winding D: ▪ Poor coupling between the primary-side and secondary-side windings (this causes high surge voltage and is seen in a design with low output voltage and high output current) ▪ Poor coupling between the auxiliary winding D and the secondary-side stabilized output winding where the output line voltage is controlled constant by the output voltage feedback (this is susceptible to surge voltage) In order to reduce the influence of surge voltage on the VCC pin, Figure 9-5 shows winding structural examples which take into consideration the placement of the auxiliary winding D: ▫ Winding structural example (a): Separating the auxiliary winding D from the primary-side windings P1 and P2. P1 and P2 are windings divided the primary-side winding into two. ▫ Winding structural example (b): Placing the auxiliary winding D within the secondary-side stabilized output winding, S1, in order to improve the coupling of those windings. S1 is a stabilized output winding of secondary-side windings, controlled to constant voltage. P1 S1 P2 Margin tape Bobbin Bobbin Margin tape S2 D P1 Margin tape S1 D S2 S1 P2 Margin tape Winding structural example (a) P1、P2 ：Primary main winding D ：Primary auxiliary winding S1 ：Secondary stabilized output winding S2 ：Secondary output winding Winding structural example (b) Figure 9-5 Winding structural examples 9.2 PCB trace layout and Component placement PCB circuit trace design and component layout significantly affects operation, EMI noise, and power dissipation. Therefore, pay extra attention to these designs. In general, trace loops shown in Figure 9-6 where high frequency currents flow should be wide, short, and small to reduce line impedance. In addition, earth ground traces affect radiated EMI noise, and wide, short traces should be taken into account. Switch-mode power supplies consist of current traces with high frequency and high voltage, and thus trace design and component layouts should be done to comply with all safety guidelines. Furthermore, because the power MOSFET has a positive thermal coefficient of RDS(ON), consider it when preparing a thermal design. Copy Right: SANKEN ELECTRIC CO., LTD. Page.17 Figure 9-6 High frequency current loops (hatched areas) STR-V600 APPLICATION NOTE Rev.1.1 Figure 9-7 shows a circuit layout design example for the IC peripheral circuit and secondary-side rectifier-smoothing circuit. IC Peripheral Circuit (1) S/OCP pin 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 the IC and C1 are distant from each other, placing a capacitor such as film or ceramic capacitor (about 0.1 μF and with proper voltage rating) close to the transformer or the IC is recommended to reduce impedance of the high frequency current loop. (2) GND Trace Layout: GND pin to C2 (negative pin) to T1 (winding D) to R2 to D2 to C2 (positive pin) to VCC pin This is the trace for supplying power to the IC, and thus it should be as wide and short as possible. If the IC and C2 are distant from each other, placing a capacitor such as film or ceramic capacitor (about 0.1 μ to 1.0 μF) close to the VCC pin and the GND pin is recommended. (3) 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 IC ground should be at a single point ground (point A in Figure 9-7) which is close to the base of ROCP, in order to reduce common impedance, and to avoid interference from switching currents to the control part in the IC. Secondary-side Rectifier-Smoothing Circuit Trace Layout: T1 (winding S) to D51 to C51 This is the trace of the rectifier-smoothing loop, carrying the switching current, and thus it should be as wide and short as possible. If this trace is thin and long, inductance resulting from the loop may increase surge voltage at turning off the power MOSFET. Proper rectifier-smoothing trace layout helps to increase margin against the power MOSFET breakdown voltage, and reduces stress on the clamp snubber circuit and losses in it. D51 T1 R1 C5 C1 P C51 D1 S D2 R2 8 1 D/ST NC VCC C2 D C4 U1 Main power circuit trace S/OCP BR GND FB/OLP 3 4 5 6 GND trace for the IC C3 PC1 ROCP A C9 Figure 9-7 Peripheral circuit example around the IC Copy Right: SANKEN ELECTRIC CO., LTD. Page.18 STR-V600 APPLICATION NOTE Rev.1.1 IMPORTANT NOTES 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. Unless otherwise agreed in writing by Sanken, Sanken makes no warranties of any kind, whether express or implied, as to the products, including product merchantability, and fitness for a particular purpose and special environment, and the information, including its accuracy, usefulness, and reliability, included in this document. 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. 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. Copy Right: SANKEN ELECTRIC CO., LTD. Page.19