STR 2A153

STR2A100 SANKEN | Alldatasheet

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Datasheet sections

• 7.1 Startup Operation-------------------------------------------------------------------9
• 7.2 Constant Output Voltage Control ---------------------------------------------
• 7.3 Soft-Start Function----------------------------------------------------------------
• 7.4 Automatic Standby Mode Function -------------------------------------------
• 7.5 Random Switching Function----------------------------------------------------
• 7.6 Latch Function---------------------------------------------------------------------
• 7.7 Overcurrent Protection Function (OCP)-------------------------------------
• 7.8 Overvoltage Protection Function (OVP) -------------------------------------
• 7.9 Overload Protection Function (OLP) -----------------------------------------
• 7.10 Thermal Shutdown Protection Function (TSD) ----------------------------

STR2A100 SERIES APPLICATION NOTE Rev. 0.3 Copy Right: SANKEN ELECTRIC CO., LTD. Page.1 STR2A100 Series Application Note (Rev.0.3) SANKEN ELECTRIC CO., LTD. http://www.sanken-ele.co.jp The contents in this application note are preliminary, and are subject to changes without notice.

STR2A100 SERIES APPLICATION NOTE Rev. 0.3 Copy Right: SANKEN ELECTRIC CO., LTD. Page.3 1. General Descriptions The STR2A100 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 power supply systems with few external components. 2. Features and Production lineup Features and benefits include the following

• DIP8 package, connecting one side (pin5 to pin8) with a power MOSFET drain. The distance between high voltage terminal and low voltage terminal is 0.762mm (0.3inches), and the wider drain trace is available to enhance thermal dissipation of the IC.
• Current Mode PWM control
• Built-in Random Switching Function, reducing EMI noise, and simplifying EMI filters, by the slight random change of PWM frequency, f OSC .
• Auto Standby Function (Input Power, P IN < 25mW at no load)
• Built-in Audible Noise Suppression Function for standby mode
• Built-in Startup Circuit, reducing power consumption in standby operation, and eliminating external components.
• Bias Assist Function, improving startup operation, suppressing V CC voltage drop in operation, and allowing use of smaller V CC capacitor. Soft Start Function, reducing stress of a power MOSFET and secondary rectifiers at startup
• Built-in Leading Edge Blanking Function
• Built-in Slope Compensation Function, avoiding subharmonic oscillation.
• Two Chip Structure, with a controller and a power MOSFET guaranteed Avalanche Energy which is available to simplify surge absorber circuits
• Protection Functions minimize OCP point variation for AC input voltage perature rise Product Lineup Part Number fOSC (kHz) MOSFET V DSS MIN (V) R DS(ON) ※2 MAX POUT ※1 ※2 230VAC / 85VAC to 265VAC Status STR2A152 3.0 Ω 30W / 23W Planning STR2A153 1.9 Ω 36W / 30W Sample available STR2A155 67 650 1.1Ω 43W / 35W Planning ※1 The open frame conditions. The listed output power is based on the thermal ratings, and the peak output power is obtained by 120 to 140% of the value stated here. In low output voltage and narrow ON-duty cycle, the output power may be less than the value stated here. ※2 The preliminary values on IC development

STR2A100 SERIES APPLICATION NOTE Rev. 0.3 Copy Right: SANKEN ELECTRIC CO., LTD. Page.4 3. Functional Block Diagram and Terminal List Functional Block Diagram Terminal List Table Number Name Functions

1 S/OCP MOSFET source / Overcurrent protection cont rol pulse input

2 V CC Power supply input for control circuit

3 GND Ground

4 FB/OLP Constant voltage control signal input / Overload protection signal input

D/ST MOSFET drain / Startup current input D/ST S/OCP GND S Q R 5~8 2 PWM OSC REG Slop Compensation Feedback Control OCP Drain Peak current Compensation VCC LEB OLP OVP TSD STRATUP UVLO DRV VREG FB/OLP V CC

STR2A100 SERIES APPLICATION NOTE Rev. 0.3 Copy Right: SANKEN ELECTRIC CO., LTD. Page.5 4. Package Information

• DIP8 package a. Type Number : 2AXXX b. Lot Number 1st letter : The last digit of year 2nd letter : Month 1 to 9 for Jan. to Sept. O for Oct. N for Nov. D for Dec. 3rd letter : Week st ～10 th : 1 11 th ～20 th : 2 21 st ～31 st : 3 c. Sanken Registration Number Material of terminal: Cu Treatment of terminal: solder plating Weight: Approx. 0.51g Unit: mm SK a b c

STR2A100 SERIES APPLICATION NOTE Rev. 0.3 Copy Right: SANKEN ELECTRIC CO., LTD. Page.6 5. Electrical Characteristics

• The STR2A153 of STR2A100 series is used as an example.
• Certain details vary among the individual products.
• The preliminary values at IC development

5.1 Absolute Maximum Ratings

Ta= 25°C, unless otherwise specified Parameter Terminal Symbol Ratings Unit Notes Drain peak current ※1 8−1 I DPEAK 4.4 A Single Pulse EAS 72 mJ Avalanche energy ※1 8−1 ILPEAK 2.46 A Single Pulse V DD =99V, L=20mH S/OCP terminal voltage 1−3 V OCP −2～6 V ― Controller IC (MIC) input voltage 2−3 V CC 32 V ― FB/OLP terminal voltage 4−3 V FB −0.3 ～14 V ― FB/OLP terminal sink current 4−3 I FB 1.0 mA ― MOSFET power dissipation ※2 8−1 P D1 1.76 W ― Controller IC (MIC) power dissipation 2−3 P D2 1.3 W ― Operating ambient temperature ― TOP −20 ～+115 °C Recommended internal frame temperature TF= 115℃(Max) Storage temperature ― Tstg −40 ～+125 °C ― Channel temperature ― Tch +150 °C ― ※1 Refer to individual product datasheet for details because these values differ among the various product types. ※2 The condition mounted on 15mm ×15mm printed circuit board. ※ Current characteristics are defined based on IC as Sink:+, Source: －.

5.2 MOSFET Electrical Characteristics Ta= 25°C, unless otherwise specified

Ratings Parameter Terminal Symbol M I N T Y P M A X Unit Drain-to-Source breakdown voltage ※1 8−1 V DSS 650 ― ― V Drain leakage current 8−1 I DSS ― ― 300 µA On-resistance ※1 8−1 R DS(ON) ― ― 1.9 Ω Switching time 8−1 t f ― ― 250 ns θch−F ― ― 20 Thermal resistance ※3 ― θch−C ― ― 30 °C/W ※3 θch−F is the thermal resistance between channel and internal frame. θch−C is the thermal resistance between channel and case. Case temperature (T C ) is measured at the center of the marking side.

STR2A100 SERIES APPLICATION NOTE Rev. 0.3 Copy Right: SANKEN ELECTRIC CO., LTD. Page.7

5.3 Electrical Characteristics Ta= 25°C, VCC = 18 V, unless otherwise specified

Ratings Parameter Terminal Symbol M I N T Y P M A X Unit Operation start voltage 2－3 V CC(ON) 13.8 15.3 16.8 V Operation stop voltage ※4 2－3 V CC(OFF) 7.3 8.1 8.9 V Circuit current in operation 2－3 ICC(ON) ― ― 2.5 mA Minimum startup voltage 8－3 V ST(ON) ― 40 ― V Startup current 8－3 Istartup −3.9 −2.5 −1.1 mA Startup current supply threshold ※4 2－3 V CC(BIAS) 8.5 9.5 10.5 V Average switching frequency 8－3 fOSC(AVE) 60 67 74 kHz Frequency modulation deviation 8－3 △f ― 5 ― kHz Maximum on-duty cycle 8－3 D MAX 65 74 83 % Leading edge blanking time ― tBW ― 350 ― ns OCP compensation coefficient ― D PC ― 17 ― mV/ µs OCP compensation duty cycle limit ― D DPC ― 36 ― % OCP threshold voltage at zero duty cycle 1－3 V OCP(L) 0.69 0.78 0.87 V OCP threshold voltage at 36% duty cycle 1－3 V OCP(H) 0.79 0.88 0.97 V Maximum feedback current 4－3 IFB(MAX) −280 −170 −90 µA Minimum feedback current 4－3 IFB(MIN) −30 −15 −7 µA Oscillation stop FB/OLP voltage 4－3 V FB(OFF) 1.05 1.15 1.25 V OLP threshold voltage 4－3 V FB(OLP) 7.3 8.1 8.9 V Operation current after OLP 2－3 ICC(OLP) ― 230 ― µA OLP delay time ― tOLP 54 68 82 ms FB/OLP terminal clamp voltage 4－3 V FB(CLAMP) 11 12.8 14 V OVP threshold voltage 2－3 V CC(OVP) 26 29 32 V Thermal shutdown operating temperature ― T ｊ(TSD) 135 ― ― ℃ ※4 The relationship between V CC(BIAS) and V CC(OFF) consists of V CC(OFF) < V CC(BIAS) . ※ Current characteristics are defined based on IC as Sink:+, Source: －.

STR2A100 SERIES APPLICATION NOTE Rev. 0.3 Copy Right: SANKEN ELECTRIC CO., LTD. Page.8 6. Typical Application Circuit A typical application circuit is shown below. The following design features should be considered:

• D/ST terminals (pin 5 to pin8) are on one side of the IC. The PCB traces from them should be as wide as possible, in order to enhance thermal dissipation.
• In applications having a power supply specified such that V DS voltage between D/T terminal and S/OCP terminal has large transient surge voltages, a clamp snubber circuit of a capacitor-resistor-diode (CRD) combination should be added between both sides of a winding P, or a damper snubber circuit of a capacitor (C) or a resistor-capacitor (C, RC) combination should be added between D/ST terminal and S/OCP terminal. Figure 6 Typical application circuit example CRD clamp snubber Damper snubber VV VVAA AACC CC PC1 VV VVOO OOUU UUTT TT GG GGNN NNDD DD P S D PC1 R C3OCP R4R1C8 578 6 21 3 4 Vcc FB/OLP D/ST D/ST D/ST D/ST GNDS/OCP STR2A100

STR2A100 SERIES APPLICATION NOTE Rev. 0.3 Copy Right: SANKEN ELECTRIC CO., LTD. Page.9 Figure 7-1 V CC peripheral circuit D P R2D/ST Vcc GND VAC 5～8 STR2A100 7. Functional Descriptions The parameter values in this section are based on the STR2A153 specification, unless otherwise specified. The polarity of current is shown as “+”for sink current and “−” for source current based on IC

7.1 Startup Operation

The startup circuit is connected to D/ST terminal. During the startup process, the constant current, I STARTUP = −2.5mA(TYP), charges C2 at VCC terminal in figure 7-1, and when VCC terminal voltage increases to VCC(ON) = 15.3V(TYP), the control circuit starts switching operation. After switching operation begins, the startup circuit turns off automatically, to zero its current consumption. The approximate startup time, t START , is calculated as follows STARTUP )INT (CC )ON (CC START I where t START is in sec, and V CC(INT) is the initial voltage on VCC terminal, in V. C2 value is 10 to 47 µF for general power supply applications. Figure 7-2 shows the relationship of V CC and I CC . When V CC terminal voltage increases to VCC(ON) = 15.3V(TYP), the control circuit starts switching operation and the circuit current, I CC , increases. In operation, when VCC terminal voltage decreases to V CC(OFF) = 8.1V(TYP), the control circuit stops operation by UVLO (Undervoltage Lockout) circuit, and reverts to the state before startup. The voltage from the auxiliary winding D in figure 7-1 becomes a power source to the control circuit in operation. The auxiliary winding voltage needs to be adjusted to about 15 to 20 V, taking account of the winding turns of the winding D so that V CC terminal voltage should become as follows within the specification of input voltage range and the output load range of power supply. )MIN (V0 .26 VV)MAX (V5 .10 V )ON (CC CC )BIAS (CC =<<= Figure 7-3 shows V CC terminal voltage behavior during the startup period. After V CC terminal voltage increases to V CC(ON) at startup, the auxiliary winding voltage on the winding D does not rise to the target operating voltage immediately (which is set by the transformer ratio between the auxiliary winding and the secondary winding), and may fall down. When V CC terminal voltage decreases to V CC(BIAS) = 9.5V(TYP), Bias Assist Function is activated so that the decrease of V CC terminal voltage is suppressed by I STARTUP provided from the startup circuit. In addition, Bias Assist Function allows C2 value to be reduced and allows the startup time to be shorter, and this function allows the response of overvoltage detection in V CC terminal to be faster. Figure 7-3 V CC behavior during startup Bias Assist period V CC(ON) 15.3V(TYP) 9.5V(TYP) V CC(BIAS) 8.1V(TYP) V CC(OFF) VAC ON Start of normal operation Target operating voltage Time Startup failure event Figure 7-2 Relationship of V CC and I CC at startup and shutdown Circuit current IC C V CC(OFF) 8.1V(TYP ） V CC(ON) 15.3V(TYP) Startup Stop 2.5mA(MAX)

STR2A100 SERIES APPLICATION NOTE Rev. 0.3 Copy Right: SANKEN ELECTRIC CO., LTD. Page.11 Figure 7-10 Drain current waveform in subharmonic oscillation Target voltage without slope compensation ID tON1 tON2 Cycle Cycle Cycle FB comparator V SC V R1 Target voltage added slope compensation signal S/OCP terminal voltage (Both sides voltage of R OCP ) Drain current ID Figure 7-9 Drain current, I D , and FB comparator in steady operation

7.2 Constant Output Voltage Control

The constant output voltage control of the power supply uses the current-mode control method (the peak current-mode), which enhances response speed and provides stable operation. When load conditions become smaller, the output voltage, V OUT , rises, and a feedback current from an error amplifier on the secondary side also rises. This current corresponded to the feedback current is sunk by a photo-coupler at FB/OLP terminal as shown in figure 7-8, and thus FB/OLP terminal voltage decreases. This voltage is fed to Feedback Control block in “3. Functional Block Diagram and Terminal List” section, and is added the slope compensation signal to create the target voltage, V SC , in figure 7-9. V SC is fed to the negative input of FB comparator. The peak detection signal, V R1 , converted from Drain current, I D , with R OCP is fed to the positive input of FB comparator. The control circuit performs to decrease the peak current of I D so that V R1 comes close to V SC . And this control prevents the output voltage from in- creasing. When load conditions become bigger, the control circuit per- forms reverse operations to the former, and increases the peak current of I D so that V R1 comes close to V SC . And this control prevents the output voltage from decreasing. Generally, in the current-mode control method, some sub- harmonic oscillations shown in figure 7-10 occur theoretically. It is called the subharmonic phenomenon. When the drain current waveform becomes a trapezoid in con- tinuous operating mode, the ON-duty cycle can not become stable in each cycle, and thus subharmonic oscillations occur in multiples of the fundamental operating frequency, according to the initial value of drain current, even if the peak current level set by the target voltage is constant. In order to avoid this, the IC incorporates Slope Compensation Function. Because the target voltage, V SC , in figure 7-9 is added the down-slope compensation signal, the wider the ON-duty cycle becomes, the smaller the peak drain current becomes to suppress subharmonic oscillations.. 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, FB comparator and/or OCP comparator may respond to the surge voltage resulting from the drain surge current in turning on a power MOSFET, and may turn off the power MOSFET irregularly. Leading Edge Blanking, t BW = 350ns(TYP), is built-in to prevent OCP comparator from malfunction caused by surge voltage in turning on the power MOSFET. Figure 7-8 FB/OLP peripheral circuit ROCP IFB VR1 FB/OLPGND 1 3 4 S/OCP PC1 STR2A100

STR2A100 SERIES APPLICATION NOTE Rev. 0.3 Copy Right: SANKEN ELECTRIC CO., LTD. Page.12

7.3 Soft-Start Function

Figure 7-11 shows the operation image waveform at startup. Soft-Start Function is built-in to reduce stress of voltage and current of a power MOSFET, secondary rectifiers and so on. The period of Soft-Start Function is fixed to 7ms internally. In this period, OCP threshold voltages increase with five steps. It is necessary to check or adjust the followings at startup;

• V CC terminal voltage should be more than V CC(OFF) ,
• The period when FB/OLP terminal voltage increases to OLP threshold voltage, VFB(OLP) = 8.1V(TYP), should be shorter enough than OLP delay time, tOLP =68ms(TYP).

7.4 Automatic Standby Mode Function

Automatic Standby Mode is activated automatically when the drain current, I D , reduces in light load condition and S/OCP terminal voltage decreases to less than 15% to 20% of the voltage of the maximum drain current (it is overcurrent protection state). And this operation becomes the burst-oscillation as shown in figure 7-12. The burst-oscillation reduces switching losses and improves power supply efficiency because there are interval periods. Generally the frequency of the burst-oscillation is set at just a few kHz, such frequencies are in the range of human hearing, to improve the efficiency in light load condition, and thus it may cause audible noises from a transformer. Because the IC series limit the drain current to less than 15% to 20% during the burst-oscillation, audible noises are well-suppressed. Figure 7-12 Automatic standby mode operation Burst -oscillation Limit of less than 15% to 20 % of the maximum drain current Normal load Standby load Normal load Output current I O UT Drain current ID Figure 7-11 Operation image waveform at startup Time V CC terminal voltage Drain current ID V CC (ON) Time V CC (OFF) Soft-start period with 7ms fixed internally This I D is limited by OCP operation. Steady state Startup

STR2A100 SERIES APPLICATION NOTE Rev. 0.3 Copy Right: SANKEN ELECTRIC CO., LTD. Page.13 Figure 7-13 Output current at OCP without input compensation Variation resulting from detection delay time Low AC input High AC input Output voltage, V OUT Output current, IOUT During the transition to the burst-oscillation, if V CC terminal voltage decreases to V CC(BIAS )= 9.5V(TYP), Bias Assist Function is activated and stabilizes the standby mode operation, because I STARTUP is provided to V CC terminal so that V CC terminal voltage does not decrease to V CC(OFF) . However, if Bias Assist Function is always activated during standby mode, the power loss increases. Therefore V CC terminal voltage should be more than V CC(BIAS) , for example, by adjusting the turns ratio between auxiliary winding and secondary winding and/or R2 in figure 7-5.

7.5 Random Switching Function

The IC modulates its switching frequency randomly within △f= 5kHz of Average Switching Frequency, fOSC(AVE ）= 67kHz(TYP), by superposing the modulating frequency on fOSC(AVE) in normal operation. The conduction noise with this function is smaller than that without this function, and this function simplifies noise filtering of the input lines of power supply.

7.6 Latch Function

The latch function stops switching operation and a protection state is latched when OVP and/or TSD protection functions activate. After stopping switching operation with latch mode, V CC terminal voltage drops. When VCC terminal voltage decreases to V CC(BIAS) = 9.5V(TYP), Bias Assist Function is activated to prevent VCC terminal voltage from reaching V CC(OFF) , and then the latch function is maintained. Releasing the latch function can be done when VCC terminal voltage reaches VCC(OFF) or less by simply turning off the AC input.

7.7 Overcurrent Protection Function (OCP)

Overcurrent Protection Function (OCP) detects each drain peak current level of a power MOSFET on pulse-by-pulse basis, and limits the output power. This function incorporates AC Input Compensation Function to reduce OCP point variation for AC input voltage, without any additional external components. This OCP function detects the drain current by a current detection resistor, R OCP , which is connected between S/OCP terminal and GND terminal. When the voltage drop on both sides of R OCP increases to internal OCP threshold voltage, the power MOSFET is turned off. PWM control ICs usually have some detection delay time on OCP detection. The steeper the slope of actual drain current in high AC input voltage is, the longer the actual detection point is, compared with internal OCP threshold voltage. And thus the actual OCP point limited the output current usually has some variation depending on AC input voltage as shown in figure 7-13. The IC incorporates a built-in Input Compensation Function that superposes a signal with a defined slope to the detection signal on S/OCP terminal as shown in figure 7-14. When AC input voltage is lower and the ON-duty cycle is wider, the OCP compensation level increases. And 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.

STR2A100 SERIES APPLICATION NOTE Rev. 0.3 Copy Right: SANKEN ELECTRIC CO., LTD. Page.14 Because the compensation signal level is designed to depend upon ON Time, OCP threshold voltage after compensation, VOCP(ONTime) , is calculated as follows. where DPC is OCP compensation coefficient shown in Electrical Characteristics table. However, in the ON Time when ON-duty cycle becomes 36% or more, OCP threshold voltage after com- pensation remains VOCP(H) = 0.88V(TYP) constantly. For example, when AC input voltage is 85VAC and the transformer is designed to become ON-duty cycle of 36% on maximum load condition, ON Time becomes about 5.6 µs. And thus OCP threshold after compensation, V OCP(5.6 µs) , becomes about 0.88V, resulting from the equation (2).

7.8 Overvoltage Protection Function (OVP)

When a voltage between V CC terminal and GND terminal increases to VCC(OVP) = 29V(TYP) or more, OVP Function is activated and stops switching operation by Latch Function. When the auxiliary winding provides V CC terminal voltage, OVP Function is available to detect the overvoltage of the output voltage, such as the detection circuit for output control is open in the secondary side, because V CC terminal voltage is proportional to the output voltage. The output voltage of the secondary side at OVP operation, VOUT(OVP) , is calculated approximately as follows. )TYP (29 V VV CC OUT OUT(OVP) Ｖ≒ ×operation normal at voltage terminal operation normal at voltage terminal ----- (3) 265VAC(for example) ON -duty cycle V OCP(ONTime) (V) After compensation 0.50 About 0.82V 0.88V(TYP) 85VAC(for example) Figure 7-14 Relationship of ON-duty cycle and V OCP(ONTime) at fOSC(AVE) = 67kHz(TYP)

STR2A100 SERIES APPLICATION NOTE Rev. 0.3 Copy Right: SANKEN ELECTRIC CO., LTD. Page.15 Figure 7-15 Each waveform on OLP operation and FB/OLP peripheral circuit IFB VCC GND FB/OLP 3 4 PC1 STR2A100 V CC(OFF) = 8.1V(TYP) V FB(OLP) = 8.1V(TYP) FB/OLP terminal voltage V FB Drain current ID V CC terminal voltage Oscillation turns off Oscillation interval period

7.9 Overload Protection Function (OLP)

When the drain peak current is limited by OCP operation, the output voltage, V OUT , decreases and the feedback current from the secondary photo-coupler becomes zero. As a result, FB/OLP terminal voltage increases. When FB/OLP terminal voltage increases to VFB(OLP) = 8.1V(TYP) or more and remains for OLP delay time, tOLP = 68ms or more, OLP function is activated, stops switching operation and reduce stress of a power MOSFET, secondary rectifiers and so on. Each waveform on OLP Function is shown in figure 7-15. When OLP Function is activated, Bias Assist Function is disabled and thus V CC terminal voltage decreases to V CC(OFF) = 8.1V(TYP). After that, the IC reverts to the initial state by UVLO (Undervoltage Lockout) circuit, and the IC starts operation when V CC terminal voltage increases to V CC(ON) = 15.3V(TYP). And thus the intermittent operation by UVLO is repeated. This operation reduces power dissipation because the switching period in this intermittent operation is short. When such an abnormal condition is removed, the IC returns to normal operation automatically.

7.10 Thermal Shutdown Protection Function (TSD)

When the temperature of the control part (MIC) of the IC increases to Tj(TSD) = 135°C(MIN) or more, Thermal Shutdown Protection Function is activated and stops switching operation by Latch Function. tOLP OLP delay time

STR2A100 SERIES APPLICATION NOTE Rev. 0.3 Copy Right: SANKEN ELECTRIC CO., LTD. Page.16 8. Design Notes

8.1 Peripheral Components

Take care to use properly rating and proper type of components.

• • •• Input and output electrolytic capacitors Apply proper design margin to ripple current, voltage and temperature rise. Use of high ripple current and low impedance types, designed for switch mode power supplies, is recommended.
• • •• Transformer Apply proper design margin to temperature rise by core loss and copper loss. Because switching currents contain high frequency currents, the some temperature rise may result from the skin-effect. If the influence of skin-effect can not be minimized, choose suitable wire gauge in consideration of RMS current in the current density of about 3 to 4A/mm 2. If measures to further reduce temperature is still necessary, use paralleled wires or litz wires to increase surface area of wires.
• • •• Current detection resistor, ROCP A high frequency switching current flows to R OCP , and may cause poor operation if a high inductance resistor is used. Choose a low inductance and surge-proof type.

8.2 Phase Compensation

A typical error amplifier circuit with a shunt regulator (Z2) of secondary side is shown in figure 8-1. C7 is recommended about 0.047 to 0.47 µF, and should be adjusted on actual operation. C3 between FB/OLP terminal and GND terminal shown in figure 8-2 is for high frequency noise reduction and phase compensation. C3 is recommended about 470pF to 0.01 µF. C3 should be connected close to FB/OLP terminal and GND terminal, and should be adjusted on actual operation. Figure 8-2 FB/OLP peripheral circuit Figure 8-1 Peripheral circuit around secondary shunt regulator S PC1 GND VOUT D2 R4 C5 R5 C7 R8 D1 R2 D ROCP 1 3 4 D/ST VCC S/OCP GND FB/OLP 25～8 PC1 STR2A100

STR2A100 SERIES APPLICATION NOTE Rev. 0.3 Copy Right: SANKEN ELECTRIC CO., LTD. Page.17

8.3 EMI Measure of the secondary rectifier

A general EMI measure of the secondary rectifier is shown in figure 8-3. A snubber capacitor, Cdi , in parallel to the secondary rectifier, is for noise reduction. If ringing waveforms occur on the drain current, it is recommended to connect a damper resistor, R di , in series to C di as shown in figure 8-4, in order to reduce ringing waveforms, and to stabilize switching operation. It is necessary to check temperature rise of R di and C di .

8.4 PCB trace layout and Component placement

PCB circuit trace design and component layout affect proper functioning during operation. Unless they are proper, mal- function, large noise and large power dissipation may occur. Circuit loop traces flowing high frequency current, as shown in figure 8-5, should be designed as wide, short and small as possible to reduce trace impedance. In addition, earth ground traces affect radiation noise, and thus it should be designed as wide and short as possible. Switching mode power supplies consist of current traces with high frequency and high voltage, and thus trace design and component layout should be done to comply with all safety guidelines. Furthermore, because an integrated power MOSFET is being used as the switching device, take account of the positive thermal coefficient of R DS(ON) for thermal design. Figure 8-6 shows a circuit layout design example. (1) S/OCP Trace Layout: S/OCP terminal to R OCP to C1 to T1 (winding P) to D/ST terminal This is the main trace containing switching currents, and thus it should be as wide and short as possible. If the trace distance between C1 and the IC is lengthy, an additional capacitor near the IC or the transformer is recommended to reduce impedance of high frequency current loop, and is recommended either electrolytic or film type capacitors, around 0.1 µF, in the withstand voltage suitable for an applied maximum voltage. (2) GND Trace Layout: GND terminal to C2 (negative terminal) and T1 (winding D) to R2 to D1 to C2 (positive terminal) to V CC terminal This trace also needs to be as wide and short as possible. If the trace distance between C2 and the IC is lengthy, placing a capacitor around 0.1 µF to 1uF (50V) with high frequency property is recommended close to VCC terminal and GND terminal. Figure 8-5 High frequency current loops (hatched areas) D P Rdi Cdi S D2 C5 D SP Cdi D2 C5 Figure 8-3 Rectifier measure example Figure 8-4 Damper resistor example Drain current I D Drain current I D