NR110K Series Application Note Surface Mount, Chopper Regulator IC NR110K Series Sep. 2015 Rev5.0 SANKEN ELECTRIC CO., LTD. The contents of this application note are subject to change without any notice for further improvements. Sanken Electric Co., Ltd. Sep. 2015 １ NR110K Series --- Contents --1. General Descriptions 1-1 Features ................................................................................................................................... 3 1-2 Applications ............................................................................................................................ 3 1-3 Type ........................................................................................................................................ 4 2. Product Specifications 2-1 Package Information ............................................................................................................... 5 2-2 Electrical Characteristics ................................................................................................... 6 - 7 2-3 Circuit Diagram ...................................................................................................................... 8 3. Terminal Descriptions 3-1 Terminal List ........................................................................................................................... 9 3-2 Terminal Functions ................................................................................................................. 9 4. Operational Descriptions 4-1 PWM Output Control .................................................................................................... 10 - 11 4-2 Overcurrent and Thermal Shutdown Protections .................................................................. 11 5. Design Notes 5-1 External Components ..................................................................................................... 12 - 17 5-2 Pattern Designs .............................................................................................................. 18 - 20 5-3 Power Supply Stabilities ....................................................................................................... 21 6. Application Information 6-1 Soft Start ............................................................................................................................... 22 6-2 Output ON / OFF Control ..................................................................................................... 23 6-3 Spike Noise Reduction .................................................................................................. 23 - 24 6-4 Reverse Bias Protection ........................................................................................................ 25 6-5 Set up Over Current Protection Value ------------------------------------------------------------ 25 7. Technical Terms ...................................................................................................................................... 26 ２ NR110K Series 1. General Descriptions The NR110K series products are Step-Down regulator ICs incorporating a power MOSFET. By applying the current mode control system, ultra low ESR capacitors such as ceramic capacitors can be used. The products have protection functions such as over-current protection, under-voltage lockout and thermal shutdown. The built-in soft-start function, adjustable by an external capacitor, prevents the excessive inrush current to flow at start-up. In addition, the IC incorporates the integrated phase compensation circuit, which simplifies the design and reduces the number of external components. The EN pin allows deactivation of the regulator and helps to achieve low power consumption requirements. The NR110K series is available in a compact and slim HSOP-8-pin package with an exposed thermal pad on the back side. When load current become less than certain value, The NR110K lower frequency to raise up efficiency. ● 1-1 Features Output Current 4.0A Maximum output current: 4.0A. High Efficiency Maximum efficiency: 90 % (VIN = 12V / VO = 5V / IO = 1A) Light load efficiency:70% (VIN=12V/ VO=5V/ IO=30mA) Variable Output Voltage: 0.8 - 24V Low ESR Output Capacitor Ceramic capacitors applicable Operation Frequency NR110K:350kHz Incorporated Over-current and Thermal Shutdown Protections Drooping type over-current protection and thermal shutdown protection circuits (auto-restart type) Programmable over-current value with external resistance Incorporated Phase Compensation Circuit No external phase compensation component Soft Start Function Controlled output voltage rising by an external capacitor during start-up ON / OFF Function Small Size Package (NR110K series) HSOP-8-pin package with an exposed thermal pad ● 1-2 Applications On-board Local Power Supplies OA Equipment Power Supplies Stabilized Secondary Voltage Regulators Telecommunication Power Supplies ３ ● 1-3 Type Type: Semiconductor IC (Monolithic IC) Structure: Plastic Package (Transfer Mould) ４ 2. Product Specifications ● 2-1 Package Information Unit: mm NR110K 2.70 *1. Part number *2. Lot number (three digits) st 1nd letter Last digit of year 2 letter Month (1 to 9 for Jan to Sep, O for Oct, N for Nov, D for Dec) rd 3 letter Week 01~05: Arabic Numerical *3. Control number (four digits) NR110K PIN Assignment 1. BS 2. VIN 3. SW 4. GND 5. FB 6. ISET 7. EN 8. SS ５ ● 2-2 Electrical Characteristics Table 1 Absolute Maximum Rating Parameter Symbol Ratings Unit V V Input Voltage VIN VIN 35 BS Voltage VBS VBS 44 8 BS － SW voltage VBS-SW VBS-SW 12 V SW Voltage VSW VSW 35 V FB Voltage VFB VFB 5.5 V EN Voltage VEN VEN 35 V SS Voltage VSS VSS 5.5 V Pd 1.69 W Junction Temperature Tj 150 °C Storage Temperature Tstg -40 - 150 °C Thermal Resistance (Junction - Case) 2) Thermal Resistance (Junction - Air) 2) θj-c 40 °C/W θj-a 74 °C/W Allowable Power Dissipation 1) 2) 1) Conditions DC Pulse width ≦30ns The incorporated thermal shutdown protection will trigger at Tj > 160°C. Mounted on a glass epoxy PCB of 30.0mm × 30.0mm (copper foil area: 25.0mm × 25.0mm) Table 2 Recommended Operating Conditions Parameter Symbol NR110K Unit DC Input Voltage 3) VIN 8.0 – 31 V Output Current IO 0 - 4.0 A DC output voltage range Vo 0.8 - 24 V Operating Ambient Temperature Top -40 - +85 °C 3) The minimum value of input voltage range shall be either of 8.0V or VO+3V, whichever is higher. When VIN < 9V, it is recommended to place a diode between VIN and BS, or to connect a diode and apply an external voltage to the BS terminal. ６ Table 3 Electrical Characteristics (Ta = 25°C, when Vo = 5V, R1 = 43kΩ, R2 = 8.2kΩ) Parameter Set-up Reference Voltage 4) VREF Output Voltage Temperature Coefficient ∆VREF/∆ T Operation Frequency Line Regulation 5) 7) Load Regulation 7) Ratings Symbol fo Unit MIN TYP MAX 0.784 0.800 0.816 ±0.05 245 350 455 Conditions V VIN = 12V,Io = 1.0A mV/°C VIN = 12V,Io = 1.0A Ta = -40°C - +85°C kHz VIN = 12V, Io = 1A VLine 50 mV VIN = 8.0 - 31V, Io = 1A VLoad 50 mV VIN = 12V, Io = 0.1 - 2.0A IS1 1.5 A VIN = 12V, RIset=OPEN IS2 5.5 A VIN = 12V, RIset=GND IIN 1 mA Over current Protection Start Current Quiescent Current 1 VIN = 12V, Io = 0A, VIN = 12V, Io = 0A, Quiescent Current 2 IIN(off) 1 10 µA VEN = 0V Source Current at Low SS Terminal *9 ISS1 6 10 14 µA VSS = 0V, VIN = 12V 16 50 µA VEN = 10V 1.4 2.1 V VIN = 12V VIN= 12V, Io=1A Level Sink Current EN Terminal ON Threshold Voltage ISET Terminal Open Voltage Maximum On Duty 7) Minimum On Time 7) IEN VC/EH 0.7 Viset 1.5 V DMAX 90 % 150 Nsec 165 °C 20 °C TON(MIN ) Thermal Shutdown Start Temperature 7) TSD Thermal Shutdown Restart Hysteresis 7) TSD_h ys 151 6) The efficiency is calculated using the following equation. VO･IO ------ (1) η(%)= VIN･IIN ×100 7) Design guaranteed value 8) The I/O characteristic graph of the figure below shows the I/O condition limited by the DMIN Be effective only if output current is less than 100mA. ７ ● 2-3 Circuit Diagram 2-3-1 Functional Block Diagram ■NR110K fig.1 2-3-2 Typical Application Circuit ■NR110K C1,C2:10μF/35V R1:100kΩ C4,C5:22μF/16V R3：22Ω R4+ R5:8.4kΩ C7: 0.1μF C3:0.1μF R9:Adjust (In case Vo=5.0V) R6:1.6kΩ L1:10μH D1: SJPW-T4(Sanken) fig.2 ８ 3. Terminal Descriptions ● 3-1 Terminal List Table 4 Terminal List Terminal No. 1 2 3 4 5 6 7 8 Symbol BS VIN SW GND FB ISET EN SS NR110K Name High-side Boost Terminal Input Terminal Switching Output Terminal Ground Terminal Reference Voltage Terminal Over current Protection Control ON / OFF Terminal Soft Start Terminal BS 1 8 SS VIN 2 7 EN SW 3 GND 4 6 ISET 5 FB ● 3-2 Terminal Functions BS (Terminal No.1): The internal power supply for the gate drive of high-side switch Nch-MOSFET The high-side Nch-MOSFET is driven by connecting a capacitor (10uF or higher) between SW terminal and BS terminal. VIN (Terminal No.2): The IC input voltage SW (Terminal No.3): The switching output terminal supplying the output power GND (Terminal No.4): Ground terminal FB (Terminal No.5): Terminal for the output voltage setting. The output voltage is set up with R4,R5 and R6. ISET (Terminal No.6): Over Current value adjust terminal The terminal is adjusted over current value by connecting a resistor between ISET terminal to ground. EN (Terminal No.7): Terminal for turning the IC ON and OFF SS (Terminal No.8): Terminal for enabling the output voltage soft start function by connecting a capacitor ９ 4. Operational Descriptions ● 4-1 PWM Output Control The NR110K series consists of total three blocks; two feedback loop systems (current control and voltage control) and one slope compensation. For the voltage control feedback, the loop makes the output voltage feedback to the PWM control. In NR110K series, the error amplifier compares the output voltage divided by resistors with the reference voltage VREF = 0.8V. For the current control feedback, the loop makes the inductor current feedback to the PWM control. The inductor current that is branched by using sense MOSFET is detected with the current sense amplifier. In terms of current control method characteristics, the slope compensation is made for current control slope, to prevent subharmonic oscillations. For NR110K series, the PWM control is achieved with current control method, by calculating the voltage control feedback, the current control feedback and the slope compensation signals. (Refer to Fig.3) fig.3 Basic Structure of Chopper Type Regulator with PWM Control by Current Control The NR110K series starts the switching operation when UVLO is released, or EN or SS terminal voltage exceeds the threshold. Initially, it operates switching with minimum ON duty or maximum ON duty. The high-side switch (M1) is the switching MOSFET that supplies output power. At first, the low-side switch turns ON and charges the boost capacitor C3 in order to drive M1. When M1 is ON, as the inductor current is increased by applying voltage to SW terminal and the inductor, the output of inductor current sense amplifier is also increased. Sum of the current sense amplifier output and slope compensation signal is compared with the error amplifier output. When the summed signal exceeds the error amplifier (Error Amp.) output voltage, the current comparator output becomes “H” and the RS flip-flop is reset. When M1 turns OFF, the regenerative current flows through D1. In NR110K series, the set signal is generated in each cycle and RS flip-flop is set. If the summed signal does not exceed the error amplifier (Error Amp.) output voltage, RS flip-flop is reset without fail by the １０ signal from OFF duty circuit. ● 4-2 Overcurrent and Thermal Shutdown Protections Output Voltage Vo [V] Overcurrent Protection Characteristics The oscillation frequency decreases as VO decreases. Output Voltage Vo [V] fig.4 Output Voltage Characteristics at Overcurrent The NR110K series incorporates the drooping type over-current protection circuit. The circuit detects the peak current of switching transistor. When the peak current exceeds the rated value, the over-current protection limits the current by forcibly shortening the ON time of transistor and decreasing the output voltage. It prevents the current from increasing at low output voltage by decreasing the switching frequency, if the output voltage drops lower. When the over-current state is released, the output voltage automatically returns. Output voltage Rated Restart Temperature Rated Protection Temperature Junction Temperature fig.5 Output Voltage Characteristics at Thermal Shutdown The thermal shutdown circuit detects the IC junction temperature. When the junction temperature exceeds the rated value (around 160°C), it shuts-down the output transistor and turns the output OFF. If the junction temperature falls below the thermal shutdown rated value by around 20°C, the operation returns automatically. * (Thermal Shutdown Characteristics) Notes The circuit protects the IC against temporary heat generation (e.g. momentary short circuit). It does not guarantee the operation including reliabilities under the continuous heat generation conditions, such as short circuit for a long time. １１ 5. Design Notes ● 5-1 External Components 5-1-1 Choke Coil L1 The choke coil L1 plays a central role of chopper type switching regulators. In order to maintain the stabilized regulator operation, the coil should be carefully selected so it must not enter saturation or over heat excessively at any conditions. The selection points of choke coil are as follows: a) Only switching regulator type coil should be used. It is recommended not to use a coil for noise filer since it causes high heat generation due to high power dissipation. b) The sub-harmonic oscillations should be prevented. Under the peak detection current control, the inductor current may fluctuate at a frequency that is an integer multiple of switching operation frequency. This phenomenon is the known as subharmonic oscillation and this phenomenon theoretically occurs in the peak detection current control mode. Therefore, in order to stabilize the operation, the inductor current compensation is made internally. The proper inductor value corresponding to the output voltage should be selected. Fig.6 ~ 7 shows the selection range of inductance L value to prevent the subharmonic oscillations. As for the upper limit of inductance L, the value is for reference, because it may vary depending on input/output Inductance L [µH] conditions and load current. Inductance L Selection Range Output voltage Vo [V] fig.6 NR110K(f=350kHz) Inductance L Value Selection Range １２ The ripple portion of choke coil current ΔIL and the peak current ILp are calculated from the following equations: IL (Vin Vout ) Vout L Vin f ------ (A) ILp IL Iout 2 ------ (B) According to the equations, the smaller the choke coil inductance L is, the bigger the ΔIL and ILp are. Therefore, if the inductance is too low, the regulator operation may be unstable because the choke coil current fluctuates largely. It is necessary to take care of the choke coil inductance decrease due to the magnetic saturation such as in overload and load shortage. High Inductance Low Inductance fig.7 c) The coil should be of proper rated current. The rated current should be higher than the maximum load current used. If the load current exceeds the rated current of coil, the inductance decreases drastically and eventually enters into the saturation state. In this status, it is necessary to take care because the high-frequency impedance decreases and the excess current runs. d) The magnetic noise should be minimized. The open magnetic circuit type core like a drum type may generate noise in peripheral circuit due to the magnetic flux passing outside of coil. Coils of closed magnetic circuit type core, such as toroidal type, EI type and EE type are preferable. １３ 5-1-2 Input Capacitor CIN The input capacitor CIN operates as a bypass capacitor of input circuit. It supplies the short current pulses to the regulator during switching and compensates the input voltage drop. Therefore, it should be placed as close as possible to the regulator IC. Even if the rectifying capacitor of AC rectifier circuit is in input circuit, the input capacitor CIN cannot be used as a rectifying capacitor unless it is placed near NR110K series. The selection points of CIN are as follows: a) The capacitor should be of proper breakdown voltage rating b) The capacitor should have sufficient allowable ripple current rating IIN VIN 1.VIN Ripple current 0 CINC1 Iv Ton T fig.8 Ip CIN Current Flow D Ton T The ripple current of input capacitor increases according to the load current increase. fig.9 CIN Current Waveform If the input capacitor is working under the conditions of excessive breakdown voltage or allowable ripple current, or without derating, the regulator may become unstable and the capacitor’s lifetime may be greatly reduced. This may result in capacitance decrease, equivalent series impedance increase or even capacitor bursting. Therefore, the selection with sufficient margins is needed. The effective value of ripple current Irms that flows across the input capacitor is calculated from the equation (2): Irms 1.2 Vo Io ------ (2) Vin For instance, where VIN = 20V, IO = 3A, VO = 5V, I r m s 1.2 5 3 0.9 A 20 Therefore, it is necessary to select the capacitor with the allowable ripple current of 0.9A or higher. CIN is C1/C2 on the typical application circuit-diagram. １４ 5-1-3 Output Capacitor COUT In the current control method, the feedback loop which detects the inductor current is added to the voltage control method. The stable operation is achieved by adding inductor current to the feedback loop without considering the effect of secondary delay factor of LC filter. Therefore, it is possible to reduce the capacitance C of LC filter that is needed to make compensations for the secondary delay, and the stable operation is achieved even by using the low ESR capacitor (ceramic capacitor). The output capacitor COUT comprises the LC low-pass filter with choke coil L1 and works as the rectifying capacitor of switching output. The current equal to ripple portion ΔIL of choke coil current charges and discharges the output capacitor. Therefore, in the same way as the input capacitor, the breakdown voltage and the allowable ripple current should be met with sufficient margins. IL Vout COUT C2 Current L1 Ripple current Waveform Io ESR RL ∆IL 0 The ripple current of output capacitor is equal COUT C2 to the ripple current of choke coil, and does not change even if the load current increases or decreases. fig.10 COUT Current Flow The ripple current effective value of output capacitor COUT is calculated from the equation (3): Irms IL 2 3 Irms 0.5 ≒ 014 . A 2 3 ------ (3) When ΔIL = 0.5A, Therefore a capacitor with the allowable ripple current of 0.14A or higher is needed. The output ripple voltage of regulator Vrip is determined by the product of choke current ripple portion ΔIL (= COUT discharge and charge current) and output capacitor COUT equivalent series resistance ESR. Vrip IL CoutESR ------ (4) It is therefore necessary to select a capacitor with low equivalent series resistance ESR in order to lower the output ripple voltage. As for general electrolytic capacitors of same product series, the ESR shall be lower for products of higher capacitance with same breakdown voltage, or of higher breakdown voltage with same capacitance. １５ When ΔIL = 0.5A, Vrip = 40mV, CoutESR 40 0.5 80m A capacitor with ESR of 80mΩ or lower should be selected. Since the ESR varies with temperature and increases at low temperature, it is required to examine the ESR at the actual operating temperatures. It is recommended to contact capacitor manufacturers for the ESR value since it is peculiar to every capacitor series. 5-1-4 Flywheel Diode D1 The flywheel diode D1 is for releasing the energy stored in the choke coil at switching OFF. It is strongly recommended to use a Schottky barrier diode for flywheel diode. If a general rectifying diode or a fast recovery diode is used, the IC may be destroyed by applying reverse voltage due to the recovery and ON voltage. Since the output voltage from the SW terminal (pin 3) of NR110K series is almost equal to the input voltage, it is necessary to use the flywheel diode with the reverse breakdown voltage of equal or higher than the input voltage. It is recommended not to use ferrite beads for flywheel diode. １６ 5-1-5 Output Voltage Vo and Output Capacitor Co Table 5 shows the comparison of output voltage and output capacitor, for maintaining the NR110K stable operations, for reference. Regarding the inductance L, it is recommended to select it according to 5-1-1 Choke Coil L1. (Refer to Fig.6 Inductance L Value Selection Range) Table 6 fo=350kHz Vo and Co Comparison Table CO(µF) Electrolytic Capacitor VO(V) Ceramic Capacitor 1.2 1.8 3.3 5 9 12 16 20 24 22 – 100 (ESR: around 100mΩ) 4.7 - 330 22 – 100 4.7 - 470 10 – 68 4.7 - 330 4.7 - 47 4.7 - 220 4.7 – 47 4.7 – 220 4.7 – 47 4.7 - 220 4.7 - 47 4.7 – 220 4.7 – 47 4.7 - 220 4.7 - 47 4.7 – 220 １７ ● 5-2 Pattern Designs 5-2-1 High Current Line High current runs in certain paths in the circuit and these paths are marked as bold lines in the circuit diagram below. These paths should be as wide and short as possible. fig.11 Circuit Diagram 5-2-2 Input / Output Capacitors The input capacitor C1 and the output capacitor C2 should be placed as close as possible to the IC. If the rectifying capacitor for AC rectifier circuit is in the input side, it can be also used as an input capacitor. However, if it is not close to the IC, the input capacitor needs to be connected in addition to the rectifying capacitor. A similar care should be taken when designing pattern for other capacitors. fig.12 Proper Pattern Example fig. 13 Improper Pattern Example １８ 5-2-3 FB Terminal (Output Voltage Set-up) The FB is the feedback detection terminal that controls the output voltage. It is recommended to connect it as close as possible to the output capacitor COUT. If they are not close, cares should be necessary because the abnormal oscillations may be caused by the poor regulation and the increased switching ripple. The output voltage setting is achieved by connecting R4,R5 and R6. Setting the IFB to around 0.5mA is recommended. (The target of IFB lower limit is 0.5mA, and the upper limit is not defined. However, it is necessary to consider that the circuit current shall increase according to the IFB value.) R4,R5,R2 and the output voltage are calculated from the following equations: IFB=VFB/R6 *VFB=0.8v±2% R4+R5= (Vo-VFB)/IFB R6=VFB/IFB fig.14 Vout=(R4+R5)× (VFB/R6) +VFB ・ R6 needs to be connected for the stable operation when set to Vo = 0.8V. ・ Regarding the relation of input / output voltages, the setting making the SW terminal ON width to be around 200nsec or wider is recommended. ● The PCB circuit traces of FB terminal, R4,R5 and R6 that run parallel to the flywheel diode should be avoided. The switching noise may affect the detection voltage and the abnormal oscillation may be caused. Especially, it is recommended to design the circuit trace short from FB terminal to R6. １９ ● Mounting Board Pattern Example fig.15 Front Side: Component Side (double sided board) fig.16 Back Side: GND Side (double sided board) (Demo-board circuit-diagram) Z1 fig.17 Pattern Circuit Diagram C1, C2: 10μF / 35V C3:0.1μF C4, C5: 22μF / 16V C6:Option C7: 0.1μF C9: Open C10: Mount R9 C11:Option C12:Option R1:510kΩ R2:Option R3:22Ω R4:18kΩ R5:2.7kΩ (Vo=5.0V) R6:3.9kΩ R7:Open R8:Option R9:Adjust R10:Option L1: 10μH D1:SJPW-T4(Sank en) D2:Option Z1：NR110K *R9:Refer to fig24(P25),and adjust R9. ２０ 5-3 Power Supply Stability The phase characteristics of chopper type regulator are the synthesis of the internal phase characteristics of regulator IC, and the combination of output capacitor Cout and load resistance Rout. The internal phase characteristics of regulator IC are generally determined by the delay time of control block and the phase characteristics of output error amplifier. Among these, the phase delay due to the delay time of control block rarely causes problems in actual use. As the phase compensation for output error amplifier is incorporated, refer to 5-1-5 Output Voltage VO and Output Capacitor COUT for the setting of output voltage and output capacitor, in order to ensure stable operation. ２１ 6. Application Information ● 6-1 Soft Start By connecting a capacitor to the terminal 8, the soft start is activated at applying the input voltage. The Vout rises according to the charging voltage of Css. Therefore, the rough estimation is made using the time constant calculation of Css charge. The capacitor Css controls the rise time by controlling the PWM OFF period. The rise time t_ss and the delay time t_delay are roughly calculated from the equations in Fig.18. The terminal 8 shall be open, when the soft start function is not used. FB Vin Vin = 6.0V Iss SS Time SS ×0.9 Css Vss 2 =1 .79 V Reference voltage (0 .8V) Vss 1 (th ) Error Amp . Vss 1= 0.9V Inside IC Time Vo T_delay ⇒ SS Pin Voltage < Vss 1(th ) = Vss 1(0.9 V ) T_ss ⇒ Vss 1(0. 9V ) Time t _ delay ≦ SS Pin Voltage ≦ Vss 2 (1. 79V ) * Example : Css = 0.1 uF tss t_ delay = Css * Vss 1/ Iss = 0.1 uF *0.9v/ 10 uA = 9 ms tss = Css *( Vss 2- Vss 1 )/ Iss/0. 9 = 0.1 uF *(1. 79 v-0.9v)/ 10 uA/ 0.9 ≒ 9.9 ms Timing Chart Discharge Time t_discharge [ns] fig.18 Soft Start Characteristics SS Capacitor Discharge Time SS Open Voltage: 3V 7 SS Discharge Capability: 500µA 6 5 The left graph shows the SS terminal voltage 4 3 changing time from 3V to 0V. 2 1 0 0.01 0.1 SS Capacitor Css [µF] 1 If there is no Css or it is extremely low, the Vout raises with the time constant that charges the output capacitor with output current limited by over-current protection Is. The time constant at output capacitor start-up t = (Co × Vo) / Is ------- (at no load) * The amount of load current is reduced from the Is value at load. ２２ ● 6-2 Output ON and OFF Control The output ON and OFF control is available using the EN (No.2) terminal. The output is turned OFF when the terminal 7 voltage falls below VENL (1.4V) which can be achieved by connecting a bipolar transistor in an open collector configuration and use it as the fig19(A). When the external ON/OFF function isn't used, connect only Pull-up resistor of 100kΩ between IN and EN, and use it as the fig19(B). It starts when a VIN voltage is inputted. 100kΩ 100kΩ (B) (A) fig.19 ON / OFF Control ● 6-3 Spike Noise Reduction 6-3-1 Spike Noise Reduction(1) The addition of the BS serial resistor The “turn-on switching speed” of the internal Power-MOSFETcan be slowed down by inserting RBS (option) of the fig20. It is tendency that Spike noise becomes small by reducing theswitching-speed. Set up 22-ohm as an upper limit when you use RBS. *Attention 1) When the resistance value of RBS is enlarged by mistake toomuch, the internal power-MOSFET becomes an under-drive,it may be damaged worst. 2) The “defective starting-up” is caused when the resistance value of RBS is too big. *The BS serial resistor RBS is R3 in the Demonstration Board. 6-3-2 Spike Noise Reduction(2) The addition of the Snubber circuit In order to reduce the spike noise, it is possible to compensate the output waveform and the recovery time of diode by connecting a capacitor and resistor parallel to the freewheel diode (snubber method). This method however may slightly reduce the efficiency. * For observing the spike noise with an oscilloscope, the probe lead (GND) should be as short as possible and connected to the root of output capacitor. If the probe GND lead is too long, the lead may act like an antenna and the observed spike noise may be much higher and may not show the real values. *The snubber circuit parts are C12 and R10. 1.BS NR11x series fig.20 The addition of the BS serial resistor 3.SW 5.IN NR11x series NR131A 4.GND R10 ≒10Ω C12 ≒1000pF fig.21 The addition of the Snubber circuit ２３ 6.3.3 Attention about the insertion of the bead-core fig.22 In the area surrounded by the red dotted line within the fig22, don't insert the bead-core such as Ferrite-bead. As for the pattern-design of printed-circuit-board, it is recommended that the parasitic-inductance of wiring-pattern is made small for the safety and the stability. When bead-core was inserted, the inductance of the bead-core is added to parasitic-inductance of the wiring-pattern. By this influence, the surge-voltage occurs often, or , GND of IC becomes unstable, and also, negative voltage occurs often. Because of this, faulty operation occurs in the IC. The IC has the possibility of damage in the worst case. About the Noise-reduction, fundamentally, Cope by "6.3.1-The addition of CR snubber circuit" and "6.3.2-The addition of BS serial resistor". ２４ ● 6-4 Reverse Bias Protection A diode for reverse bias protection may be needed between input and output in case the output voltage is expected to be higher than the input terminal voltage (a common case in battery charger applications). 2.VIN 3.SW NR885K NR110K fig.23 Reverse Bias Protection Diode ● 6-5 Set up Over Current Protection Value An OCP activation point can be adjusted by the setup value of RISET. However, because OCP-characteristic has the dispersion, the value of the Ip-detection to start OCP, it becomes the dispersion of between the 過電流開始ピーク電流 [A][A] Protection Value Over Current curve(A) and the curve(B) in the fig24. RISET-ILpeak NR110K Setup Over Current Protection Value 8.00 設定値_MAX 8.00 7.00 7.00 ↑curve(A) 6.00 6.00 設定値_MIN 5.00 5.00 4.00 4.00 ↑curve(B) 3.00 3.00 2.00 2.00 1.00 1.00 0.00 0.00 10 10 100 100 1000 10000 1000 100000 10000 過電流開始電流 設定抵抗Rset [kΩ] ISET terminal Resistance Riset [kΩ] fig.24 Setup Over Current Protection Value The vertical axis of the graph becomes the OCP start peak current. The next expression is an expression to exchanging a peak current (ILpeak) to for an output current (IO). IO=ILpeak－⊿IL×0.5 Only continuous current mode are applied ⊿IL = Vo×(1-Vo/VIN)/(L×fo) ２５ What is described in this document is subject to change without notice due to improvements in the performance, reliability and manufacturability of the product. Therefore, the user is cautioned to verify that the information in this publication is current before placing an order 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. When using the products herein, the applicability and suitability of such products for intended purpose object shall be reviewed at the user’s responsibility. 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.). Whenever Sanken products are intended to be used in the applications where high 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 and obtain written consent of your specifications. 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. ２６