NJW4131 Switching Regulator IC for Boost Converter w/ 40V/1.4A or 40V/1A MOSFET ■ PACKAGE OUTLINE GENERAL DESCRIPTION The NJW4131 is a boost converter with 40V/1.4A or 40V/1A MOSFET. It corresponds to high oscillating frequency, and Low ESR Output Capacitor (MLCC) within wide input range from 4.0V to 35V. Therefore, the NJW4131 can realize downsizing of an application with a few external parts. Also, it has a soft start function, an over current protection and a thermal shutdown circuit. It is suitable for power supply to a Car Accessory, Office Automation equipment, Industrial Instrument, LED and so on. FEATURES Output Switch Voltage Wide Operating Voltage Range Switching Current NJW4131GM1-A (HSOP8) NJW4131R-B (MSOP8 (VSP8)) 40V max. 4V to 35V 1.4A (min.) @ A version 1.0A (min.) @ B version PWM Control Wide Oscillation Frequency 300kHz to 1MHz Soft-Start Function 4ms typ. UVLO (Under Voltage Lockout) Over Current Protection / Thermal Shutdown Protection Standby Function Package Outline NJW4131GM1: HSOP8 NJW4131R: MSOP8(VSP8)* *MEET JEDEC MO-187-DA PRODUCT CLASSFICATION PART NUMBER NJW4131GM1-A NJW4131R-B Ver.2012-08-03 VERSION A B SWITCHING CURRENT LIMIT (MIN.) 1.4A 1.0A PACKAGE HSOP8 MSOP8(VSP8) OPERATING TEMPERATURE RANGE -40°C to +85°C -40°C to +85°C -1- NJW4131 ■ PIN CONFIGURATION 1 8 2 7 3 6 4 5 1 8 2 7 3 6 4 5 PIN FUNCTION 1. SW 2. ON/OFF 3. V+ 4. RT 5. IN6. FB 7. AGND 8. PGND Exposed PAD on backside connect to GND NJW4131GM1-A NJW4131R-B BLOCK DIAGRAM + V Regulator UVLO ON/OFF High: ON Low : OFF (Standby) TSD Standby ON/OFF 400kΩ Low Frequency Control SW PWM FB OSC ER⋅AMP Buffer IN- Vref OCP Soft Start Pulse by Pulse 1.0V RT -2- AGND PGND Ver.2012-08-03 NJW4131 ABSOLUTE MAXIMUM RATINGS PARAMETER SYMBOL Supply Voltage V+ SW pin Voltage VSW IN- pin Voltage VINON/OFF pin Voltage VON/OFF Power Dissipation PD (Ta=25°C) UNIT V V V V MAXIMUM RATINGS +40 +40 -0.3 to +6 +40 HSOP8 790 (*1) 2,500 (*2) mW MSOP8(VSP8) 595 (*1) 805 (*2) -40 to +150 -40 to +85 -40 to +150 °C °C °C (*1): Mounted on glass epoxy board. (76.2×114.3×1.6mm:EIA/JDEC standard size, 2Layers) (*2): Mounted on glass epoxy board. (76.2×114.3×1.6mm:EIA/JDEC standard size, 4Layers), internal foil area: 74.2×74.2mm Junction Temperature Range Operating Temperature Range Storage Temperature Range Tj Topr Tstg RECOMMENDED OPERATING CONDITIONS PARAMETER SYMBOL MIN. Supply Voltage V+ 4.0 Timing Resistance RT 18 Oscillating Frequency fosc 300 Ver.2012-08-03 TYP. – 27 700 MAX. 35 68 1,000 UNIT V kΩ kHz -3- NJW4131 (Unless other noted, V+=VON/OFF=12V, RT=27kΩ, Ta=25°C) ELECTRICAL CHARACTERISTICS PARAMETER SYMBOL Under Voltage Lockout Block ON Threshold Voltage OFF Threshold Voltage Hysteresis Voltage VT_ON VT_OFF VHYS TSS Soft Start Block Soft Start Time Oscillator Block Oscillation Frequency Oscillation Frequency (Low Frequency Control) RT pin Voltage Oscillate Supply Voltage Fluctuations Oscillate Temperature Fluctuations TEST CONDITION MIN. TYP. MAX. UNIT V+= L → H V+= H → L 3.8 3.7 60 3.9 3.8 100 4.0 3.9 – V V mV VB=0.95V 2 4 8 ms 630 700 770 kHz – 270 – kHz 0.240 0.275 0.310 V fOSC fOSC_LOW VIN-=0.4V, VFB=0.65V VRT + fDV V =4V to 35V – 1 – % fDT Ta=-40°C to +85°C – 3 – % VFB=1V, VIN-=0.9V VFB=1V, VIN-=1.1V -1.0% -0.1 – – 8 1 1.00 – 80 0.6 16 2 +1.0% +0.1 – – 24 4 V µA dB MHz µA mA VIN-=0.9V 85 90 95 % A version, ISW=1A B version, ISW=1A A version B version VON/OFF=0V, VSW=40V – – 1.4 1 – 0.2 0.2 1.7 1.35 – 0.4 0.4 2.0 1.7 1 Ω Ω A A µA VON/OFF= L → H VON/OFF= H → L 1.6 0 – – – 400 V+ 0.5 – V V kΩ – – 2.3 – 2.8 1 mA µA Error Amplifier Block Reference Voltage Input Bias Current Open Loop Gain Gain Bandwidth Output Source Current Output Sink Current VB IB AV GB IOM+ IOM- PWM Comparate Block Maximum Duty Cycle MAXDUTY Output Block Output ON Resistance RON Switching Current Limit ILIM Switching Leak Current ILEAK ON/OFF Block ON Control Voltage OFF Control Voltage Pull-down Resistance VON VOFF RPD General Characteristics Quiescent Current Standby Current -4- IDD IDD_STB RL=no load, VIN-=0.9V, VFB=0.65V VON/OFF=0V Ver.2012-08-03 NJW4131 TYPICAL APPLICATIONS L SBD COUT V OUT V IN CFB ON/OFF High: ON Low: OFF (Standby) CIN2 R2 RFB CIN1 4 3 2 1 RT V+ ON/OFF SW NJW4131 RT RNF Ver.2012-08-03 R1 IN- FB AGND PGND 5 6 7 8 CNF -5- NJW4131 CHARACTERISTICS Timing Resistor vs.Oscillation Frequency Maximum Duty Cycle vs. Oscillator Frequency (V+=12V, Ta=25oC) Maximum Duty Cycle M D (%) IN- 95 90 AX UTY OSC 100 10 85 80 100 100 Timing Resistor R T (kΩ) 1000 Oscillator Frequency f OSC (kHz) Oscillation Frequency vs. Supply Voltage Reference Voltage vs. Supply Voltage (R =27kΩ, Ta=25 C) T (Ta=25oC) 1.01 B (V) 710 705 Reference Voltage V Oscillation Frequency f OSC (kHz) o 700 695 690 0 10 20 30 + Supply Voltage V (V) 1.005 1 0.995 0.99 40 0 o + (R =27kΩ, R =no load, V =0.9V, V =0.65V, Ta=25 C) IN- FB 60 Voltage Gain Av (dB) DD (mA) Quiescent Current I 4 3 2 1 0 -6- L 0 10 20 30 + Supply Voltage V (V) 40 Error Amplifier Block Voltage Gain, Phase vs. Frequency Quiescent Current vs. Supply Voltage T 10 20 30 + Supply Voltage V (V) 40 o (V =12V, Gain=40dB, Ta=25 C) 45 Phase 180 135 Gain 30 90 15 45 0 0.1 1 10 100 1000 Frequency f (kHz) Phase Φ (deg) Oscillation Frequency f (V+=12V, V =0.9V, Ta=25oC) 100 (kHz) 1000 0 10000 Ver.2012-08-03 NJW4131 CHARACTERISTICS Oscillator Frequency vs. Temperature Reference Voltage vs. Temperature + (V =12V, R =27kΩ) T 1.01 (V+=12V) 1.005 B 720 Reference Voltage V Oscillator Frequency f OSC (V) (kHz) 740 700 680 1 0.995 0.99 -50 -25 0 25 50 75 100 125 150 Ambient Temperature Ta ( oC) 2.2 V+=12V 2 + V =35V 1.8 1.6 1.4 1.2 + V =4.0V 1 -50 -25 0 25 50 75 100 125 150 Ambient Temperature Ta ( oC) ( Ω) Output ON Resistance vs.Temperature (A ver., I SW =1A) ON 0.5 0.4 0.3 V+=4.0V,12V,40V 0.2 0.1 0 -50 -25 0 25 50 75 100 125 150 o Ambient Temperature Ta ( C) Ver.2012-08-03 Limited switching Current I LIM 2.4 (A) Limited Switching Current vs. Temperature (A ver.) 2.6 Output ON Resistance R Output ON Resistance R ON ( Ω) Limited switching Current I LIM (A) 660 -50 -25 0 25 50 75 100 125 150 Ambient Temperature Ta ( oC) Limited Switching Current vs. Temperature (B ver.) 2.2 2 1.8 V+=12V 1.6 V+=35V 1.4 1.2 1 V+=4.0V 0.8 0.6 -50 -25 0 25 50 75 100 125 150 Ambient Temperature Ta ( oC) 0.5 Output ON Resistance vs.Temperature (B ver., I SW =1A) 0.4 0.3 V+=4.0V,12V,40V 0.2 0.1 0 -50 -25 0 25 50 75 100 125 150 o Ambient Temperature Ta ( C) -7- NJW4131 CHARACTERISTICS 3.95 VT_ON 3.9 3.85 3.8 VT_OFF 3.75 6 5 4 3 2 -50 -25 88 86 84 -50 -25 0 25 50 75 100 125 150 o Ambient Temperature Ta ( C) ( µA) ( µA) DD_STB V+=35V 2 1.5 V+=4.0V V+=12V 1 0.5 0 -50 -25 0 25 50 75 100 125 150 Ambient Temperature Ta ( oC) -8- 75 100 125 150 (V+=12V,V ON/OFF =0V, VSW =40V) 2.5 2 1.5 1 0.5 0 -50 -25 0 25 50 75 100 125 150 Ambient Temperature Ta ( oC) 1 Standby Current I Quiescent Current I DD (mA) Quiescent Current vs. Temperature (R =27kΩ, R =no load, V =0.9V, V =0.65V) L INFB 3T 2.5 3 LEAK 90 50 Switching Leak Current vs. Temperature Switching Leak Current I AX UTY Maximum Duty Cycle (%) M D 92 25 o + 94 0 Ambient Temperature Ta ( C) Maximum Duty Cycle vs. Temperature 96 B 7 3.7 -50 -25 0 25 50 75 100 125 150 Ambient Temperature Ta ( oC) (V =12V, RT=27kΩ. VIN-=0.9V) (V+=12V, V =0.95V) 8 Soft Start Time Tss (ms) Threshold Voltage (V) 4 Soft Start Time vs. Temperature Under Voltage Lockout Voltage vs. Temperature Standby Current vs. Temperature (VON/OFF=0V) 0.8 0.6 0.4 0.2 + V =35V V+=12V V+=4.0V 0 -50 -25 0 25 50 75 100 125 150 o Ambient Temperature Ta ( C) Ver.2012-08-03 NJW4131 ApplicationNJW4131 Manual Technical Information PIN DISCRIPTION PIN NUMBER 1 PIN NAME FUNCTION SW Switch Output pin of Power MOSFET ON/OFF Control pin The ON/OFF pin internally pulls down with 400kΩ. Normal Operation at the time of High Level. Standby Mode at the time of Low Level or OPEN. Power Supply pin for IC Control Oscillating Frequency Setting pin by Timing Resistor. Oscillating Frequency should set between 300kHz and 1MHz. Output Voltage Detecting pin Connects output voltage through the resistor divider tap to this pin in order to voltage of the IN- pin become 1.0V. Feedback Setting pin The feedback resistor and capacitor are connected between the FB pin and the IN- pin. Analog GND pin Power GND pin 2 ON/OFF 3 V+ 4 RT 5 IN- 6 FB 7 8 AGND PGND Exposed PAD – Connect to GND (only HSOP8 PKG) Description of Block Features 1. Basic Functions / Features Error Amplifier Section (ER⋅AMP) 1.0V±1% precise reference voltage is connected to the non-inverted input of this section. To set the output voltage, connects converter's output to inverted input of this section (IN- pin). If requires output voltage, inserts resistor divider. This AMP section has high gain and external feedback pin (FB pin). It is easy to insert a feedback resistor and a capacitor between the FB pin and the IN- pin, making possible to set optimum loop compensation for each type of application. Oscillation Circuit Section (OSC) Oscillation frequency can be set by inserting resistor between the RT pin and GND. Referring to the sample characteristics in "Timing Resistor and Oscillation Frequency", set oscillation between 300kHz and 1MHz. Ver.2012-08-03 -9- NJW4131 NJW4131Application Manual Technical Information Description of Block Features (Continued) PWM Comparator Section (PWM) This section controls the switching duty ratio. PWM comparator receives the signal of the error amplifier and the triangular wave, and controls the duty ratio between 0% and 90% (typ.). The timing chart is shown in Fig.1. Max Duty setting FB pin Voltage OSC Waveform (IC internal) Maximum duty: 90% ON SW pin OFF Fig. 1. Timing Chart PWM Comparator and SW pin Power MOSFET (SW Output Section) The power is stored in the inductor by the switch operation of built-in power MOSFET. The output current is limited to 1.4A(min.) @A version and 1.0A(min.) @B version by the overcurrent protection function. Power Supply, GND pin (V+ and PGND, AGND) In line with switching element drive, current flows into the IC according to frequency. If the power supply impedance provided to the power supply circuit is high, it will not be possible to take advantage of IC performance due to input voltage fluctuation. Therefore insert a bypass capacitor close to the V+ pin – the AGND pin connection in order to lower high frequency impedance. - 10 - Ver.2012-08-03 NJW4131 ApplicationNJW4131 Manual Technical Information Description of Block Features (Continued) 2. Additional and Protection Functions / Features Under Voltage Lockout (UVLO) The UVLO circuit operating is released above V+=3.9V(typ.) and IC operation starts. When power supply voltage is low, IC does not operate because the UVLO circuit operates. There is 100mV width hysteresis voltage at rise and decay of power supply voltage. Hysteresis prevents the malfunction at the time of UVLO operating and releasing. Soft Start Function (Soft Start) The output voltage of the converter gradually rises to a set value by the soft start function. The soft start time is 4ms (typ). It is defined with the time of the error amplifier reference voltage becoming from 0V to 0.95V. The soft start circuit operates after the release UVLO and/or recovery from thermal shutdown. The operating frequency is controlled with a low frequency, approximately 40% of the set value by the timing resistor, until voltage of the IN- pin becomes approximately 0.4V. 1.0V Vref, IN- pin Voltage Max Duty setting FB pin Voltage OSC Waveform ON SW pin OFF UVLO(3.9V typ.) Release, Standby, Recover from Thermal Shutdow n Low Frequency Control V IN-=approx 0.4V Soft Start time: Tss=4ms(typ.) to V B=0.95V Steady Operaton Soft Start effective period to V B=1.0V Fig. 2. Startup Timing Chart Ver.2012-08-03 - 11 - NJW4131 NJW4131Application Manual Technical Information Description of Block Features (Continued) Over Current Protection Circuit (OCP) At when the switching current becomes ILIM or more, the overcurrent protection circuit is stopped the MOSFET output. The switching output holds low level down to next pulse output at OCP operating. The NJW4131 output returns automatically along with release from the over current condition because the OCP is pulse-by-pulse type. Fig.3. shows the timing chart of the over current protection detection. If voltage of the IN- pin becomes less than 0.4V, the oscillation frequency decreases to approximately 40% and the energy consumption is suppressed. Max Duty setting FB pin Voltage OSC Waveform ON SW pin OFF Sw itching Current ILIM 0 Static Status Detect Overcurrent Static Status Fig3. Timing Chart at Over Current Detection If temperature increases, switching current limit (ILIM) decreases due to thermal characteristics (see characteristics "Limited Switching Current vs. Temperature"). You should consider application temperature and set a peak current less than switching current limit. Thermal Shutdown Function (TSD) When Junction temperature of the NJW4131 exceeds the 170°C*, internal thermal shutdown circuit function stops SW function. When junction temperature decreases to 150°C* or less, SW operation returns with soft start operation. The purpose of this function is to prevent malfunctioning of IC at the high junction temperature. Therefore it is not something that urges positive use. You should make sure to operate within the junction temperature range rated (150°C). (* Design value) ON/OFF Function (Standby Control) The NJW4131 stops the operating and becomes standby status when the ON/OFF pin becomes less than 0.5V. The ON/OFF pin internally pulls down with 400kΩ, therefore the NJW4131 becomes standby mode when the ON/OFF pin is OPEN. You should connect this pin to V+ when you do not use ON/OFF function. - 12 - Ver.2012-08-03 NJW4131 ApplicationNJW4131 Manual Technical Information Application Information Inductors Current Peak Current Ipk Large currents flow into inductor, therefore you must provide current capacity that does not saturate. Inductor (1) Continuous Conduction Mode Reducing L, the size of the inductor can be smaller. Current ∆IL However, peak current increases and adversely affecting (2) Critical Mode efficiency. (3) Continuous On the other hand, increasing L, peak current can be 0 Conduction Mode reduced at switching time. Therefore conversion Frequency tON tOFF fOSC efficiency improves, and output ripple voltage reduces. Above a certain level, increasing inductance windings increases loss (copper loss) due to the resistor element. Fig. 4. Inductor Current State Transition Ideally, the value of L is set so that inductance current is in continuous conduction mode. However, as the load current decreases, the current waveform changes from (1) CCM: Continuous Conduction Mode → (2) Critical Mode → (3) DCM: Discontinuous Conduction Mode (Fig. 4.). In discontinuous mode, peak current increases with respect to output current, and conversion efficiency tend to decrease. Depending on the situation, increase L to widen the load current area to maintain continuous mode. Catch Diode When the switch element is in OFF cycle, power stored in the inductor flows via the catch diode to the output capacitor. Therefore during each cycle current flows to the diode in response to load current. Because diode's forward saturation voltage and current accumulation cause power loss, a Schottky Barrier Diode (SBD), which has a low forward saturation voltage, is ideal. An SBD also has a short reverse recovery time. If the reverse recovery time is long, through current flows when the switching transistor transitions from OFF cycle to ON cycle. This current may lower efficiency and affect such factors as noise generation. When the switch element is in ON cycle, a reverse voltage flows to SBD. Therefore you should select a SBD that has reverse voltage rating greater than maximum output voltage. The power loss, which stored in output capacitor, will be increase due to increasing reverse current through SBD at high temperature. Therefore, there is cases preferring reverse current characteristics to forward current characteristic in order to improve efficiency. Input Capacitor Transient current flows into the input section of a switching regulator responsive to frequency. If the power supply impedance provided to the power supply circuit is large, it will not be possible to take advantage of NJW4131 performance due to input voltage fluctuation. Therefore insert an input capacitor as close to the MOSFET as possible. Output Capacitor An output capacitor stores power from the inductor, and stabilizes voltage provided to the output. When selecting an output capacitor, you must consider Equivalent Series Resistance (ESR) characteristics, ripple current, and breakdown voltage. Also, the ambient temperature affects capacitors, decreasing capacitance and increasing ESR (at low temperature), and decreasing lifetime (at high temperature). Concerning capacitor rating, it is advisable to allow sufficient margin. Output capacitor ESR characteristics have a major influence on output ripple noise. A capacitor with low ESR can further reduce ripple voltage. Be sure to note the following points; when ceramic capacitor is used, the capacitance value decreases with DC voltage applied to the capacitor. Ver.2012-08-03 - 13 - NJW4131 NJW4131Application Manual Technical Information Application Information (Continued) Board Layout In the switching regulator application, because the current flow corresponds to the oscillation frequency, the substrate (PCB) layout becomes an important. You should attempt the transition voltage decrease by making a current loop area minimize as much as possible. Therefore, you should make a current flowing line thick and short as much as possible. Fig.5. shows a current loop at Boost converter. L V IN SBD CIN NJW4131 Built-in SW L COUT V IN SBD CIN (a) Boost Converter SW ON COUT NJW4131 Built-in SW (b) Boost Converter SW OFF Fig. 5. Current Loop at Boost Converter Concerning the GND line, it is preferred to separate the power system and the signal system, and use single ground point. The voltage sensing feedback line should be as far away as possible from the inductance. Because this line has high impedance, it is laid out to avoid the influence noise caused by flux leaked from the inductance. Fig. 6. shows example of wiring at boost converter. Fig. 7 shows the PCB layout example. L SBD V OUT SW V IN V CIN COUT + RL PGND (Bypass Capacitor) NJW4131 RFB RT RT CFB INR2 AGND Separate Digital(Signal) GND from Pow er GND R1 To avoid the influence of the voltage drop, the output voltage should be detected near the load. Because IN- pin is high impedance, the voltage detection resistance: R1/R2 is put as much as possible near IC(IN-). Fig. 6. Board Layout at Boost Converter - 14 - Ver.2012-08-03 NJW4131 ApplicationNJW4131 Manual Technical Information Application Information (Continued) ON/OFF L SBD Signal GND Area VIN CIN2 RT VOUT COUT CFB RFB R1 R2 RNF CNF CIN1 GND IN Feed back signal Power GND Area GNDOUT Connect Signal GND line and Power GND line on backside pattern Fig. 7 Layout Example (upper view) Ver.2012-08-03 - 15 - NJW4131 NJW4131Application Manual Technical Information Calculation of Package Power A lot of the power consumption of boost converter occurs from the internal switching element (Power MOSFET). Power consumption of NJW4131 is roughly estimated as follows. Input Power: Output Power: Diode Loss: NJW4131 Power Consumption: Where: VIN VOUT VF OFF duty PIN = VIN × IIN [W] POUT = VOUT × IOUT [W] PDIODE = VF × IL(avg) × OFF duty [W] PLOSS = PIN − POUT − PDIODE [W] : Input Voltage for Converter : Output Voltage of Converter : Diode's Forward Saturation Voltage : Switch OFF Duty IIN IOUT IL(avg) : Input Current for Converter : Output Current of Converter : Inductor Average Current Efficiency (η) is calculated as follows. η = (POUT ÷ PIN) × 100 [%] You should consider temperature derating to the calculated power consumption: PD. You should design power consumption in rated range referring to the power dissipation vs. ambient temperature characteristics (Fig. 8). NJW4131GM1 (HSOP8 Package) Power Dissipation vs. Ambient Temperature NJW4131R (MSOP8(VSP8) Package) Power Dissipation vs. Ambient Temperature o At on 4 layer PC Board At on 2 layer PC Board 800 D (mW) (mW) Power Dissipation P D 2000 1500 1000 500 0 -50 (Tj= ~150 C) 1000 At on 4 layer PC Board At on 2 layer PC Board 2500 Power Dissipation P o (Tj= ~150 C) 3000 -25 0 25 50 75 100 125 Ambient Temperature Ta (oC) 150 600 400 200 0 -50 -25 0 25 50 75 100 125 Ambient Temperature Ta (oC) 150 Mounted on glass epoxy board. (76.2×114.3×1.6mm:EIA/JDEC standard size, 2Layers) Mounted on glass epoxy board. (76.2×114.3×1.6mm:EIA/JDEC standard size, 4Layers), internal Cu area: 74.2×74.2mm Fig.8. Power Dissipation vs. Ambient Temperature Characteristics - 16 - Ver.2012-08-03 NJW4131 ApplicationNJW4131 Manual Technical Information Application Design Examples Step-Up Application Circuit IC : NJW4131GM1-A Input Voltage : VIN=12V Output Voltage : VOUT=24V Output Current : IOUT=0.3A Oscillation frequency : fosc=700kHz L 47µH/1.52A SBD COUT 10µF/50V V OUT =24V V IN=12V ON/OFF High: ON Low: OFF (Standby) CIN1 10µF/50V RT 27kΩ Ver.2012-08-03 Qty. 1 1 1 2 1 1 1 1 1 1 1 1 RFB 27kΩ 4 3 2 1 RT V+ ON/OFF SW R2 300kΩ R1 13kΩ NJW4131 IN- FB AGND PGND 5 6 7 8 RNF 8.2kΩ Reference IC L D CIN1, COUT CIN2 CNF CFB R1 R2 RT RNF RFB CFB 120pF CIN2 0.1µF/50V CNF 6,800pF Part Number NJW4131GM1-A CDRH8D38NP-470N CMS11 UMK325BJ106MM 0.1µF 6,800pF 120pF 13kΩ 300kΩ 27kΩ 8.2kΩ 27kΩ Description Internal 40V MOSFET SW.REG. IC Inductor 47µH, 1.52A Schottky Diode 40V, 2A Ceramic Capacitor 3225 10µF, 50V, X5R Ceramic Capacitor 1608 0.1µF, 50V, B Ceramic Capacitor 1608 6,800pF, 50V, B Ceramic Capacitor 1608 120pF, 50V, CH Resistor 1608 13kΩ, ±1%, 0.1W Resistor 1608 300kΩ, ±1%, 0.1W Resistor 1608 27kΩ, ±1%, 0.1W Resistor 1608 8.2kΩ, ±5%, 0.1W Resistor 1608 27kΩ, ±5%, 0.1W Manufacturer New JRC Sumida Toshiba Taiyo Yuden Std. Std. Std. Std. Std. Std. Std. Std. - 17 - NJW4131 NJW4131Application Manual Technical Information Application Design Examples (Continued) Setting Oscillation Frequency From the Oscillation frequency vs. Timing Resistor Characteristic, RT=27 [kΩ], t=1.43[µs] at fosc=700kHz. Step-Up converter duty ratio is shown with the following equation. ⎛ V Duty = ⎜⎜1 − IN ⎝ VOUT ⎞ ⎛ 12 ⎞ ⎟⎟ × 100 = ⎜1 − ⎟ × 100 = 50 [%] ⎝ 24 ⎠ ⎠ Therefore, tON=0.72 [µs], tOFF=0.71 [µs] Peak Current: Ipk Inductance Current: ∆IL Output Current: IOUT 0 Period: t Frequency: fOSC=1/t tON tOFF Fig. 9. Inductor Current Waveform Selecting Inductance The inductor's average current equals input current (IIN). Estimated efficiency (η) is 90% and calculates input current. IIN = VOUT × IOUT 24 × 0.3 = = 0.67 [A ] η × VIN 0.9 × 12 To assume maximum output current: 0.3A, and the inductor ripple current should be set not to exceed the minimum switching limiting current: ILIM=1.4A (min.). ∆IL is Inductance ripple current. When to ∆IL= input current 30%: ∆IL = 0.3 × IIN = 0.3 × 0.67 = 0.2 [A] This obtains inductance L. L= 12 VIN × 0.72µ = 43.2 ⇒ 47 [µH] × t ON = 0 .2 ∆IL Inductance L is a theoretical value. The optimum value varies according such factors as application specifications and components. Fine-tuning should be done on the actual device. This obtains the peak current Ipk at switching time. Ipk = IIN + ∆I L 0.2 = 0.67 + = 0.77 [ A ] 2 2 The current that flows into the inductance provides sufficient margin for peak current at switching time. In the application circuit, use L=47µH, 1.52A. - 18 - Ver.2012-08-03 NJW4131 ApplicationNJW4131 Manual Technical Information Application Design Examples (Continued) Selecting the Output Capacitor The output capacitor is an important component that determines output ripple noise. Equivalent Series Resistance (ESR), ripple current, and capacitor breakdown voltage are important in determining the output capacitor. The output ripple noise can be expressed by the following formula. ESR = Vripple ( p − p ) ∆I L When selecting output capacitance, select a capacitor that allows for sufficient ripple current. The effective ripple current that flows in a capacitor (Irms) is obtained by the following equation. Irms = IPK − IOUT = 0.77 2 − 0.3 2 = 0.71 [ Arms ] 2 2 Consider sufficient margin, and use a capacitor that fulfills the above spec. In the application circuit, use COUT=10µF/50V. Setting Output Voltage The output voltage VOUT is determined by the relative resistances of R1, R2. The current that flows in R1, R2 must be a value that can ignore the bias current that flows in ER AMP. ⎛ R2 ⎞ ⎛ 300k ⎞ VOUT = ⎜ + 1⎟ × VB = ⎜ + 1⎟ × 1 = 24.07 [ V ] R 1 13 k ⎝ ⎠ ⎝ ⎠ It is easy to make a feedback loop, because the error amplifier output connects to FB pin. DC gain affects voltage sensing of the error amplifier. If AC gain increases, it affects stability of regulator due to AC gain which contains switching noise, ripple noise and the others. Recommended way of feedback, is high DC gain and low AC gain. In this application, a feedback resistor RNF=8.2kΩ and capacitor CNF=6,800pF are connected in serial. However, if the AC gain is lowered too much, it happens slower transient response against fast load changes. The optimum value varies according such factors as application specifications and components. Fine-tuning should be done on the actual device. Ver.2012-08-03 - 19 - NJW4131 NJW4131Application Manual Technical Information ■ Application Characteristics :NJW4131GM1-A Efficiency vs. OutputCurrent (VOUT=24V) 100 f=700kHz L=47µH 90 Efficiency [%] 80 70 60 VIN =9V 50 VIN =12V 40 VIN =18V 30 20 10 0 1 10 100 1000 Output Current IOUT [mA] Load Regulation 25.0 Output Voltage VOUT [V] 24.8 f=700kHz L=47µH 24.6 24.4 24.2 24.0 23.8 23.6 VIN =9V 23.4 VIN =12V 23.2 VIN =18V 23.0 1 10 100 1000 Output Current IOUT [mA] [CAUTION] The specifications on this databook are only given for information , without any guarantee as regards either mistakes or omissions. The application circuits in this databook are described only to show representative usages of the product and not intended for the guarantee or permission of any right including the industrial rights. - 20 - Ver.2012-08-03