ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter ■General description ELM613DA is 550KHz fixed frequency PWM synchronous step-down regulator. ELM613DA is operated from 4.75V to 20V, the generated output is adjustable from 0.923V to 18V, and the output current can be up to 2A. The integrated two MOSFET switches is with turn on resistance of 0.085Ω. Current mode control provides fast transient response and cycle-by-cycle over current protection. The shutdown current is 1μA typical. Adjustable soft start prevents inrush current at turn on. ELM613DA is with thermal shutdown. ■Features ■Application • • • • • • • • • • • • • • • • Programmable soft start Short circuit protection Thermal shutdown protection Input voltage : 4.75V to 20V Output voltage : 0.923V to 18V Output current : 2A High efficiency : Max.93% Power MOSFET switches : 85mΩ Shutdown current : Typ.1µA Fixed frequency : Typ.550kHz Package : SOP-8 Distributed power system Network system FPGA, DSP, ASIC power supply Notebook computer Green electronics and appliance ■Maximum absolute ratings Parameter VIN power supply voltage Apply voltage to SW Apply voltage to BS Apply voltage to FB Apply voltage to COMP Apply voltage to EN Apply voltage to SS Power dissipation Operating temperature range Storage temperature range Symbol Vin Vsw Vbs Vfb Vcomp Ven Vss Pd Top Tstg Limit -0.3 to +21 -0.3 to Vin+0.3 Vsw-0.3 to Vsw+6 -0.3 to +6 -0.3 to +6 -0.3 to +6 -0.3 to +6 630 -40 to +85 -65 to +150 Caution:Permanent damage to the device may occur when ratings above maximum absolute ones are used. Unit V V V V V V V mW °C °C ■Selection guide ELM613DA-N Symbol a b c Package Product version Taping direction D: SOP-8 A N: Refer to PKG file ELM613DA - N ↑↑ ↑ ab c * Taping direction is one way. 11 - 1 Rev.1.3 ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter ■Pin configuration SOP-8(TOP VIEW) 1 8 2 7 3 6 4 5 Pin No. 1 2 3 4 5 6 7 8 Pin name BS VIN SW GND FB COMP EN SS Pin description High-side gate drive boost input Power input Power switching output Ground Feedback input Compensation node Enable input Soft start control input ■Standard circuit Input R4=100k Cin= 10µF/25V Ceramic 7 8 2 1 VIN EN BS ELM613DA SW FB COMP SS GND 4 C2= 0.1µF C3=10nF Output= 3.3V/2A R1=12.1kΩ 5 1% 6 C1=3.3nF C4 Option L=10µH 3 Cout= 22µF/6.3V Ceramic×2 R2=4.7kΩ 1% R3=15kΩ Note: EN pin is clamped to 5.6V. If EN pin needs to be pulled-up, EN input current has to be lower than 200μA with R4 (about 100kΩ). ■Block diagram 1.1V FB 5 0.3V SS OVP + - Oscillator 170kHz & 550kHz + - 8 0.923V + + Error amplifier Current sense amplifier + RAMP CLK + Current comparator BS R Q 3 SW 4 GND M2 85mΩ EN 6 1.2V EN 1 M1 85mΩ OVP COMP VIN - S Q 6µA 2 5V 7 1.5V + IN<4.10V IN Internal regulators Shutdown comparator 11 - 2 5V Rev.1.3 ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter ■Electrical characteristics Parameter Supply voltage Output voltage Output current Shutdown current Supply current Feedback voltage Feedback over-voltage threshold Error amplifier voltage gain Error amplifier transconductance High-side switch-on resistance Low-side switch-on resistance High-side switch leakage current Upper switch current limit Lower switch current limit COMP to current sense transconductance Oscillation frequency Short circuit oscillation frequency Maximum duty cycle Minimum on time EN shutdown threshold voltage EN shutdown threshold voltage hysteresis EN lockout threshold voltage EN lockout hysteresis Input under voltage lockout threshold Input under voltage lockout threshold hysteresis Soft-start current Soft-start period Thermal shutdown Symbol Vin Vout Iout Is Iss Vfb Vfbo-th Aea Gea Rds(on)1 Rds(on)2 Ileak Ilim_usw Ilim_lsw Gcs Fosc1 Fosc2 Dmax To Vens_th Vin=+12V, Top=+25°C, unless otherwise noted. Test condition Min. Typ. Max. Unit 4.75 20.00 V 0.923 18.000 V 2.0 A Ven=0V 1.0 3.0 µA Ven=2.0V, Vfb=1.0V 1.3 1.5 mA 4.75V ≤ Vin ≤ 20V 0.900 0.923 0.946 V 1.1 V 400 V/V ∆Ic = ±10µA 800 µA/V 85 mΩ 85 mΩ Ven = 0V, Vsw = 0V 10 µA Minimum duty cycle 2.4 4.0 A From drain to source 1.1 A 3.5 A/V 500 550 600 kHz Vfb = 0V 120 170 220 kHz Vfb = 0.78mV 90 % 140 ns Ven falling 1.39 V Vens_hys 210 mV Venl_th Venl_hys Vth Vin rising 1.64 210 4.10 V mV V Vth_hys 210 mV 6 15 160 µA ms °C Isoft Psoft Tsd Vss = 0V Vss = 0.1µF 11 - 3 Rev.1.3 ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter ■Application notes ELM613DA is synchronous rectified, current-mode, step-down regulator. It regulates input voltages from 4.75V to 20V down to an output voltage as low as 0.923V, and supplies up to 2A of load current. ELM613DA uses current-mode control to regulate the output voltage. The output voltage is measured at FB through a resistive voltage divider and amplified through the internal transconductance error amplifier. The voltage at the COMP pin is compared to the switch current measured internally to control the output voltage. The converter uses internal N-Channel MOSFET switches to step-down the input voltage to the regulated output voltage. Since the high side MOSFET requires a gate voltage greater than the input voltage, a boost capacitor connected between SW and BS is needed to drive the high side gate. The boost capacitor is charged from the internal 5V rail when SW is low. When ELM613DA FB pin exceeds 20% of the nominal regulation voltage of 0.923V, the over voltage comparator is tripped and the COMP pin and the SS pin are discharged to GND, forcing the high-side switch off. 1. Pin description BS: High side gate drive boost input BS supplies the drive for the high-side N-Channel MOSFET switch. Connect a 0.01μF or greater capacitor from SW to BS to power the high side switch. VIN: Power input VIN supplies the power to the IC, as well as the step-down converter switches. Drive VIN with a 4.75V to 20V power source. Bypass VIN to GND with a suitably large capacitor to eliminate noise on the input to the IC. SW: Power switch output SW is the switching node that supplies power to the output. Connect the output LC filter from SW to the output load. Note that a capacitor is required from SW to BS to power the high-side switch. GND: Ground Connect to PCB wiring which is lower than high frequency impedance. FB: Feedback Input FB senses the output voltage to regulate that voltage. Drive FB with a resistive voltage divider from the output voltage. The feedback threshold is 0.923V. COMP: Compensation node COMP is used to compensate the regulation control loop. Connect a series RC network from COMP to GND to compensate the regulation control loop. In some cases, an additional capacitor from COMP to GND is required. EN: Enable input EN is a digital input that turns the regulator on or off. Drive EN high to turn on the regulator, drive it low to turn it off. If EN pin needs to be pulled-up, EN input current has to be lower than 200μA with R4 (about 100kΩ). SS: Soft-start control input SS controls the soft start period. Connect a capacitor from SS to GND to set the soft-start period. A 0.1μF capacitor sets the soft-start period to 15ms. To disable the soft-start feature, leave SS unconnected. 2. Setting output voltage The output voltage is set using a resistive voltage divider from the output voltage to FB pin. The voltage divider divides the output voltage down to the feedback voltage by the ratio: Vfb = Vout × R2 / (R1 + R2) 11 - 4 Rev.1.3 ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter Where Vfb is the feedback voltage and Vout is the output voltage. Thus the output voltage is: Vout = 0.923 × (R1 + R2) / R2 R2 can be as high as 100kΩ, but a typical value is 10kΩ. Using the typical value for R2, R1 is determined by: R1 = 10.83 × (Vout − 0.923) (kΩ) 3. Inductor The inductor is required to supply constant current to the output load while being driven by the switched input voltage. A larger value inductor will result in less ripple current that will result in lower output ripple voltage. However, the larger value inductor will have a larger physical size, higher series resistance, and/or lower saturation current. A good rule for determining the inductance to use is to allow the peak-to-peak ripple current in the inductor to be approximately 30% of the maximum switch current limit. Also, make sure that the peak inductor current is below the maximum switch current limit. The inductance value can be calculated by: L = [ Vout / (fs × ΔIl) ] × (1 − Vout/Vin) Where Vout is the output voltage, Vin is the input voltage, fs is the switching frequency, and ΔIl is the peak-topeak inductor ripple current. Choose an inductor that will not saturate under the maximum inductor peak current. The peak inductor current can be calculated by: Ilp = Iload + [ Vout / (2 × fs × L) ] × (1 − Vout/Vin) Where Iload is the load current. The choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI requirements. 4. Optional Schottky diode During the transition between high-side switch and low-side switch, the body diode of the low-side power MOSFET conducts the inductor current. The forward voltage of this body diode is high. An optional Schottky diode may be paralleled between the SW pin and GND pin to improve overall efficiency. Table 1 lists example Schottky diodes and their Manufacturers. Part number Voltage and current rating Vendor B130 30V, 1A Diodes Inc. SK13 30V, 1A Diodes Inc. MBRS130 30V, 1A International Rectifier Table 1: Diode selection guide. 5. Input capacitor The input current to the step-down converter is discontinuous, therefore a capacitor is required to supply the AC current to the step-down converter while maintaining the DC input voltage. Use low ESR capacitors for the best performance. Ceramic capacitors are preferred, but tantalum or low-ESR electrolytic capacitors may also suffice. Choose X5R or X7R dielectrics when using ceramic capacitors. Since the input capacitor (Cin) absorbs the input switching current it requires an adequate ripple current rating. The RMS current in the input capacitor can be estimated by: Icin = Iload × [ (Vout/Vin) × (1 − Vout/Vin) ]1/2 The worst-case condition occurs at Vin = 2Vout, where Icin = Iload/2. For simplification, choose the input capacitor whose RMS current rating greater than half of the maximum load current. 11 - 5 Rev.1.3 ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter The input capacitor can be electrolytic, tantalum or ceramic. When using electrolytic or tantalum capacitors, a small, high quality ceramic capacitor, i.e. 0.1μF, should be placed as close to the IC as possible. When using ceramic capacitors, make sure that they have enough capacitance to provide sufficient charge to prevent excessive voltage ripple at input. The input voltage ripple for low ESR capacitors can be estimated by: ΔVin = [ Iload/(Cin × fs) ] × (Vout/Vin) × (1 − Vout/Vin) Where Cin is the input capacitance value. 6. Output capacitor The output capacitor is required to maintain the DC output voltage. Ceramic, tantalum, or low ESR electrolytic capacitors are recommended. Low ESR capacitors are preferred to keep the output voltage ripple low. The output voltage ripple can be estimated by: ΔVout = [ Vout/(fs × L) ] × (1 − Vout/Vin) × [ Resr + 1 / (8 × fs × Cout) ] Where Cout is the output capacitance value and Resr is the equivalent series resistance (ESR) value of the output capacitor. In the case of ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance. The output voltage ripple is mainly caused by the capacitance. For simplification, the output voltage ripple can be estimated by: ΔVout = [ Vout/(8 × fs2 × L × Cout) ] × (1 − Vout/Vin) In the case of tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated to: ΔVout = [ Vout/(fs × L) ] × (1 − Vout/Vin) × Resr The characteristics of the output capacitor also affect the stability of the regulation system. ELM613DA can be optimized for a wide range of capacitance and ESR values. 7. Compensation components ELM613DA employs current mode control for easy compensation and fast transient response. The system stability and transient response are controlled through the COMP pin. COMP pin is the output of the internal transconductance error amplifier. A series capacitor and resistor combination sets a pole-zero combination to control the characteristics of the control system. The DC gain of the voltage feedback loop is given by: Avdc = Rload × Gcs × Aea × Vfb/Vout Where Aea is the error amplifier voltage gain; Gcs is the current sense transconductance and Rload is the load resistor value. The system has two poles of importance. One is due to the compensation capacitor (C1) and the output resistor of the error amplifier, and the other is due to the output capacitor and the load resistor. These poles are located at: fp1 = Gea / (2π × C1 × Aea), fp2 = 1 / (2π × Cout × Rload) Where Gea is the error amplifier transconductance. The system has one zero of importance, due to the compensation capacitor (C1) and the compensation resistor (R3). This zero is located at: fz1 = 1 / (2π × C1 × R3) The system may have another zero of importance, if the output capacitor has a large capacitance and/or a high ESR value. The zero, due to the ESR and capacitance of the output capacitor, is located at: fesr = 1 / (2π × Cout × Resr) 11 - 6 Rev.1.3 ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter In this case, a third pole set by the compensation capacitor (C4) and the compensation resistor (R3) is used to compensate the effect of the ESR zero on the loop gain. This pole is located at: fp3 = 1 / (2π × C4 × R3) The goal of compensation design is to shape the converter transfer function to get a desired loop gain. The system crossover frequency where the feedback loop has the unity gain is important. Lower crossover frequencies result in slower line and load transient responses, while higher crossover frequencies could cause system instability. A good rule of thumb is to set the crossover frequency below one-tenth of the switching frequency. To optimize the compensation components, the following procedure can be used. 1) Choose the compensation resistor (R3) to set the desired crossover frequency. Determine the R3 value by the following equation: R3 = [ (2π × Cout × fc) / (Gea × Gcs) ] × (Vout/Vfb) < [ (2π × Cout × 0.1 × fs) / (Gea × Gcs) ] × (Vout/Vfb) Where fC is the desired crossover frequency which is typically below one tenth of the switching frequency. 2) Choose the compensation capacitor (C1) to achieve the desired phase margin. For applications with typical inductor values, setting the compensation zero, fz1, below one-forth of the crossover frequency provides sufficient phase margin. Determine the C1 value by the following equation: C1 > 4 / (2π × R3 × fc) Where R3 is the compensation resistor. 3) Determine if the second compensation capacitor (C4) is required. It is required if the ESR zero of the output capacitor is located at less than half of the switching frequency, or the following relationship is valid: 1 / (2π × Cout × Resr) < fs/2 If this is the case, then add the second compensation capacitor (C4) to set the pole fP3 at the location of the ESR zero. Determine the C4 value by the equation: C4 = (Cout × Resr) / R3 8. External bootstrap diode An external bootstrap diode may enhance the efficiency of the regulator, the applicable conditions of external BS diode are: Vout = 5V or 3.3V, and duty cycle is high: D = Vout/Vin > 65% In these cases, an external BS diode is recommended from the output of the voltage regulator to BS pin, as shown in Figure 1. External BS diode IN4148 BS ELM613DA SW ◄ Cbs 0.1 to 1µF L 5V or 3.3V Cout Figure 1. Add optional external bootstrap diode to enhance efficiency. The recommended external BS diode is IN4148, and the BS capacitor is 0.1 to 1μF. 11 - 7 Rev.1.3 ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter when Vin≤ 6V, for the purpose of promote the efficiency, it can add an external Schottky diode between IN and BS pins, as shown in Figure 2. Schottky (B0520LW) ▲ BS VIN 5V to 6V ELM613DA Vout SW GND Figure 2: Add a Schottky diode to promote efficiency when Vin ≤ 6V. 9. PCB layout guide PCB layout is very important to achieve stable operation. Please follow the guidelines below. 1) Keep the path of switching current short and minimize the loop area formed by Input capacitor, high-side MOSFET and low-side MOSFET. 2) Bypass ceramic capacitors are suggested to be put close to the VIN Pin. 3) Ensure all feedback connections are short and direct. Place the feedback resistors and compensation components as close to the chip as possible. 4) Rout SW away from sensitive analog areas such as FB. 5) Connect IN, SW, and especially GND respectively to a large copper area to cool the chip to improve thermal performance and long-term reliability. Table2 : BOM of ELM613DA Vout=5.0V L 10µH R1 15K R2 6.8K R3 16K Cout 22µF C1 3.3nF 15K Vout=3.3V 10µH 12K 100 4.7K 15K 22µF 3.3nF Vout=2.5V Vout=1.8V Vout=1.2V 10µH 10µH 9.1K 6.8K 470 1K 5.6K 8.2K 13K 6.8K 22µF 22µF 3.3nF 3.3nF 4.7µH 1.5K 1.5K 10K 5.1K 22µF 3.3nF Vout=1.0V 3.3µH 1K 1K 24K 4.7K 22µF 3.3nF ■Marking SOP-8 LV1482SN abcdef ghijk Mark LV1482SN Content Product ID a to k Assembly lot No.: 0 to 9 & A to Z repeated 11 - 8 Rev.1.3 ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter ■Typical characteristics • Vout=1.8V : Cin=10µF, Cout=22µF, L=10µH, R1=9.5k, R2=10k, R3=15k C1=3.3nF, C2=0.1µF, C3=10nF, Top=25°C • V=1.8V EFFICIENCY-Iout 100 2 80 EFFICIENCY (%) Vout (V) Vout-Vin 2.5 1.5 Iout=10mA 1 Iout=1000mA Iout=100mA 0.5 0 5 10 15 20 Vin (V) 60 Vin=12V 40 20 0 0.1 25 Vin=5V 1 10 100 Iout (mA) Vout-Iout 1000 10000 Vfb-Top 2.5 Vin=12V, Iout=100mA) 0.95 2.4 2.3 0.94 2.1 Vfb (V) Vout (V) 2.2 Vin=12V 2.0 1.9 0.93 0.92 1.8 1.7 1.6 1 10 100 Iout (mA) 1000 0.9 -40 10000 Start Response 0 20 Top (°C) 40 60 80 Load Transient Response Vin=12V, Iout=1mA~1A Vout (V) Vin=12V, No load 1 2.5 2.0 1.5 0 1.0 2 1 0 0.5 Ven (V) Vout (V) 2 -20 0 Time (4ms/div) Iout (A) 1.5 0.1 0.91 Vin=5V Time (100µs/div) 11 - 9 Rev.1.3 ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter • Vout=3.3V : Cin=10µF, Cout=22µF, L=10µH, R1=12k, R2=4.7k, R3=15k C1=3.3nF, C2=0.1µF, C3=10nF, Top=25°C • V=3.3V EFFICIENCY-Iout Vout-Vin 100 4.0 3.5 2.5 Iout=1000mA EFFICIENCY (%) Vout (V) 3.0 Iout=10mA 2.0 1.5 1.0 Iout=100mA 5 1 60 Vin=12V 40 20 0.5 0 Vin=5V 80 15 2 Vin (V) 0 0.1 25 1 10 100 Iout (mA) 1000 10000 Vfb-Top Vout-Iout Vin=12V, Iout=100mA 0.95 3.50 3.45 3.40 3.35 3.30 Vfb (V) Vout (V) 0.94 Vin=12V 3.25 3.20 3.15 Vin=5V 0.93 0.92 0.91 3.10 3.05 3.00 0.1 1 10 100 Iout (mA) 1000 0.9 -40 10000 Start Response 0 20 Top (°C) 40 60 80 Load Transient Response Vin=12V, Iout=1mA~1A Vout (V) Vin=12V, No load 3 2 3.5 3.0 0 1.0 2 1 0 0.5 0 Time (4ms/div) Iout (A) 1 Ven (V) Vout (V) 4 -20 Time (100µs/div) 11 - 10 Rev.1.3 ELM613DA 2A, 20V, 550kHz, synchronous step-down DC/DC converter • Vout=5.0V : Cin=10µF, Cout=22µF, L=10µH, R1=30K R2=6.8K R3=15K C1=3.3nF, C2=0.1µF, C3=10nF, Top=25°C • V=5.0V EFFICIENCY-Iout 100 80 EFFICIENCY (%) Vout (V) Vout-Vin 6.0 5.5 5.0 4.5 4.0 3.5 3.0 2.5 2.0 1.5 1.0 0.5 Iout=10mA Iout=100mA Iout=1000mA 5 0 10 15 Vin (V) 60 40 20 0 0.1 20 Vin=12V 1 10 100 Iout (mA) Vout-Iout 1000 10000 Vfb-Top 5.5 Vin=12V, Iout=100mA 0.95 5.4 5.3 0.94 Vin=12V 5.1 Vfb (V) Vout (V) 5.2 5.0 4.9 0.93 0.92 4.8 4.7 0.91 4.6 1 10 100 Iout (mA) 1000 0.90 -40 10000 Start Response 0 20 40 Top (°C) 60 80 Load Transient Response Vin=12V, No load Vout (V) 6.0 6 4 2 Vin=12V, Iout=1mA~1A 5.5 5.0 4.5 0 1.0 2 1 0 0.5 Ven (V) Vout (V) -20 0 Time (4ms/div) Iout (A) 4.5 0.1 Time (100µs/div) 11 - 11 Rev.1.3