2A, 23V, Synchronous-Rectified Step-Down Converter General Description EC3283A Features The EC3283A is a monolithic synchronous buck regulator. The device integrates two 90mΩ MOSFETs, and provides 2A of continuous load current over a wide input voltage of 4.75V to 23V. Current mode control provides fast transient Response and cycle-by-cycle current limit. An adjustable soft-start prevents inrush current at turn-on, and in shutdown mode the supply current drops to 1µA. This device, available in an SOP-8(Exposed PAD) Package provides a very compact solution with minimal external components. ● 2A Output Current ● Wide 4.75V to 23V Operating Input Range ● Integrated 90mΩ Power MOSFET Switches ● Output Adjustable from 0.923V to 20V ● Up to 93% Efficiency ● Programmable Soft-Start ● Stable with Low ESR Ceramic Output Capacitors ● Fixed 340KHz Frequency ● Cycle-by-Cycle Over Current Protection ● Input Under Voltage Lockout Applications ● Distributed Power Systems ● Networking Systems ● FPGA, DSP, ASIC Power Supplies ● Green Electronics/ Appliances ● Notebook Computers Package Types Figure 1. Package Types of EC3283A E-CMOS Corp. (www.ecmos.com.tw) Page 1 of 13 3J17N-Rev.F001 2A, 23V, Synchronous-Rectified Step-Down Converter EC3283A Pin Configurations Figure 2 Pin Configuration of EC3283A(Top View) Pin Description Pin Number Description Pin Name High-Side Gate Drive Boost Input. BS supplies the drive for the high-side N-Channel 1 BS MOSFET switch. Connect a 0.01µF or greater capacitor from SW to BS to power the high side switch. Power Input. IN supplies the power to the IC, as well as the step-down converter 2 IN switches. Drive IN with a 4.75V to 23V power source. Bypass IN to GND with a suitably large capacitor to eliminate noise on the input to the IC. See Input Capacitor. Power Switching Output. SW is the switching node that supplies power to the output. 3 SW 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. 4 GND 5 FB Ground. 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. See Setting the Output Voltage. Compensation Node. COMP is used to compensate the regulation control loop. 6 COMP 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. See Compensation Components. Enable Input. EN is a digital input that turns the regulator on or off. Drive EN high to 7 EN turn on the regulator, drive it low to turn it off. Pull up with 100kΩ resistor for automatic startup. Soft-Start Control Input. SS controls the soft start period. Connect a capacitor from SS 8 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. E-CMOS Corp. (www.ecmos.com.tw) Page 2 of 13 3J17N-Rev.F001 2A, 23V, Synchronous-Rectified Step-Down Converter EC3283A Ordering Information Part Number Package Marking EC3283ANMHR SOP-8L (Exposed PAD) 3283A LLLLL YYWWT Marking Information LLLLL is Lot Number YYWW is date code T is internal tracking code Function Block Figure 3 Function Block Diagram of EC3283A E-CMOS Corp. (www.ecmos.com.tw) Page 3 of 13 3J17N-Rev.F001 2A, 23V, Synchronous-Rectified Step-Down Converter EC3283A Absolute Maximum Ratings Parameter Symbol Value Unit Supply Voltage VIN -0.3 to 23 V Switch Node Voltage VSW 21 V Boost Voltage VBS VSW – 0.3V to VSW +6V V Output Voltage VOUT 0.923V to 20 V –0.3V to +6V V All Other Pins Operating Junction Temperature TJ 150 ºC Operating Ambient Temperature TA -40 to 80 ºC Storage Temperature TSTG -65 to 150 ºC Lead Temperature (Soldering, 10 sec) TLEAD 260 ºC 2000 V ESD (HBM) MSL Level3 Thermal Resistance-Junction to Ambient Thermal Resistance-Junction to Case E-CMOS Corp. (www.ecmos.com.tw) RθJA RθJC Page 4 of 13 90 45 ºC / W ºC / W 3J17N-Rev.F001 2A, 23V, Synchronous-Rectified Step-Down Converter EC3283A Electrical Characteristics (VIN = 12V, TA = 25℃ unless otherwise specified.) Parameters Symbol Shutdown Supply Current Min. VEN = 0V VEN = 2.0V; VFB = Supply Current Feedback Voltage Test Condition 1.0V VFB 4.75V ≤ VIN ≤ 23V 0.900 Feedback Overvoltage Threshold Typ. Max. Unit 1 3.0 µA 1.3 1.5 mA 0.923 0.946 V 1.1 V 400 V/V 800 µA/V Error Amplifier Voltage Gain * AEA Error Amplifier Transconductance GEA High-Side Switch On Resistance * RDS(ON)1 90 mΩ Low-Side Switch On Resistance * RDS(ON)2 90 mΩ High-Side Switch Leakage ∆IC = ±10µA VEN = 0V, VSW = 0V Current Upper Switch Current Limit Minimum Duty Cycle Lower Switch Current Limit From Drain to Source COMP to Current Sense Transconductance Oscillation Frequency Short Circuit Oscillation Frequency Maximum Duty Cycle 10 2.3 GCS Fosc1 3.4 A 1.1 A 4.8 A/V 340 KHz Fosc2 VFB = 0V 100 KHz DMAX VFB = 1.0V 90 % 220 ns Minimum On Time * EN Shutdown Threshold Voltage µA VEN Rising 1.1 1.5 2.0 V EN Shutdown Threshold Voltage Hysteresis 210 EN Lockout Threshold Voltage 2.2 EN Lockout Hysteresis E-CMOS Corp. (www.ecmos.com.tw) 2.5 210 Page 5 of 13 mV 2.7 V mV 3J17N-Rev.F001 2A, 23V, Synchronous-Rectified Step-Down Converter EC3283A Electrical Characteristics(Cont.) (VIN = 12V, TA = 25℃ unless otherwise specified.) Parameters Symbol Input Under Voltage Lockout Threshold Test Condition VIN Rising Input Under Voltage Lockout Min. 3.80 Typ. Max. 4.10 4.40 Unit V 210 mV 6 µA Threshold Hysteresis Soft-Start Current VSS = 0V Soft-Start Period CSS = 0.1µF Thermal Shutdown * 15 ms 160 °C Typical Performance Characteristics Figure 4. Steady State Test E-CMOS Corp. (www.ecmos.com.tw) Figure 5. Steady State Test Page 6 of 13 3J17N-Rev.F001 2A, 23V, Synchronous-Rectified Step-Down Converter EC3283A Typical Performance Characteristics(Cont.) Figure 6. Start up through Enable Figure 7. Startup Through Enable Figure 8.Shutdown through Enable E-CMOS Corp. (www.ecmos.com.tw) Figure 9. Shutdown through Enable Page 7 of 13 3J17N-Rev.F001 2A, 23V, Synchronous-Rectified Step-Down Converter EC3283A Typical Performance Characteristics(Cont.) Figure 10. Load Transient Test Figure 11. Short Circuit test Figure 12. Short Circuit Recovery E-CMOS Corp. (www.ecmos.com.tw) Page 8 of 13 3J17N-Rev.F001 2A, 23V, Synchronous-Rectified Step-Down Converter EC3283A Typical Application Circuit Fig13. EC3283A with 3.3V Output, 22µF/6.3V Ceramic Output Capacitor E-CMOS Corp. (www.ecmos.com.tw) Page 9 of 13 3J17N-Rev.F001 2A, 23V, Synchronous-Rectified Step-Down Converter EC3283A Function Description Component Selection Setting the 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: Where VFB is the feedback voltage and VOUT is the output voltage. Thus the output voltage is: R2 can be as high as 100kΩ, but a typical value is 10kΩ. Using the typical value for R2, R1 is determined by: For example, for a 3.3V output voltage, R2 is 10kΩ, and R1 is 26.1kΩ. 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: E-CMOS Corp. (www.ecmos.com.tw) Where VOUT is the output voltage, VIN is the input voltage, fS is the switching frequency, and ∆IL is the peak-to-peak inductor ripple current. Choose an inductor that will not saturate under the maximum inductor peak current. The peak inductor current can be calculated by: 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. Optional Schottky Diode During the transition between high-side switch and low-side switch, the body diode of the lowside 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/Current Vendor B130 30V, 1A Diodes, Inc. SK13 30V, 1A Diodes, Inc. MBRS130 30V, 1A International Rectifier 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. Page 10 of 13 3J17N-Rev.F001 2.2A, 23V, Synchronous-Rectified Step-Down Converter Since the input capacitor (C1) absorbs the input switching current it requires an adequate ripple current rating. The RMS current in the input capacitor can be estimated by: The worst-case condition occurs at VIN = 2VOUT,where IC1 = ILOAD/2. For simplification, choose the input capacitor whose RMS current rating greater than half of the maximum load current. 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: Where C1 is the input capacitance value. 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: Where C2 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: E-CMOS Corp. (www.ecmos.com.tw) EC3283A 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: The characteristics of the output capacitor also affect the stability of the regulation system. The EC3283A can be optimized for a wide range of capacitance and ESR values. Compensation Components EC3283A 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-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: Where AVEA 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 (C3) 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: Where GEA is the error amplifier transconductance. Page 11 of 13 3J17N-Rev.F001 2.2A, 23V, Synchronous-Rectified Step-Down Converter The system has one zero of importance, due to the compensation capacitor (C3) and the compensation resistor (R3). This zero is located at: 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: In this case (as shown in Figure 14), a third pole set by the compensation capacitor (C6) and the compensation resistor (R3) is used to compensate the effect of the ESR zero on the loop gain. This pole is located at: 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: Where fC is the desired crossover frequency which is typically below one tenth of the switching frequency. 2. Choose the compensation capacitor (C3) 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. E-CMOS Corp. (www.ecmos.com.tw) EC3283A Determine the C3 value by the following equation: Where R3 is the compensation resistor. 3. Determine if the second compensation capacitor (C6) 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: If this is the case, then add the second compensation capacitor (C6) to set the pole fP3 at the location of the ESR zero. Determine the C6 value by the equation: External Bootstrap Diode An external bootstrap diode may enhance the efficiency of the regulator, the applicable conditions of external BST diode are: ●VOUT=5V or 3.3V; and ●Duty cycle is high: In these cases, an external BST diode is recommended from the output of the voltage regulator to BST pin, as shown in Fig.14 Figure14. Add Optional External Bootstrap Diode to Enhance Efficiency The recommended external BST diode is IN4148, and the BST cap is 0.1~1μF. Page 12 of 13 3J17N-Rev.F001 2.2A, 23V, Synchronous-Rectified Step-Down Converter EC3283A Package Information SOP-8(Exposed PAD) Package Outline Dimensions E-CMOS Corp. (www.ecmos.com.tw) Page 13 of 13 3J17N-Rev.F001