MP1484M/TR

MP1484 3A, 18V, 340KHz Synchronous Rectified Step-Down Converter DESCRIPTION FEATURES The MP1484 is a monolithic synchronous buck regulator. The device integrates top and bottom 85mΩ MOSFETS that provide 3A of continuous load current over a wide operating input voltage of 4.75V to 18V. 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 below 1µA. The MP1484 is PIN compatible to the MP1482 2A/18V/Synchronous Step-Down Converter. 3A Continuous Output Current Wide 4.75V to 18V Operating Input Range Integrated 85mΩ Power MOSFET Switches Output Adjustable from 0.925V to 15V Up to 95% Efficiency Programmable Soft-Start Stable with Low ESR Ceramic Output Capacitors Fixed 340KHz Frequency Cycle-by-Cycle Over Current Protection Input Under Voltage Lockout Thermally Enhanced 8-Pin SOIC Package APPLICATIONS • • • • FPGA, ASIC, DSP Power Supplies LCD TV Green Electronics/Appliances Notebook Computers “MPS” and “The Future of Analog IC Technology” are Registered Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION Efficiency vs Load Current 100 95 7 8 EN SS GND 4 1 BS SW FB COMP 90 EFFICIENCY (%) 2 IN 3 5 6 VIN = 5V VIN = 12V 85 80 75 70 65 60 55 50 0.1 http://www.hgsemi.com.cn 1 1.0 LOAD CURRENT (A) 2016 MAR 10 MP1484 ABSOLUTE MAXIMUM RATINGS (1) PACKAGE REFERENCE Supply Voltage VIN ....................... –0.3V to +24V Switch Voltage VSW ................. –1V to VIN + 0.3V Boost Voltage VBS ..........VSW – 0.3V to VSW + 6V All Other Pins................................. –0.3V to +6V Junction Temperature...............................150°C Lead Temperature ....................................260°C Storage Temperature .............–65°C to +150°C TOP VIEW BS 1 8 SS IN 2 7 EN SW 3 6 COMP GND 4 5 FB Recommended Operating Conditions Input Voltage VIN ............................ 4.75V to 18V Output Voltage VOUT .................... 0.925V to 15V Ambient Operating Temp .............. –20°C to +85°C EXPOSED PAD ON BACKSIDE CONNECT TO GND PIN Thermal Resistance Part Number* MP1484EN * Package (2) (3) θJA θJC SOIC8N(Exposed Pad) .......... 50 ...... 10... °C/W Temperature SOIC8N –20°C to +85°C (Exposed Pad) Notes: 1) Exceeding these ratings may damage the device. 2) The device is not guaranteed to function outside of its operating conditions. 3) Measured on approximately 1” square of 1 oz copper. For Tape & Reel, add suffix –Z (e.g. MP1484EN -Z) For Lead Free, add suffix –LF (e.g. MP1484EN - LF-Z) ELECTRICAL CHARACTERISTICS VIN = 12V, TA = +25°C, unless otherwise noted. Parameter Symbol Condition Shutdown Supply Current Supply Current Feedback Voltage VEN = 0V VEN = 2.0V, VFB = 1.0V VFB Feedback Overvoltage Threshold Error Amplifier Voltage Gain (4) AEA Error Amplifier Transconductance GEA High-Side/Low-Side Switch OnResistance (4) 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 (4) EN Shutdown Threshold Voltage EN Shutdown Threshold Voltage Hysterisis http://www.hgsemi.com.cn Min 4.75V ≤ VIN ≤ 18V 0.900 ∆IC = ±10µA VEN = 0V, VSW = 0V Minimum Duty Cycle From Drain to Source 3.8 Max Units 0.3 1.3 3.0 1.5 µA mA 0.925 0.950 V 1.1 400 V V/V 820 µA/V 85 mΩ 0 5.3 0.9 10 5.2 GCS Fosc1 Fosc2 DMAX TON Typ 300 VFB = 0V VFB = 1.0V VEN Rising 1.1 340 110 90 220 1.5 220 2 µA A A A/V 380 2.0 KHz KHz % ns V mV 2016 MAR MP1484 ELECTRICAL CHARACTERISTICS (continued) VIN = 12V, TA = +25°C, unless otherwise noted. Parameter Symbol Condition EN Lockout Threshold Voltage EN Lockout Hysterisis Input Under Voltage Lockout Threshold Input Under Voltage Lockout Threshold Hysteresis Soft-Start Current Soft-Start Period Thermal Shutdown (4) VIN Rising VSS = 0V CSS = 0.1µF Min Typ Max Units 2.2 2.5 210 2.7 V mV 3.80 4.05 4.40 V 210 mV 6 15 160 µA ms °C Note: 4) Guaranteed by design, not tested. PIN FUNCTIONS Pin # Name 1 BS 2 IN 3 SW 4 GND 5 FB 6 COMP 7 EN 8 SS Description 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. Power Input. IN supplies the power to the IC, as well as the step-down converter switches. Drive IN with a 4.75V to 18V power source. See Input Capacitor. Power Switching 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. Ground (Connect the exposed pad to Pin 4). Feedback Input. FB senses the output voltage and regulates it. Drive FB with a resistive voltage divider connected to it from the output voltage. The feedback threshold is 0.925V. See Setting the Output Voltage. Compensation Node. COMP is used to compensate the regulation control loop. Connect a series RC network from COMP to GND. 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 turn on the regulator; low to turn it off. Attach to IN with a 100kΩ pull up resistor for automatic startup. 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. http://www.hgsemi.com.cn 3 2016 MAR MP1484 TYPICAL PERFORMANCE CHARACTERISTICS C1 = 4.7µF, C2 = 2 x 10µF, L= 10µH, CSS= 0.1µF, TA = +25°C, unless otherwise noted. http://www.hgsemi.com.cn 4 2016 MAR MP1484 OPERATION 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. FUNCTIONAL DESCRIPTION The MP1484 regulates input voltages from 4.75V to 18V down to an output voltage as low as 0.925V, and supplies up to 3A of load current. The MP1484 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. When the FB pin voltage exceeds 20% of the nominal regulation value of 0.925V, the over voltage comparator is tripped and the COMP pin and the SS pin are discharged to GND, forcing the high-side switch off. + CURRENT SENSE AMPLIFIER OVP 1.1V -OSCILLATOR + FB 340KHz 0.3V RAMP 5V BS ---- + 0.925V + -- CLK + SS IN + ERROR AMPLIFIER S Q R Q SW CURRENT COMPARATOR COMP -- EN 2.5V + GND EN OK 1.2V OVP IN < 4.05V LOCKOUT COMPARATOR IN + INTERNAL REGULATORS 1.5V -- SHUTDOWN COMPARATOR Figure 1—Functional Block Diagram http://www.hgsemi.com.cn 5 2016 MAR MP1484 APPLICATIONS INFORMATION The inductance value can be calculated by: COMPONENT SELECTION Setting the Output Voltage The output voltage is set using a resistive voltage divider connected from the output voltage to FB. The voltage divider divides the output voltage down to the feedback voltage by the ratio: VFB = VOUT L= Choose an inductor that will not saturate under the maximum inductor peak current, calculated by: Thus the output voltage is: R1 + R2 R2 ILP = ILOAD + R2 can be as high as 100kΩ, but a typical value is 10kΩ. Using the typical value for R2, R1 is determined by: Optional Schottky Diode During the transition between the 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 2 lists example Schottky diodes and their Manufacturers. Table 1—Recommended Resistance Values R1 R2 1.8V 2.5V 3.3V 5V 12V 9.53kΩ 16.9kΩ 26.1kΩ 44.2kΩ 121kΩ 10kΩ 10kΩ 10kΩ 10kΩ 10kΩ ⎞ ⎟⎟ ⎠ The choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI constraints. For example, for a 3.3V output voltage, R2 is 10kΩ, and R1 is 26.1kΩ. Table 1 lists recommended resistance values of R1 and R2 for standard output voltages. VOUT ⎛ VOUT V × ⎜1 − OUT 2 × f S × L ⎜⎝ VIN Where ILOAD is the load current. R1 = 10.81 × ( VOUT − 0.925 ) (kΩ) Table 2—Diode Selection Guide Inductor The inductor is required to supply constant current to the load while being driven by the switched input voltage. A larger value inductor will result in less ripple current that will in turn 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 inductance is to allow the peak-topeak ripple current 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. http://www.hgsemi.com.cn ⎞ ⎟⎟ ⎠ 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. R2 R1 + R2 VOUT = 0.925 × ⎛ V VOUT × ⎜⎜1 − OUT VIN f S × ∆I L ⎝ Part Number Voltage/Current Rating B130 SK13 30V, 1A 30V, 1A MBRS130 30V, 1A Vendor Diodes, Inc. Diodes, Inc. International Rectifier Input Capacitor The input current to the step-down converter is discontinuous, therefore a capacitor is required to supply the AC current 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 will also suffice. Choose X5R or X7R dielectrics when using ceramic capacitors. 6 2016 MAR MP1484 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: I C1 = ILOAD × When using tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated to: VOUT ⎛⎜ VOUT ⎞⎟ × 1− VIN ⎜⎝ VIN ⎟⎠ ∆VOUT = V VOUT ⎛ × ⎜1 − OUT VIN f S × L ⎜⎝ ⎞ ⎟⎟ × R ESR ⎠ The worst-case condition occurs at VIN = 2VOUT, where IC1 = ILOAD/2. For simplification, use an input capacitor with a RMS current rating greater than half of the maximum load current. The characteristics of the output capacitor also affect the stability of the regulation system. The MP1484 can be optimized for a wide range of capacitance and ESR values. 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: Compensation Components MP1484 employs current mode control for easy compensation and fast transient response. The system stability and transient response are controlled through the COMP pin. COMP is the output of the internal transconductance error amplifier. A series capacitor-resistor combination sets a pole-zero combination to govern the characteristics of the control system. ∆VIN = ILOAD V × OUT C1 × fS VIN ⎛ V × ⎜⎜1 − OUT VIN ⎝ The DC gain of the voltage feedback loop is given by: ⎞ ⎟⎟ ⎠ A VDC = R LOAD × G CS × A EA × Where C1 is the input capacitance value. Where VFB is the feedback voltage (0.925V), AVEA is the error amplifier voltage gain, GCS is the current sense transconductance and RLOAD is the load resistor value. Output Capacitor The output capacitor (C2) is required to maintain the DC output voltage. Ceramic, tantalum, or low ESR electrolytic capacitors are recommended. Under typical application conditions ， a minimum ceramic capacitor value of 20 µF is recommended on the output. Low ESR capacitors are preferred to keep the output voltage ripple low. The output voltage ripple can be estimated by: ∆VOUT ⎛ V V = OUT × ⎜⎜1 − OUT fS × L ⎝ VIN VFB VOUT 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: ⎞ ⎞ ⎛ 1 ⎟ ⎟⎟ × ⎜ R ESR + ⎜ ⎟ 8 f C 2 × × S ⎠ ⎝ ⎠ Where C2 is the output capacitance value and RESR is the equivalent series resistance (ESR) value of the output capacitor. fP1 = GEA 2π × C3 × A VEA fP2 = 1 2π × C2 × R LOAD Where GEA is the error amplifier transconductance. When using ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance which is the main cause for the output voltage ripple. For simplification, the output voltage ripple can be estimated by: ∆VOUT = ⎛ V × ⎜⎜1 − OUT VIN × L × C2 ⎝ VOUT 8 × fS 2 http://www.hgsemi.com.cn ⎞ ⎟⎟ ⎠ 7 2016 MAR MP1484 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. The system has one zero of importance, due to the compensation capacitor (C3) and the compensation resistor (R3). This zero is located at: f Z1 = 1 2π × C3 × 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 = C3 > 4 2π × R3 × f C Where R3 is the compensation resistor. 1 2π × C2 × R ESR In this case, a third pole set by compensation capacitor (C6) and compensation resistor (R3) is used compensate the effect of the ESR zero on loop gain. This pole is located at: fP 3 = Determine C3 by the following equation: 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: the the to the f 1 < S 2π × C2 × R ESR 2 1 2π × C6 × R3 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 C6 by the equation: 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 standard is to set the crossover frequency below one-tenth of the switching frequency. C6 = C2 × R ESR R3 External Bootstrap Diode An external bootstrap diode may enhance the efficiency of the regulator, the applicable conditions of external BS diode are: z VOUT is 5V or 3.3V; and To optimize the compensation components, the following procedure can be used. z Duty cycle is high: D= VOUT >65% VIN In these cases, an external BS diode is recommended from the output of the voltage regulator to BS pin, as shown in Fig.2 1. Choose the compensation resistor (R3) to set the desired crossover frequency. Determine R3 by the following equation: External BST Diode IN4148 2π × C2 × fC VOUT 2π × C2 × 0.1 × fS VOUT × < R3 = × GEA × GCS VFB GEA × GCS VFB BS MP1484 Where fC is the desired crossover frequency which is typically below one tenth of the switching frequency. SW CBST L 5V or 3.3V COUT Figure 2—Add Optional External Bootstrap Diode to Enhance Efficiency The recommended external BS diode is IN4148, and the BS cap is 0.1~1µF. http://www.hgsemi.com.cn 8 2016 MAR MP1484 TYPICAL APPLICATION CIRCUIT 2 7 8 IN EN SS GND 1 BS SW FB COMP 4 3 5 6 Figure 3—MP1484 with 3.3V Output, 2X10µF Ceramic Output Capacitor http://www.hgsemi.com.cn 9 2016 MAR MP1484 PCB LAYOUT GUIDE 2) PCB layout is very important to achieve stable operation. It is highly recommended to duplicate EVB layout for optimum performance. 3) If change is necessary, please follow these guidelines and take Figure4 for reference. 4) 1) Keep the path of switching current short and minimize the loop area formed by Input cap, high-side MOSFET and low-side MOSFET. 5) Bypass ceramic capacitors are suggested to be put close to the Vin Pin. Ensure all feedback connections are short and direct. Place the feedback resistors and compensation components as close to the chip as possible. Rout SW away from sensitive analog areas such as FB. Connect IN, SW, and especially GND respectively to a large copper area to cool the chip to improve thermal performance and long-term reliability. C5 INPUT 4.75V to 23V R4 2 7 8 C1 1 IN BS SW EN MP1484 SS GND FB COMP 4 L1 3 OUTPUT R1 5 6 C3 C4 D1 (optional) R2 C2 R3 MP1484 Typical Application Circuit R3 FB 5 COMP 6 C3 EN 7 C4 SS 8 R4 PGND R1 R2 SGND R1 C5 4 GND 3 SW 2 IN 1 BS PGND D1 C2 C1 L1 Top Layer Bottom Layer Figure 4—MP1484 Typical Application Circuit and PCB Layout Guide http://www.hgsemi.com.cn 10 2016 MAR