MP1472 2A, 18V Synchronous Rectified Step-Down Converter The Future of Analog IC Technology DESCRIPTION FEATURES The MP1472 is a monolithic synchronous buck regulator. The device integrates a 175m highside MOSFET and a 115m low-side MOSFET that provide 2A of continuous load current over a wide 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 to 1A. This device, available in an 8-pin TSOT23-8 package, provides a very compact solution with minimal external components. EVALUATION BOARD REFERENCE Board Number Dimensions EV1472GJ-00A 2.5"X x 2.5"Y x 0.5"Z 2A Output Current Wide 4.75V to 18V Operating Input Range Integrated Power MOSFET Switches Output Adjustable from 0.923V 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 8-Pin TSOT23-8 APPLICATIONS Distributed Power Systems Networking Systems FPGA, DSP, ASIC Power Supplies Green Electronics/ Appliances Notebook Computers For MPS green status, please visit MPS website under Quality Assurance. "MPS" and "The Future of Analog IC Technology" are Registered Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION Efficiency vs. Load Current 100 90 VOUT=3.3V EFFICIENCY (%) 80 60 VIN=12V 50 40 30 20 10 0 0.01 MP1472 Rev. 1.0 9/2/2011 VIN=4.75V 70 VIN=18V 0.1 1 LOAD CURRENT (A) www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. (c) 2011 MPS. All Rights Reserved. 10 1 MP1472 - 2A, 18V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER ORDERING INFORMATION Part Number Package TSOT23-8 MP1472GJ* Top Marking ACW *For Tape & Reel, add suffix -Z (e.g. MP1472GJ-Z); PACKAGE REFERENCE TOP VIEW SS 1 8 BST EN 2 7 IN COMP 3 6 SW FB 4 5 GND ABSOLUTE MAXIMUM RATINGS (1) Thermal Resistance Supply Voltage VIN ........................-0.3V to +20V Switch Node Voltage VSW ............................ 21V Boost Voltage VBS ..........VSW - 0.3V to VSW + 6V All Other Pins ..................................-0.3V to +6V Junction Temperature ...............................150C Continuous Power Dissipation (TA = +25C) TSOT23-8 .............................. 100 ..... 55... C/W (2) .......................................................1.25W Lead Temperature ....................................260C Storage Temperature .............. -65C to +150C Recommended Operating Conditions (3) Input Voltage VIN ............................ 4.75V to 18V Output Voltage VOUT ..................... 0.923V to 15V Maximum Junction Temp. (TJ) ............... +125C MP1472 Rev. 1.0 9/2/2011 (4) JA JC Notes: 1) Exceeding these ratings may damage the device. 2) The maximum allowable power dissipation is a function of the maximum junction temperature TJ(MAX), the junction-toambient thermal resistance JA, and the ambient temperature TA. The maximum allowable continuous power dissipation at any ambient temperature is calculated by PD(MAX)=(TJ(MAX)TA)/ JA. Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. Internal thermal shutdown circuitry protects the device from permanent damage. 3) The device is not guaranteed to function outside of its operating conditions. 4) Measured on JESD51-7 4-layer PCB. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. (c) 2011 MPS. All Rights Reserved. 2 MP1472 - 2A, 18V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER ELECTRICAL CHARACTERISTICS VIN = 12V, TA = +25C, unless otherwise noted. Parameter Symbol Condition Shutdown Supply Current Supply Current Min VEN = 0V VEN = 5.0V; VFB = 1.0V Feedback Voltage VFB Feedback Overvoltage Threshold Error Amplifier Voltage Gain (5) AEA Error Amplifier Transconductance GEA (5) High-Side Switch On Resistance Low-Side Switch On Resistance (5) 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 (5) EN Shutdown Threshold Voltage EN Shutdown Threshold Voltage Hysteresis 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 (5) 4.75V VIN 18V 0.900 IC = 10A RDS(ON)1 RDS(ON)2 VEN = 0V, VSW = 0V Minimum Duty Cycle From Drain to Source 3 GCS Fosc1 Fosc2 DMAX Typ Max Units 1 1.3 3.0 1.5 A mA 0.923 0.946 V 1.1 400 V V/V 800 A/V 175 115 m m A A A 4.1 1.1 10 5.3 3.5 305 VFB = 0V VFB = 0.8V VEN Rising 1.1 340 100 90 220 1.5 A/V 375 2.0 210 VIN Rising VSS = 0V CSS = 0.1F kHz kHz % ns V mV 2.2 2.5 210 2.7 V mV 3.40 3.80 4.20 V 210 mV 6 15 160 A ms C Note: 5) Guaranteed by design, not tested. MP1472 Rev. 1.0 9/2/2011 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. (c) 2011 MPS. All Rights Reserved. 3 MP1472 - 2A, 18V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER PIN FUNCTIONS Pin # Name 1 SS 2 EN 3 COMP 4 FB 5 GND 6 SW 7 IN 8 BS MP1472 Rev. 1.0 9/2/2011 Description Soft-Start Control Input. SS controls the soft start period. Connect a capacitor from SS to GND to set the soft-start period. A 0.1F capacitor sets the soft-start period to 15ms. To disable the soft-start feature, leave SS unconnected. 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. Pull up with 100k resistor for automatic startup. 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. See Compensation Components. 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. Ground. 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. 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. Bypass IN to GND with a suitably large capacitor to eliminate noise on the input to the IC. See Input Capacitor. High-Side Gate Drive Boost Input. BS supplies the drive for the high-side N-Channel MOSFET switch. Connect a 0.01F or greater capacitor from SW to BS to power the high side switch. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. (c) 2011 MPS. All Rights Reserved. 4 MP1472 - 2A, 18V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS VIN = 12V, VO = 3.3V, CIN = 10F, COUT = 22F, L = 10H, TA = +25C, unless otherwise noted. 100 90 90 80 80 70 70 60 60 50 50 40 40 30 30 20 20 10 0 0.01 10 0.1 1 10 0 0.01 VO/AC 20mV/div. VO/AC 20mV/div. SW 10V/div. SW 10V/div. IINDUCTOR 1A/div. IINDUCTOR 1A/div. 5 4.5 IPEAK (A) 100 4 3.5 3 0.1 1 10 2.5 40 60 80 100 IINDUCTOR 2A/div. SW 10V/div. VO 2V/div. EN 5V/div. SW 10V/div. IINDUCTOR 2A/div. IINDUCTOR 2A/div. IINDUCTOR 2A/div. MP1472 Rev. 1.0 9/2/2011 20 VO 2V/div. EN 5V/div. SW 10V/div. VO 2V/div. EN 5V/div. SW 10V/div. VO 2V/div. EN 5V/div. 0 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. (c) 2011 MPS. All Rights Reserved. 5 MP1472 - 2A, 18V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER 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 MP1472 is a synchronous rectified, current-mode, step-down regulator. It regulates input voltages from 4.75V to 18V down to an output voltage as low as 0.923V, and supplies up to 2A of load current. The MP1472 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 MP1472 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. + VOUT CURRENT SENSE AMPLIFIER OVP 1.1V -OSCILLATOR FB + 340kHz 0.3V RAMP 5V BS -+ -- + 0.923V + VIN -- CLK -SS IN + ERROR AMPLIFIER S Q R Q 0.175 SW CURRENT COMPARATOR 0.115 VOUT COMP -- EN 2.5V + GND EN OK 1.2V LOCKOUT COMPARATOR OVP IN < 3.8V IN + INTERNAL REGULATORS 1.5V -- SHUTDOWN COMPARATOR Figure 1--Functional Block Diagram MP1472 Rev. 1.0 9/2/2011 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. (c) 2011 MPS. All Rights Reserved. 6 MP1472 - 2A, 18V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER APPLICATIONS INFORMATION 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: VFB VOUT R2 R1 R2 Where VFB is the feedback voltage and VOUT is the output voltage. 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 Thus the output voltage is: VOUT 0.923 R1 R2 R2 R2 can be as high as 100k, but a typical value is 10k. Using the typical value for R2, R1 is determined by: R1 10.83 ( VOUT 0.923 ) (k) 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: For example, for a 3.3V output voltage, R2 is 10k, and R1 is 26.1k. 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 VOUT V 1 OUT f S IL VIN ILP ILOAD VOUT V 1 OUT 2 fS L VIN Where ILOAD is the load current. Table 1 lists a number of suitable inductors from various manufacturers. The choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI requirement. Table 1--Inductor Selection Guide Inductance (H) Max DCR () Current Rating (A) Dimensions L x W x H (mm3) 7440650068 6.8 0.033 3.6 10x10x2.8 744066100 10 0.035 3.6 10x10x3.8 744066150 15 0.050 3.2 10x10x3.8 SLF10165T-6R8N4R33PF 6.8 0.014 4.3 SLF10165T-100M3R83PF 10 0.0185 3.8 SLF10165T-150M3R13PF 15 0.027 3.1 10x10x4.5 10x10x4.5 10x10x4.5 6.8 0.035 3.1 10.4x10.4x4.8 Part Number Wurth Electronics TDK Toko #B952AS-6R8N #B892NAS-100M 10 0.0225 4.2 12.3x12.3x4.5 #B892NAS-150M 15 0.0355 3.2 12.3x12.3x4.5 MP1472 Rev. 1.0 9/2/2011 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. (c) 2011 MPS. All Rights Reserved. 7 MP1472 - 2A, 18V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER 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 2 lists example Schottky diodes and their Manufacturers. Table 2--Diode Selection Guide Part Number Voltage/Current Rating B230 SL23 30V, 2A 30V, 2A MBRS230 30V, 2A Vendor Diodes, Inc. Vishay, 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 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 (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 VOUT VOUT 1 VIN VIN 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. 0.1F, 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: MP1472 Rev. 1.0 9/2/2011 VIN ILOAD V V OUT 1 OUT C1 fS VIN VIN 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: VOUT VOUT V 1 OUT f S L VIN 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. 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: VOUT V 1 OUT VIN L C2 VOUT 8 fS 2 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: VOUT VOUT V 1 OUT fS L VIN R ESR The characteristics of the output capacitor also affect the stability of the regulation system. The MP1472 can be optimized for a wide range of capacitance and ESR values. Compensation Components MP1472 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. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. (c) 2011 MPS. All Rights Reserved. 8 MP1472 - 2A, 18V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER The DC gain of the voltage feedback loop is given by: A VDC R LOAD G CS A EA VFB VOUT 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: fP1 GEA 2 C3 A VEA fP2 1 2 C2 R LOAD Where GEA is the error amplifier transconductance. 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 2 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 1 2 C2 R ESR In this case, 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: fP 3 1 2 C6 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 MP1472 Rev. 1.0 9/2/2011 crossover frequencies could cause system instability. A good rule of thumb is to set the crossover frequency below one-tenth of the switching frequency. Table 3 lists the typical values of compensation components for some standard output voltages with various output capacitors and inductors. The values of the compensation components have been optimized for fast transient responses and good stability at given conditions. Table 3--Compensation Values for Output Voltage/Capacitor Combinations Typical VOUT L1 C2 R3 C3 C6 1.8V 6.8uH 22F/6.3V Ceramic 3.3k 5.6nF None 3.3V 10H 22F/6.3V Ceramic 5.6k 3.3nF None 5.0V 15H 22F/6.3V Ceramic 10k 2.2nF None 12.0V 22H 22F/16V Ceramic 15k 1.0nF None 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 2 C2 fC VOUT 2 C2 0.1 fS VOUT GEA GCS VFB GEA GCS VFB 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. Determine the C3 value by the following equation: C3 4 2 R3 f C where R3 is the compensation resistor. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. (c) 2011 MPS. All Rights Reserved. 9 MP1472 - 2A, 18V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER 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: f 1 S 2 C2 RESR 2 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: C2 R ESR C6 R3 In these cases, an external BST diode is recommended from the output of the voltage regulator to BST pin, as shown in Figure 2 External BST Diode IN4148 BST MP1472 SW CBST 0.01 L + COUT 5V or 3.3V Figure 2--Add Optional External Bootstrap Diode to Enhance Efficiency The recommended external BST diode is IN4148, and the BST cap is 0.01F. External Bootstrap Diode An external bootstrap diode may enhance the efficiency of the regulator, and it will be a must if the applicable condition is: VOUT=5V or 3.3V; and duty cycle is high: D= MP1472 Rev. 1.0 9/2/2011 VOUT >65% VIN www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. (c) 2011 MPS. All Rights Reserved. 10 MP1472 - 2A, 18V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER typical Application circuit Figure 3--MP1472 with 1.8V Output, 22F/6.3V Ceramic Output Capacitor Figure 4--MP1472 with 5.0V Output, 22F/6.3V Ceramic Output Capacitor MP1472 Rev. 1.0 9/2/2011 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. (c) 2011 MPS. All Rights Reserved. 11 MP1472 - 2A, 18V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER PCB LAYOUT GUIDE 2) PCB layout is very important to achieve stable operation. It is highly recommended to duplicate EVB layout for optimum performance. 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) Route 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. If change is necessary, please follow these guidelines and take Figure 5 for reference. 1) Keep the path of switching current short and minimize the loop area formed by input cap, high-side MOSFET and low-side MOSFET. MP1472 Typical Application Circuit Top Layer Bottom Layer Figure 5--MP1472 Typical Application Circuit and PCB Layout Guide MP1472 Rev. 1.0 9/2/2011 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. (c) 2011 MPS. All Rights Reserved. 12 MP1472 - 2A, 18V SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER PACKAGE INFORMATION TSOT23-8 NOTICE: The information in this document is subject to change without notice. Please contact MPS for current specifications. Users should warrant and guarantee that third party Intellectual Property rights are not infringed upon when integrating MPS products into any application. MPS will not assume any legal responsibility for any said applications. MP1472 Rev. 1.0 9/2/2011 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. (c) 2011 MPS. All Rights Reserved. 13 Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: Monolithic Power Systems (MPS): MP1472GJ-Z MP1472GJ-P MP1472GJ-LF-Z MP1472GJ-LF-P