MP2365 3A, 28V, 1.4MHz Step-Down Converter The Future of Analog IC Technology DESCRIPTION FEATURES The MP2365 is a 1.4MHz step-down regulator with a built-in Power MOSFET. It achieves 3A continuous output current over a wide input supply range with excellent load and line regulation. • Current mode operation provides fast transient response and eases loop stabilization. Fault condition protection includes cycle-bycycle current limiting and thermal shutdown. Adjustable soft-start reduces the stress on the input source at turn-on. In shutdown mode the regulator draws 20µA of supply current. The MP2365 is available in an 8-pin SOIC package with an exposed pad, and requires a minimum number of readily available external components to complete a 3A step-down DC to DC converter solution. EVALUATION BOARD REFERENCE Board Number Dimensions EV2365DN-00A 2.0” x 1.9” x 0.4” • • • • • • • • • • • 3A Continuous Output Current, 4A Peak Output Current Programmable Soft-Start 100mΩ Internal Power MOSFET Switch Stable with Low ESR Output Ceramic Capacitors Up to 90% Efficiency 20µA Shutdown Mode Fixed 1.4MHz Frequency Thermal Shutdown Cycle-by-Cycle Over Current Protection Wide 4.75V to 28V Operating Input Range Output is Adjustable From 0.92V to 21V Under Voltage Lockout APPLICATIONS • • • Distributed Power Systems Battery Chargers Pre-Regulator for Linear Regulators “MPS” and “The Future of Analog IC Technology” are Registered Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION Efficiency Curve INPUT 4.75V to 28V 7 8 10nF 1 2 IN BS SW EN MP2365 SS GND FB COMP 4 6 OPEN 3 5 B330A 5.6nF OUTPUT 3.3V 3A VOUT=5V EFFICIENCY (%) OPEN = AUTOMATIC STARTUP 100 90 VOUT=3.3V 80 70 VIN=12V 60 MP2365 Rev. 0.91 7/10/2006 0 0.5 1.0 1.5 2.0 2.5 LOAD CURRENT (A) www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 3.0 1 MP2365 – 3A, 28V, 1.4MHz STEP-DOWN CONVERTER ABSOLUTE MAXIMUM RATINGS (1) PACKAGE REFERENCE Supply Voltage VIN ....................... –0.3V to +30V Switch Voltage VSW .............. –0.5V 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 28V Ambient Operating Temp ..........–40°C to +85°C EXPOSED PAD CONNECT TO PIN 4 Thermal Resistance * (2) (3) θJA θJC SOIC8N .................................. 50 ...... 10... °C/W Part Number* Package Temperature MP2365DN SOIC8N –40°C to +85°C 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 (eg. MP2365DN–Z) For RoHS compliant packaging, add suffix –LF (eg. MP2365DN–LF–Z) ELECTRICAL CHARACTERISTICS VIN = 12V, TA = +25°C, unless otherwise noted. Parameters Symbol Condition Shutdown Supply Current Supply Current VEN = 0V VEN = 3V, VFB =1.4V Feedback Voltage VFB Error Amplifier Voltage Gain AVEA Error Amplifier Transconductance GEA High-Side Switch-On Resistance Low-Side Switch-On Resistance High-Side Switch Leakage Current Short Circuit Current Limit Current Sense to COMP Transconductance Oscillation Frequency Short Circuit Oscillation Frequency Maximum Duty Cycle Minimum On Time EN Threshold Voltage Enable Pull Up Current Under Voltage Lockout Threshold Rising Under Voltage Lockout Threshold Hysteresis Soft-Start Period Min 4.75V ≤ VIN ≤ 28V, VCOMP < 2V 0.90 ∆ICOMP = ±10µA 330 VEN = 0V, VSW = 0V GCS fS VFB = 0V VFB = 0.8V VEN = 0V 0.9 0.9 2.3 CSS = 0.1µF Thermal Shutdown MP2365 Rev. 0.91 7/10/2006 Max Units 20 1.3 30 1.5 µA mA 0.92 0.94 V 400 RDS(ON)1 RDS(ON)2 DMAX TON Typ 530 100 10 0.1 6.5 6.2 1.4 220 65 130 1.2 1.6 2.6 210 10 160 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. V/V 730 10 1.5 2.3 2.9 µA/V mΩ Ω µA A A/V MHz KHz % ns V µA V mV ms °C 2 MP2365 – 3A, 28V, 1.4MHz STEP-DOWN CONVERTER PIN FUNCTIONS Pin # 1 2 3 4 5 6 7 8 Name Description High-Side Gate Drive Boost Input. BS supplies the drive for the high-side N-Channel MOSFET BS switch. Connect a 10nF 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. IN Drive IN with a 4.75V to 28V 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. Connect SW 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 the exposed pad on backside to Pin 4. Feedback Input. FB senses the output voltage to regulate said voltage. Drive FB with a FB resistive voltage divider from the output voltage. The feedback threshold is 0.92V. See Setting the Output Voltage Compensation Node. COMP is used to compensate the regulation control loop. Connect a COMP 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 Enable Input. EN is a digital input that turns the regulator on or off. Drive EN higher than 2.9V EN to turn on the regulator, lower than 0.9V to turn it off. For automatic startup, leave EN unconnected. Soft-Start Control Input. SS controls the soft start period. Connect a capacitor from SS to GND SS to set the soft-start period. A 0.1µF capacitor sets the soft-start period to 10ms. To disable the soft-start feature, leave SS unconnected. MP2365 Rev. 0.91 7/10/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 3 MP2365 – 3A, 28V, 1.4MHz STEP-DOWN CONVERTER ELECTRICAL CHARACTERISTICS VIN = 12V, C1 = 10µF, C2 = 47µF, L = 4.7µH and TA = +25°C, unless otherwise noted. Steady State Operation Steady State Operation VOUT = 1.8V, IOUT = 1.5A VOUT = 1.8V, IOUT = 3A Peak Current vs Duty Cycle VOUT AC Coupled 20mV/div. VOUT AC Coupled 20mV/div. VSW 10V/div. VSW 10V/div. IINDUCTOR 2A/div. IINDUCTOR 2A/div. PEAK CURRENT (A) 8.0 7.5 7.0 6.5 6.0 5.5 400ns/div. VOUT AC Coupled 50mV/div. 5.0 400ns/div. 0 20 40 60 DUTY CYCLE (%) Startup Through Enable Startup Through Enable VOUT = 3.3V, I = 1.5A (Resistance Load) VOUT = 3.3V, I = 3A (Resistance Load) VEN 5V/div. VEN 5V/div. VOUT 1V/div. VOUT 1V/div. IINDUCTOR 1A/div. VSW 10V/div. VSW 10V/div. ILOAD 1A/div. IINDUCTOR 2A/div. IINDUCTOR 2A/div. 4ms/div. 4ms/div. Shutdown Through Enable Shutdown Through Enable VOUT = 3.3V, I = 1.5A (Resistance Load) VOUT = 3.3V, I = 3A (Resistance Load) VEN 5V/div. VEN 5V/div. VOUT 1V/div. VOUT 1V/div. VSW 10V/div. VSW 10V/div. IINDUCTOR 2A/div. IINDUCTOR 2A/div. MP2365 Rev. 0.91 7/10/2006 80 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 4 MP2365 – 3A, 28V, 1.4MHz STEP-DOWN CONVERTER OPERATION The converter uses an internal N-Channel MOSFET switch to step-down the input voltage to the regulated output voltage. Since the MOSFET requires a gate voltage greater than the input voltage, a boost capacitor connected between SW and BS drives the gate. The capacitor is internally charged while SW is low. The MP2365 is a current-mode step-down regulator. It regulates input voltages from 4.75V to 28V down to an output voltage as low as 0.92V, and is able to supply up to 3A of load current. The MP2365 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 error amplifier. The output current of the transconductance error amplifier is presented at COMP where a network compensates the regulation control system. The voltage at COMP is compared to the switch current measured internally to control the output voltage. An internal 10Ω switch from SW to GND is used to insure that SW is pulled to GND when SW is low to fully charge the BS.capa IN 2 CURRENT SENSE AMPLIFIER INTERNAL REGULATORS OSCILLATOR 220KHz/ 1.5MHz 1.2V -- EN 7 -- SLOPE COMP 5V -- CLK + + + SHUTDOWN COMPARATOR -- 1 BS S Q R Q 3 SW CURRENT COMPARATOR LOCKOUT COMPARATOR 8 SS 2.60V/ 2.39V + -- + 4 GND 1.8V FREQUENCY FOLDBACK COMPARATOR -- 0.6V 0.92V 5 FB + ERROR AMPLIFIER 6 COMP Figure 1—Functional Block Diagram MP2365 Rev. 0.91 7/10/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 5 MP2365 – 3A, 28V, 1.4MHz STEP-DOWN CONVERTER APPLICATION INFORMATION COMPONENT SELECTION (Refer to Figure 3) 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 . Thus the output voltage is: VOUT = 0.92 × R1 + R2 R2 A typical value for R2 can be as high as 100kΩ, but a typical value is 10kΩ. Using that value, R1 is determined by: R1 = 8.18 × ( VOUT − 0.92)(kΩ ) 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 V × ⎜⎜1 − OUT fS × ∆IL ⎝ VIN Choose an inductor that will not saturate under the maximum inductor peak current. The peak inductor current can be calculated by: 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 Vendor/ Model Package Dimensions (mm) Core Type Core Material W L H CR75 Open Ferrite 7.0 7.8 5.5 CDH74 Open Ferrite 7.3 8.0 5.2 CDRH5D28 Shielded Ferrite 5.5 5.7 5.5 CDRH5D28 Shielded Ferrite 5.5 5.7 5.5 Sumida CDRH6D28 Shielded Ferrite 6.7 6.7 3.0 CDRH104R Shielded Ferrite 10.1 10.0 3.0 Ferrite 5.0 5.0 3.0 Toko D53LC Type A Shielded D75C Shielded Ferrite 7.6 7.6 5.1 D104C Shielded Ferrite 10.0 10.0 4.3 D10FL Open Ferrite 9.7 1.5 4.0 DO3308 Open Ferrite 9.4 13.0 3.0 DO3316 Open Ferrite 9.4 13.0 5.1 Coilcraft ⎞ ⎟⎟ ⎠ Where VIN is the input voltage, fS is the 1.4MHz switching frequency and ∆IL is the peak-to-peak inductor ripple current. MP2365 Rev. 0.91 7/10/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 6 MP2365 – 3A, 28V, 1.4MHz STEP-DOWN CONVERTER Output Rectifier Diode The output rectifier diode supplies the current to the inductor when the high-side switch is off. To reduce losses due to the diode forward voltage and recovery times, use a Schottky diode. Choose a diode whose maximum reverse voltage rating is greater than the maximum input voltage, and whose current rating is greater than the maximum load current. Table 2 lists example Schottky diodes and manufacturers. 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 caused by capacitance can be estimated by: ∆VIN = Table 2—Diode Selection Guide Voltage/Current Manufacture Rating Diode SK33 SK34 B330 B340 MBRS330 MBRS340 30V, 3A 40V, 3A 30V, 3A 40V, 3A 30V, 3A 40V, 3A Diodes Inc. Diodes Inc. Diodes Inc. Diodes Inc. On Semiconductor On Semiconductor 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. 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 I = LOAD 2 For simplification, choose the input capacitor whose RMS current rating greater than half of the maximum load current. MP2365 Rev. 0.91 7/10/2006 ⎛ ILOAD V V × OUT × ⎜1 − OUT fS × C1 VIN ⎜⎝ VIN ⎞ ⎟⎟ ⎠ Output Capacitor The output capacitor (C2) 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 fS × L ⎝ VIN ⎞ ⎞ ⎛ 1 ⎟ ⎟⎟ × ⎜ R ESR + ⎜ 8 × f S × C2 ⎟⎠ ⎠ ⎝ Where L is the inductor 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 f S × L ⎜⎝ VIN ⎞ ⎟⎟ × R ESR ⎠ The characteristics of the output capacitor also affect the stability of the regulation system. The MP2365 can be optimized for a wide range of capacitance and ESR values. www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 7 MP2365 – 3A, 28V, 1.4MHz STEP-DOWN CONVERTER Compensation Components MP2365 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: A VDC = R LOAD × G CS × A VEA × 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 error amplifier, and the other is due to the output capacitor and the load resistor. These poles are located at: fP1 = GEA 2π × C3 × A VEA fP2 = 1 2π × C2 × R LOAD Where GEA is the transconductance, 530µA/V. error amplifier 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 = MP2365 Rev. 0.91 7/10/2006 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: f P3 = 1 2π × 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 crossover frequencies could cause system unstable. A good rule of thumb is to set the crossover frequency to approximately one-tenth of the switching frequency or lower. The switching frequency for the MP2365 is 1.4MHz, so the desired crossover frequency is equal to or less than 140KHz. 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 Typical Output Voltage/Capacitor Combinations VOUT (V) L (µH) C2 (µF, Ceramic) R3 (kΩ) C3 (nF) C6 1.8 2.2 47 7.5 3.3 None 2.5 2.2 - 4.7 47 10 4.7 None 3.3 2.2 - 4.7 47 15 5.6 None 5 4.7 – 6.8 2 x 22 20 4.7 None 12 6.8 - 10 2 x 22 44.2 2.2 None 1 2π × C2 × R ESR www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 8 MP2365 – 3A, 28V, 1.4MHz STEP-DOWN CONVERTER To optimize the compensation components for conditions not listed in Table 3, 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 × C2 × f C VOUT × G EA × G CS VFB Where fC is the desired crossover 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 2π × R3 × f C 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 1.4MHz switching frequency, or the following relationship is valid: f 1 < S 2π × C2 × R ESR 2 MP2365 Rev. 0.91 7/10/2006 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: C6 = C2 × R ESR R3 External Bootstrap Diode It is recommended that an external bootstrap diode be added when the system has a 5V fixed input or the power supply generates a 5V output. This helps improve the efficiency of the regulator. The bootstrap diode can be a low cost one such as IN4148 or BAT54. 5V BS 10nF MP2365 SW Figure 2—External Bootstrap Diode This diode is also recommended for high duty cycle operation (when VOUT >65%) and high VIN output voltage (VOUT>12V) applications. www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 9 MP2365 – 3A, 28V, 1.4MHz STEP-DOWN CONVERTER TYPICAL APPLICATION CIRCUITS C5 10nF INPUT 4.75V to 28V OPEN = AUTOMATIC STARTUP 2 1 BS 3 SW IN 7 EN OUTPUT 2.5V 3A MP2365 8 SS GND FB COMP 4 5 6 C3 4.7nF C6 OPEN D1 B330A Figure 3—2.5V Output Typical Application Schematic C5 10nF INPUT 4.75V to 28V OPEN = AUTOMATIC STARTUP 2 1 BS 3 SW IN 7 EN OUTPUT 3.3V 3A MP2365 8 SS GND FB COMP 4 5 6 C6 OPEN C3 5.6nF D1 B330A Figure 4—3.3V Output Typical Application Schematic MP2365 Rev. 0.91 7/10/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 10 MP2365 – 3A, 28V, 1.4MHz STEP-DOWN CONVERTER PACKAGE INFORMATION SOIC8N (EXPOSED PAD) 0.189(4.80) 0.197(5.00) 8 0.124(3.15) 0.136(3.45) 5 0.150(3.80) 0.157(4.00) PIN 1 ID 1 0.228(5.80) 0.244(6.20) 0.089(2.26) 0.101(2.56) 4 TOP VIEW BOTTOM VIEW SEE DETAIL "A" 0.013(0.33) 0.020(0.51) 0.051(1.30) 0.067(1.70) SEATING PLANE 0.000(0.00) 0.006(0.15) 0.0075(0.19) 0.0098(0.25) SIDE VIEW 0.050(1.27) BSC FRONT VIEW 0.010(0.25) x 45o 0.020(0.50) GAUGE PLANE 0.010(0.25) BSC 0.024(0.61) 0.050(1.27) 0o-8o 0.016(0.41) 0.050(1.27) 0.063(1.60) DETAIL "A" 0.103(2.62) 0.138(3.51) RECOMMENDED LAND PATTERN 0.213(5.40) NOTE: 1) CONTROL DIMENSION IS IN INCHES. DIMENSION IN BRACKET IS IN MILLIMETERS. 2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH , PROTRUSIONS OR GATE BURRS. 3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. 4) LEAD COPLANARITY(BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.004" INCHES MAX. 5) DRAWING CONFORMS TO JEDEC MS-012, VARIATION BA. 6) DRAWING IS NOT TO SCALE. NOTICE: The information in this document is subject to change without notice. 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. MP2365 Rev. 0.91 7/10/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 11