The Future of Analog IC Technology MP363 3A, 7, 365KHz Step-Down Converter DESCRIPTION The MP363 is a non-synchronous step-down regulator with an integrated 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 0µA of supply current. The MP363 requires a minimum number of readily available external components to complete a 3A step-down DC to DC converter solution. The MP363 is available in 8-pin SOICN and PDIP packages. EALUATION BOARD REFERENCE Board Number Dimensions E363DN-00A.0 X x.9 Y x 0. Z FEATURES 3A Continuous Output Current, A Peak Output Current Programmable Soft-Start 00mΩ Internal Power MOSFET Switch Stable with Low ESR Output Ceramic Capacitors Up to 95% Efficiency 0µA Shutdown Mode Fixed 365KHz frequency Thermal Shutdown Cycle-by-Cycle Over Current Protection Wide.75 to 7 Operating Input Range Output is Adjustable From 0.9 to Under oltage 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 INPUT.75 to 7 OPEN = AUTOMATIC STARTUP 7 8 IN EN SS GND 0nF BS 3 MP363 5 OPEN 6 B330A 6.8nF PUT.5 3A EFFICIENCY (%) 00 90 80 70 60 Efficiency Curve IN = =.5 =5.0 =3.3 50 0 0.5.0.5.0.5 3.0 3.5 LOAD CURRENT (A) MP363 Rev..3 www.monolithicpower.com 00 MPS. All Rights Reserved.
PACKAGE REFERENCE BS IN GND 3 EXPOSED PAD (BACKSIDE) OF SOIC8N ONLY CONNECT TO PIN TOP IEW Part Number* Package Temperature MP363DN SOIC8N 0 C to +85 C **MP363DP **PDIP8 * For Tape & Reel, add suffix Z (eg. MP363DN Z) For RoHS Compliant Packaging, add suffix LF (eg. MP363DN LF Z) ** Contact Factory for Availability 8 7 6 5 SS EN ABSOLUTE MAXIMUM RATINGS () Supply oltage IN... 0.3 to +8 Switch oltage... to IN + 0.3 Boost oltage BS... 0.3 to + 6 All Other Pins... 0.3 to +6 Junction Temperature...50 C Lead Temperature...60 C Storage Temperature... 65 C to +50 C Recommended Operating Conditions () Input oltage IN....75 to 7 Ambient Operating Temp... 0 C to +85 C Thermal Resistance (3) θ JA θ JC SOIC8N... 50... 0... C/W PDIP8... 0... 5... C/W Notes: ) Exceeding these ratings may damage the device. ) The device is not guaranteed to function outside of its operating conditions. 3) Measured on approximately square of oz copper. ELECTRICAL CHARACTERISTICS IN =, T A = +5 C, unless otherwise noted. Parameters Symbol Condition Min Typ Max Units Shutdown Supply Current EN = 0 0 30 µa Supply Current EN = 3, =..0. ma Feedback oltage.75 IN 7 0.90 0.9 0.9 Error Amplifier oltage Gain () A EA 00 / Error Amplifier Transconductance G EA I = ±0µA 500 800 0 µa/ High-Side Switch On-Resistance () R DS(ON) 00 mω Low-Side Switch On-Resistance R DS(ON) 6 Ω High-Side Switch Leakage Current EN = 0, = 0 0. 0 µa Short Circuit Current Limit.5 5.7 A Current Sense to Transconductance G CS 7.0 A/ Oscillation Frequency f S 35 365 5 KHz Short Circuit Oscillation Frequency = 0 0 35 50 KHz Maximum Duty Cycle D MAX = 0.8 88 % Minimum On Time () T ON 0 ns EN Threshold oltage 0.9..5 Enable Pull Up Current EN = 0 0.9.. µa Under oltage Lockout Threshold IN Rising.37.5.7 Under oltage Lockout Threshold Hysteresis 0 m Thermal Shutdown () 60 C Note: ) Guaranteed by design. MP363 Rev..3 www.monolithicpower.com 00 MPS. All Rights Reserved.
PIN FUNCTIONS Pin # Name Description BS High-Side Gate Drive Boost Input. BS supplies the drive for the high-side N-Channel MOSFET switch. Connect a 0nF or greater capacitor from to BS to power the high-side switch. IN Power Input. IN supplies the power to the IC, as well as the step-down converter switches. Drive IN with a.75 to 7 power source. Bypass IN to GND with a suitably large capacitor to eliminate noise on the input to the IC. See Input Capacitor section of Application Information. 3 Power Switching Output. is the switching node that supplies power to the output. Connect the output LC filter from to the output load. Note that a capacitor is required from to BS to power the high-side switch. GND Ground. Connect the exposed pad on backside to Pin. 5 Feedback Input. senses the output voltage to regulate said voltage. Drive with a resistive voltage divider from the output voltage. The feedback threshold is 0.9. See Setting the Output oltage section of Application Information. 6 Compensation Node. is used to compensate the regulation control loop. Connect a series RC network from to GND to compensate the regulation control loop. In some cases, an additional capacitor from to GND is required. See Compensation section of Application Information. 7 EN Enable Input. EN is a digital input that turns the regulator on or off. Drive EN higher than.7 to turn on the regulator, lower than 0.9 to turn it off. For automatic startup, leave EN unconnected. 8 SS Soft Start Control Input. SS controls the soft start period. Connect a capacitor from SS to GND to set the soft-start period. Soft-start cap is always recommended to eliminate the start-up inrush current and for a smooth start-up waveform. TYPICAL PERFORMANCE CHARACTERISTICS IN =, =.5, L = 5µH, C = 0µF, C = µf, T A = +5 C, unless otherwise noted. EFFICIENCY (%) Efficiency Curve vs Load Current = 3.3 95 90 IN =9 85 80 75 IN = IN = 70 65 60 55 50 0 0.5.0.5.0.5 3.0 3.5 LOAD CURRENT (A) EFFICIENCY (%) Efficiency Curve vs Load Current = 5 00 95 IN =9 90 85 80 75 70 65 60 55 50 IN = IN = 0 0.5.0.5.0.5 3.0 3.5 LOAD CURRENT (A) CURRENT LIMIT (A) 7.0 6.5 6.0 5.5 5.0.5 Limit Current vs Duty Cycle.0 0 0. 0. 0.3 0. 0.5 0.6 0.7 DUTY CYCLE (%) MP363 Rev..3 www.monolithicpower.com 3 00 MPS. All Rights Reserved.
TYPICAL PERFORMANCE CHARACTERISTICS (continued) IN =, =.5, L = 5µH, C = 0µF, C = µf, T A = +5 C, unless otherwise noted. ITCHING FREQUENCY (KHz) Switching Frequency vs Die Temperature 00 390 380 370 360 350 30 330 30-0 -0 0 0 0 60 80 00 0 DIE TEMPERATURE ( o C) AC Coupled 00m/div. I LOAD A/div. I L A/div. 0m/div. IN 00m/div. 0/div. Steady State Test =.5A Resistive Load Steady State Test I = 3A Resistive Load Startup through Enable I =.5A Resistive Load Startup through Enable I = 3A Resistive Load I L A/div. 0m/div. IN 00m/div. 0/div. /div. I L A/div. /div. I L A/div. ms/div. ms/div. Shutdown through Enable I =.5A Resistive Load Shutdown through Enable I = 3A Resistive Load /div. /div. I L A/div. I L A/div. MP363 Rev..3 www.monolithicpower.com 00 MPS. All Rights Reserved.
OPERATION The MP363 is a current-mode step-down regulator. It regulates an input voltage between.75 to 7 down to an output voltage as low as 0.9, and is able to supply up to 3A of load current. The MP363 uses current-mode control to regulate the output voltage. The output voltage is measured at the pin through a resistive voltage divider and amplified through the internal error amplifier. The output current of the transconductance error amplifier is presented at where a network compensates the regulation control system. The voltage at is compared to the switch current measured internally to control the output voltage. 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 and BS drives the gate. The capacitor is charged by an internal 5 supply while is low. An internal 0Ω switch from to GND is used to insure that is pulled to GND when is low to fully charge the boost.capacitor. IN INTERNAL REGULATORS CURRENT SENSE AMPLIFIER + 5 OSCILLATOR 35KHz/ 365KHz SLOPE -- BS CLK + + S Q EN 7. -- -- SHUTDOWN ARATOR LOCK ARATOR -- R Q CURRENT ARATOR 3.5/.33 + + --.8 GND FREQUENCY FOLDBACK ARATOR -- 0.35 0.9 + 5 SS 8 ERROR AMPLIFIER 6 Figure Functional Block Diagram MP363 Rev..3 www.monolithicpower.com 5 00 MPS. All Rights Reserved.
APPLICATION INFORMATION ONENT SELECTION (Refer to the Typical Application Circuit on page 0) Setting the Output oltage The output voltage is set using a resistive voltage divider from the output voltage to pin. The voltage divider divides the output voltage down to the feedback voltage by the ratio: R = R + R Where is the feedback voltage and is the output voltage. Thus the output voltage is: R + R = 0.9 R A typical value for R can be as high as 00kΩ, but a typical value is 0kΩ. Using that value, R is determined by: R = 0 ( - )(kω) 0.9 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 = fs IL IN Where IN is the input voltage, f S is the 365KHz switching frequency, and I L 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: I LP = ILOAD + fs L IN Where I LOAD is the load current and f S is the 365KHz switching frequency. Table 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 Inductor Selection Guide endor/ Model Sumida Core Type Package Dimensions Core (mm) Material W L H CR75 Open Ferrite 7.0 7.8 5.5 CDH7 Open Ferrite 7.3 8.0 5. CDRH5D8 Shielded Ferrite 5.5 5.7 5.5 CDRH5D8 Shielded Ferrite 5.5 5.7 5.5 CDRH6D8 Shielded Ferrite 6.7 6.7 3.0 CDRH0R Shielded Ferrite 0. 0.0 3.0 Toko D53LC Type A Shielded Ferrite 5.0 5.0 3.0 D75C Shielded Ferrite 7.6 7.6 5. D0C Shielded Ferrite 0.0 0.0.3 D0FL Open Ferrite 9.7.5.0 Coilcraft DO3308 Open Ferrite 9. 3.0 3.0 DO336 Open Ferrite 9. 3.0 5. 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. MP363 Rev..3 www.monolithicpower.com 6 00 MPS. All Rights Reserved.
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 lists example Schottky diodes and manufacturers. Diode Table Diode Selection Guide oltage/current Rating Manufacture SK33 30, 3A Diodes Inc. SK3 0, 3A Diodes Inc. B330 30, 3A Diodes Inc. B30 0, 3A Diodes Inc. MBRS330 30, 3A On Semiconductor MBRS30 0, 3A 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 (C) absorbs the input switching current it requires an adequate ripple current rating. The RMS current in the input capacitor can be estimated by: I C = I LOAD IN IN I LOAD is the load current, is the output voltage, and IN is the input voltage. The worstcase condition occurs at IN =, where: ILOAD IC = 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.µF, 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: ILOAD = IN fs C IN IN Output Capacitor The output capacitor (C) 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: = RESR + f S L IN 8 fs C Where L is the inductor value and R ESR 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: = 8 fs L C IN 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: = R f IN S L ESR The characteristics of the output capacitor also affect the stability of the regulation system. The MP363 can be optimized for a wide range of capacitance and ESR values. MP363 Rev..3 www.monolithicpower.com 7 00 MPS. All Rights Reserved.
Compensation Components MP363 employs current mode control for easy compensation and fast transient response. The system stability and transient response are controlled through the pin. 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 DC = RLOAD GCS A EA Where A EA is the error amplifier voltage gain, 00/; G CS is the current sense transconductance, 7A/, and R LOAD 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: f f P P GEA = π C3 A = π C R EA LOAD Where G EA is the error amplifier transconductance, 800µA/. The system has one zero of importance, due to the compensation capacitor (C3) and the compensation resistor (R3). This zero is located at: f Z = π 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: f ESR = π C 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: f P 3 = π 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 can cause system instability. A good rule of thumb is to set the crossover frequency to approximately one-tenth of the switching frequency. Switching frequency for the MP363 is 365KHz, so the desired crossover frequency is around 36.5KHz. 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 alues for Typical Output oltage/capacitor Combinations L C R3 C3 C6.8.7µH 00µF 5.6kΩ 3.3nF None Ceramic.5.7 0µH 7µF Ceramic 3.3 6.8 0µH µfx Ceramic 5 0 5µH µfx Ceramic 5 0µH µfx Ceramic 3.3kΩ 6.8nF None.0kΩ 8.nF None 6.9kΩ 0nF None 5kΩ.7nF None MP363 Rev..3 www.monolithicpower.com 8 00 MPS. All Rights Reserved.
To optimize the compensation components for conditions not listed in Table, the following procedure can be used.. Choose the compensation resistor (R3) to set the desired crossover frequency. Determine the R3 value by the following equation: π C fc R 3 = G G EA CS Where f C is the desired crossover frequency (which typically has a value no higher than 37.5KHz).. Choose the compensation capacitor (C3) to achieve the desired phase margin. For applications with typical inductor values, setting the compensation zero, f Z, below one forth of the crossover frequency provides sufficient phase margin. Determine the C3 value by the following equation: C3 > π R3 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 365KHz switching frequency, or the following relationship is valid: π C R f C f < S ESR If this is the case, then add the second compensation capacitor (C6) to set the pole f P3 at the location of the ESR zero. Determine the C6 value by the equation: C R C6 = R3 ESR Soft-Start Capacitor To reduce input inrush current during startup, a programmable soft-start is provided by connecting a capacitor (C) from pin SS to GND. The soft-start time is given by: t SS (ms) = 5 CSS ( µ F) To reduce the susceptibility to noise, do not leave SS pin open. Use a capacitor with small value if you do not need soft-start function. PCB Layout Guide PCB layout is very important to achieve stable operation. Please follow these guidelines and take Figure and 3 for references. ) Keep the path of switching current short and minimize the loop area formed by Input cap, high-side MOSFET and schottky diode. ) Keep the connection of schottky diode between pin and input power ground as short and wide as possible. 3) Ensure all feedback connections are short and direct. Place the feedback resistors and compensation components as close to the chip as possible. ) Route away from sensitive analog areas such as. 5) Connect IN,, and especially GND respectively to a large copper area to cool the chip to improve thermal performance and long-term reliability. For single layer, do not solder exposed pad of the IC. Figure PCB Layout for Single Layer MP363 Rev..3 www.monolithicpower.com 9 00 MPS. All Rights Reserved.
R R 3 BS IN GND SS/REF EN 8 7 6 5 Top Layer Bottom Layer Figure3 PCB Layout for Double Layer External Bootstrap Diode An external bootstrap diode may enhance the efficiency of the regulator, the applicable conditions of external BST diode are: =5 or 3.3; Duty cycle is high: D = > 65% IN In these cases, an external BST diode is recommended from the output of the voltage regulator to BST pin, as shown in Fig.. The recommended external BST diode is IN8, and the BST cap is 0.~µF. MP363 BST C External BST Diode IN8 BST L C 5 or 3.3 Figure Add Optional External Bootstrap Diode to Enhance Efficiency MP363 Rev..3 www.monolithicpower.com 0 00 MPS. All Rights Reserved.
TYPICAL APPLICATION CIRCUITS INPUT.75 to 7 OPEN = AUTOMATIC STARTUP 8 7 IN EN SS GND MP363 C6 OPEN BS 3 5 6 C3 8.nF C5 0nF D B330A PUT 3.3 3A Figure 5 MP363 for 3.3 Output with 7µF, 6.3 Ceramic Output Capacitor INPUT.75 to 7 OPEN = AUTOMATIC STARTUP 7 IN EN MP363 BS 3 C5 0nF PUT 5 3A 8 SS GND 5 C6 OPEN 6 C3 0nF D Figure 6 MP363 for 5 Output with 7µF, 6.3 Ceramic Output Capacitor MP363 Rev..3 www.monolithicpower.com 00 MPS. All Rights Reserved.
PACKAGE INFORMATION SOIC8N (EXPOSED PAD) 0.89(.80) 0.97(5.00) 8 5 0.(3.5) 0.36(3.5) PIN ID 0.50(3.80) 0.57(.00) 0.8(5.80) 0.(6.0) 0.089(.6) 0.0(.56) TOP IEW BOTTOM IEW SEE DETAIL "A" 0.03(0.33) 0.00(0.5) 0.05(.30) 0.067(.70) SEATING PLANE 0.000(0.00) 0.006(0.5) 0.050(.7) BSC SIDE IEW 0.0075(0.9) 0.0098(0.5) FRONT IEW 0.00(0.5) 0.00(0.50) x 5o GAUGE PLANE 0.00(0.5) BSC 0.0(0.6) 0.063(.60) 0.050(.7) 0 o -8 o 0.06(0.) 0.050(.7) DETAIL "A" 0.38(3.5) 0.03(.6) RECOMMENDED LAND PATTERN 0.3(5.0) NOTE: ) CONTROL DIMENSION IS IN INCHES. DIMENSION IN BRACKET IS IN MILLIMETERS. ) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. 3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. ) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.00" INCHES MAX. 5) DRAWING CONFORMS TO JEDEC MS-0, ARIATION BA. 6) DRAWING IS NOT TO SCALE. MP363 Rev..3 www.monolithicpower.com 00 MPS. All Rights Reserved.
PACKAGE INFORMATION (continued) PDIP8 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. MP363 Rev..3 www.monolithicpower.com 3 00 MPS. All Rights Reserved.