MP2270 1.8A, 24V, 700kHz Step-Down Converter The Future of Analog IC Technology DESCRIPTION FEATURES The MP2270 is a monolithic step-down switch mode converter with a built-in internal power MOSFET. It achieves 1.8A 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-by-cycle current limiting and thermal shutdown. * * * The MP2270 requires a minimum number of readily available standard external components. The MP2270 is available in a 10-pin exposed pad MSOP package. * * * * * * * 1.8A Continuous Output Current 0.3 Internal Power MOSFET Switch Stable with Low ESR Output Ceramic Capacitors 0.1A Shutdown Mode Fixed 700kHz Frequency Thermal Shutdown Cycle-by-Cycle Over Current Protection Wide 4.5V to 24V Operating Input Range Output Adjustable from 0.81V to 20V Available in a 10-pin Exposed Pad MSOP Package APPLICATIONS * * * * * Broadband Communications Equipment Digital Entertainment Systems Distributed Power Systems Battery Charger Pre-Regulator for Linear Regulators "MPS" and "The Future of Analog IC Technology" are Registered Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION VIN 5 IN BST MP2270 OFF ON 6 EN GND SW 1 3 CB 10nF D1 B230A FB VOUT 3.3V 10 VIN IOUT_MAX=1.8 8 MP2270 Rev. 1.1 4/16/2010 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2010 MPS. All Rights Reserved. 1 MP2270 - 1.8A, 24V, 700KHz STEP-DOWN CONVERTER ORDERING INFORMATION Part Number* Package Top Marking Free Air Temperature (TA) MP2270DH MSOP10w/Exposed Pad 2270D -40C to +85C * For Tape & Reel, add suffix -Z (e.g. MP2270DH-Z). For RoHS Compliant packaging, add suffix -LF (e.g. MP2270DH-LF-Z) PACKAGE REFERENCE TOP VIEW BST 1 10 FB N/C 2 9 N/C SW 3 8 GND N/C 4 7 N/C IN 5 6 EN EXPOSED PAD ON BACKSIDE Connect to GND ABSOLUTE MAXIMUM RATINGS (1) Thermal Resistance Supply Voltage VIN ....................................... 26V VSW ........................................-0.3V to VIN + 0.3V VBS ....................................................... VSW + 6V All Other Pins ..................................-0.3V to +6V (2) Continuous Power Dissipation (TA = +25C) ..........................................................2.3W Junction Temperature ...............................150C Lead Temperature ....................................260C Storage Temperature............... -65C to +150C MSOP10 w/Exposed Pad .......55 ...... 12 ... C/W Recommended Operating Conditions (3) Supply Voltage VIN ...........................4.5V to 24V Operating Junct. Temp (TJ)...... -40C to +125C MP2270 Rev. 1.1 4/16/2010 (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. Unauthorized Photocopy and Duplication Prohibited. (c) 2010 MPS. All Rights Reserved. 2 MP2270 - 1.8A, 24V, 700KHz STEP-DOWN CONVERTER ELECTRICAL CHARACTERISTICS VIN = 12V, TA = +25C, unless otherwise noted. Parameters Symbol Condition Feedback Voltage Feedback Current (5) Switch On-Resistance Switch Leakage Current Limit (5) Oscillator Frequency Fold-back Frequency Maximum Duty Cycle Minimum On-Time (5) Under-Voltage Lockout Threshold Rising Under-Voltage Lockout Threshold Hysteresis EN Input Low Voltage EN Input High Voltage EN Input Current Supply Current (Shutdown) Supply Current (Quiescent) Thermal Shutdown (5) VFB 4.5V VIN 24V IFB VFB = 0.8V Min Typ Max Units 0.790 0.810 0.830 V RDS(ON) fSW VEN = 0V, VSW = 0V Duty Cycle = 40% VFB = 0.6V VFB = 0V VFB = 0.6V 2.0 tON 2.5 10 nA 0.3 0 2.5 700 230 87 100 2.8 150 A A kHz kHz % ns V mV V V 10 3.1 0.4 1.5 VEN = 2V VEN = 0V VEN = 0V VEN = 2V, VFB = 1V 2.1 0.01 0.1 0.8 150 A 1.0 1.0 A mA C Note: 5) Guaranteed by design. MP2270 Rev. 1.1 4/16/2010 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2010 MPS. All Rights Reserved. 3 MP2270 - 1.8A, 24V, 700KHz STEP-DOWN CONVERTER PIN FUNCTIONS Pin # 2, 4, 9, 7 3 5 6 10 8 1 Name Description NC No Connect. SW Switch Output. Supply Voltage. The MP2270 operates from a +4.5V to +24V unregulated input. C1 is needed IN to prevent large voltage spikes from appearing at the input. EN On/Off Control Input. Pull above 1.2V to turn the device on. Feedback. An external resistor divider from the output to GND, tapped to the FB pin sets the output voltage. To prevent current limit run away during a short circuit fault condition the FB frequency foldback comparator lowers the oscillator frequency when the FB voltage is below 250mV. Ground. This pin is the voltage reference for the regulated output voltage. For this reason GND, care must be taken in its layout. This node should be placed outside of the D1 to C1 ground Exposed path to prevent switching current spikes from inducing voltage noise into the part. Exposed pad pad must be connected to a ground plane for proper thermal operation. Bootstrap. This capacitor is needed to drive the power switch's gate above the supply BST voltage. It is connected between SW and BST pins to form a floating supply across the power switch driver. MP2270 Rev. 1.1 4/16/2010 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2010 MPS. All Rights Reserved. 4 MP2270 - 1.8A, 24V, 700KHz STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS VIN = 12V, VOUT = 1.8V, L=6.8H, ILOAD=0.5A - 1.8A, TA = +20C, unless otherwise noted. 900 3.0 880 2.5 860 840 2.0 820 800 1.5 780 1.0 760 740 0.5 720 700 5 10 15 20 0 5 10 15 20 25 0 0 20 40 60 80 100 40 35 30 VOUT_MAX DMAX Limit VIN=20V 25 20 VIN=12V Minimum On Time Limit 15 10 VFB_MIN 5 0 0 MP2270 Rev. 1.1 4/16/2010 0.5 1.0 1.5 2.0 0 5 10 15 20 25 0 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2010 MPS. All Rights Reserved. 1 5 MP2270 - 1.8A, 24V, 700KHz STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN = 12V, VOUT = 1.8V, L=6.8H, ILOAD=0.5A - 1.8A, TA = +20C, unless otherwise noted. MP2270 Rev. 1.1 4/16/2010 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2010 MPS. All Rights Reserved. 6 MP2270 - 1.8A, 24V, 700KHz STEP-DOWN CONVERTER OPERATION The MP2270 is a current mode buck regulator. That is, the EA output voltage is proportional to the peak inductor current. At the beginning of a cycle, M1 is off. The EA output voltage is higher than the current sense amplifier output, and the current comparator's output is low. The rising edge of the 700KHz CLK signal sets the RS Flip-Flop. Its output turns on M1 thus connecting the SW pin and inductor to the input supply. The increasing inductor current is sensed and amplified by the Current Sense Amplifier. Ramp compensation is summed to Current Sense Amplifier output and compared to the Error Amplifier output by the PWM Comparator. When the sum of the Current Sense Amplifier output and the Slope Compensation signal exceeds the EA output voltage, the RS FlipFlop is reset and the M1 is turned off. The external Schottky rectifier diode (D1) conducts the inductor current. If the sum of the Current Sense Amplifier output and the Slope Compensation signal does not exceed the EA output for a whole cycle, then the falling edge of the CLK resets the Flip-Flop. The output of the Error Amplifier integrates the voltage difference between the feedback and the 0.81V bandgap reference. The polarity is such that a FB pin voltage lower than 0.8V increases the EA output voltage. Since the EA output voltage is proportional to the peak inductor current, an increase in its voltage also increases current delivered to the output. IN x20 CURRENT SENSE AMPLIFIER + -- D REGULATOR BST EN REGULATOR OSCILLATOR 700KHz S + -1pF REFERENCE FB Q DRIVER M1 R CURRENT LIMIT COMPARATOR R SW 27pF +EA -- ERROR AMPLIFIER + -- PWM COMPARATOR GND Figure 1--Functional Block Diagram MP2270 Rev. 1.1 4/16/2010 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2010 MPS. All Rights Reserved. 7 MP2270 - 1.8A, 24V, 700KHz STEP-DOWN CONVERTER APPLICATION INFORMATION Setting Output Voltage The external resistor divider is used to set the output voltage (see the schematic on front page). The feedback resistor R1 also sets the feedback loop bandwidth with the internal compensation capacitor (see Figure 1). R2 can be determined by: R2 = R1 VOUT -1 0.81V Table 1--Resistor Selection for Common Output Voltages VOUT (V) R1 (k) R2 (k) 1.8 2.5 3.3 5 80.6 (1%) 49.9 (1%) 49.9 (1%) 49.9 (1%) 64.9 (1%) 23.7 (1%) 16.2 (1%) 9.53 (1%) Selecting the Inductor A 1H to 10H inductor with a DC current rating of at least 25% percent higher than the maximum load current is recommended for most applications. For highest efficiency, the inductor's DC resistance should be less than 200m. For most designs, the required inductance value can be derived from the following equation. L= Selecting the Input Capacitor The input capacitor reduces the surge current drawn from the input and the switching noise from the device. The input capacitor impedance at the switching frequency should be less than the input source impedance to prevent high frequency switching current from passing through the input. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. For most applications, a 10F capacitor is sufficient. Selecting the Output Capacitor The output capacitor keeps output voltage ripple small and ensures loop stability. The output capacitor impedance should be low at the switching frequency. Ceramic capacitors with X5R or X7R dielectrics are recommended for their low ESR characteristics. For most applications, a 22F ceramic capacitor will be sufficient. PC Board Layout The high current paths (GND, IN and SW) should be placed very close to the device with short, direct and wide traces. The input capacitor needs to be as close as possible to the IN and GND pins. The external feedback resistors should be placed next to the FB pin. Keep the switch node traces short and away from the feedback network. VOUT x ( VIN - VOUT ) VIN x IL x f OSC Where IL is the inductor ripple current. Choose an inductor with a rating current of approximately 30% higher than the maximum load current if the maximum load current is 1.8A. The maximum inductor peak current is calculated from: IL(MAX ) = ILOAD + I L 2 Under light load conditions below 100mA, a larger inductance is recommended for improved efficiency. See Table 2 for suggested inductors. MP2270 Rev. 1.1 4/16/2010 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2010 MPS. All Rights Reserved. 8 MP2270 - 1.8A, 24V, 700KHz STEP-DOWN CONVERTER External Bootstrap Diode An external bootstrap diode may enhance the efficiency of the regulator, the applicable conditions of external BST diode are: z VOUT=5V or 3.3V; and z Duty cycle is high: D= VOUT >65% VIN In these cases, an external BST diode is recommended from the output of the voltage regulator to BST pin, as shown in Fig.2 External BST Diode IN4148 BST CBST MP2270 SW L 5V or 3.3V COUT Figure 2--Add Optional External Bootstrap Diode to Enhance Efficiency The recommended external BST diode is IN4148, and the BST cap is 0.1~1F. Table 2--Suggested Surface Mount Inductors Manufacturer Part Number Inductance(H) Max DCR() Current Rating (A) Dimensions L x W x H (mm3) Wurth Electronics Toko Coiltronics 7447785004 A916CY-4R7M DR73-4R7 4.7 4.7 4.7 0.060 0.026 0.03 2.5 2.5 3 5.9 x 6.2 x 3.3 6.2 x 6.3 x 3.5 6.0 x 7.6 x 3.5 MP2270 Rev. 1.1 4/16/2010 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2010 MPS. All Rights Reserved. 9 MP2270 - 1.8A, 24V, 700KHz STEP-DOWN CONVERTER PACKAGE INFORMATION MSOP 10 (EXPOSED PAD) 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. MP2270 Rev. 1.1 4/16/2010 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. (c) 2010 MPS. All Rights Reserved. 10