TM MP2309 1A, 23V, 340KHz Synchronous Rectified Step-Down Converter The Future of Analog IC Technology TM DESCRIPTION FEATURES The MP2309 is a monolithic synchronous buck regulator. The device integrates 140mΩ MOSFETS that provide 1A continuous load current over a wide operating input voltage of 4.75V to 23V. Current mode control provides fast transient response and cycle-by-cycle current limit. • • • • • • • • • • An adjustable soft-start prevents inrush current at turn-on. Shutdown mode drops the supply current to 1µA. This device, available in an 8-pin SOIC package, provides a very compact system solution with minimal reliance on external components. APPLICATIONS • • • • • EVALUATION BOARD REFERENCE Board Number Dimensions EV2309DS-00A 2.0”X x 1.5”Y x 0.5”Z 1A Output Current Wide 4.75V to 23V Operating Input Range Integrated 140mΩ Power MOSFET Switches Output Adjustable from 0.923V to 20V 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 Distributed Power Systems Networking Systems FPGA, DSP, ASIC Power Supplies Green Electronics/ Appliances Notebook Computers “MPS” and “The Future of Analog IC Technology” are Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION C5 10nF INPUT 4.75V to 23V Efficiency vs Load Current 100 90 7 1 IN OUTPUT 3.3V 1A BS 3 SW EN MP2309 8 SS GND 4 FB COMP 5 1% 6 C3 3.3nF EFFICIENCY (%) 2 80 VIN = 5V 70 VIN = 12V 60 VIN = 23V 50 40 30 20 0 0.25 0.5 0.75 LOAD CURRENT (A) MP2309-TAC01 MP2309 Rev. 1.4 3/13/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 1.0 MP2309-EC01 1 TM MP2309 – 1A, 23V, 340KHz SYNCHRONOUS RECTIFIED STEP-DOWN CONVERTER ABSOLUTE MAXIMUM RATINGS (1) PACKAGE REFERENCE BS 1 8 SS IN 2 7 EN Supply Voltage VIN ....................... –0.3V to +26V 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 SW 3 6 COMP Recommended Operating Conditions GND 4 5 FB Input Voltage VIN ............................ 4.75V to 23V Output Voltage VOUT .................... 0.923V to 20V Ambient Operating Temperature .... –40°C to +85°C TOP VIEW MP2309_PD01_SOIC8 Thermal Resistance (3) θJA (2) θJC SOIC8..................................... 90 ...... 45... °C/W Part Number* Package Temperature MP2309DS SOIC8 –40° to +85°C * For Tape & Reel, add suffix –Z (eg. MP2309DS–Z) For Lead Free, add suffix –LF (eg. MP2309DS–LF–Z) 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. ELECTRICAL CHARACTERISTICS VIN = 12V, TA = +25°C, unless otherwise noted. Parameter Symbol Condition Shutdown Supply Current Supply Current Feedback Voltage Error Amplifier Transconductance High-Side Switch On Resistance (4) Low-Side Switch On Resistance (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 EN Shutdown Threshold Hysteresis EN Lockout Threshold Voltage EN Lockout Hysteresis MP2309 Rev. 1.4 3/13/2006 VEN = 0V VEN = 2.0V, VFB = 1.0V VFB Feedback Overvoltage Threshold Error Amplifier Voltage Gain (4) Min 4.75V ≤ VIN ≤ 23V 0.900 AEA GEA ∆IC = ±10µA RDS(ON)1 RDS(ON)2 VEN = 0V, VSW = 0V Minimum Duty Cycle From Drain to Source 1.4 VFB = 0V VFB = 0.8V VEN Rising Max Units 1 1.3 3.0 1.5 µA mA 0.923 0.946 V 1.1 400 V V/V 800 µA/V 140 140 2 0.8 mΩ mΩ µA A A 2.4 A/V 340 100 90 220 1.5 210 2.5 210 KHz KHz % nS V mV V mV 10 GCS Fosc1 Fosc2 DMAX Typ 1.1 2.2 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 2.0 2.7 2 TM MP2309 – 1A, 23V, 340KHz SYNCHRONOUS RECTIFIED STEP-DOWN CONVERTER ELECTRICAL CHARACTERISTICS (continued) VIN = 12V, TA = +25°C, unless otherwise noted. Parameter Input Under Voltage Lockout Threshold Input Under Voltage Lockout Threshold Hysteresis Soft-Start Current Soft-Start Period Thermal Shutdown (4) Symbol Condition Min Typ Max Units VIN Rising 3.80 4.10 4.40 V VSS = 0V CSS = 0.1µF 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 MP2309 Rev. 1.4 3/13/2006 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 23V 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 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. 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. 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. 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 100kΩ 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. www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 3 TM MP2309 – 1A, 23V, 340KHz SYNCHRONOUS RECTIFIED STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS VIN = 12V, VOUT = 3.3V, L = 10µH, C1 = 10µF, C2 = 22µF, TA = +25°C, unless otherwise noted. No Load Operation Full Load Operation No Load 1A Load VIN, AC 200mV/div. VIN, AC 20mV/div. VO, AC 20mV/div. VO, AC 20mV/div. IL 1A/div. IL 1A/div. VSW 10V/div. VSW 10V/div. VEN 5V/div. VOUT 2V/div. IL 1A/div. VSW 10V/div. 2ms/div. MP2309-TPC01 MP2309-TPC03 MP2309-TPC02 Shutdown through Enable Shutdown through Enable VIN = 12V, VOUT = 3.3V, IOUT = 1A (Resistance Load) VIN = 12V, VOUT = 3.3V, No Load VEN 5V/div. VOUT 2V/div. VEN 5V/div. VEN 5V/div. VOUT 2V/div. VOUT 2V/div. IL 1A/div. IL 1A/div. IL 1A/div. VSW 10V/div. VSW 10V/div. 2ms/div. VSW 10V/div. 2ms/div. 2ms/div. MP2309-TPC04 Load Transient Test Short Circuit Recovery Short Circuit Entry VIN = 12V, VOUT = 3.3V, IOUT = 0.2A to 1A steps VOUT 200mV/div. MP2309-TPC06 MP2309-TPC05 VOUT 2V/div. VOUT 2V/div. IL 1A/div. iLOAD 1A/div. IL 1A/div. MP2309-TPC07 MP2309 Rev. 1.4 3/13/2006 IL 1A/div. MP2309-TPC8 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. MP2309-TPC09 4 TM MP2309 – 1A, 23V, 340KHz SYNCHRONOUS RECTIFIED STEP-DOWN CONVERTER OPERATION FUNCTIONAL DESCRIPTION The MP2309 is a synchronous rectified, current-mode, step-down regulator. It regulates input voltages from 4.75V to 23V down to an output voltage as low as 0.923V, and supplies up to 1A of load current. The MP2309 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. 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. When the MP2309 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. + CURRENT SENSE AMPLIFIER OVP 1.1V -OSCILLATOR + FB 5 100/340KHz 0.3V RAMP IN 1 BS 3 SW 4 GND 5V -- CLK ---+ + SS 8 + 2 0.923V + 2.5V + ERROR AMPLIFIER S Q R Q CURRENT COMPARATOR COMP 6 1.2V EN EN OK -- OVP IN < 4.10V LOCKOUT COMPARATOR IN + EN 7 INTERNAL REGULATORS 1.5V -- SHUTDOWN COMPARATOR 5V MP2309_F01_BD01 Figure 1—Functional Block Diagram MP2309 Rev. 1.4 3/13/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 5 TM MP2309 – 1A, 23V, 340KHz 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 L= ⎛ VOUT V × ⎜⎜1 − OUT f S × ∆L ⎝ VIN ⎞ ⎟⎟ ⎠ Where 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: Thus the output voltage is: VOUT = 0.923 × the maximum switch current limit. The inductance value can be calculated by: R1 + R2 R2 ILP = ILOAD + ⎛ VOUT V × ⎜1 − OUT 2 × f S × L ⎜⎝ VIN ⎞ ⎟⎟ ⎠ Where VOUT is the output voltage and VFB is the feedback voltage. Where ILOAD is the load current. R2 can be as high as 100kΩ, but a typical value is 10kΩ. Using the typical value for R2, R1 is determined by: The choice of which style inductor to use mainly depends on the price vs. size requirements and any EMI requirements. R1 = 10.87 × ( VOUT − 0.923 ) 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. For example, for a 3.3V output voltage, R2 is 10kΩ, and R1 is 26.1kΩ. Table 1 lists recommended resistor values. Table1—Recommended Resistors VOUT 1.8V 2.5V 3.3V 5V 12V R1 9.53kΩ 16.9kΩ 26.1kΩ 44.2Ω 121kΩ R2 10kΩ 10kΩ 10kΩ 10kΩ 10kΩ 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 MP2309 Rev. 1.4 3/13/2006 Table 2—Diode Selection Guide Part Number Voltage/Current Rating B130 SK13 MBRS130 30V, 1A 30V, 1A 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 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. www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 6 TM MP2309 – 1A, 23V, 340KHz SYNCHRONOUS RECTIFIED STEP-DOWN CONVERTER 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 ⎟⎠ 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 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 characteristics of the output capacitor also affect the stability of the regulation system. The MP2309 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 caused by capacitance can be estimated by: Compensation Components MP2309 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. ∆VIN = ILOAD VOUT × C1 VIN ⎛ V × ⎜⎜1 − OUT VIN ⎝ ⎞ ⎟⎟ ⎠ A VDC = R LOAD × G CS × A VEA × 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 = MP2309 Rev. 1.4 3/13/2006 ⎛ V × ⎜⎜1 − OUT VIN × L × C2 ⎝ VOUT 8 × fS 2 The DC gain of the voltage feedback loop is given by: VFB VOUT Where VFB is the feedback voltage, 0.923V; AVEA is the error amplifier voltage gain; GCS is the current sense transconductance and RLOAD is the load resistor value. The system has 2 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 transconductance. the error amplifier ⎞ ⎟⎟ ⎠ www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 7 TM MP2309 – 1A, 23V, 340KHz SYNCHRONOUS RECTIFIED STEP-DOWN CONVERTER 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 1 = 2π × C2 × R ESR In this case (as shown in Figure 2), 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 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 below one-tenth of the switching frequency. Determine the R3 value by the following equation: R3 = 2π × C2 × fC VOUT 2π × 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. To optimize the compensation components, the following procedure can be used. 1. Choose the compensation resistor (R3) to set 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 Where R3 is the compensation resistor. 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 2π × C2 × R ESR 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: 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 MP2309 SW MP2309_F02 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. MP2309 Rev. 1.4 3/13/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 8 TM MP2309 – 1A, 23V, 340KHz SYNCHRONOUS RECTIFIED STEP-DOWN CONVERTER TYPICAL APPLICATION CIRCUIT C5 10nF INPUT 4.75V to 23V 2 7 1 IN OUTPUT 3.3V 1A BS 3 SW EN MP2309 8 SS GND FB COMP 4 5 6 C6 (optional) C3 3.3nF 1% D1 B130 (optional) MP2309-F03 Figure 3—MP2309 with 3.3V Output, 22uF/6.3V Ceramic Output Capacito MP2309 Rev. 1.4 3/13/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 9 TM MP2309 – 1A, 23V, 340KHz SYNCHRONOUS RECTIFIED STEP-DOWN CONVERTER PACKAGE INFORMATION SOIC8 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. MP2309 Rev. 1.4 3/13/2006 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. 10