TM MP1591 2A, 32V, 330KHz Step-Down Converter The Future of Analog IC Technology TM DESCRIPTION FEATURES The MP1591 is a high voltage step-down converter ideal for automotive power adapter battery chargers. Its wide 6.5V to 32V input voltage range covers the automotive battery’s requirements and it achieves 2A continuous output for quick charge capability. • • • • • Current mode operation provides fast transient response and eases loop stabilization. Fault protection includes cycle-by-cycle current limiting and thermal shutdown. In shutdown mode, the converter draws only 20µA of supply current. • • • • • • • • • The MP1591 requires a minimum number of readily available external components to complete a 2A step-down DC to DC converter solution. EVALUATION BOARD REFERENCE Board Number Dimensions EV0020 2.1”X x 1.4”Y x 0.5”Z Wide 6.5V to 32V Input Operating Range 34V Absolute Maximum Input 2A Output Current 120mΩ Internal Power MOSFET Switch Stable with Low ESR Output Ceramic Capacitors Up to 95% Efficiency 20µA Shutdown Mode Fixed 330KHz Frequency Thermal Shutdown Cycle-by-Cycle Over Current Protection Output Adjustable From 1.23V to 21V Under Voltage Lockout Reference Voltage Output Available in 8-Pin SOIC Packages APPLICATIONS • • • • Automotive Power Adapters PDA and Cellular Phone Battery Chargers Distributed Power Systems Automotive Aftermarket Electronics “MPS” and “The Future of Analog IC Technology” are Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION C2 10nF INPUT 6.5V to 32V Efficiency vs Load Current 100 VOUT=5V 90 2 OPEN NOT USED 8 1 IN BS 3 SW EN D1 MP1591 REF GND 4 FB COMP OUTPUT 2.5V 2A 5 6 C3 OPEN C4 4.7nF EFFICIENCY (%) OFF ON 7 VOUT=3.3V 80 70 60 50 40 VIN=12V 30 20 0 0.5 1 1.5 LOAD CURRENT (A) MP1591_TAC_S01 MP1591 Rev. 1.8 7/22/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 2 MP1591_EC01 1 TM MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER ABSOLUTE MAXIMUM RATINGS (1) PACKAGE REFERENCE IN Supply Voltage........................ –0.3V to +34V SW Voltage............................. –1V to VIN + 0.3V BS Voltage ....................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 REF IN 2 7 EN SW 3 6 COMP GND 4 5 FB EXPOSED PAD ON BACKSIDE (SOIC8N ONLY) CONNECT TO PIN 4 Recommended Operating Conditions Input Voltage ................................... 6.5V to 32V Operating Temperature .............–40°C to +85°C MP1591_PD01-SOIC8/N Thermal Resistance Part Number* Package Temperature MP1591DN SOIC8N –40°C to +85°C MP1591DS SOIC8 –40°C to +85°C * (2) For Tape & Reel, add suffix –Z (eg. MP1591DN–Z) For Lead Free, add suffix –LF (eg. MP1591DN–LF–Z) (3) θJA θJC SOIC8 (w/ Exposed Pad) ....... 50 ...... 10... °C/W SOIC8..................................... 90 ...... 45... °C/W 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 Shutdown Supply Current Supply Current Symbol Condition VEN = 0V VEN = 5V, VFB = 1.4V 6.5V ≤ VIN ≤ 32V, VCOMP < 2V Feedback Voltage Min Typ 20 1.0 Max 35 1.2 Units µA mA 1.202 1.230 1.258 V Error Amplifier Voltage Gain 400 Error Amplifier Transconductance ∆IC = ±10µA 500 700 2.5 120 8.5 0 3.6 (4) High-Side Switch On Resistance Low-Side Switch On Resistance (4) High-Side Switch Leakage Current Current Limit (5) Current Sense to COMP Transconductance Oscillation Frequency Short Circuit Oscillation Frequency Maximum Duty Cycle (4) Minimum Duty Cycle (4) EN Threshold Voltage Enable Pull-Up Current Under Voltage Lockout Threshold Under Voltage Lockout Threshold Hysteresis MP1591 Rev. 1.8 7/22/2005 VEN = 0V, VSW = 0V V/V 1100 µA/V 10 4.9 mΩ Ω µA A 3.5 280 330 35 90 0.8 1.2 1.8 2.6 VFB = 0V VFB = 1.0V VFB = 1.5V VEN = 0V VIN Rising 2.4 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 250 A/V 380 0 1.6 2.8 KHz KHz % % V µA V mV 2 TM MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER ELECTRICAL CHARACTERISTICS (continued) VIN = 12V, TA = +25°C, unless otherwise noted. Parameter Symbol Condition Thermal Shutdown Min (4) Typ 160 REF Voltage REF Load Regulation (4) REF Line Regulation (4) IREF = 0 ∆IREF = 0 to 1mA IREF = 100µA, VIN = 6.5 to 32V 5.0 100 30 Max Units °C V mV mV Notes: 4) These parameters are guaranteed by design, not production tested. 5) Equivalent output current = 1.5A ≥ 50% Duty Cycle 2.0A ≤ 50% Duty Cycle Assumes ripple current = 30% of load current. Slope compensation changes current limit. PIN FUNCTIONS Pin # Name Description 1 BS High-Side Gate Drive Boost Input. BS supplies the drive for the high-side N-Channel MOSFET switch. Connect a 10nF or greater capacitor from SW to BS to power the high-side switch. 2 IN Power Input. IN supplies the power to the IC, as well as the step-down converter switches. Drive IN with a 6.5V to 32V power source. Bypass IN to GND with a suitably large capacitor to eliminate noise on the input to the IC. See Input Capacitor. 3 SW 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. 4 GND 5 FB 6 Ground. For the MP1591DN, connect the Exposed Pad to pin 4. 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 1.230V. See Setting the Output Voltage. COMP 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. 7 EN Enable Input. EN is a digital input that turns the regulator on or off. Drive EN high to turn on the regulator and low to turn it off. For automatic startup, leave EN unconnected. 8 REF Reference Output. REF is the 5V reference voltage output. It can supply up to 1mA to external circuitry. If used, bypass REF to GND with 10nF or greater capacitor. Leave REF unconnected if not used. MP1591 Rev. 1.8 7/22/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 3 TM MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER OPERATION The voltage at COMP 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 SW and BS drives the gate. The capacitor is internally charged while SW is low. An internal 10Ω switch from SW to GND is used to insure that SW is pulled to GND when the switch is off to fully charge the BS capacitor. The MP1591 is a current mode step-down regulator. It regulates input voltages from 6.5V to 32V down to an output voltage as low as 1.230V and is able to supply up to 2A of load current. The MP1591 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. IN 2 5V REF 8 CURRENT SENSE AMPLIFIER INTERNAL REGULATORS OSCILLATOR 35/330KHz + 1.2V -- EN 7 -2.60V/ 2.35V + FREQUENCY FOLDBACK COMPARATOR + SLOPE COMP -- CLK + SHUTDOWN COMPARATOR -- S Q R Q CURRENT COMPARATOR 1 BS 3 SW 4 GND M1 M2 LOCKOUT COMPARATOR 1.8V -- + -- 0.7V 1.230V 5 FB + ERROR AMPLIFIER 6 COMP MP1591_BD01 Figure 1—Functional Block Diagram MP1591 Rev. 1.8 7/22/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 4 TM MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER APPLICATION INFORMATION COMPONENT SELECTION Setting the Output Voltage The output voltage is set using a resistive voltage divider from the output voltage to FB. The voltage divider divides the output voltage down 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 = 1.230 × (R1 + R2) R2 A typical value for R2 can be as high as 100kΩ, but 10kΩ is recommended. Using that value, R1 is determined by: R1 ≅ 8.18 × ( VOUT − 1.230 ) The inductance value can be calculated by the equation: L1 = VOUT × ( VIN − VOUT ) ( VIN × f × ∆I) Where VIN is the input voltage, f is the switching frequency and ∆I is the peak-to-peak inductor ripple current. Table 1 lists a number of suitable inductors from various manufacturers. Table 1—Inductor Selection Guide Package Dimensions (mm) Vendor/ Core Core Model Type Material W L H Sumida 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 For example, for a 3.3V output voltage, R2 is 10kΩ, and R1 is 17kΩ. CDRH5D28 Shielded Ferrite 5.5 5.7 5.5 CDRH6D28 Shielded Ferrite 6.7 6.7 3.0 Inductor (L1) The inductor is required to supply constant current to the output load while being driven by the switched input voltage. A larger value inductor results in less ripple current that results in lower output ripple voltage. However, the larger value inductor has a larger physical size, higher series resistance, and/or lower saturation current. Choose an inductor that does not saturate under the worst-case load conditions. A good rule to use for determining the inductance is to allow the peak-to-peak ripple current in the inductor to be approximately 30% of the maximum load current. Also, make sure that the peak inductor current (the load current plus half the peak-topeak inductor ripple current) is below the 2.3A minimum current limit. CDRH104R Shielded Ferrite 10.1 10.0 3.0 MP1591 Rev. 1.8 7/22/2005 Toko D53LC Type A Shielded Ferrite 5.0 5.0 3.0 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 DO3308 Open Ferrite 9.4 13.0 3.0 DO3316 Open Ferrite 9.4 13.0 5.1 4.0 Coilcraft Input Capacitor (C1) The input current to the step-down converter is discontinuous, and so a capacitor is required to supply the AC current to the step-down converter while maintaining the DC input voltage. A low ESR capacitor is required to keep the noise at the IC to a minimum. Ceramic capacitors are preferred, but tantalum or low ESR electrolytic capacitors may also suffice. www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 5 TM MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER The input capacitor value should be greater than 10µF. The capacitor can be electrolytic, tantalum or ceramic. However, since it absorbs the input switching current it requires an adequate ripple current rating. Its RMS current rating should be greater than approximately 1/2 of the DC load current. For insuring stable operation C1 should be placed as close to the IC as possible. Alternately, a smaller high quality ceramic 0.1µF capacitor may be placed closer to the IC and a larger capacitor placed farther away. If using this technique, it is recommended that the larger capacitor be a tantalum or electrolytic type. All ceramic capacitors should be placed close to the MP1591. Output Capacitor (C5) The output capacitor is required to maintain the DC output voltage. Low ESR capacitors are preferred to keep the output voltage ripple low. The characteristics of the output capacitor also affect the stability of the regulation control system. Ceramic, tantalum or low ESR electrolytic capacitors are recommended. In the case of ceramic capacitors, the impedance at the switching frequency is dominated by the capacitance, and so the output voltage ripple is mostly independent of the ESR. The output voltage ripple is estimated to be: VRIPPLE ⎛f ≅ 1.4 × VIN × ⎜⎜ LC ⎝ f SW ⎞ ⎟ ⎟ ⎠ 2 Where VRIPPLE is the output ripple voltage, fLC is the resonant frequency of the LC filter, fSW is the switching frequency. In the case of tantalum or low-ESR electrolytic capacitors, the ESR dominates the impedance at the switching frequency, and so the output ripple is calculated as: VRIPPLE ≅ ∆I × R ESR Output Rectifier Diode (D1) 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 rectifier. Table 2 provides some recommended Schottky rectifiers based on the maximum input voltage and current rating. Table 2—Diode Selection Guide VIN (Max) 15V 20V 30V 34V 2A Load Current Part Vendor Number 30BQ15 4 B220 1 SK23 6 SR22 6 20BQ030 4 B230 1 SK23 6 SR23 3, 6 SS23 2, 3 21DQ04 4 MBRS240L 5 SK24 6 SS24 2, 3 3A Load Current Part Vendor Number B320 SK33 SS32 B330 B340L MBRD330 SK33 SS33 B340L MBRS340 SK34 SS34 1 1, 6 3 1 1 4, 5 1, 6 2, 3 1 4 1, 6 2, 3 Table 3 lists manufacturer’s websites. Table 3—Schottky Diode Manufacturers # Vendor Web Site 1 Diodes, Inc. www.diodes.com 2 Fairchild Semiconductor www.fairchildsemi.com 3 General Semiconductor www.gensemi.com 4 International Rectifier www.irf.com 5 On Semiconductor www.onsemi.com 6 Pan Jit International www.panjit.com.tw Choose a rectifier whose maximum reverse voltage rating is greater than the maximum input voltage, and whose current rating is greater than the maximum load current. Where VRIPPLE is the output voltage ripple and RESR is the equivalent series resistance of the output capacitors. MP1591 Rev. 1.8 7/22/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 6 TM MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER Compensation The system stability is controlled through the COMP pin. COMP 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 loop gain is: A VDC = VREF × A VEA × G CS × R LOAD VOUT Where VREF is the feedback threshold voltage, 1.230V, AVEA is the transconductance error amplifier voltage gain, 400 V/V, and GCS is the current sense gain (roughly the output current divided by the voltage at COMP), 3.5 A/V. The system has 2 poles of importance; one is due to the compensation capacitor (C4) and the other is due to the output capacitor (C5). These are: fP1 R3 C3 C4 2.5V 22µF Ceramic 3.9kΩ None 4.7nF 3.3V 22µF Ceramic 5.1kΩ None 3.9nF 5V 22µF Ceramic 7.5kΩ None 2.7nF 12V 22µF Ceramic 18kΩ None 1.2nF 2.5V 47µF SP-Cap 8.2kΩ None 2.2nF 1 3.3V 47µF SP-Cap 10kΩ None 2.2nF (2π × R LOAD × C5) 5V 47µF SP-Cap 16kΩ None 1.5nF 12V 47µF SP-Cap 36kΩ None 1nF 2.5V 560µF/6.3V, AL 30mΩ ESR 100kΩ 150pF 1nF 3.3V 560µF/6.3V, AL 30mΩ ESR 120kΩ 120pF 1nF 5V 470µF/10V, AL 30mΩ ESR 150kΩ 82pF 1nF 12V 220µF/25V, AL 30mΩ ESR 180kΩ 33pF 1nF The system has one zero of importance due to the compensation capacitor (C4) and the compensation resistor (R3) which is 1 = (2π × R3 × C4) If large value capacitors with relatively high equivalent-series-resistance (ESR) are used, the zero due to the capacitance and ESR of the output capacitor can be compensated by a third pole set by R3 and C3 f P3 = MP1591 Rev. 1.8 7/22/2005 Table 4—Compensation Values for Typical Output Voltage/Capacitor Combinations C5 Where fP1 is the first pole, and GMEA is the error amplifier transconductance (770µS) and f Z1 Choosing the Compensation Components The values of the compensation components given in Table 4 yield a stable control loop for the output voltage and given capacitor. VOUT G MEA = (2π × A VEA × C4) fP2 = The system crossover frequency fC, (the frequency where the loop gain drops to 1, or 0dB) is important. A good rule of thumb is to set the crossover frequency to approximately one tenth of the switching frequency. In this case, the switching frequency is 330KHz, so use a crossover frequency of 33KHz. Lower crossover frequencies result in slower response and worse transient load recovery. Higher crossover frequencies can result in instability. Note: “AL” = Electrolytic 1 (2π × R3 × C3) www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 7 TM MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER To optimize the compensation components that are not listed in Table 4, use the following procedure. Choose the compensation resistor to set the desired crossover frequency. Determine the value by the following equation: R3 = 2π × C5 × VOUT × f C G EA × G CS × VREF Putting in the know constants and setting the crossover frequency to the desired 33KHz: R3 ≅ 6.88 × 10 7 × C5 × VOUT Choose the compensation capacitor to set the zero below one fourth of the crossover frequency. Determine the value by the following equation: C4 > 2 1.93 × 10 −5 ≈ R3 π × R3 × f C Determine if the second compensation capacitor, C3, is required. It is required if the ESR zero of the output capacitor occurs at less than four times the crossover frequency, or Example: VOUT = 5V, C5 = 22µF Ceramic (ESR = 10mΩ) R3 ≈ 6.88x107 (22x10-6) (5) = 7568Ω Use the nearest standard value of 7.5kΩ. C4 > 1.93x10-5 / 7.5K = 2.57nF Use standard value of 2.7nF. 8π x C5 x RESR x fC = 0.22, which is less than 1. Therefore, no second compensation capacitor (C3) is required. 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 MP1591 SW 8π × C5 × R ESR × f C ≥ 1 If this is the case, then add the second compensation resistor. Determine the value by the equation: C3 = C5 × R ESR(MAX ) R3 MP1591_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. Where RESR(MAX) is the maximum ESR of the output capacitor. MP1591 Rev. 1.8 7/22/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 8 TM MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER TYPICAL APPLICATION CIRCUITS C2 10nF INPUT 6.5V to 32V 2 OFF ON OPEN NOT USED 7 8 1 IN BS 3 SW EN MP1591 REF GND FB COMP 4 5 D1 OUTPUT 2.5V 2A 6 C4 4.7nF C3 OPEN MP1591_F03 Figure 3—MP1591 with Murata 22µF / 10V Ceramic Output Capacitor C2 10nF INPUT 6.5V to 32V 2 OFF ON OPEN NOT USED 7 8 1 IN BS 3 SW EN D1 MP1591 REF GND 4 FB COMP OUTPUT 2.5V 2A 5 6 C3 OPEN C4 2.2nF MP1591_F04 Figure 4—MP1591 with Panasonic 47µF / 6.3V Special Polymer Output Capacitor MP1591 Rev. 1.8 7/22/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 9 TM MP1591 – 2A, 32V, 330KHz STEP-DOWN CONVERTER PACKAGE INFORMATION SOIC8 OR SOIC8N (WITH EXPOSED PAD) PIN 1 IDENT. 0.229(5.820) 0.244(6.200) 0.0075(0.191) 0.0098(0.249) 0.150(3.810) 0.157(4.000) SEE DETAIL "A" NOTE 2 0.110(2.794) 0.150(3.810) 0.011(0.280) x 45o 0.020(0.508) 0.013(0.330) 0.020(0.508) 0.050(1.270)BSC 0.189(4.800) 0.197(5.004) 0.053(1.350) 0.068(1.730) 0o-8o 0.049(1.250) 0.060(1.524) 0.016(0.410) 0.050(1.270) DETAIL "A" SEATING PLANE 0.001(0.030) 0.004(0.101) NOTE: 1) Control dimension is in inches. Dimension in bracket is millimeters. 2) Heat Slug Option Only (N Package) 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. MP1591 Rev. 1.8 7/22/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 10