TM MP1580 2A, 380 KHz Step-Down Converter The Future of Analog IC Technology TM DESCRIPTION FEATURES The MP1580 is a monolithic step-down switch mode converter with a built in internal power MOSFET. It achieves 2A 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. In shutdown mode the regulator draws 23µA of supply current. The MP1580 requires a minimum number of readily available standard external components. A synchronization pin allows the part to be driven to 600KHz. EVALUATION BOARD REFERENCE Board Number Dimensions EV0007 2.3”X x 1.5”Y x 0.5”Z • • • • • • • • • • 2A Output Current 0.18Ω Internal Power MOSFET Switch Stable with Low ESR Output Ceramic Capacitors Up to 95% Efficiency 23µA Shutdown Mode Fixed 380KHz Frequency Thermal Shutdown Cycle-by-Cycle Over Current Protection Wide 4.75 to 25V Operating Input Range Output Adjustable from 1.22V to 21V Programmable Under Voltage Lockout Frequency Synchronization Input Available in an 8-Pin SO Package APPLICATIONS • • • Distributed Power Systems Battery Chargers Pre-Regulator for Linear Regulators “MPS” and “The Future of Analog IC Technology” are Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION INPUT 4.75V to 25V OPEN NOT USED 95 2 7 8 VOUT = 5.0V 1 IN BS SW EN MP1580 SYNC FB GND 4 3 5 D1 OUTPUT 2.5V / 2A COMP 6 C6 OPEN C3 2.2nF 90 EFFICIENCY (%) OFF ON Efficiency vs Output Current Voltage C5 10nF VOUT = 3.3V VOUT = 2.5V 85 80 75 VIN = 10V 70 0 MP1580_TAC_S01 0.5 1 1.5 2 OUTPUT CURRENT (A) MP1580_TAC_EC01 MP1580 Rev. 3.0 12/5/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 1 TM MP1580 – 2A, 380KHz STEP-DOWN CONVERTER PACKAGE REFERENCE TOP VIEW TOP VIEW BS 1 8 SYNC IN 2 7 EN SW 3 6 COMP GND 4 5 FB BS 1 8 SYNC IN 2 7 EN SW 3 6 COMP GND 4 5 FB MP1580_PD01-SOIC8 MP1580_PD02-PDIP8 Part Number* Package Temperature Part Number** Package Temperature MP1580HS SOIC8 –40°C to +125°C MP1580HP PDIP8 –40°C to +125°C * For Tape & Reel, add suffix –Z (eg. MP1580HS–Z) For Lead Free, add suffix –LF (eg. MP1580HS –LF–Z) ** For Tape & Reel, add suffix –Z (eg. MP1580HP–Z) For Lead Free, add suffix –LF (eg. MP1580HP –LF–Z) ABSOLUTE MAXIMUM RATINGS (1) Recommended Operating Conditions Supply Voltage (VIN)..................................... 27V Switch Voltage (VSW).................. –1V to VIN + 1V Bootstrap Voltage (VBS) ....................... VSW + 6V Feedback Voltage (VFB) .................–0.3V to +6V Enable/UVLO Voltage (VEN)...........–0.3V to +6V Comp Voltage (VCOMP) ...................–0.3V to +6V Sync Voltage (VSYNC)......................–0.3V to +6V Junction Temperature ............................ +150°C Lead Temperature ................................. +260°C Storage Temperature.............. –65°C to +150°C Input Voltage (VIN) ......................... 4.75V to 25V Operating Temperature...............–40°C to +125°C Thermal Resistance (3) θJA (2) θJC SOIC8.................................... 105 ..... 50... °C/W PDIP8 ..................................... 95 ...... 55... °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 Symbol Condition 4.75V ≤ VIN ≤ 25V VCOMP < 2V Feedback Voltage Upper Switch-On Resistance Lower Switch-On Resistance Upper Switch Leakage Current Limit (4) Current Limit Gain. Output Current to Comp Pin Voltage Error Amplifier Voltage Gain Error Amplifier Transconductance Oscillator Frequency Short Circuit Frequency Sync Frequency MP1580 Rev. 3.0 12/5/2005 Min Typ Max Units 1.198 1.222 1.246 V 2.4 0.18 10 0 3.0 10 3.6 Ω Ω µA A VEN = 0V, VSW = 0V 1.95 A/V 400 V/V ∆IC = ±10µA 500 770 1100 µA/V VFB = 0V Sync Drive 0V to 2.7V 342 20 445 380 35 418 54 600 KHz KHz KHz www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 2 TM MP1580 – 2A, 380KHz STEP-DOWN CONVERTER ELECTRICAL CHARACTERISTICS (continued) VIN = 12V, TA = +25°C, unless otherwise noted. Parameter Symbol Condition Maximum Duty Cycle Minimum Duty Cycle EN Shutdown Threshold Voltage Enable Pull-Up Current EN UVLO Threshold Rising EN UVLO Threshold Hysteresis VFB = 1.0V VFB = 1.5V ICC > 100µA VEN = 0V VEN Rising Supply Current (Shutdown) VEN ≤ 0.4V Supply Current (Quiescent) VEN ≥ 2.6V, VFB = 1.4V Thermal Shutdown Min Typ Max Units 0 1.3 1.8 2.62 % % V µA V mV 23 36 µA 1.0 1.2 mA 90 0.7 1.15 2.37 1.0 1.46 2.495 210 160 °C Note: 4) Derate current limit 0.011A/°C. PIN FUNCTIONS Pin # Name 1 BS 2 IN 3 SW 4 GND 5 FB 6 COMP 7 EN 8 SYNC MP1580 Rev. 3.0 12/5/2005 Description Bootstrap (C5). This capacitor is needed to drive the power switch’s gate above the supply voltage. It is connected between SW and BS pins to form a floating supply across the power switch driver. The voltage across C5 is about 5V and is supplied by the internal +5V supply when the SW pin voltage is low. Supply Voltage. The MP1580 operates from a +4.75V to +25V unregulated input. C1 is needed to prevent large voltage spikes from appearing at the input. Switch. This connects the inductor to either IN through M1 or to GND through M2. Ground. This pin is the voltage reference for the regulated output voltage. For this reason care must be taken in its layout. This node should be placed outside of the D1 to C1 ground path to prevent switching current spikes from inducing voltage noise into the part. 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 frequency foldback comparator lowers the oscillator frequency when the FB voltage is below 700mV. Compensation. This node is the output of the transconductance error amplifier and the input to the current comparator. Frequency compensation is done at this node by connecting a series R-C to ground. See the compensation section for exact details. Enable/UVLO. A voltage greater than 2.62V enables operation. For complete low current shutdown the EN pin voltage needs to be less than 700mV. Synchronization Input. This pin is used to synchronize the internal oscillator frequency to an external source. There is an internal 11kΩ pull down resistor to GND; therefore leave SYNC unconnected if unused. www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 3 TM MP1580 – 2A, 380KHz STEP-DOWN CONVERTER OPERATION MP1580 reverts to its initial M1 off, M2 on, state. If the Current Sense Amplifier plus Slope Compensation signal does not exceed the COMP voltage, then the falling edge of the CLK resets the Flip-Flop. The MP1580 is a current mode regulator; the COMP pin voltage is proportional to the peak inductor current. At the beginning of a cycle: the upper transistor M1 is off; the lower transistor M2 is on (refer to Figure 1); the COMP pin voltage is higher than the current sense amplifier output and the current comparator’s output is low. The rising edge of the 380KHz CLK signal sets the RS Flip-Flop. Its output turns off M2 and 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 Current Comparator. When the Current Sense Amplifier plus Slope Compensation signal exceeds the COMP pin voltage, the RS Flip-Flop is reset and the The output of the Error Amplifier integrates the voltage difference between the feedback and the 1.222V bandgap reference. The polarity is such that an FB pin voltage less than 1.222V increases the COMP pin voltage. Since the COMP pin voltage is proportional to the peak inductor current, an increase in its voltage increases the current delivered to the output. The lower 10Ω switch ensures that the bootstrap capacitor voltage is charged during light load conditions. An external Schottky Diode D1 carries the inductor current when M1 is off (see Figure 1). IN 2 CURRENT SENSE AMPLIFIER INTERNAL REGULATORS OSCILLATOR SYNC 8 40/380kHz + 0.7V -- EN 7 -2.285V/ 2.495V + FREQUENCY FOLDBACK COMPARATOR + SLOPE COMP 5V -- CLK + SHUTDOWN COMPARATOR -- S Q R Q CURRENT COMPARATOR 1 BS 3 SW 4 GND LOCKOUT COMPARATOR 1.8V -- + -- 0.7V 1.222V 5 FB + ERROR AMPLIFIER 6 COMP MP1580_BD01 Figure 1—Functional Block Diagram MP1580 Rev. 3.0 12/5/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 4 TM MP1580 – 2A, 380KHz STEP-DOWN CONVERTER APPLICATION INFORMATION COMPONENT SELECTION Sync Pin Operation The SYNC pin driving waveform should be a square wave with a rise time less than 20ns. The Minimum High voltage level is 2.7V and the Low level is less than 0.8V. The frequency of the external sync signal needs to be greater than 445KHz. A rising edge on the SYNC pin forces a reset of the oscillator. The upper transistor M1 is switched off immediately if it is not already off. 250ns later M1 turns on connecting SW to VIN. Setting the Output Voltage The output voltage is set using a resistive voltage divider from the output to FB (see Figure 3). The voltage divider divides the output voltage down by the ratio: VFB = VOUT A good rule 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-to-peak inductor ripple current) is below the 2.4A minimum current limit. The inductance value can be calculated by the equation: L = VOUT × ( VIN − VOUT ) VIN × f × ∆I Where VIN is the input voltage, f is the oscillator 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 R2 R1 + R2 Where VFB is the feedback voltage and VOUT is the output voltage. Thus the output voltage is: VOUT = 1.222 × R1 + R2 R2 R2 can be as high as 100kΩ, but a typical value is 10kΩ. Using this value, R1 is determined by: R1 ≅ 8.18 × ( VOUT − 1.222) For example, for a 3.3V output voltage, R2 is 10kΩ and R1 is 17kΩ. 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 results in less ripple current that in turn results in lower output ripple voltage. Vendor/ Model Sumida CR75 CDH74 CDRH5D28 CDRH5D28 CDRH6D28 CDRH104R Toko D53LC Type A D75C D104C D10FL Coilcraft DO3308 DO3316 Package Dimensions (mm) W L H Core Type Core Material Open Open Shielded Shielded Shielded Shielded Ferrite Ferrite Ferrite Ferrite Ferrite Ferrite 7.0 7.3 5.5 5.5 6.7 10.1 7.8 8.0 5.7 5.7 6.7 10.0 5.5 5.2 5.5 5.5 3.0 3.0 Shielded Ferrite 5.0 5.0 3.0 Shielded Shielded Open Ferrite Ferrite Ferrite 7.6 10.0 9.7 7.6 10.0 11.5 5.1 4.3 4.0 Open Open Ferrite Ferrite 9.4 9.4 13.0 13.0 3.0 5.1 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. MP1580 Rev. 3.0 12/5/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 5 TM MP1580 – 2A, 380KHz STEP-DOWN CONVERTER Input Capacitor The input current to the step-down converter is discontinuous, 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 lowESR electrolytic capacitors will also suffice. 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. To ensure stable operation, C1 should be placed as close to the IN pin as possible. Alternately, a smaller high quality ceramic 0.1µF capacitor may be placed closer to the IN pin and a larger capacitor placed further away. If using this technique, it is recommended that the larger capacitor be a tantalum or electrolytic type capacitor. All ceramic capacitors should be placed close to the MP1580. Output Capacitor 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 oscillator frequency is dominated by the capacitance, so the output voltage ripple is mostly independent of the ESR. The output voltage ripple is estimated to be: ⎛f VRIPPLE ≅ 1.4 × VIN × ⎜⎜ LC ⎝ f ⎞ ⎟⎟ ⎠ 2 Where VRIPPLE is the output ripple voltage, fLC is the resonant frequency of the LC filter and f is the oscillator frequency. In the case of tantalum or low-ESR electrolytic capacitors, the ESR dominates the impedance at the oscillator frequency, therefore the output ripple is calculated as: VRIPPLE ≅ ∆I × R ESR Where VRIPPLE is the output voltage ripple and RESR is the equivalent series resistance of the output capacitors. Output Rectifier Diode The output rectifier diode supplies the current to the inductor when the upper transistor M1 is off. To reduce losses due to the diode forward voltage and recovery times, use a Schottky rectifier. Table 2 provides the Schottky rectifier part numbers based on the maximum input voltage and current rating. Table 2—Schottky Rectifier Selection Guide VIN (Max) 15V 20V 26V 2A Load Current Part Number Vendor 30BQ015 4 B220 1 SK23 6 SR22 6 20BQ030 4 B230 1 SK23 6 SR23 3, 6 SS23 2, 3 Table 3 lists some rectifier manufacturers. Table 3—Schottky Diode Manufacturers Vendor Web Site Diodes, Inc. Fairchild Semiconductor General Semiconductor International Rectifier On Semiconductor Pan Jit International www.diodes.com www.fairchildsemi.com www.gensemi.com www.irf.com www.onsemi.com www.panjit.com.tw Choose a rectifier that has a maximum reverse voltage rating greater than the maximum input voltage, and a current rating greater than the maximum load current. MP1580 Rev. 3.0 12/5/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 6 TM MP1580 – 2A, 380KHz 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. In this case, the switching frequency is 380KHz, so use a crossover frequency, fC, of 40KHz. Lower crossover frequencies result in slower response and worse transient load recovery. Higher crossover frequencies can result in instability. The DC loop gain is: Choosing the Compensation Components The values of the compensation components given in Table 4 yield a stable control loop for the output voltage and capacitor given. A VDC = R LOAD × G CS × A VEA × VFB VOUT Where AVEA is the transconductance error amplifier voltage gain, 400 V/V, GCS is the current sense gain, (roughly the output current divided by the voltage at COMP), 1.95 A/V and RLOAD is the load resistance (VOUT / IOUT where IOUT is the output load current). The system has 2 poles of importance, one is due to the compensation capacitor (C3), and the other is due to the output capacitor (C2). These are: fP1 = GEA 2π × C3 × A VEA Where P1 is the first pole and GEA is the error amplifier transconductance (770µA/V). and fP2 1 = 2π × C2 × R LOAD The system has one zero of importance, due to the compensation capacitor (C3) and the compensation resistor (R3). The zero is: f Z1 = 1 2π × C3 × R3 If a large value capacitor (C2) with relatively high equivalent-series-resistance (ESR) is used, the zero due to the capacitance and ESR of the output capacitor can be compensated by a third pole set by R3 and C6. The pole is: f P3 1 = 2π × C6 × R3 The system crossover frequency (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 1/10 of the switching frequency. MP1580 Rev. 3.0 12/5/2005 Table 4—Compensation Values for Typical Output Voltage/Capacitor Combinations VOUT C2 R3 C3 C6 2.5V 3.3V 5V 12V 22µF Ceramic 22µF Ceramic 22µF Ceramic 22µF Ceramic 560µF/6.3V (30mΩ ESR) 560µF/6.3V (30mΩ ESR) 470µF/10V (30mΩ ESR) 220µF/25V (30mΩ ESR) 7.5kΩ 10kΩ 15kΩ 33kΩ 2.2nF 2nF 1.2nF 1nF None None None None 200kΩ 1nF 100pF 200kΩ 1nF 82pF 250kΩ 1nF 56pF 250kΩ 1nF 27pF 2.5V 3.3V 5V 12V To optimize the compensation components for conditions 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 × C2 × f C VOUT × G EA × G CS VFB Putting in the known constants and setting the crossover frequency to the desired 40KHz: R3 ≈ 1.37 × 10 8 × C2 × VOUT Choose the compensation capacitor to set the zero below ¼ of the crossover frequency. Determine the value by the following equation: C3 > 0.22 × C2 × VOUT R3 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 7 TM MP1580 – 2A, 380KHz STEP-DOWN CONVERTER Determine if the second compensation capacitor, C6, is required. It is required if the ESR zero of the output capacitor happens at less than four times the crossover frequency. Or: 8π × C2 × R ESR × f C ≥ 1 or 7.34 × 10 −5 × R3 × R ESR ≥1 VOUT If this is the case, add the second compensation capacitor. Determine the value by the equation: C6 = C2 × R ESR(MAX ) R3 Negative Output Voltage The MP1580 can be configured as a buckboost regulator to supply negative output voltage. Because the GND pin of the IC is now connected to the negative output voltage, the maximum allowable input voltage is the IC input voltage rating (25V) minus the negative output voltage value. A typical application circuit is shown in Figure 3. 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. Where RESR(MAX) is the maximum ESR of the output capacitor. For example: 5V BS VOUT = 3.3V 10nF MP1580 C2= 22µF Ceramic (ESR = 10mΩ) SW R3 ≈ (1.37 × 10 8 ) × (22 × 10 −6 ) × (3.3) = 9.9kΩ Use the nearest standard value of 10kΩ. C3 > 0.22 × (22 × 10 −6 ) × 3.3 10 × 10 3 = 1.6nF Use a standard value of 2nF MP1580_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. 2π × C2 × R ESR × f C = 0.014 which is less than 1, therefore no second compensation capacitor is required. Table 5—Recommended Components for Standard Output Voltages VOUT R1 L1 Minimum 1.22V 1.5V 1.8V 2.5V 3.3V 5.0V 0Ω 2.32kΩ 4.75kΩ 10.5kΩ 16.9kΩ 30.9kΩ 6.8µH 6.8µH 10µH 10µH 15µH 22µH MP1580 Rev. 3.0 12/5/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 8 TM MP1580 – 2A, 380KHz STEP-DOWN CONVERTER TYPICAL APPLICATION CIRCUITS C5 10nF INPUT 4.75V to 25V OFF ON OPEN NOT USED 2 1 IN 7 BS 3 SW EN MP1580 8 SYNC GND D1 5 FB OUTPUT 2.5V / 2A COMP 4 6 C3 2.2nF C6 OPEN MP1580_F03 Figure 3—Application Circuit for -5V Supply C5 10nF INPUT 4.75V to 20V OFF ON OPEN NOT USED 2 7 8 1 IN BS SW EN MP1580 SYNC FB GND 4 3 5 D1 B230 COMP 6 C6 OPEN C3 10nF OUTPUT -5V / 0.8A MP1580_F04 Figure 4—MP1580 with Murata 22µF/10V Ceramic Output Capacitor MP1580 Rev. 3.0 12/5/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 9 TM MP1580 – 2A, 380KHz STEP-DOWN CONVERTER PACKAGE INFORMATION SOIC8 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" 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. 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. MP1580 Rev. 3.0 12/5/2005 www.MonolithicPower.com MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2005 MPS. All Rights Reserved. 10