MP1570 MPS | Alldatasheet

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3A, 23V, 340KHz Synchronous Rectified Step-Down Converter MP1570 Rev. 1.5 www.MonolithicPower.com 1 1/31/2006 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. The Future of Analog IC Technology TM TM

DESCRIPTION

The MP1570 is a monolithic synchronous buck regulator. The device integrates 100m Ω MOSFETS that provide 3A 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. In shutdown mode, the output is actively discharged by transferring energy in the output capacitor to the input capacitor, dropping 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. EVALUATION BOARD REFERENCE Board Number Dimensions EV1570DN-00A 2.0”X x 1.5”Y x 0.5”Z

FEATURES

  • 3A Output Current
  • Wide 4.75V to 23V Operating Input Range
  • Integrated 100m Ω Power MOSFET Switches
  • Output Adjustable from 1.23V 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
  • Thermally Enhanced 8-Pin SOIC Package

APPLICATIONS

  • Distributed Power Systems
  • Pre-Regulator for Linear Regulators
  • Notebook Computers “MPS” and “The Future of Analog IC Technology” are Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION INPUT 4.75V to 23V OUTPUT 3.3V 3.3nF B130 (optional) 10nF MP1570 BSIN FB SW SS GND COMP EN (optional) MP1570_TAC01 100 EFFICIENCY (%) LOAD CURRENT (A) MP1570-EC02 Efficiency vs. Load Current VIN=9V VIN=12V VIN=23V VOUT=5V

MP1570 – 3A, 23V, 340KHz SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER MP1570 Rev. 1.5 www.MonolithicPower.com 2 1/31/2006 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. TM PACKAGE REFERENCE Part Number* Package Temperature MP1570DN SOIC8N (Exposed Pad) –40° to +85°C * For Tape & Reel, add suffix –Z (eg. MP1570DN–Z) For Lead Free, add suffix –LF (eg. MP1570DN–LF–Z) ABSOLUTE MAXIMUM RATINGS (1) Recommended Operating Conditions (2) Ambient Operating Temperature ... –40°C to +85°C Thermal Resistance (3) θJA θJC 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 Min Typ Max Units Shutdown Supply Current V EN = 0V 0.3 3.0 µA Supply Current V EN = 2.7V, VFB = 1.4V 1.3 1.5 mA Feedback Voltage V FB 4.75V ≤ VIN ≤ 23V, VCOMP < 2V 1.202 1.230 1.258 V Feedback Overvoltage Threshold 1.4 1.5 1.6 V Error Amplifier Voltage Gain (4) A EA 400 V/V Error Amplifier Transconductance G EA ∆IC = ±10µA 550 820 1100 µA/V High Side Switch On Resistance (4) R DS(ON)1 100 m Ω Low Side Switch On Resistance (4) R DS(ON)2 100 m Ω High Side Switch Leakage Current V EN = 0V, VSW = 0V 0 10 µA Upper Switch Current Limit 4.0 5.8 7.6 A Lower Switch Current Limit From Drain to Source 0.9 A COMP to Current Sense Transconductance GCS 4.0 5.4 6.8 A/V Oscillation Frequency F osc1 300 340 380 KHz Short Circuit Oscillation Frequency F osc2 V FB = 0V 110 KHz Maximum Duty Cycle D MAX V FB = 1.0V 90 % Minimum On Time (4) 220 ns EN Shutdown Threshold Voltage V EN Rising 1.1 1.5 2.0 V EN Shutdown Threshold Voltage Hysteresis 220 mV BS IN SW GND SS EN COMP FB TOP VIEW MP1570_PD01-SOIC8N

MP1570 – 3A, 23V, 340KHz SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER MP1570 Rev. 1.5 www.MonolithicPower.com 3 1/31/2006 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. TM ELECTRICAL CHARACTERISTICS (continued) VIN = 12V, TA = +25°C, unless otherwise noted. Parameter Symbol Condition Min Typ Max Units EN Lockout Threshold Voltage 2.2 2.5 2.7 V EN Lockout Hysteresis 210 mV Input Under Voltage Lockout Threshold V IN Rising 3.80 4.05 4.30 V Input Under Voltage Lockout Threshold Hysteresis 210 mV Soft-Start Current V SS = 0V 6 µA Soft-Start Period C SS = 0.1µF 20 ms Thermal Shutdown (4) 160 °C Note: 4) Guaranteed by design, not tested. TYPICAL PERFORMANCE CHARACTERISTICS VIN = 12V, VOUT = 3.3V, TA = +25°C, unless otherwise noted. VOUT 1V/div. IL 1A/div. IL 1A/div. VOUT 10mV/div. VSW 10V/div. VIN 100mV/div. MP1570-TPC03 VOUT 50mV/div. IL 1A/div. VOUT 1V/div. IL 1A/div. 4ms/div. MP1570-TPC01 Load Transient Waveforms 1A - 2A STEP MP1570-TPC04 MP1570-TPC02

MP1570 – 3A, 23V, 340KHz SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER MP1570 Rev. 1.5 www.MonolithicPower.com 4 1/31/2006 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. TM 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 0.01µF 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 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. 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 Ground (Connect 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.

6 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 Components. 7 EN 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. 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. A 0.1µF capacitor sets the soft-start period to 20ms. To disable the soft-start feature, leave SS unconnected. BLOCK DIAGRAM MP1570_BD01 LOCKOUT COMPARATOR INTERNAL REGULATORS IN EN ERROR AMPLIFIER 1.2V OVP RAMP CLK 1.23V 0.3V CURRENT COMPARATOR CURRENT SENSE AMPLIFIER1.5V SHUTDOWN COMPARATOR COMP 6 SS 8 FB 5 GND4 OSCILLATOR 100/340KHz S R Q SW3 BS1 IN OVP IN < 4.05V EN OK Q LATCH 1.5V 2.5V Figure 1—Functional Block Diagram

MP1570 – 3A, 23V, 340KHz SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER MP1570 Rev. 1.5 www.MonolithicPower.com 5 1/31/2006 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. TM OPERATION FUNCTIONAL DESCRIPTION The MP1570 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 1.230V, and supplies up to 3A of load current. The MP1570 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 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 MP1570 FB pin exceeds 20% of the nominal regulation voltage of 1.230V, the over voltage comparator is tripped and latched; the COMP pin and the SS pin are discharged to GND, forcing the high-side switch off. Latch cannot be cleared unless the EN or IN pin is reset. Following discharge, the MP1570 actively recycles the energy stored in the output capacitor. Initially the low-side synchronous rectifier turns on. Once the internal, negative 900mA current limit is reached, the low-side switch turns off, forcing inductor current to flow through the high-side switch body diode. The inductor current is recycled back into the input as an energy saving feature. This cycle continues until the output voltage is discharged below 10% of the initial regulation voltage (0.123V at FB), at which time the low-side switch turns off. 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: 2R1R 2RVV OUTFB += Thus the output voltage is: 2R1R23.1VOUT +×= Where VFB is the feedback voltage and V OUT is the output voltage. A typical value for R2 can be as high as 100k Ω, but a typical value is 10kΩ. Using that value, R1 is determined by: )k)(23.1V(18.81R OUT Ω−×= 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 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

MP1570 – 3A, 23V, 340KHz SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER MP1570 Rev. 1.5 www.MonolithicPower.com 6 1/31/2006 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. TM peak inductor current is below the maximum switch current limit. The inductance value can be calculated by: ⎛ −××= IN OUT S OUT V V1∆If VL Where VIN is the input voltage, f S is the 340KHz 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: IN OUT S OUT LOADLP V V1Lf2 VII Where ILOAD is the load current. Table 1 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 1—Inductor Selection Guide Package Dimensions (mm) Vendor/ Model Core Type Core 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 CDRH5D28 Shielded Ferrite 5.5 5.7 5.5 CDRH6D28 Shielded Ferrite 6.7 6.7 3.0 CDRH104R Shielded Ferrite 10.1 10.0 3.0 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 4.0 Coilcraft DO3308 Open Ferrite 9.4 13.0 3.0 DO3316 Open Ferrite 9.4 13.0 5.1 Optional Schottky Diode During the transition between high-side switch and low-side switch, the body diode of the low- side 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. Table 2—Diode Selection Guide Part Number Voltage/Current Rating Vendor B130 30V, 1A Diodes, Inc. SK13 30V, 1A Diodes, Inc. MBRS130 30V, 1A 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. 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: × −×= IN OUT IN OUTLOAD1C V V1V VII The worst-case condition occurs at V IN = 2VOUT, where: II LOAD 1C = For simplification, choose the input capacitor whose RMS current rating greater than half of the maximum load current.

MP1570 – 3A, 23V, 340KHz SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER MP1570 Rev. 1.5 www.MonolithicPower.com 7 1/31/2006 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. TM 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 volt age ripple at input. The input voltage ripple caused by capacitance can be estimated by: IN OUT IN OUT S LOAD IN V V1V V 1Cf IV 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: 1RV V1Lf VV S ESR IN OUT S OUT OUT 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: ⎛ −× ××× IN OUT S OUT OUT V 2CLf8 V∆V 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: ESRIN OUT S OUT OUT RV V1Lf V∆V ×⎟⎟ ⎛ −××= The characteristics of the output capacitor also affect the stability of the regulation system. The MP1570 can be optimized for a wide range of capacitance and ESR values. Compensation Components MP1570 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. The DC gain of the voltage feedback loop is given by: OUT FB VEACSLOADVDC V VAGRA ×××= Where A VEA is the error amplifier voltage gain, 400V/V; G CS is the current sense transconductance, 5.4A/V; R LOAD 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: VEA EA 1P A3C2 Gf ××π= LOAD 2P R2C2 1f ××π= Where, G EA is the error amplifier transconductance, 800µA/V. The system has one zero of importance, due to the compensation capacitor (C3) and the compensation resistor (R3). This zero is located at: 3R3C2 1f 1Z ××π=

MP1570 – 3A, 23V, 340KHz SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER MP1570 Rev. 1.5 www.MonolithicPower.com 8 1/31/2006 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. TM 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: ESR ESR R2C2 1f ××π= 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: 3R6C2 1f 3P ××π= 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 to approximately one-tenth of the switching frequency. Switching frequency for the MP1570 is 340KHz, so the desired crossover frequency is 34KHz. 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 Values for Typical Output Voltage/Capacitor Combinations VOUT L C2 R3 C3 C6 1.8V 4.7µH 100µF Ceramic 5.6kΩ 3.3nF None 2.5V 4.7- 6.8µH 47µF Ceramic 4.7kΩ 4.7nF None 3.3V 6.8- 10µH 22µFx2 Ceramic 5.6kΩ 3.3nF None 5V 10- 15µH 22µFx2 Ceramic 7.5kΩ 3.3nF None 12V 15- 22µH 22µFx2 Ceramic 10kΩ 1.2nF None 1.8 4.7µH 100µF SP-CAP 10kΩ 2.2nF 100pF 2.5V 4.7- 6.8µH 47µF SP-CAP 5.6kΩ 3.3nF None 3.3V 6.8- 10µH 47µF SP-CAP 6.8kΩ 2.2nF None 5V 10- 15µH 47µF SP CAP 10kΩ 2.2nF None 2.5V 4.7- 6.8µH 560µF Al. 30mΩ ESR 10kΩ 7.5nF 1.5nF 3.3V 6.8- 10µH 560µF Al 30mΩ ESR 10kΩ 10nF 1.5nF 5V 10- 15µH 470µF Al. 30mΩ ESR 15kΩ 7.5nF 1nF 12V 15- 22µH 220µF Al. 30mΩ ESR 15kΩ 10nF 390pF To optimize the compensation components for conditions not listed in Table 2, the following procedure can be used. 1. Choose the compensation resistor (R3) to set the desired crossover frequency. Determine the R3 value by the following equation: FB OUT CSEA C V V GG f2C23R ×× ××π= Where f C is the desired crossover frequency, 34KHz.

MP1570 – 3A, 23V, 340KHz SYNCHRONOUS RECTIFIED, STEP-DOWN CONVERTER NOTICE: The information in this document is subject to change wi thout notice. Please contact MPS for current specifications. Users should warrant and guarantee that third party Intellectual Property rights ar e not infringed upon when integrating MPS products into any application. MPS will not assume any legal responsibility for any said applications. MP1570 Rev. 1.5 www.MonolithicPower.com 11 1/31/2006 MPS Proprietary Information. Unauthorized Photocopy and Duplication Prohibited. © 2006 MPS. All Rights Reserved. TM

PACKAGE INFORMATION

SOIC8N (EXPOSED PAD) NOTE: 1) Control dimension is in inches. Dimension in bracket is millimeters. Recommend Solder Board Area: 2.80mm x 3.82mm = 10.7mm 2 (16.6 mil2) With the mold flash included, over-all length of the package is 0.2087in. (5.3mm) max. With the mold flash included, over-all width of the package is 0.177in. (4.5mm) max. 0.016(0.410) 0.050(1.270) 0o-8o DETAIL "A" 0.011(0.280) 0.020(0.508) x 45 o SEE DETAIL "A" 0.0075(0.191) 0.0098(0.249) 0.229(5.820) 0.244(6.200) Land Pattern .028.050 0.140 (3.55mm) 0.200 (5.07 mm) 0.060 0.150(3.810) 0.157(4.000) PIN 1 IDENT. 0.050(1.270)BSC 0.013(0.330) 0.020(0.508) NOTE 2 NOTE 4 SEATING PLANE 0.001(0.030) 0.004(0.101) 0.189(4.800) 0.197(5.000) 0.053(1.350) 0.068(1.730) 0.049(1.250) 0.060(1.524) NOTE 3