MT1471

MT1471 3A,4.5V-16V Input,500kHz Synchronous Step-Down Converter FEATURES ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ ⚫ GENERAL DESCRIPTION High Efficiency: Up to 96% 500KHz Frequency Operation 3A Output Current No Schottky Diode Required 4.5V to 16V Input Voltage Range 0.8V Reference Slope Compensated Current Mode Control for Excellent Line and Load Transient Response Integrated internal compensation Stable with Low ESR Ceramic Output Capacitors Over Current Protection with Hiccup-Mode Thermal Shutdown Inrush Current Limit and Soft Start Available in SOT23-6 Package -40°C to +85°C Temperature Range The MT1471 is a fully integrated, high efficiency 3A synchronous rectified step-down converter. The MT1471 operates at high efficiency over a wide output current load range. This device offers two operation modes, PWM control and PFM Mode switching control, which allows a high efficiency over the wider range of the load. The MT1471 requires a minimum number of readily available standard external components and is available in an 6-pin SOT23 ROHS compliant package. APPLICATIONS ⚫ ⚫ ⚫ ⚫ ⚫ Distributed Power Systems Digital Set Top Boxes Flat Panel Television and Monitors Wireless and DSL Modems Notebook Computer TYPICAL APPLICATION C2 1uF VIN VIN BS SW MT1471 CIN 22μF EN GND FB L 10μH R1 100k 1% R2 19k 1% VOUT C1 22pF opt. COUT 22μF*3 Figure 1. Basic Application Circuit MT2492 Rev1.0 www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 1 AEROSEMI MT1471 3A ,500kHz Synchronous Step-Down Converter ABSOLUTE MAXIMUM RATINGS (Note 1) Input Supply Voltage…………….…-0.3V to 17V EN Voltages…………………………-0.3V to 6V FB Voltages…………………………-0.3V to 6V SW Voltage………………...-0.3V to (VIN+0.5V) BS Voltage……………..(VSW-0.3V) to (VSW+5V) Power Dissipation………………………...0.6W Thermal Resistance θJC……………….130°C/W Thermal Resistance θJA……….……….170°C/W Junction Temperature(Note2)………..........150°C Operating Temperature Range…….-40°C to 85°C Lead Temperature(Soldering,10s)………...300°C Storage Temperature Range……..-65°C to 150°C ESD HBM(Human Body Mode)……………...2kV ESD MM(Machine Mode)………………….200V PACKAGE/ORDER INFORMATION Order Part Number Package Top Marking MT1471 SOT23-6 AS4FDC TOP VIEW GND 1 6 BS SW 2 5 EN VIN 3 4 FB 6-LEAD PLASTIC SOT-23 TJMAX = 150°C, θJA = 170°C/ W, θJC = 130°C/W F:version, D:Year,C:Week PIN DESCRIPTION Pin Name Pin Number Description GND SW VIN 1 2 3 FB 4 EN 5 BS 6 Analog ground pin. Switching Pin. Power supply Pin Adjustable version feedback input. Connect FB to the center point of the external resistor divider Drive this pin to a logic-high to enable the IC. Drive to a logic-low to disable the IC and enter micro-power shutdown mode. For automatic start-up, connect EN to VIN using a 200kΩ resistor. Bootstrap. A capacitor connected between SW and BS pins is required to form a floating supply across the high-side switch driver. MT2492 Rev1.0 www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 2 AEROSEMI MT1471 3A ,500kHz Synchronous Step-Down Converter ELECTRICAL CHARACTERISTICS (Note 3) (VIN=12V, VOUT=5V, TA = 25°C, unless otherwise noted.) PARAMETER CONDITIONS Input Voltage Range Supply Current in VEN=3.0V, VFB=2V Operation Supply Current in VEN =0 or EN = GND Shutdown Regulated Feedback TA = 25°C, 4.5V≤ VIN ≤16V Voltage High-Side Switch On-Resistance Low-Side Switch On-Resistance High-Side Switch VEN=0V, VSW=0V Leakage Current Low-Side Switch VEN=0V, VSW=12V Leakage Current Upper Switch Current Minimum Duty Cycle Limit Oscillation Frequency Maximum Duty Cycle VFB=0.8V Minimum On-Time Soft-start Time Tss Thermal Shutdown MIN 4.5 TYP MAX 16 UNIT V 0.6 0.8 mA 1 0.780 0.800 µA 0.820 90 mΩ 55 mΩ 1 µA 1 µA 5 400 V 500 92 60 1 180 A 580 KHz % nS mS ℃ Note 1: Absolute Maximum Ratings are those values beyond which the life of a device may be impaired. Note 2: TJ is calculated from the ambient temperature TA and power dissipation PD according to the following formula: TJ = TA + (PD) x (170°C/W). Note 3: 100% production test at +25°C. Specifications over the temperature range are guaranteed by design and characterization. MT2492 Rev1.0 www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 3 AEROSEMI MT1471 3A ,500kHz Synchronous Step-Down Converter TYPICAL PERFORMANCE CHARACTERISTICS IN:12V OUT:5V/0.1A IN:16V MT2492 Rev1.0 OUT:5V/0.1A IN:12V OUT:5V/3A IN:16V OUT:5V/3A www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 4 AEROSEMI MT1471 3A ,500kHz Synchronous Step-Down Converter FUNCTIONAL BLOCK DIAGRAM VIN VCC REGULATOR + ∑ RSEN - VCC CURRENT SENSE AMPLIFIER BOOST REGULATOR BS OSCILLATOR + EN COMPARATOR - REFERENCE CURRENT LIMIT COMPARATOR 1pF 1M 56pF FB HS DRIVER 400k VCC SW ON TIME CONTROL LOGIC CONTROL LS DRIVER + + - GND ERROR AMPLIFIER Figure 2. MT1471 Block Diagram MT2492 Rev1.0 www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 5 AEROSEMI MT1471 3A ,500kHz Synchronous Step-Down Converter FUNCTIONAL DESCRIPTION Internal Regulator The MT1471 is a current mode step down DC/DC converter that provides excellent transient response with no extra external compensation components. This device contains an internal, low resistance, high voltage power MOSFET, and operates at a high 500K operating frequency to ensure a compact, high efficiency design with excellent AC and DC performance. Error Amplifier The error amplifier compares the FB pin voltage with the internal FB reference (VFB) and outputs a current proportional to the difference between the two. This output current is then used to charge or discharge the internal compensation network to form the COMP voltage, which is used to control the power MOSFET current.The optimized internal compensation network minimizes the external component counts and simplifies the control loop design. Internal Soft-Start The soft-start is implemented to prevent the converter output voltage from overshooting during startup. When the chip starts, the internal circuitry generates a soft-start voltage (SS) ramping up from 0V to 0.8V. When it is lower than the internal reference (REF), SS overrides REF so the error amplifier uses SS as the reference. When SS is higher than REF, REF regains control. The SS time is internally fixed to 1ms. MT2492 Rev1.0 Over-Current-Protection and Hiccup The MT1471 has cycle-by-cycle over current limit when the inductor current peak value exceeds the set current limit threshold. Meanwhile, output voltage starts to drop until FB is below the Under-Voltage (UV) threshold, typically 30% below the reference. Once a UV is triggered, the MT1471 enters hiccup mode to periodically restart the part. This protection mode is especially useful when the output is dead-short to ground. The average short circuit current is greatly reduced to alleviate the thermal issue and to protect the regulator. The MT1471 exits the hiccup mode once the over current condition is removed. Startup and Shutdown If both VIN and EN are higher than their appropriate thresholds, the chip starts. The reference block starts first, generating stable reference voltage and currents, and then the internal regulator is enabled. The regulator provides stable supply for the remaining circuitries. Three events can shut down the chip: EN low, VIN low and thermal shutdown. In the shutdown procedure, the signaling path is first blocked to avoid any fault triggering. The COMP voltage and the internal supply rail are then pulled down. The floating driver is not subject to this shutdown command. www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 6 AEROSEMI MT1471 3A ,500kHz Synchronous Step-Down Converter APPLICATIONS INFORMATION Setting the Output Voltage The external resistor divider is used to set the output voltage (see Typical Application on page 1). The feedback resistor R1 also sets the feedback loop bandwidth with the internal compensation capacitor. Choose R1 to be around 100kΩ for optimal transient response. R2 is then given by: R2 = R1 VOUT −1 VFB Use a T-type network for when VOUT is low. Figure 3: T-Type Network Table 1 lists the recommended T-type resistors value for common output voltages. Inductor Selection A 4.7μH to 22μH 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 DC resistance should be less than 15mΩ. For most designs, the inductance value can be derived from the following equation. L= VOUT  (VIN − VOUT ) VIN  ΔIL  fOSC Where Δ IL is the inductor ripple current. Choose inductor ripple current to be MT2492 Rev1.0 approximately 30% if the maximum load current 3A. The maximum inductor peak current is: IL(MAX) = ILOAD + ΔIL 2 Under light load conditions below 100mA, larger inductance is recommended for improved efficiency. Input Capacitor Selection The input capacitor reduces the surge current drawn from the input and switching noise from the device. The input capacitor impedance at the switching frequency should be less than input source impedance to prevent high frequency switching current passing to the input. A low ESR input capacitor sized for maximum RMS current must be used. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. A 22µF ceramic capacitor for most applications is sufficient. A large value may be used for improved input voltage filtering. Output Capacitor Selection The output capacitor (COUT) 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: ΔVOUT = VOUT  (VIN − VOUT )  1   R ESR + VIN  fOSC  L 8  fOSC  C OUT     Where L is the inductor 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 www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 7 AEROSEMI MT1471 3A ,500kHz Synchronous Step-Down Converter voltage ripple can be estimated by: ΔVOUT = VOUT 2 8  fOSC  L  C OUT  V   1 − OUT  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: ΔVOUT = VOUT V  (1 − OUT )  R ESR fOSC  L VIN The characteristics of the output capacitor also affect the stability of the regulation system. The MT1471 can be optimized for a wide range of capacitance and ESR values. PCB Layout Recommendations PCB layout is very important to achieve stable operation. It is highly recommended to duplicate EVB layout for optimum performance. If change is necessary, please follow these guidelines and take Figure 3 for reference. ➢ Keep the path of switching current short and minimize the loop area formed by Input capacitor, high-side MOSFET and low-side MOSFET. ➢ Bypass ceramic capacitors are suggested to be put close to the VIN Pin. ➢ Ensure all feedback connections are short and direct. Place the feedback resistors and compensation components as close to the chip as possible. ➢ VOUT, SW away from sensitive analog areas such as FB. ➢ Connect IN, SW, and especially GND respectively to a large copper area to cool the chip to improve thermal performance and long-term reliability. ➢ An example of 2-layer PCB layout is shown in Figure 3 for reference. Figure 3. MT1471 Suggested Layout MT2492 Rev1.0 www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 8 AEROSEMI MT1471 3A ,500kHz Synchronous Step-Down Converter PACKAGE DESCRIPTION SOT23-6 2.80 3.00 0.95 BSC 0.60 TYP 1.20 TYP EXAMPLE TOP MARK AAAA 1.50 1.70 2.60 TYP 2.60 3.00 PIN 1 TOP VIEW RECOMMENDED SOLDER PAD LAYOUT GAUGE PLANE 0.25 BSC 0.90 1.30 1.45 MAX SEATING PLANE 0.30 0.50 0.95 BSC 0.00 0.15 FRONT VIEW 0°~8° 0.30 0.55 0.09 0.20 SIDE VIEW NOTE: 1.DIMENSIONS ARE IN MILLIMETERS. 2.DRAWING NOT TO SCALE. 3.DIMENSIONS ARE INCLUSIVE OF PLATING. 4.DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR. MT2492 Rev1.0 www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 9 AEROSEMI MT1471 3A ,500kHz Synchronous Step-Down Converter IMPORTANT NOTICE Xi’an Aerosemi Technology Co.,Ltd reserve the right to make corrections, enhancements, improvements and other changes to its semiconductor products and services. Xi’an Aerosemi Technology Co.,Ltd is not responsible or liable for such altered documentation. Information of third parties may be subject to additional restrictions. Xi’an Aerosemi Technology Co.,Ltd does not assume any responsibility for use of any its products for any particular purpose, nor does Xi’an Aerosemi Technology Co.,Ltd assume any liability arising out of the application or use of any its products or circuits. Copyright © 2011, Xi’an Aerosemi Technology Co.,Ltd Http://www.aerosemi.com MT2492 Rev1.0 www.aerosemi.com Aerosemi Proprietary Information.Unauthorized Photocopy and Duplication Prohibited. All Rights Reserved. 10