MP8676 4.5A, 42V, 420kHz Step-Down Converter with Synchronizable Gate Driver The Future of Analog IC Technology DESCRIPTION FEATURES The MP8676 is a monolithic step-down switch mode converter with a built in internal power MOSFET. It achieves 4.5A 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. The MP8676 requires a minimum number of readily available standard external components and is available in an 8-pin SOIC package with exposed pad. Wide 4.5V to 42V Operating Input Range 4.5A Continuous Output Current 100mΩ Internal Power MOSFET Switch Synchronizable Gate Driver Delivers up to 95% Efficiency Fixed 420kHz Frequency Synchronizable up to 1.5MHz Cycle-by-Cycle Over Current Protection with Hiccup retry Thermal Shutdown Output Adjustable from 0.8V Stable with Low ESR Output Ceramic Capacitors Available in a Thermally Enhanced 8-Pin SOIC Package APPLICATIONS Digital Set Top Boxes Personal Video Recorders Broadband Communications Flat Panel Television and Monitors All MPS parts are lead-free and adhere to the RoHS directive. For MPS green status, please visit MPS website under Quality Assurance. “MPS” and “The Future of Analog IC Technology” are Registered Trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION VIN 8 IN BST MP8676 SW 3 7 1 VOUT 3.3V VCC BG OFF ON 2 EN/SYNC FB 4 6 GND 5 MP8676 Rev.1.0 5/7/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 1 MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER ABSOLUTE MAXIMUM RATINGS (1) PACKAGE REFERENCE Supply Voltage VIN ....................................... 45V VSW...................... –0.3V (–5V for < 10ns) to 46V VBST – VSW ...................................................... 6V All Pins ........................................... –0.3V to +6V Junction Temperature ............................... 150C Lead Temperature .................................... 260C Storage Temperature .............. –65C to +150C TOP VIEW SW 1 8 IN BST 2 7 EN/SYNC VCC 3 6 FB Recommended Operating Conditions BG 4 5 GND Supply Voltage VIN ........................... 4.5V to 42V Output Voltage Range…………… 0.8V to 38V Operating Temperature ............. –40C to +85C EXPOSED PAD ON BACKSIDE * Thermal Resistance Part Number* Package Temperature MP8676DN SOIC8E –40C to +85C For Tape & Reel, add suffix –Z (eg. MP8676DN–Z) For RoHS Compliant Packaging, add suffix –LF (eg. MP8676DN–LF–Z) (3) θJA (2) θJC SOIC8E .................................. 50 ...... 10... 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 JESD51-7, 4-layer PCB. ELECTRICAL CHARACTERISTICS VIN = 12V, TA = +25C, unless otherwise noted. Parameters Feedback Voltage Feedback Current Switch On Resistance (4) Switch Leakage Current Limit (4) Oscillator Frequency Fold-back Frequency Maximum Duty Cycle Minimum On Time (4) Under Voltage Lockout Threshold Rising Under Voltage Lockout Threshold Hysteresis EN Input Low Voltage EN Input High Voltage Symbol Condition VFB 4.5V VIN 42V IFB VFB = 0.8V RDS(ON) VEN = 0V, VSW = 0V IO-MAX Duty=40% fSW VFB = 0.6V VFB = 0V VFB = 0.6V tON 240 25 85 3.90 Typ 0.808 10 100 0.1 6.5 420 115 90 100 4.10 880 Max 0.828 10 600 205 4.30 0.4 2 VEN = 2V VEN = 0V EN Input Current Sync Frequency Range (Low) Sync Frequency Range (High) Enable Turnoff Delay Supply Current (Shutdown) Supply Current (Quiescent) Thermal Shutdown BG Driver Bias Supply Voltage Gate Driver Sink Impedance (4) Gate Driver Source Impedance (4) Gate Drive Current Sense Trip Threshold Min 0.788 FSYNCL FSYNCH TOFF VEN = 0V VEN = 2V, VFB = 1V VCC RSINK RSOURCE VSW ICC = 5mA 4.5 2 0.1 300 1.5 5.0 1 0.9 150 5.0 1 4 20 Units V nA mΩ μA A kHz kHz % ns V mV V V μA 10 1.1 KHz MHz μs μA mA °C V Ω Ω mV Note: 4) Guaranteed by design. MP8676 Rev.1.0 5/7/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 2 MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER PIN FUNCTIONS Pin # Name 1 SW 2 3 4 5 6 7 8 Description Switch Output. Bootstrap. This capacitor is needed to drive the power switch’s gate above the supply BST voltage. It is connected between SW and BS pins to form a floating supply across the power switch driver. VCC BG Driver Bias Supply. Decouple with a 1µF ceramic capacitor. BG Gate Driver Output. Connect this pin to the gate of the synchronous MOSFET. Ground. This pin is the voltage reference for the regulated output voltage. For this reason GND care must be taken in its layout. This node should be placed outside of the M2 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 FB frequency foldback comparator lowers the oscillator frequency when the FB voltage is below 250mV. EN/SYNC On/Off Control and External Frequency Synchronization Input. Supply Voltage. The MP8676 operates from a +4.5V to +42V unregulated input. C1 is IN needed to prevent large voltage spikes from appearing at the input. MP8676 Rev.1.0 5/7/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 3 MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER TYPICAL PERFORMANCE CHARACTERISTICS VIN = 12V, VOUT = 3.3V, L = 4.3µH, TA = +25ºC, unless otherwise noted. 0 Case Temperature Rise vs. Output Current Operating Range Load Regulation 10 1 MP8676 Rev.1.0 5/7/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 4 MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER TYPICAL PERFORMANCE CHARACTERISTICS VIN = 12V, VOUT = 3.3V, L =4.3µH, TA = +25ºC, unless otherwise noted. (continued) MP8676 Rev.1.0 5/7/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 5 MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER OPERATION IN CURRENT SENSE AMPLIFIER D -+ REGULATOR BST EN/SYNC REGULATOR OSCILLATOR 420KHz S + -- VCC Q DRIVER R CURRENT LIMIT COMPARATOR R SW Q VCC REFERENCE FB VCC + -- ERROR AMPLIFIER COMP + -- DRIVER PWM COMPARATOR BG GND Figure 1—Functional Block Diagram The MP8676 is a fixed frequency, synchronous, step-down switching regulator with an integrated high-side power MOSFET and a gate driver for a low-side external MOSFET. It achieves 4.5A continuous output current over a wide input supply range with excellent load and line regulation. It provides a single highly efficient solution with current mode control for fast loop response and easy compensation. The MP8676 operates in a fixed frequency, peak current control mode to regulate the output voltage. A PWM cycle is initiated by the internal clock. The integrated high-side power MOSFET is turned on and remains on until its current reaches the value set by the COMP voltage. When the power switch is off, it remains off until the next clock cycle starts. If, in 90% of one PWM period, the current in the power MOSFET does not reach the COMP set current value, the power MOSFET will be forced to turn off. MP8676 Rev.1.0 5/7/2012 Error Amplifier The error amplifier compares the FB pin voltage with the internal 0.8V reference (REF) 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 Regulator Most of the internal circuitries are powered from the 5V internal regulator. This regulator takes the VIN input and operates in the full VIN range. When VIN is greater than 5.0V, the output of the regulator is in full regulation. When VIN is lower than 5.0V, the output decreases. Since this internal regulator provides the bias current for the bottom gate driver that requires significant amount of current depending upon the external MOSFET selection, a 1µF ceramic capacitor for decoupling purpose is required. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 6 MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER Enable/Synch Control The MP8676 has a dedicated Enable/Synch control pin (EN/SYNC). By pulling it high or low, the IC can be enabled and disabled by EN. Tie EN to VIN for automatic start up. To disable the part, EN must be pulled low for at least 5µs. The MP8676 can be synchronized to external clock range from 300kHz up to 1.5MHz through the EN/SYNC pin. The internal clock rising edge is synchronized to the external clock rising edge. Under-Voltage Lockout (UVLO) Under-voltage lockout (UVLO) is implemented to protect the chip from operating at insufficient supply voltage. The MP8676 UVLO comparator monitors the output voltage of the internal regulator, VCC. The UVLO rising threshold is about 4.1V while its falling threshold is a consistent 3.2V. 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 1.2V. 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. Over-Current-Protection (OCP) The MP8676 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 output UV is triggered, the MP8676 enters hiccup mode, which is especially useful to ensure system safety under fault condition. The MP8676 exits the hiccup mode once the EN or input power is re-cycled. MP8676 Rev.1.0 5/7/2012 Thermal Shutdown Thermal shutdown is implemented to prevent the chip from operating at exceedingly high temperatures. When the silicon die temperature is higher than 150C, it shuts down the whole chip. When the temperature is lower than its lower threshold, typically 140C, the chip is enabled again. Floating Driver and Bootstrap Charging The floating power MOSFET driver is powered by an external bootstrap capacitor. This floating driver has its own UVLO protection. This UVLO’s rising threshold is 2.2V with a hysteresis of 150mV. The bootstrap capacitor voltage is regulated internally by VIN through D1, M3, C4, L1 and C2 (Figure 2). If (VIN-VSW) is more than 5V, U2 will regulate M3 to maintain a 5V BST voltage across C4. D1 VIN M3 + 5V + -- BST U2 -- C4 VOUT SW L1 C2 Figure 2—Internal Bootstrap Charging Circuit 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.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 7 MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER APPLICATION INFORMATION The schematic on the front page shows a typical MP8676 application. The IC can provide up to 4.5A output current at a nominal output voltage of 3.3V. For proper thermal performance, the exposed pad of the device must be soldered down to the printed circuit board. Synchronous MOSFET The external synchronous MOSFET is used to freewheel the inductor current when the internal high-side switch is off. It significantly reduces the power loss compared against a Schottky rectifier. Setting the Output Voltage The external resistor divider is used to set the output voltage (see the schematic on front page). The feedback resistor R1 also sets the feedback loop bandwidth with the internal compensation capacitor (see Figure 1). Choose R1 to be around 40.2kΩ for optimal transient response. R2 is then given by: Selecting the Input Capacitor The input capacitor (C1) reduces the surge current drawn from the input and the switching noise from the device. The input capacitor impedance at the switching frequency should be less than the input source impedance to prevent high frequency switching current from passing to the input. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. For 4.5A output applications, a 22µF capacitor is sufficient. R2 R1 VOUT 1 0 .8 V Table 1—Resistor Selection for Common Output Voltages VOUT (V) 1.8 2.5 3.3 5 R1 (kΩ) 40.2 (1%) 40.2 (1%) 40.2 (1%) 40.2 (1%) R2 (kΩ) 32.4 (1%) 19.1 (1%) 13 (1%) 7.68 (1%) Selecting the Output Capacitor The output capacitor (C2) keeps output voltage small and ensures regulation loop stability. The output capacitor impedance should be low at the switching frequency. Ceramic capacitors with X5R or X7R dielectrics are recommended. Selecting the Inductor A 1µH to 10µH inductor with a DC current rating of at least 25% 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 IL f OSC Where ΔIL is the inductor ripple current. Choose inductor ripple current to be approximately 30% of the maximum load current, 4.5A. The maximum inductor peak current is: IL(MAX ) ILOAD I L 2 Under light load conditions below 100mA, larger inductance is recommended for improving efficiency. MP8676 Rev.1.0 5/7/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 8 MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER PCB Layout Guide PCB layout is very important to achieve stable operation. Please follow these guidelines and take Figure3 for references. 1) Keep the path of switching current short and minimize the loop area formed by Input cap, high-side and low-side MOSFETs. 2) Keep the connection of low-side MOSFET between SW pin and input power ground as short and wide as possible. 3) Ensure all feedback connections are short and direct. Place the feedback resistors and compensation components as close to the chip as possible. 4) Route SW away from sensitive analog areas such as FB. 5) Connect IN, SW, and especially GND respectively to a large copper area to cool the chip to improve thermal performance and long-term reliability. SGND LGATE GND R1 FB BST IN SW 8 Rb 7 6 Bottom Layer Figure 3—PCB Layout External Bootstrap Diode An external bootstrap diode may enhance the efficiency of the regulator, the applicable conditions of external BST diode are: VOUT=5V or 3.3V; and Duty cycle is high: D= C3 VCC EN SGND In these cases, an external BST diode is recommended from the output of the voltage regulator to BST pin, as shown in Fig.4 5 C1 L1 External BST Diode IN4148 BST MP8676 1 2 3 SW 4 PGND C2 Top Layer VOUT >65% VIN CBST L 5V or 3.3V COUT Figure 4—Add Optional External Bootstrap Diode to Enhance Efficiency The recommended external BST diode is IN4148, and the BST cap is 0.1~1µF. MP8676 Rev.1.0 5/7/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 9 MP8676 – 4.5A, 42V, 420KHZ STEP-DOWN WITH SYNCHRONIZABLE GATE DRIVER PACKAGE INFORMATION SOIC8E (EXPOSED PAD) 0.189(4.80) 0.197(5.00) 0.124(3.15) 0.136(3.45) 8 5 0.150(3.80) 0.157(4.00) PIN 1 ID 1 0.228(5.80) 0.244(6.20) 0.089(2.26) 0.101(2.56) 4 TOP VIEW BOTTOM VIEW SEE DETAIL "A" 0.051(1.30) 0.067(1.70) SEATING PLANE 0.000(0.00) 0.006(0.15) 0.013(0.33) 0.020(0.51) 0.0075(0.19) 0.0098(0.25) SIDE VIEW 0.050(1.27) BSC FRONT VIEW 0.010(0.25) x 45o 0.020(0.50) GAUGE PLANE 0.010(0.25) BSC 0.050(1.27) 0.024(0.61) 0o-8o 0.016(0.41) 0.050(1.27) 0.063(1.60) DETAIL "A" 0.103(2.62) 0.138(3.51) RECOMMENDED LAND PATTERN 0.213(5.40) NOTE: 1) CONTROL DIMENSION IS IN INCHES. DIMENSION IN BRACKET IS IN MILLIMETERS. 2) PACKAGE LENGTH DOES NOT INCLUDE MOLD FLASH, PROTRUSIONS OR GATE BURRS. 3) PACKAGE WIDTH DOES NOT INCLUDE INTERLEAD FLASH OR PROTRUSIONS. 4) LEAD COPLANARITY (BOTTOM OF LEADS AFTER FORMING) SHALL BE 0.004" INCHES MAX. 5) DRAWING CONFORMS TO JEDEC MS-012, VARIATION BA. 6) DRAWING IS NOT TO SCALE. NOTICE: The information in this document is subject to change without notice. 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. MP8676 Rev. 1.0 5/7/2012 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2012 MPS. All Rights Reserved. 10