MPQ2451 Industrial/Automotive-Grade 36V, 2MHz, 0.6A Step-Down Converter AEC-Q100 Qualified The Future of Analog IC Technology FEATURES DESCRIPTION • The MPQ2451 is a high frequency, step-down, switching regulator with an integrated highvoltage high-side power MOSFET. It efficiently provides up to a 0.6A output with current-mode control for fast loop response. • • • • • • • • The wide 3.3V-to-36V input range accommodates a variety of automotive step-down applications, and the 3μA shutdown-mode quiescent current allows use in battery-powered applications. The MPQ2451 achieves high power-conversion efficiency over a wide load range by scaling down the switching frequency under light-load condition to reduce the switching and gate driving losses. • • • • Frequency fold-back prevents inductor current runaway during start-up. Thermal shutdown provides reliable, fault-tolerant operation. Guaranteed Industrial/Automotive Temp. Range Limits 130μA Operating Quiescent Current Wide 3.3V-to-36V Operating Input Range 500mΩ Internal Power MOSFET 2MHz Fixed Switching Frequency Internally Compensated Stable with Ceramic Output Capacitors Internal Soft-Start Precision Current Limit Without Current Sensing Resistor >90% Efficiency Output Adjustable from 0.8V to 0.9·VIN 6-Lead SOT23 and QFN Packages Available in AEC-Q100 Grade 1 APPLICATIONS • • • • • The MPQ2451 is available in a cost-effective SOT23-6L and QFN-6L packages. High-Voltage Power Conversion Automotive Systems Industrial Power Systems Distributed Power Systems Battery-Powered Systems 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 Efficiency BST SW 6 D1 MPQ2451 GND VIN VIN 5 C1 3 C3 33pF FB EN L1 4 Control 95 VOUT 5V/0.6A VOUT=5V VIN=8V 90 VIN=24V 85 EFFICIENCY (%) 1 C4 100nF VIN=12V 80 75 VIN=36V 70 65 60 55 50 0 0.1 0.2 0.3 0.4 0.5 OUTPUT CURRENT(A) MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 0.6 1 MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED ORDERING INFORMATION Part Number Package Top Marking Junction Temperature (TJ) MPQ2451DT* SOT23-6L V7 -40°C to +125°C MPQ2451DT-AEC1 SOT23-6L V7 -40°C to +125°C MPQ2451DG** QFN-6L V7 -40°C to +125°C MPQ2451DG-AEC1 QFN-6L V7 -40°C to +125°C * For Tape & Reel, add suffix –Z (e.g. MPQ2451DT–Z). For RoHS Compliant packaging, add suffix –LF (e.g. MPQ2451DT–LF–Z) ** For Tape & Reel, add suffix -Z (e.g. MPQ2451DG-Z) For RoHS Compliant packaging, add suffix -LF (e.g. MPQ2451DG-LF-Z) PACKAGE REFERENCE TOP VIEW BST 1 6 SW GND 2 5 VIN FB 3 4 EN SOT23-6L QFN-6L ABSOLUTE MAXIMUM RATINGS (1) Supply Voltage (VIN)..................... -0.3V to +40V Switch Voltage (VSW)............ -0.3V to (VIN+0.3V) BST to SW .....................................-0.3 to +5.0V All Other Pins ............................. –0.3V to +5.0V (2) Continuous Power Dissipation (TA = 25°C) SOT23-6L ................................................ 0.57W QFN-6L .................................................... 1.56W Junction Temperature .............................. 150°C Lead Temperature ................................... 260°C Storage Temperature ............... -65°C to +150°C Recommended Operating Conditions (3) Supply Voltage VIN .......................... 3.3V to 36V Output Voltage VOUT................... 0.8V to 0.9·VIN Maximum Junction Temp. (TJ) ............... +125°C Thermal Resistance (4) θJA θJC SOT23-6L .............................. 220 .... 110 .. °C/W QFN-6L................................... 80 ...... 16 ... °C/W Notes: 1) Exceeding these ratings may damage the device. 2) The maximum allowable power dissipation is a function of the maximum junction temperature TJ (MAX), the junction-toambient thermal resistance θJA, and the ambient temperature TA. The maximum allowable continuous power dissipation at any ambient temperature is calculated by PD (MAX) = (TJ (MAX)-TA)/θJA. Exceeding the maximum allowable power dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. Internal thermal shutdown circuitry protects the device from permanent damage. 3) The device is not guaranteed to function outside of its operating conditions. 4) Measured on JESD51-7, 4-layer PCB. MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 2 MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED ELECTRICAL CHARACTERISTICS VIN = 12V, VEN = 2V, TJ= -40°C to +125°C, unless otherwise noted. Typical values are at TJ = 25°C. Parameter Feedback Voltage Symbol VFB Condition Min Typ Max 4.0V < VIN < 36V 0.774 0.794 0.814 3.3V < VIN < 4.0V 0.766 0.794 0.05 0.822 1.0 Feedback Bias Current Upper Switch On Resistance RDS(ON) Upper Switch Leakage Current Limit ILIM COMP to Current Sense Transconductance GCS VBST-VSW =5V TJ= 25°C 500 VEN = 0V, VSW = 0V 0.5 0.65 VIN UVLO Up Threshold fSW tON Shutdown Supply Current IS Quiescent Supply Current IQ Thermal Shutdown Enable High Threshold Enable Threshold Hysteresis FB from 0 to 0.794V VIH 1.4 VEN < 0.3V No load, VFB=0.9, no switching Low-to-High 1.35 V μA mΩ 2 μA 1 A 3 A/V 2.7 VIN UVLO Hysteresis Soft-Start Time Oscillator Frequency Minimum Switch On Time Units 3.29 V 0.4 0.5 2 100 1 2.6 V ms MHz ns 3 30 μA 130 200 µA 1.8 °C V mV 150 1.5 400 MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 3 MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED PIN FUNCTIONS SOT23-6L Pin # QFN-6L Pin # Name 1 6 BST Bootstrap. Positive power supply for the internal floating high-side MOSFET driver. Connect a bypass capacitor between this pin and SW pin. 2 5 GND Ground. Connect the output capacitor as close to this pin as possible. Avoid routing near high-current switch paths. 3 4 FB 4 3 EN 5 2 VIN Input Supply. Supplies power to all internal control circuitry; both BS regulators and the high side switch. Requires a decoupling capacitor to ground close to this pin to reduce switching spikes. 6 1 SW Switch Node. Output of the high-side switch. Requires a low VF Schottky diode to ground close to this pin to reduce switching spikes. Description Feedback. Input to the error amplifier. Connected to an external resistive divider between output and GND; compared against the internal 0.8V reference to set the regulation voltage. Enable Input. Pull this pin below the specified threshold to shut the chip down. Pull it above the specified threshold to enable the chip. Float this pin to disable the chip. MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 4 MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED TYPICAL CHARACTERISTICS MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 5 MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED TYPICAL PERFORMANCE CHARACTERISTICS VIN = 12V, C1 = 4.7µF, C2 = 10µF, L = 3.3µH and TA= 25°C, unless otherwise noted. Efficiency Efficiency VOUT=2.5V VOUT=3.3V 90 90 VIN=6V 80 EFFICIENCY (%) EFFICIENCY (%) VIN=8V 85 85 VIN=12V 75 70 VIN=12V 80 75 VIN=24V 70 65 65 60 60 0 0.1 0.2 0.3 0.4 0.5 OUTPUT CURRENT(A) Steady State VIN=12V,VOUT=5V,IOUT=0.1A VOUT 0.6 0 0.1 0.2 0.3 0.4 0.5 OUTPUT CURRENT(A) 0.6 Steady State Startup Through EN VIN=12V,VOUT=5V,IOUT=0.6A VIN=12V,VOUT=5V,IOUT=0.1A VOUT (AC coupled) 10mV/div. (AC coupled) 10mV/div. VSW 10V/div. IL 500mA/div. VSW 10V/div. VEN 2V/div. VSW 10V/div. IL 500mA/div. IL 500mA/div. 400ns/div. 400ns/div. Shutdown Through EN Startup Through EN VEN 2V/div. VSW 10V/div. IL 500mA/div. Shutdown Through EN VIN=12V,VOUT=5V,IOUT=0.1A VIN=12V,VOUT=5V,IOUT=0.6A VOUT 5V/div. VOUT 5V/div. VIN=12V,VOUT=5V,IOUT=0.6A VOUT 5V/div. VEN 2V/div. VOUT 5V/div. VEN 2V/div. VSW 10V/div. VSW 10V/div. IL 500mA/div. IL 500mA/div. . 2ms/div. MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 6 MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN = 12V, C1 = 4.7µF, C2 = 10µF, L = 3.3µH and TA = 25°C, unless otherwise noted. Short Circuit Entry Short Circuit Recovery IOUT=0A to Short IOUT= Short to 0A VOUT 2V/div. VOUT 2V/div. IL 500mA/div IL 500mA/div MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 7 MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED FUNCTIONAL BLOCK DIAGRAM VIN INTERNAL REGULATOR REFERENCE UVLO EN BST ISW 0.5ms SS + SS LOGIC ISW SW FB SS 0.8V -- COMP + OSCILATOR 2MHz GND Figure 1: Functional Block Diagram MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 8 MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED OPERATION The MPQ2451 is a 2MHz, non-synchronous, step-down switching regulator with an integrated high-side high voltage power MOSFET. It provides an internally-compensated, highlyefficient output of up to 0.6A with current mode control. It also features wide input voltage range, internal soft-start control, and a precision current limit. Its very low operational quiescent current makes it suitable for battery-powered applications. PWM Control At moderate-to-high output current, the MPQ2451 operates in a fixed-frequency peakcurrent–control mode to regulate the output voltage. A PWM cycle—initiated by the internal clock—turns the power MOSFET on, and the MOSFET remains on until its current reaches the value set by COMP voltage. When the PWM signal goes low, the power switch turns off and remains off for at least 100ns before the next cycle starts. If the current in the power MOSFET does not reach COMP set current value within one PWM cycle, the power MOSFET remains on to avoid a turn-off operation. Pulse-Skipping Mode Under light-load conditions, the MPQ2451 goes into pulse-skipping mode to improve efficiency. Pulse-skipping triggers when the COMP voltage drops below the internal sleep threshold, which generates a PAUSE command to block the turnon clock pulse so the power MOSFET does not turn ON; this procedure reduces gate driving and switching losses. This PAUSE command causes the whole chip to enter sleep mode, reducing the quiescent current to further improve the light load efficiency. When the COMP voltage exceeds the sleep threshold, the PAUSE signal resets and the chip resumes normal PWM operation. Whenever the PAUSE changes state from low to high, the PWM signal immediately goes HIGH and turns on the power MOSFET. Error Amplifier The error amplifier is composed of an internal opamp with an RC feedback network connected between its output node (internal COMP node) and its negative input node (FB). When the FB voltage drops below the internal reference voltage (VREF), the op-amp drives the COMP output high, causing a higher switch peak current output and delivering more energy to the output. Conversely, when the FB voltage rises above VREF, the switch peak current output drops. When using the FB pin, connect to the tap of a voltage divider that is connected between VOUT and GND composed of R1 and R2; R1 also serves to control the gain of the error amplifier in addition to the internal compensation RC network. Internal Regulator The 2.6V internal regulator powers most of the internal circuitry. This regulator takes the VIN input and operates in the full VIN range. When VIN is greater than 3.0V, the output of the regulator is in full regulation. When VIN drops below 3.0V, the output degrades. Enable Control The MPQ2451 has a dedicated enable control pin, EN. When VIN rises above threshold, the EN pin can enable or disable the chip for HIGH effective logic. Its falling threshold is 1.2V, and its rising threshold is about 1.6V. When floated, the EN pin is internally pulled down to GND to disable the. When the EN voltage is pulled to 0V, the chip enters the lowest shutdown current mode. When the EN voltage rises above 0V but lower than rising threshold, the chip remains in shutdown mode with a slightly higher shutdown current. Under Voltage Lockout (UVLO) VIN under-voltage lockout (UVLO) protects the chip from operating at an insufficient supply voltage. The UVLO rising threshold is approximately 2.9V while its falling threshold is 2.6V. MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 9 MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED Internal Soft-start A reference-type soft-start (SS) prevents the converter-output voltage from overshooting during startup. When the chip starts, the internal circuitry generates a soft-start voltage (VSS) that ramps up from 0V over the SS time. When VSS is less than VREF, VSS overrides VREF as the error amplifier reference. The maximum VSS is approximately the same as VFB; i.e. if VFB falls, the maximum of VSS falls. This accommodates short-circuit recovery; when the short-circuit is removed, VSS ramps up to prevent output voltage overshoot. Thermal Shutdown Thermal shutdown prevents thermal runaway. When the silicon die temperature exceeds its upper threshold, the entire chip shuts down. When the temperature drops below its lower threshold, 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 with a rising threshold of about 2.4V and a falling threshold of about 300mV. During this UVLO, VSS resets to zero. When the UVLO is removed, the controller enters soft-start. The bootstrap capacitor is charged and regulated to about 5V by the dedicated internal bootstrap regulator. When the voltage between the BST and SW nodes falls below its regulation, a PMOS pass transistor connected from VIN to BST turns on. The charging current path goes from VIN, BST and then to SW. The external circuit must provide enough voltage headroom to facilitate the charging. If VIN is sufficiently higher than VSW, the bootstrap capacitor will charge. When the power MOSFET is ON, VIN is equal to VSW so the bootstrap capacitor does not charge. Optimal charging occurs when the difference between VIN and VSW reaches its apex when the external freewheeling diode is on. When there is no current in the inductor, SW equals VOUT so the difference between VIN and VOUT can charge the bootstrap capacitor. voltage and time to charge the bootstrap capacitor, add an extra external circuit to ensure the bootstrap voltage in normal operation region. The floating driver’s UVLO is not communicated to the controller. Make sure the bleed-through current at SW node is at least higher than the floating driver’s DC quiescent current of about 20µA. Current Comparator and Current Limit A current-sense MOSFET senses the power MOSFET current. This value is input to the highspeed current comparator for current-mode control. When the power MOSFET turns on, the comparator is first blanked to limit noise, and then compares the power switch current against the COMP voltage. When the sensed value exceeds the COMP voltage, the comparator output goes low to turn off the power MOSFET. The maximum current of the internal power MOSFET is internally limited cycle-by-cycle. Startup and Shutdown If both VIN and VEN exceed their respective thresholds, the chip starts. The reference block first starts to generate a stable reference voltage and current, and then the internal regulator starts to provide a stable supply for the rest circuit. While the internal supply rail is up, an internal timer turns the power MOSFET off for about 50µs to blank startup noise. When the internal softstart block is enabled, it first holds its SS output low to ensure the rest of the circuit is ready before ramping up. Three events shut down the chip: EN low, VIN low, thermal shutdown. In shutdown procedure, the signaling path is blocked first to avoid any fault triggering. The COMP voltage and the internal supply rail are then pulled low. The floating driver is not subject to this shutdown command but its charging path is disabled. At a higher duty cycle, the bootstrap capacitor may not be charged sufficiently because of a shorter charging period. If there is insufficient MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 10 MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED APPLICATION INFORMATION COMPONENT SELECTION Setting the Output Voltage The output voltage is set using a resistive voltage divider from the output voltage to the FB pin. The voltage divider sets VOUT and VFB using the following equation: VFB = VOUT R2 R1 + R2 Thus the output voltage is: VOUT = VFB (R1 + R2) R2 The feedback resistor R1 also sets the feedback loop bandwidth with the internal compensation capacitor. Choose R1 around 124kΩ for optimal transient response. R2 is then given by: R2 = R1 VOUT −1 0.8V Table 1: Resistor Selection vs. Output Voltage Setting VOUT R1 R2 0.8V 124kΩ (1%) NS 1.2V 124kΩ (1%) 249kΩ (1%) 3.3V 124kΩ (1%) 40.2kΩ (1%) 5V 124kΩ (1%) 23.7kΩ (1%) Inductor The inductor supplies constant current to the output load while being driven by the switched input voltage. A larger-value inductor will result in less ripple current and lower output ripple voltage. However, the larger-value inductor is typically physically larger, has a higher series resistance, or has a lower saturation current. To determine the inductance, allow the peak-topeak ripple current in the inductor to be approximately 30% of the maximum load current. Also, chose a peak inductor current below the maximum switch current limit. The inductance value can be calculated by: L1 = ⎛ ⎞ VOUT V × ⎜⎜1 − OUT ⎟⎟ fS × ΔIL ⎝ VIN ⎠ Where VOUT is the output voltage, VIN is the input voltage, fS is the switching frequency, and ΔIL 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: ILP = ILOAD + ⎛ ⎞ V VOUT × ⎜⎜1 − OUT ⎟⎟ 2 × fS × L1 ⎝ VIN ⎠ Where ILOAD is the load current. Table 2 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. MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 11 MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED Table 2: Inductor Selection Guide Inductance (µH) Max DCR (Ω) Current Rating (A) Dimensions 3 L x W x H (mm ) 7440430022 2.2 0.028 2.5 4.8x4.8x2.8 744043003 3.3 0.035 2.15 4.8x4.8x2.8 7447785004 TOKO 4.7 0.078 2.4 5.9x6.2x3.2 D63CB-#A916CY-2R0M 2.0 0.019 2.36 6.2x6.3x3.0 D62CB-#A916CY-3R3M 3.3 0.026 2.17 6.2x6.3x3.0 D62CB-#A916CY-4R7M 4.7 0.032 2.1 6.2x6.3x3.0 2.2 0.04 3.2 5.2x5.0x2.2 3.3 0.06 2.5 5.2x5.0x2.2 4.7 0.081 2.0 5.2x5.0x2.2 2.2 0.031 2.8 5.2x5.2x2.5 3.3 0.038 2.21 5.2x5.2x2.5 4.7 0.047 1.83 5.2x5.2x2.5 Part Number Wurth Electronics TDK LTF5022T-2R2N3R2 LTF5022T-3R3N2R5 LTF5022T-4R7N2R0 COOPER BUSSMANN SD25-2R2 SD25-3R3 SD25-4R7 The input capacitor (C1) can be electrolytic, tantalum or ceramic. When using electrolytic or tantalum capacitors, add a small, high quality ceramic capacitor—for example, a 0.1μF—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 voltage ripple at input. The input voltage ripple caused by capacitance can be estimated by: ΔVIN = ⎛ ILOAD V V × OUT × ⎜1 − OUT fS × C1 VIN ⎜⎝ VIN ⎞ ⎟ ⎟ ⎠ Output Capacitor The output capacitor (C2) 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 ⎛ V × ⎜⎜1 − OUT fS × L ⎝ VIN ⎞ ⎞ ⎛ 1 ⎟ ⎟⎟ × ⎜ R ESR + ⎜ 8 × f S × C2 ⎟⎠ ⎠ ⎝ 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 voltage ripple can be estimated by: ΔVOUT = ⎞ ⎛ V × ⎜⎜1 − OUT ⎟⎟ V × L × C2 ⎝ IN ⎠ VOUT 8 × fS 2 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 f S × L ⎜⎝ VIN ⎞ ⎟⎟ × R ESR ⎠ The characteristics of the output capacitor also affect the stability of the regulation system. MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 12 MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED Compensation Components The goal of compensation design is to shape the converter transfer function to get a desired loop gain. Lower crossover frequencies result in slower line and load transient responses, while higher crossover frequencies can cause system instability. Generally, set the crossover frequency to equal approximately one-tenth of the switching frequency. If using an electrolytic capacitor, select a loop bandwidth is no higher than 1/4 of the ESR zero frequency (fESR), where fESR is given by: fESR 1 = 2π × C2 × R ESR The Table 3 lists the typical values of compensation components of some standard output voltages with various output capacitors (ceramic) and inductors. The values of the compensation components have been optimized for fast transient responses and good stability under the given conditions. Table 3: Compensation Values for Typical VOUT (V) L (µH) C2 (µF) R2 (kΩ) C3 (pF) 1.2 2.5 3.3 5 12 2.2 2.2 2.2 3.3 6.2 10 10 10 10 10 249 57.6 40.2 23.7 8.87 22 22 33 33 47 Note: With the compensation, the control loop has the bandwidth at about 1/10 switching frequency and the phase margin higher than 45 degree. External Bootstrap Diode An external bootstrap diode may enhance the efficiency of the regulator. Connect an external BST diode from 5V to the BST pin if: z There is a 5V rail available to the system; z VIN ≤ 5V; z 3.3V < VOUT < 5V; This diode is also recommended for high-duty– cycle (VOUT/VIN > 65%) applications. A low-cost bootstrap diode, such as IN4148 or BAT54, is suitable for such applications. 5V BS MPQ2451 SW Figure 2: External Bootstrap Diode At no load or light load, the converter may operate in pulse-skipping mode in order to regulate the output voltage and leave less time to refresh the BST voltage. To ensure sufficient gate voltage, select (VIN - VOUT) > 3V. For example, if VOUT is 3.3V, VIN needs to be higher than 3.3V+3V=6.3V at no load or light load. To meet this requirement, the EN pin can be used to program the input UVLO voltage to VOUT+3V. MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 13 MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED PCB Layout greater switching losses at high switching frequencies. PCB layout requires high-frequency noise considerations to limit voltage spikes on the SW node and to limit EMI noise. Keep the path of the input decoupling capacitor, catch diode, the VIN pin, SW pin, and PGND as short as possible using short and wide traces, with the passive components as close to the device as possible. Add a grid of thermal vias under the exposed pad to improve thermal conductivity. Use small vias (15mil barrel diameter) so that the hole fills during the plating process, and to avoid solder wicking during the reflow process associated with larger vias. Use a pitch (distance between the centers) of approximately 40mil between the thermal vias. Please refer to the layout example on EVQ2451 datasheet. Run the feedback trace far from the inductor and noisy power traces: if possible, run the feedback trace on the opposite side of the PCB from the inductor, separated by a ground plane. Expect TYPICAL APPLICATION CIRCUITS (SOT23-6L) H Figure 3: Low Input Voltage With Boost Diode Application Schematic 1 BST SW 6 MPQ2451 2 GND VIN C4 100nF 5 VIN 18-36V VOUT 12V D1 C1 3 C3 47pF FB EN 4 Control Figure 4: 12V Output Typical Application Schematic MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 14 MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED PACKAGE INFORMATION SOT23-6L MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 15 MPQ2451―INDUSTRIAL-GRADE 36V, 2MHz, 0.6A, STEP-DOWN CONVERTER, AEC-Q100 QUALIFIED QFN6 (2mmx2mm) PIN 1 ID MARKING 1.90 2.10 0.30 0.40 0.20 0.30 1.90 2.10 PIN 1 ID INDEX AREA 0.65 0.85 PIN 1 ID SEE DETAIL A 1 6 1.25 1.45 0.65 BSC 3 4 TOP VIEW BOTTOM VIEW 0.80 1.00 0.20 REF PIN 1 ID OPTION A 0.30x45º TYP. PIN 1 ID OPTION B R0.20 TYP. 0.00 0.05 SIDE VIEW DETAIL A 1.90 0.70 0.70 0.25 1.40 0.65 RECOMMENDED LAND PATTERN 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. MPQ2451 Rev 1.03 www.MonolithicPower.com 4/9/2014 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2014 MPS. All Rights Reserved. 16