MPQ28261 21V, 3A, 500kHz Synchronous Step-Down Coverter The Future of Analog IC Technology DESCRIPTION FEATURES The MPQ28261 is a synchronous, rectified, step-down, switch-mode converter with built-in 120mΩ high-side MOSFET and 20mΩ low-side MOSFET. It offers a very compact solution to achieve a continuous 3A output current over a wide input supply range, with excellent load and line regulation. Its synchronous mode operation increases its efficiency over its output current load range, and uses a fixed 500kHz switching frequency. • • • Current mode operation provides a fast transient response and improves loop stabilization. Full protection features include over-current protection and thermal shut down. The MPQ28261 has an external SS pin to program the soft-start time and power-good signal output. The MPQ28261 requires a minimal number of readily-available standard external components and is available in a space saving 3mmx4mm 14-pin QFN package. • • • • • • • • Wide 4.5V-to-21V Operating Input Range 3A Maximum Continuous Output Current Integrated 120mΩ High-Side and 20mΩ Low-Side Power MOSFETs 1% Reference Voltage Accuracy Up to 85% Efficiency (for Drops of 12V to 1.2V) Fixed 500kHz Switching Frequency External Soft-Start PG Output OCP and Thermal Shutdown Output Adjustable from 0.603V to 18V Available in a 3mm x 4mm 14-pin QFN Package. APPLICATIONS • • • • DSL Modems Cable Modems Set-Top Boxes Telecom All MPS parts are lead-free and adhere to the RoHS directive. For MPS green status, please visit MPS website under Products, Quality Assurance page. “MPS” and “The Future of Analog IC Technology” are registered trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION C1 22uF 1 BST Efficiency vs. Load Current 6 VCC R10 100K MPQ28261 9 11 C4 0.1uF ON/OFF IN SW PG 2,3,4,5 Rt 24K VCC FB 7 EN SS GND 12,13 AGND 14 8 10 C7 47nF VOUT=1.2V 100 C3 0.1uF L1 2.8uH VOUT 1.2V/3A R1 10K C2 47uF R2 10K 90 80 EFFICIENCY (%) 4.5V-21V VIN 70 V IN=4.5V 60 V IN=12V 50 40 30 V IN=21V 20 10 0 0 0.5 1 1.5 2 2.5 3 3.5 LOAD CURRENT (A) MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 1 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER ORDERING INFORMATION Part Number* MPQ28261DL Package QFN14 (3x4mm) Top Marking 28261 Operation Junction Temperature (Tj) -40°C to +125°C * For Tape & Reel, add suffix –Z (e.g. MPQ28261DL–Z); For RoHS, compliant packaging, add suffix –LF (e.g. MPQ28261DL–LF–Z). PACKAGE REFERENCE TOP VIEW PIN 1 ID 1 14 2 13 3 12 4 11 5 10 6 9 7 8 ABSOLUTE MAXIMUM RATINGS (1) Thermal Resistance VIN ................................................-0.3V to +23V VSW .............. -0.3V(-5V for <10ns) to (VIN +0.3V) VBST ...................................................... VSW + 6V Enable Current IEN(2) ................................. 0.2mA All Other Pins ..................................-0.3V to +6V Continuous Power Dissipation (TA = 25°C) (3) ............................................................. 2.6W Junction Temperature ...............................150°C Lead Temperature ....................................260°C Storage Temperature............... -65°C to +150°C QFN14 (3x4mm) ..................... 48 ...... 11... °C/W Recommended Operating Conditions (4) Supply Voltage VIN ...........................4.5V to 21V Output Voltage VOUT .....................0.603V to 18V Maximum Junction Temp. (TJ) ................ 125°C (5) θJA θJC Notes: 1) Exceeding these ratings may damage the device. 2) Refer to the section “Configuring the EN Control”. 3) 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. 4) The device is not guaranteed to function outside of its operating conditions. 5) Measured on JESD51-7, 4-layer PCB. MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 2 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER ELECTRICAL CHARACTERISTICS VIN = 12V, TJ = -40°C to +125°C, unless otherwise noted. Typical value is tested at TJ = +25°C. Parameters Supply Current Supply Current (Shutdown) Supply Current (Quiescent, Not Switching) MOSFET HS Switch On Resistance(6) LS Switch On Resistance(6) Switch Leakage Current Limit Current Limit Timer Oscillator Frequency Minimum On Time(6) Maximum Duty Cycle Reference And Soft Start Symbol IIN VEN = 0V Iq VEN = 2V, VFB = 1V HSRDS-ON LSRDS-ON SWLKG ILIMIT fSW tON-MIN DMAX Feedback Voltage VFB Feedback Current Soft-Start Current Enable and UVLO EN Rising Threshold EN Threshold Hysteresis IFB ISS EN Input Current VIN Under-Voltage Lockout Threshold Rising VIN Under-Voltage Lockout Threshold Hysteresis Power Good Power-Good Rising Threshold Power-Good Falling Threshold Power-Good Delay(6) Power-Good Leakage Current Condition 0.45 Typ 0.7 120 20 0.1 VEN = 0V, VSW = 0V or 12V D=40% 4.2 5.2 VFB=550mV , TJ= +25°C 425 500 VFB=550mV , TJ= -40°C to +125°C 400 VFB = 550mV 89 TJ= +25°C TJ= -40°C to +125°C VFB = 650mV VSS=0 597 594 VEN_RISING VEN_HYS IEN Min 9 603 10 12 Units 1 μA 0.9 mA 1 mΩ mΩ μA A 575 kHz 575 kHz 95 ns % 609 612 50 15 mV mV nA μA 1.1 1.3 0.4 2 0.1 1.4 V V μA μA 3.8 4.0 4.2 V VEN=2V VEN=0V INUVVth 60 92 Max INUVHYS 880 mV PGVth-Hi PGVth-Lo 0.9 0.8 VFB VFB 0.25 tSS PGTd IPG_LEAK Start Up VPG = 3.3V MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 200 nA 3 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER ELECTRICAL CHARACTERISTICS (continued) VIN = 12V, TJ = -40°C to +125°C, unless otherwise noted. Typical value is tested at TJ = +25°C. Parameters VCC Regulator VCC Regulator VCC Load Regulation Thermal Protection Thermal Shutdown(6) Thermal Shutdown Hysteresis(6) Symbol Condition VCC VCC_REG ICC=5mA TSD TSD_HYS Min Typ Max Units 5.1 5 V % 150 25 °C °C Notes: 6) Guaranteed by design MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 4 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER PIN FUNCTIONS QFN14 (3x4mm) Pin # Name 1 IN 2,3,4,5 SW 6 BST 7 EN 8 FB 9 PG 10 SS 11 VCC 12,13, Exposed Pad GND 14 AGND Description Supply Voltage. Supplies power for the internal MOSFET and regulator. The MPQ28261 operates from a 4.5V-to-21V input rail. Requires a low-ESR and low-inductance capacitor (C1) to decouple the input rail. Place the input capacitor close to this pin and connect it with wide PCB traces and multiple vias. Switch Output. Connect to the inductor and bootstrap capacitor. The internal high-side MOSFET drives these pins up to the VIN voltage during the PWM duty-cycle on-time. The inductor current drives the SW pins negative during the off-time. The on-resistance of the low-side switch and the internal Schottky diode fixes the negative voltage. Connect using wide PCB traces and multiple vias. Bootstrap. Use a capacitor connected between SW and BST pins to form a floating supply across the high-side switch driver. Enable. Connected internally to a 1MΩ pull-down resistor. EN=1 to enable the MPQ28261. Pull EN low to disable the part. Feedback. Connect to the tap of an external resistor divider from the output to GND to set the output voltage. The frequency fold-back comparator lowers the oscillator frequency when the FB voltage is below 100mV to prevent current-limit runaway during a short circuit fault condition. Place the resistor divider as close to FB pin as possible. Avoid vias on the FB traces. Power-Good Output. Active high. Pin output goes to open drain of an internal switch. Power-good low-to-high threshold is 90% of regulation value. There is delay from FB ≥ 90% to PG high during start up, which is about 1/4 of SS time. Power-good high-to-low threshold is 80% of regulation value. Soft-Start. Connect an external capacitor to program the soft-start time of the switchmode regulator. The soft-start pin connects to an internal reference source and to the non-inverting input of an error amplifier. When the soft-start period begins, an internal 10µA current source begins charging the capacitor. The soft-start voltage continues to rise until the voltage exceeds the reference voltage of 0.6V. Bias Supply. Typical level of around 5.1V. Decouple with a 0.1μF-up-to-0.22μF capacitor. Provides most of the power to the device’s internal circuits. Powered by VIN, and operates in the full VIN range. When VIN exceeds 5.1V, VCC operates at maximum output. When VIN falls below 5.1V, VCC decreases. System Ground. Reference ground for the regulated output voltage. Requires special care for PCB layout. Connect exposed pad to GND plane for optimal thermal performance. Signal Ground. AGND is not internally connected to System Ground—connect to System Ground on PCB. MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 5 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS Performance curves are tested on the evaluation board of the Design Example section. VIN = 12V, VOUT = 1.2V, L = 2.8µH, TA = 25°C, unless otherwise noted. MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 6 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) Performance curves are tested on the evaluation board of the Design Example section. VIN = 12V, VOUT = 1.2V, L = 2.8µH, TA = 25°C, unless otherwise noted. MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 7 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) Performance curves are tested on the evaluation board of the Design Example section. VIN = 12V, VOUT = 1.2V, L = 2.8µH, TA = 25°C, unless otherwise noted. Efficiency Efficiency VOUT=1.2V 100 90 90 80 80 70 70 V IN=4.5V 60 VOUT=2.5V 100 90 80 V IN=4.5V 60 50 40 40 50 40 V IN=21V 30 30 20 20 20 10 10 10 30 V IN=21V 0 0 0.5 1 1.5 2 2.5 3 3.5 LOAD CURRENT (A) 0 0 0.5 V IN=4.5V 70 V IN=12V 60 V IN=12V 50 Efficiency VOUT=1.8V 100 V IN=12V V IN=21V 0 1 1.5 2 2.5 LOAD CURRENT (A) 3 3.5 0 0.5 1 1.5 2 2.5 3 3.5 LOAD CURRENT (A) Efficiency VOUT=3.3V 100 90 80 V IN=4.5V 70 V IN=12V 60 50 40 V IN=21V 30 20 10 0 0 0.5 1 1.5 2 2.5 3 3.5 LOAD CURRENT (A) MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 8 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) Performance curves are tested on the evaluation board of the Design Example section. VIN = 12V, VOUT = 1.2V, L = 2.8µH, TA = 25°C, unless otherwise noted. MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 9 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL PERFORMANCE CHARACTERISTICS (continued) Performance curves are tested on the evaluation board of the Design Example section. VIN = 12V, VOUT = 1.2V, L = 2.8µH, TA = 25°C, unless otherwise noted. MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 10 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER FUNCTIONAL BLOCK DIAGRAM IN VCC Regulator VCC Boost Regulator PG Comparator PG RSEN Current Sense Amplifier Oscillator HS Driver 1pF Reference EN 50pF 400 k BST Current Limit Comparator Comparator On Time Control Logic Control SW VCC LS Driver 1MEG FB Error Amplifier GND SS Figure 1: Functional Block Diagram MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 11 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER OPERATION The MPQ28261 is a high-frequency, synchronous, rectified, step-down, switch mode converter with built-in internal power MOSFETs. It offers a very compact solution to output a 3A continuous output current over a wide input supply range, with excellent load and line regulation. The MPQ28261 operates in a fixed-frequency peak-current–control mode to regulate the output voltage. Around the start of a PWM cycle, the integrated high-side power MOSFET (HSFET) turns on and remains on until its current reaches the value set by the COMP voltage. When the power switch turns off, it remains off until the next clock cycle starts. If the current in the HS-FET does not reach the COMP set value for 90% of one PWM period, the HS-FET will turn off. Error Amplifier The error amplifier compares VFB against the internal 0.6V reference (VREF) and outputs a current proportional to the difference. The output current both charges and discharges the internal compensation network to form the COMP voltage, which controls the power MOSFET current. The optimized internal compensation network minimizes the external component counts and simplifies the control loop design. Internal Regulator The 5V regulator powers most of the internal circuitry. This regulator takes the VIN input and operates in the full VIN range When VIN exceeds 5.1V, the regulator outputs at its maximum level; when VIN falls below 5.1V, the output decreases. The regulator requires a 0.1µF ceramic capacitor for decoupling purposes. Configuring the Enable Control The MPQ28261 has a dedicated Enable control pin (EN): pulling this pin high or low enables or disables the IC. Tie EN to VIN through a resistor for automatic start up. Choose the values of the pull-up resistor (RUP from the IN pin to the EN pin) and the pull-down resistor (RDOWN from the EN pin to GND) to determine the automatic start-up voltage: VIN−START = 1.4 × (RUP + RDOWN ) (V) RDOWN For example, for RUP=100kΩ and RDOWN=51kΩ, the VIN-START is set at 4.15V. To reduce noise, add a 10nF ceramic capacitor from EN to GND. An internal zener diode on the EN pin clamps the EN pin voltage to prevent run away. The maximum pull up current assuming the worst case 6V for the internal zener clamp should be less than 0.2mA. Therefore, when driving EN with an external logic signal, use an EN voltage less than 6V. When connecting EN to IN through a pull-up resistor or a resistive voltage divider, select a resistance that ensures a maximum pull-up current less than 0.2mA. If using a resistive voltage divider and VIN exceeds 6V, then the minimum resistance for the pull-up resistor RUP should meet: VIN − 6V 6V − ≤ 0.2mA RUP RDOWN With only RUP (the pull-down resistor, RDOWN, is not connected), then the VCC UVLO threshold determines VIN-START, so the minimum resistor value is: RUP ≥ VIN − 6V (Ω) 0.2mA Under-Voltage Lockout Under-voltage lockout (UVLO) protects the chip from operating at insufficient supply voltages. The UVLO comparator monitors the output voltage of the internal regulator, VCC. The UVLO rising threshold is about 4.0V while its falling threshold is 3.2V. Power Good Indicator MPQ28261 uses the open drain of an NMOS for the Power Good (PG) indicator. When VFB rises above 90% of the reference voltage, PG pin is pulled up to VCC by an external resistor MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 12 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER after a delay. The PG delay time is about 1/4 of SS time. If VFB falls below 80% of the reference voltage, PG pin is pulled down to ground by an internal MOSFET. External Soft-Start Connecting a capacitor from the soft-start (SS) pin to ground adjusts the SS time. During SS initiation, an internal 12µA current source charges the external capacitor. The SS pin connects internally to the non-inverting input of the error amplifier. The SS continues to charge until the voltage on the SS capacitor exceeds the 0.6V reference voltage. Then the reference voltage functions as the non-inverting input of the error amplifier. The following equation estimates the SS time: t SS (ms) = 0.6V × CSS (nF) 12μA Table 1 lists SS times with different external capacitor values. If the output capacitor is large, use a large SS capacitor to ensure proper device start-up. Table 1: Soft Start Time vs. Capacitor Value CSS (nF) tSS (ms) 0.5 10 1.65 33 2.35 47 3.4 68 5 100 If the output of the MPQ28261 is pre-biased to a certain voltage during startup, the IC will disable switching on both the HS-FET and LSFET until the voltage on the internal SS capacitor exceeds the sensed output VFB, as Figure 2 shows. Over-Current Protection The MPQ28261 has hiccup over-current limit protection for when the inductor current peak value exceeds the set current limit threshold: hiccup occurs when the output voltage drops below 70% of the reference voltage and the inductor current exceeds the current limit. This is especially useful to ensure system safety under fault conditions. The hiccup function is enabled during SS duration. Current Limit I INDUCTOR 0A V OUT 0V t Figure 3: Over-Current Behavior in Hiccup Figure 3 shows the hiccup function. After the hiccup occurs, the SS pin voltage goes low and MPQ28261 begins SS shortly after. During the SS period, if the inductor current hits current limit and the output voltage is less than 70% of the reference, the SS voltage will go low. Thermal Shutdown Thermal shutdown prevents the chip from operating at exceedingly high temperatures. EN FB Pre-bias Vref takes control after SS SS SW Figure 2: Pre-Biased Soft-Start MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 13 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER When the silicon die temperature exceeds 150°C, the whole chip shuts down: The HS-FET and LS-FET turn off, and the SS pin voltage goes low. When the temperature drops below the lower threshold—typically 140°C—the chip restarts with an SS. Floating Driver and Bootstrap Charging The floating power MOSFET driver has several features to ensure stability and functionality, such as its own UVLO protection with a rising threshold of 2.2V and a hysteresis of 150mV. An external bootstrap capacitor—regulated internally by VIN through D1, M1, C4, L1 and C2 (see Figure 4)—powers this driver. U1 regulates M1 to maintain a 5V BST voltage across C4 whenever (VIN-VSW) > 5V. Startup and Shutdown When VIN and EN exceed their respective thresholds, the chip starts. The reference block starts first, generating stable reference voltages and currents, and then the internal regulator is enabled. The regulator provides a stable power supply for the rest of the device. Three events can shut down the chip: EN low, VIN low, and thermal shutdown. In shutdown, the signaling path shuts down first to avoid triggering any faults. Then the COMP voltage and the internal supply rail are pulled down. The floating driver is not subject to this shutdown command. D1 VIN M1 BST 5V U1 C4 VOUT SW L1 C2 Figure 4: Internal Bootstrap Charging Circuit MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 14 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER APPLICATION INFORMATION COMPONENT SELECTION Output Voltage Selection The external resistor divider sets the output voltage (see Typical Application circuits on pages 1 and 17). The feedback resistor R1 also sets the bandwidth of the feedback loop in conjunction with the internal compensation capacitor. Choose R1 with a value of ~10kΩ. Use the following equation to then estimate R2: R2 = VOUT Choose the inductor current to equal ~30% of the maximum load current. Estimate the maximum inductor peak current as: R1 RT VOUT × (VIN − VOUT ) VIN × ΔIL × fOSC Where ΔIL is the inductor ripple current. −1 Use a T-type network for low values VOUT, as shown in Figure 5. 8 L1 = R1 0.6V FB Inductor Selection For most applications, chose an inductor value between 1µH and 10µH with a DC current rating that is at least 25% percent higher than the maximum load current. Select an inductor with a DC resistance less than 15mΩ for best efficiency. Use the following equation to estimate the inductance value for most designs: IL(MAX ) = ILOAD + VOUT R2 Figure 5: T-Type Network Table 2 lists the recommended T-type resistors value for common output voltages. Table 2: Resistor Selection for Common VOUT (V) R1 (kΩ) R2 (kΩ) Rt (kΩ) 1.0 10(1%) 15(1%) 24 (1%) 1.2 10(1%) 10(1%) 24 (1%) 1.8 10(1%) 4.99(1%) 24 (1%) 2.5 10(1%) 3.16(1%) 24 (1%) 3.3 10(1%) 2.20(1%) 24 (1%) 5 10(1%) 1.36(1%) 24 (1%) ΔIL 2 A larger value inductor provides a higher maximum load current, and reduces the output voltage ripple. If the load is lower than the maximum load current, then a lower-value inductor will suffice and the chip then operates with higher ripple current; this allows for the use of a either a physically smaller inductor, or one with a lower DCR that can result in higher efficiency. If the inductance differs from the conditions described above, then the maximum load current will depend on the input voltage. Choose an inductor value that allows for maximum output current near the switch current limit. Table 3 lists some of the recommended inductors. Table 3: Recommended Inductor Part Number Manufacturer Inductance ( µH ) DCR ( mΩ ) Current Rating ( A ) HC8LP-1R2 Cooper 1.2 7.5 12.4 D104C-919AS-1R8N TOKO 1.8 7.6 10.4 7443552280 Wurth 2.8 10.5 11 FDA1055-3R3M TOKO 3.3 7.3 11.7 7447709004 Wurth 4.7 11 13 MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 15 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER Selecting the Input Capacitor The MPQ28261 requires an input capacitor (C1) to supply the AC current to the step-down converter while maintaining the DC input voltage, because the input current to the stepdown converter is discontinuous. Use capacitors with low equivalent series resistance (ESR)—such as ceramic capacitors with X5R or X7R dielectrics with low ESR and small temperature coefficients. For most applications, use a 22µF capacitor. Since C1 absorbs the input switching current, it must withstand significant ripple current. The RMS current in the input capacitor can be estimated by: I C1 = ILOAD VOUT ⎛⎜ VOUT × 1− × VIN ⎜⎝ VIN ⎞ ⎟ ⎟ ⎠ The worse case condition occurs at VIN = 2VOUT, where: IC1 = ILOAD 2 For simplification, choose an input capacitor with an RMS current rating greater than half of the maximum load current. The input capacitor can be electrolytic, tantalum or ceramic. Include a small ceramic capacitor with a value of ~0.1µF as close to the IC as possible when using electrolytic or tantalum capacitors. Use sufficiently-large ceramic capacitors that can provide sufficient charge to prevent excessive voltage ripple. The capacitorinduced input voltage ripple can be estimated by: ⎛ V ⎞ I V ΔVIN = LOAD × OUT × ⎜ 1 − OUT ⎟ fS × C1 VIN ⎝ VIN ⎠ Selecting the Output Capacitor The output capacitor (C2) maintains the DC output voltage. Use ceramic, tantalum, or lowESR electrolytic capacitors to minimize the output voltage. The output voltage ripple can be estimated as: ΔVOUT = ⎞ VOUT ⎛ V ⎞ ⎛ 1 × ⎜ 1 − OUT ⎟ × ⎜ RESR + ⎟ fS × L1 ⎝ VIN ⎠ ⎝ 8 × fS × C2 ⎠ Where L1 is the inductor value and RESR is the ESR value of the output capacitor. For ceramic capacitors, the capacitor dominates the impedance at the switching frequency, and subsequently dominates the output voltage ripple. For simplicity, the output voltage ripple can be estimated as: ΔVOUT = ⎛ V ⎞ VOUT × ⎜ 1 − OUT ⎟ 8 × fS × L1× C2 ⎝ VIN ⎠ 2 For tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. Subsequently, the output ripple can be approximated as: ΔVOUT = VOUT ⎛ V × 1 − OUT fS × L1 ⎜⎝ VIN ⎞ ⎟ × RESR ⎠ The characteristics of the output capacitor also affect the system regulation stability. The MPQ28261 can be optimized for a wide range of capacitances and ESR values. The maximum capacitance is 1100μF. (Tested on Chroma 63030, CCH mode, 3A load current, soft start capacitor is 100nF, VOUT=5V). External Bootstrap Diode An external bootstrap diode may enhance the efficiency of the regulator under the following applicable conditions: z VOUT is 5V or 3.3V; and z Duty cycle is high: D= VOUT >65% VIN In these cases, an external BST diode is recommended from the VCC pin to BST pin, as shown in Figure 6. BST MPQ28261 SW External BST Diode IN4148 VCC CBST L + COUT Figure 6: Add Optional External Bootstrap Diode to Enhance Efficiency The recommended external BST diode is IN4148 where the BST capacitor value is between 0.1 and 1μF. MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 16 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER TYPICAL APPLICATIONS U1 VIN VIN VCC VCC 1 C1B C1A BST SW VCC 6 C3 MPQ28261 11 SW L1 SW 2,3,4,5 C6 15pF C4 R4 100k GND R5 20 IN VOUT C2A R6 0 C2B 1.0V/3A C2C VOUT FB EN PG SS SS FB C5 NS PG VIN VCC VCC 1 C1B C1A SS R7 51 R1 10k GND 10 R2 15k C7 47nF Figure 7: VOUT = 1V R5 20 IN BST SW VCC 6 C3 MPQ28261 11 SW L1 SW 2,3,4,5 C6 15pF C4 R4 100k GND AGND 9 GND R8 24k GND R3 20k U1 VIN 8FB 14 PG EN 12 R9 100k 7 13 EN VOUT C2A R6 0 C2B 1.2V/3A C2C VOUT FB EN PG SS SS FB C5 NS VIN VCC VCC 1 C1B C1A SS GND 10 R2 10k C7 47nF Figure 8: VOUT = 1.2V R5 20 IN BST SW VCC 6 C3 MPQ28261 11 SW L1 SW 2,3,4,5 C6 15pF C4 R4 100k GND AGND PG GND 9 R7 51 R1 10k R8 24k GND R3 20k U1 VIN 8FB 14 PG EN 12 R9 100k 7 13 EN R6 0 VOUT C2A C2B C2C 3.3V/3A VOUT FB EN PG SS SS FB 8FB C5 NS AGND GND PG GND R8 24k 9 14 PG R3 20k EN 13 R9 100k 7 12 EN SS R1 10k R7 51 10 C7 GND R2 2.2k 47nF Figure 9: VOUT = 3.3V MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 17 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER U1 VIN VIN VCC VCC 1 C1B C1A BST SW VCC 6 C3 MPQ28261 11 SW L1 SW 2,3,4,5 C6 15pF C4 R4 100k GND R5 20 IN R6 0 VOUT C2A C2B C2C 5.0V/3A VOUT FB EN PG SS SS FB 8FB C5 NS AGND PG GND 9 GND R8 24k 14 PG EN 13 R9 100k R3 20k 7 12 EN SS R1 10k R7 51 10 C7 GND R2 1.36k 47nF Figure 10: VOUT = 5V MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 18 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER Layout Recommendation 1) Lay the large switching current paths (GND, IN, and SW) very close to the device using short, wide, and direct traces. Minimize the loop length and area formed by these components. These components, including the inductor and output capacitor, should be placed on the same side of the circuit board, with their connections on that layer. Place a localized unbroken ground plane below these components. 2) Place input capacitors as close as possible to the IN and GND pins with wide PCB traces to avoid excess inductance and to prevent large spikes. Add thermal vias to the bottom side to improve thermal performance. 3) 4) 5) 6) Place the decoupling capacitor as close as possible to the VCC and GND pins. Avoid routing the VCC trace near the noisy SWto-BST trace. Place the inductor as close as possible to the SW pin. Keep the switching node SW short and away from the sensitive nodes such as the feedback network. Place external feedback resistors next to the FB pin. Make sure that there is no via on the FB trace and keep the FB trace short. Route the FB trace away from the noisy SW and BST node. Keep the BST voltage path (BST, C3, and SW) as short as possible. Keep the BST trace should away from sensitive nodes. VIN GND C1 IN 1 SW C3 SW 2 13 GND SW 3 12 GND SW 4 11 VCC SW 5 10 SS BST 6 9 PG 7 8 FB EN L1 14 AGND C4 C7 R10 Rt R2 R1 U1 C2 VOUT GND Top Layer GND Bottom Layer Figure 11: PCB Layout MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 19 MPQ28261 – 21V, 3A, 500kHz SYNCHRONOUS STEP-DOWN CONVERTER PACKAGE INFORMATION QFN14 (3mmx4mm) 2.90 3.10 1.65 1.75 0.35 0.45 PIN 1 ID SEE DETAIL A PIN 1 ID MARKING 1 14 0.20 0.30 3.25 3.35 3.90 4.10 PIN 1 ID INDEX AREA 0.50 BSC 7 8 TOP VIEW BOTTOM VIEW 0.80 1.00 0.20 REF PIN 1 ID OPTION A 0.30x45” TYP. PIN 1 ID OPTION B R0.20 TYP. 0.00 0.05 SIDE VIEW DETAIL A 2.90 0.70 NOTE: 1.70 1) ALL DIMENSIONS ARE IN MILLIMETERS. 2) EXPOSED PADDLE SIZE DOES NOT INCLUDE MOLD FLASH. 3) LEAD COPLANARITY SHALL BE 0.10 MILLIMETER MAX. 4) DRAWING CONFORMS TO JEDEC MO-229, VARIATION VEED-5. 5) DRAWING IS NOT TO SCALE. 0.25 3.30 0.50 RECOMMENDED LAND PATTERN 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. MPQ28261 Rev. 1.12 www.MonolithicPower.com 10/10/2013 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2013 MPS. All Rights Reserved. 20