MP2148 1A Synchronous Step-down Converter with 11µA Iq in Ultra-small 1x1.5mm QFN The Future of Analog IC Technology DESCRIPTION FEATURES The MP2148 is a monolithic, step-down, switchmode converter with built-in internal power MOSFETs. It achieves 1A continuous output current from a 2.3V-to-5.5V input voltage with excellent load and line regulation. The output voltage can be regulated to as low as 0.6V. • • • • • • • • The Constant-On-Time control scheme provides fast transient response and eases loop stabilization. Fault protections include cycle-bycycle current limiting and thermal shutdown. • • • • The MP2148 is available in an ultra-small QFN6 (1.0mmx1.5mm) package and requires a minimal number of readily available standard external components. • The MP2148 is ideal for a wide range of applications including high performance DSPs, wireless power, portable and mobile devices, and other low-power systems. Low IQ: 11μA 2.2MHz Switching Frequency EN for Power Sequencing Power Good Only for Fixed Output Version Wide 2.3V-to-5.5V Operating Input Range Output Adjustable from 0.6V Up to 1A Output Current 120mΩ and 80mΩ Internal Power MOSFET Switches Output Discharge 100% Duty Cycle Short-Circuit Protection with Hiccup Mode Stable with Low ESR Output Ceramic Capacitors Available in a QFN-6 (1.0mmx1.5mm) Package APPLICATIONS • • • • Wireless/Networking Cards Portable and Mobile Devices Battery Powered /Wearable Devices Low Voltage I/O System Power All MPS parts are lead-free, halogen 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 L1 1μH VIN 5V SW VIN OUT C1 10μF R1 200kΩ MP2148 EN EN C2 10μF FB GND MP2148 Rev. 1.11 5/25/2015 VOUT 1.2V/1A R2 200kΩ www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 1 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN ORDERING INFORMATION Part Number* MP2148GQD MP2148GQD-12 MP2148GQD-15 MP2148GQD-18 MP2148GQD-25 MP2148GQD-33 Package QFN-6 (1.0mmx1.5mm) Top Marking See Below See Below See Below See Below See Below See Below VOUT Range Adjustable Fixed 1.2V Fixed 1.5V Fixed 1.8V Fixed 2.5V Fixed 3.3V * For Tape & Reel, add suffix –Z (e.g. MP2148GQD–Z); TOP MARKING CF: product code of MP2148GQD; LL: lot number; TOP MARKING DH: product code of MP2148GQD-12; LL: lot number; TOP MARKING DQ: product code of MP2148GQD-15; LL: lot number; MP2148 Rev. 1.11 5/25/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 2 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN TOP MARKING DJ: product code of MP2148GQD-18; LL: lot number; TOP MARKING DZ: product code of MP2148GQD-25; LL: lot number; TOP MARKING DN: product code of MP2148GQD-33; LL: lot number; MP2148 Rev. 1.11 5/25/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 3 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN PACKAGE REFERENCE TOP VIEW MP2148GQD TOP VIEW MP2148GQD-12 MP2148GQD-15 MP2148GQD-18 MP2148GQD-25 MP2148GQD-33 QFN-6 (1.0mmx1.5mm) ABSOLUTE MAXIMUM RATINGS (1) Thermal Resistance Supply Voltage VIN ........................................6 V VSW .................................................................... -0.3V (-5V for <10ns) to 6V (8V for <10ns or 10V for <3ns) All Other Pins ................................... -0.3V to 6V Junction Temperature .............................. 150°C Lead Temperature ................................... 260°C (2) Continuous Power Dissipation (TA = +25°C) ……….….. .................................................0.6W Storage Temperature ............... -65°C to +150°C QFN-6 (1mm x1.5mm)………… 220 Recommended Operating Conditions (3) Supply Voltage VIN ......................... 2.3V to 5.5V Operating Junction Temp. (TJ). -40°C to +125°C MP2148 Rev. 1.11 5/25/2015 (4) θJA θJC 110 °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. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 4 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN ELECTRICAL CHARACTERISTICS VIN = 3.6V, TJ = -40°C to +125°C, Typical value is tested at TJ = +25°C. The limit over temperature is guaranteed by characterization, unless otherwise noted. Parameter Symbol Feedback Voltage (MP2148GQD Only) VFB (7) Fixed Output Voltage Feedback Current (MP2148GQD only) PFET Switch On Resistance NFET Switch On Resistance IFB RDSON RDSON Condition Min Typ Max 2.3V ≤ VIN ≤ 5.5V, TJ=25°C 594 600 606 TJ=-40°C to +125°C 588 1.188 1.2 1.212 V Only for MP2148GQD12, IOUT=10mA, TJ=-40°C to +125°C 1.176 1.2 1.224 V Only for MP2148GQD15, IOUT=10mA, TJ=+25°C 1.485 1.5 1.515 V Only for MP2148GQD15, IOUT=10mA, TJ=-40°C to +125°C 1.470 1.5 1.530 V Only for MP2148GQD18, IOUT=10mA, TJ=+25°C 1.782 1.8 1.818 V Only for MP2148GQD18, IOUT=10mA, TJ=-40°C to +125°C 1.764 1.8 1.836 V Only for MP2148GQD25, IOUT=10mA, TJ=+25°C 2.475 2.5 2.525 V Only for MP2148GQD25, IOUT=10mA, TJ=-40°C to +125°C 2.450 2.5 2.550 V Only for MP2148GQD33, IOUT=10mA, TJ=+25°C 3.267 3.3 3.333 V Only for MP2148GQD33, IOUT=10mA, TJ=-40°C to +125°C 3.234 3.3 3.366 V 50 100 nA VFB = 0.63V 120 80 P N VEN = 0V, TJ=25°C PFET Peak Current Limit Sourcing NFET Valley Current Limit Sourcing, valley current limit ZCD MP2148 Rev. 1.11 5/25/2015 TON mV Only for MP2148GQD12, IOUT=10mA, TJ=+25°C Switch Leakage Current On Time (MP2148GQD only) 612 Units VIN=5V, VOUT=1.2V VIN=3.6V, VOUT=1.2V 0 1.8 mΩ mΩ 1 μA 2.4 A 1.5 A 0 mA 110 150 ns www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 5 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN ELECTRICAL CHARACTERISTICS VIN = 3.6V, TJ = -40°C to +125°C, Typical value is tested at TJ = +25°C. The limit over temperature is guaranteed by characterization, unless otherwise noted. Parameter Symbol Switching Frequency Minimum Off Time fs Condition VIN=5V, VOUT=1.2V, (5) IOUT=500mA, TJ=25°C VIN=5V, VOUT=1.2V, IOUT=500mA ,TJ=-40°C to (5) +125°C Min Typ Max Units 1760 2200 2640 kHz 1650 2200 2750 kHz TMIN-OFF 60 ns Minimum On Time TMIN-ON 60 ns Soft-Start Time TSS-ON 0.5 ms (5) VOUT rise from 10% to 90% Under Voltage Lockout Threshold Rising 2 Under Voltage Lockout Threshold Hysteresis 150 EN Input Logic Low Voltage 1.2 RDIS EN Input Current Supply Current (Shutdown) Supply Current (Quiescent) Power Good Leakage Current (MP2148GQD-XX only) Power Good Upper Trip Threshold (MP2148GQD-XX only) Power Good Lower Trip Threshold (MP2148GQD-XX only) Power Good Delay (MP2148GQD-XX only) Power Good Sink Current Capability (MP2148GQD-XX only) Thermal Shutdown (6) Thermal Hysteresis (6) VEN=0V, VOUT=1.2V VEN=2V V mV 0.4 EN Input Logic High Voltage Output Discharge Resistor 2.25 V V 1 1.2 kΩ μA VEN=0V 0 μA VEN=0V, TJ=25°C VEN=2V, VFB=0.63V, VIN=3.6V,5V, TJ=25°C 0 1 μA 11 13 μA 50 100 nA IPG Vo with Respect to the Regulation 90 % 85 % 70 μs Sink 1mA 400 mV 160 °C 30 °C Notes: 5) Guaranteed by characterization. 6) Guaranteed by design. 7) Without Sleep Mode. MP2148 Rev. 1.11 5/25/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 6 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN TYPICAL PERFORMANCE CHARACTERISTICS VIN = 5V, VOUT = 1.2V, L =1.0µH, TA = +25ºC, unless otherwise noted. MP2148 Rev. 1.11 5/25/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 7 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN = 5V, VOUT = 1.2V, L =1.0µH, TA = +25ºC, unless otherwise noted. MP2148 Rev. 1.11 5/25/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 8 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN = 5V, VOUT = 1.2V, L =1.0µH, TA = +25ºC, unless otherwise noted. Steady State Steady State Steady State without Load with 1A Load VIN=3.6V, VOUT=3.3V, IOUT=0A,AAM VOUT/AC 10mV/div. VOUT/AC 50mV/div. VOUT/AC 100mV/div. VIN 5V/div. VIN 5V/div. VIN 5V/div. VSW 2V/div. VSW 2V/div. IL 500mA/div. VSW 5V/div. IL 0.2A/div. IL 1A/div. Steady State VIN=3.6V, VOUT=3.3V, IOUT=0.05A, AAM Steady State Steady State VIN=3.6V, VOUT=3.3V, IOUT=0.25A, AAM VIN=3.6V, VOUT=3.3V, IOUT=1A VOUT/AC 20mV/div. VOUT/AC 50mV/div. VIN 5V/div. VIN 5V/div. VIN 5V/div. VSW 2V/div. VSW 2V/div. VOUT/AC 100mV/div. VSW 2V/div. IL 0.2A/div. IL 0.2A/div. VIN Power Up IL 1A/div. VIN Power Up without Load VIN Shut Down with 1A Load without Load VOUT 1V/div. VIN 5V/div. VOUT 1V/div. VIN 5V/div. VOUT 1V/div. VIN 5V/div. VSW 5V/div. VSW 5V/div. VSW 5V/div. IL 1A/div. IL 1A/div. IL 1A/div. MP2148 Rev. 1.11 5/25/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 9 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN = 5V, VOUT = 1.2V, L =1.0µH, TA = +25ºC, unless otherwise noted. MP2148 Rev. 1.11 5/25/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 10 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN = 5V, VOUT = 1.2V, L =1.0µH, TA = +25ºC, unless otherwise noted. MP2148 Rev. 1.11 5/25/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 11 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN PIN FUNCTIONS Pin # 1 Name Description MP2148GQD: Feedback Pin. An external resistor divider from the output to GND, tapped to the FB pin, sets the output voltage. FB/PG MP2148GQD-XX: Power Good Indicator. The output of this pin is an open drain output. Keep PG pulls up voltage is lower than Vin. 2 GND 3 VIN 4 SW 5 EN 6 OUT MP2148 Rev. 1.11 5/25/2015 Power Ground. Supply Voltage. The MP2148 operates from a +2.3V to +5.5V unregulated input. Decouple capacitor is needed to prevent large voltage spikes from appearing at the input. Output Switching Node. SW is the drain of the internal high-side P-Channel MOSFET. Connect the inductor to SW to complete the converter. On/Off Control. Output Voltage Power Rail and Input Sense Pin for Output Voltage. Connect load to this pin. Output capacitor is needed to decrease the output voltage ripple. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 12 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN BLOCK DIAGRAM Figure 1: Functional Block Diagram Note: Optional 1: FB pin is only for MP2148GQD Optional 2: PG pin is only for MP2148GQD-XX MP2148 Rev. 1.11 5/25/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 13 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN OPERATION The MP2148 uses constant on-time control with input voltage feed forward to stabilize the switching frequency over the full input range. It achieves 1A continuous output current from a 2.3V-to-5.5V input voltage with excellent load and line regulation. The output voltage can be regulated to as low as 0.6V. regulated to the internal reference voltage, thus, the average output voltage is slightly higher than the output voltage at DCM or CCM mode. The on-time pulse at sleep mode is around 40% larger than that on DCM or CCM mode. Figure 3 shows the average FB pin voltage relationship with the internal reference at sleep mode. Constant On-Time Control Compare to fixed frequency PWM control, constant on-time control offers a simpler control loop and a faster transient response. By using input-voltage feed forward, the MP2148 maintains a nearly constant switching frequency across the input and output voltage ranges. The switching pulse on time can be estimated as: TON = VOUT ⋅ 0.454μs VIN To prevent inductor current runaway during load transient, MP2148 has fixed minimum off time of 60ns. Sleep Mode Operation MP2148 features sleep mode to get high efficiency at extreme light load. In sleep-mode, most of the circuit blocks are turned off, except the error amplifier and PWM comparator, thus the operation current is reduced to a minimal value, as Figure 2. Figure 3: FB Average Voltage at Sleep Mode When MP2148 is in sleep mode, the average output voltage is higher than the internal reference voltage. The EAO is kept low and clamped in sleep mode. When the loading increases, the PWM switching period decreases in order to keep the output voltage regulated and the output voltage ripple is decrease relatively. Once EAO is more than internal low threshold, MP2148 will be out of sleep mode and enter DCM or CCM mode depending on the loading. In DCM or CCM mode, the EA regulates the average output voltage to the internal reference which is shown in Figure 4. Figure 4: DCM Mode Control There is always a loading hysteresis of entering sleep mode and leaving sleep mode due to the error amplifier clamping response time. AAM Operation at Light-Load Operation The MP2148 has AAM (Advanced Asynchronous Modulation) power-save mode together with ZCD (Zero Current Cross Detection) circuit for light load. Figure 2: Operation Blocks at Sleep Mode When the loading gets lighter, the ripple of the output voltage is bigger and it drives the error amplifier output (EAO) lower. When EAO hits an internal low threshold, it will be clamped at that level, MP2148 enters sleep mode. During sleep mode, the valley of the FB pin voltage is MP2148 Rev. 1.11 5/25/2015 The MP2148 has AAM power-save mode for light load. Simplified AAM control theory is as Figure 5. AAM current IAAM is set internally. The SW on pulse time is decided by on-timer generator and AAM comparator. At light load condition, the SW on pulse time is the longer one. If the AAM comparator pulse is longer than www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 14 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN on-timer generator, the operation mode is below in Figure 6. VFB EN COT Generator VREF FBCOMP S Q HS_ driver Figure 8: AAM Blank Time in Sleep Mode R IL_ sense IAAM AAMCOMP Figure 5: Simplified AAM Control Logic Figure9 shows AAM threshold decreases with Ton increasing gradually. For the CCM state, Io needs more than half of AAM threshold at least. Figure 6: AAM Comparator Control Ton If the AAM comparator pulse is shorter than ontimer generator, the operation mode is below in Figure 7. Generally, using very small inductance may bring this case. AAM Io IL a. Light load in on-timer AAM Io Figure 9: AAM Threshold decreases with Ton Increases. MP2148 have a zero current cross detect circuit (ZCD) to judge if the inductor current starts to reverse. When the inductor current reaches ZCD threshold, the low side switch will be turned off. AAM mode together with ZCD circuit make MP2148 always work on DCM mode at light load, even if Vo is closed to Vin. Enable IL b. Increase load in on-timer Figure 7: On-Timer Control Ton Except upper on-timer method, AAM circuit has another 150ns AAM blank time in sleep mode. That means if on-timer is less than 150ns, the high side MOSFET may turn off after on-timer generator pulse without AAM control. Just a remind, the on-time pulse at sleep mode is around 40% larger than that on DCM or CCM mode. At this condition, IL may not reach AAM threshold as Figure 8. When input voltage is greater than the undervoltage lockout threshold (UVLO), typically 2V, MP2148 can be enabled by pulling EN pin to higher than 1.2V. Leaving EN pin float or pull down to ground will disable MP2148. There is an internal 1Meg Ohm resistor from EN pin to ground. When the device is disabled, the part goes into output discharge mode automatically and its internal discharge MOSFET provides a resistive discharge path for the output capacitor. Soft Start The MP2148 has a built-in soft start that ramps up the output voltage at a controlled slew rate to avoid overshoot at startup. The soft start time is about 0.5ms typically. MP2148 Rev. 1.11 5/25/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 15 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN Power Good Indictor (only for MP2148GQDXX) The MP2148 has an open drain and need a external pull-up resistor (100kΩ~500kΩ) for the power good indicator (Note: Keep PG pull up voltage is lower than Vin). When VFB is within 10% of regulation voltage, VPG is pulled up to Vo/Vin by the external resistor. If VFB exceeds the -10% window, the internal MOSFET pulls the PG to ground. The MOSFET has a maximum RDSON of less than 400Ω. Current limit The MP2148 typically has a 2.4A high-side switch current limit. When the high side switch hits its current limit, the MP2148 will remain in hiccup mode until the current drops. This prevents the inductor current from continuing to rise and damage components. Short Circuit and Recovery The MP2148 will also enter short-circuit protection mode when it hits the current limit, and tries to recover with hiccup mode: The MP2148 will disable the output power stage, discharge the soft-start capacitor and then automatically try soft-start again. If the short circuit condition remains after soft-start ends, the MP2148 repeats this cycle until the short circuit disappears and output rises back to regulation level. MP2148 Rev. 1.11 5/25/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 16 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN APPLICATION INFORMATION COMPONENT SELECTION metal alloy or multiplayer chip power are best candidates for application, can decrease the Setting the Output Voltage(Only for MP2148GQD) influence effectively. Table2 is some suggested inductors. The external resistor divider sets the output voltage (see the Typical Application on Figure13). Select the feedback resistor R1 that consider reducing VOUT leakage current, typically between 100kΩ to 200kΩ. There is not strict requirement on feedback resistor. Select R1>10kΩ is reasoned for application. R2 = R1 Vout −1 0.6 Table 2: Suggested Inductor List Manufacturer P/N Inductance( μH ) Manufacturer PIFE25201B-1R0MS 1.0 CYNTEC CO. LTD. 1239AS-H-1R0M 1.0 Tokyo 74438322010 1.0 Wurth For most designs, estimate the inductance value from the following equation. L1 = Figure 10 shows the feedback circuit. VOUT × (VIN − VOUT ) VIN × ΔIL × fOSC Where ΔIL is the inductor ripple current. Choose an inductor current to be approximately 30% of the maximum load current. The maximum inductor peak current is: IL(MAX ) = ILOAD + Figure 10: Feedback Network Table 1 lists the recommended resistors value for common output voltages. Table 1: Resistor Values for Common Output Voltages VOUT (V) R1 (kΩ) R2 (kΩ) 1.0 1.2 1.8 2.5 200(1%) 200(1%) 200(1%) 200(1%) 300(1%) 200(1%) 100(1%) 63.2(1%) 3.3 200(1%) 44.2(1%) Selecting the Inductor Most applications work best with a 0.47µH to 1.5µH inductor. Select an inductor with a DC resistance less than 15mΩ to optimize efficiency. High frequency switch mode power supply with magnetic device has strong electronic magnetic inference for system. Any un-shield power inductor should be avoided applying as poor magnetic shielding. Shield inductor, such as MP2148 Rev. 1.11 5/25/2015 Δ IL 2 Selecting the Input Capacitor The input current to the step-down converter is discontinuous, and therefore requires a capacitor to supply the AC current to the stepdown converter while maintaining the DC input voltage. Use low ESR capacitors for the best performance. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. For most applications, a 10µF capacitor is sufficient. Higher output voltages may require a 22μF capacitor to increase system stability. The input capacitor requires an adequate ripple current rating because it absorbs the input switching current. Estimate the RMS current in the input capacitor with: ⎛ V V ⎞ IC1 = ILOAD × OUT ×⎜⎜1− OUT ⎟⎟ ⎜ VIN ⎝ VIN ⎟⎠ The worst case occurs at VIN = 2VOUT, where: IC1 = ILOAD 2 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 17 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN 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. When using electrolytic or tantalum capacitors, add a small and high quality ceramic 0.1μF capacitor 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 the input. The input voltage ripple caused by capacitance can be estimated as: ⎛ I V V ⎞ ΔVIN = LOAD × OUT × ⎜ 1 − OUT ⎟ fS × C1 VIN ⎝ VIN ⎠ Selecting the Output Capacitor The output capacitor (C2) stabilizes the DC output voltage. Ceramic capacitors are recommended. Low ESR capacitors are preferred to limit the output voltage ripple. Estimate the output voltage ripple as: ΔVOUT = ⎞ VOUT ⎛ VOUT ⎞ ⎛ 1 × ⎜1− ⎟ × ⎜ RESR + ⎟ fS × L1 ⎝ VIN ⎠ ⎝ 8 × fS × C2 ⎠ ΔVOUT = VOUT ⎛ V × ⎜ 1 − OUT fS × L1 ⎝ VIN ⎞ ⎟ × RESR ⎠ The characteristics of the output capacitor also affect the stability of the regulation system. PCB Layout Proper layout of the switching power supplies is very important, and sometimes critical for proper function. For the high-frequency switching converter, poor layout design can result in poor line or load regulation and stability issues. Place the high-current paths (GND, IN and SW) very close to the device with short, direct and wide traces. The input capacitor needs to be as close as possible to the IN and GND pins. Place the external feedback resistors next to the FB pin. Keep the switching node SW short and away from the feedback network. Vout sense line need as short as possible or keeps away from power inductor, especial forbids surrounding inductor. Figure11 is advised PCB layout. Where L1 is the inductor value and RESR is the equivalent series resistance (ESR) value of the output capacitor. When using ceramic capacitors, capacitance dominates the impedance at switching frequency, and causes most of output voltage ripple. For simplification, output voltage ripple can be estimated as: ΔVOUT = the the the the ⎛ V ⎞ VOUT × ⎜ 1 − OUT ⎟ 8 × fS × L1 × C2 ⎝ VIN ⎠ For tantalum or electrolytic capacitors, the ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated as: MP2148 Rev. 1.11 5/25/2015 Figure 11: Two Ends of Input Decoupling Capacitor Close to Pin 2 and Pin3. 2 . www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 18 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN TYPICAL APPLICATION CIRCUITS VIN 2.3V to 5.5V L1 1µH U1 SW VIN R3 100kΩ EN C1A NS VOUT 1.2V/1A OUT C1 10 µF MP2148GQD EN R1 200k Ω C2 10µF C2A NS FB R2 200kΩ GND Figure 12: Typical Application Circuit for MP2148GQD Note: VIN<3.3V may need more input capacitor. Figure 13: Typical Application Circuit for MP2148GQD-XX Note: 1. VIN<3.3V may need more input capacitor; 2. VIN>VOUT for application. MP2148 Rev. 1.11 5/25/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 19 MP2148 –1A SYNCHRONOUS STEP-DOWN CONVERTER WITH 11µA IQ IN ULTRA-SMALL 1X1.5mm QFN PACKAGE INFORMATION QFN-6 (1.0mmx1.5mm) PIN 1 ID PIN 1 ID MARKING PIN 1 ID INDEX AREA BOTTOM VIEW TOP VIEW SIDE VIEW NOTE: 1) ALL DIMENSIONS ARE IN MILLIMETERS. 2) EXPOSED PADDLE SIZE DOES NOT INCLUDE MOLD FLASH. 3) LEAD COPLANARITY SHALL BE 0.10 MILLIMETERS MAX. 4) JEDEC REFERENCE IS MO-220. 5) DRAWING IS NOT TO SCALE. 0 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. MP2148 Rev. 1.11 5/25/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 20