MPM3686 18V 20A Step-Down Power Module in 12x15x4mm QFN The Future of Analog IC Technology DESCRIPTION FEATURES The MPM3686 is an easy-to-use fully integrated 20A step-down DC/DC power module. It integrates the DC/DC converter, power inductor, input/output capacitors and the necessary resistors/capacitors in a compact QFN 12mmX15mmX4mm package. This total power solution needs as few as two external components (one resistor and one capacitor) to work. MPM3686 can deliver 20A output current over a wide input supply voltage range with excellent load and line regulation. The MPM3686 uses Constant-On-Time (COT) control to provide fast transient response and ease the loop stabilization. The default under voltage lockout threshold is internally set around 4.1V, but a resistor network on the enable pin can increase this threshold. The MPM3686 has an internal LDO to power the control circuits and the integrated power devices. This LDO can be disabled by an external 5V to boost the efficiency. The MPM3686 has an internal about 3ms soft start (SS) timer. It can be increased with an extra SS capacitor. An open drain power good signal indicates that the output voltage is within nominal voltage range. The MPM3686 has fully integrated protection features that include over-current protection, over-voltage protection and thermal shutdown. Complete 20A DC-to-DC Solution Wide Input Voltage Range from 2.5V: -- 2.5V to 18V with External 5V Bias -- 4.5V to 18V with Internal Bias 1% Reference Voltage Over 0˚C to 70˚C Junction Temperature Range Adaptive COT Control for Ultrafast Transient Response Programmable Switching Frequency from 200KHz to 1MHz Support Pre-Bias Start Up Programmable Soft-Start Time with Default 3ms Non-latch OCP, OVP and Thermal Shutdown Output Adjustable from 0.65V to 5V QFN-65 (12mmx15mmx4mm) Package APPLICATIONS Telecom and Networking Systems Base Stations Servers Personal Video Recorders Flat Panel Television and Monitors Distributed Power Systems All MPS parts are lead-free, halogen-free, and adhere to the RoHS directive. For MPS green status, please visit the MPS website under Quality Assurance. “MPS” and “The Future of Analog IC Technology” are registered trademarks of Monolithic Power Systems, Inc. MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 1 MPM3686 – 18V 20A STEP-DOWN POWER MODULE TYPICAL APPLICATION MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 2 MPM3686 – 18V 20A STEP-DOWN POWER MODULE ORDERING INFORMATION Part Number* MPM3686GRU Package QFN-65 (12mmx15mmx4mm) Top Marking See Below TOP MARKING MPS: MPS prefix: YY: year code; WW: week code: MP3686: first six digits of the part number; M: LLLLLLLLL: lot number; PACKAGE REFERENCE TOP VIEW MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 3 MPM3686 – 18V 20A STEP-DOWN POWER MODULE ABSOLUTE MAXIMUM RATINGS (1) Recommended Operating Conditions Supply Voltage VIN to GND ............. -0.3V to 21V VSW(DC) to GND .......................... –1V to VIN+0.3V VSW5 (30ns) to GND ............. –3 V to VIN+3V or 24V VBST .......................................... –0.3 V to VIN+6V All Other Pins to AGND.................. –0.3V to +6V Continuous Output Current ......................... 22A Junction Temperature ...............................150C Lead Temperature ....................................260C Storage Temperature .............. –55C to +150C MSL ................................................... Level 3(5) ESD (HBM) ................................................. 2kV ESD (CDM) ............................................... 500V Supply Voltage VIN ........................... 4.5V to 18V Output Voltage VOUT ........................ 0.65V to 5V Enable Current IEN……………………..…....1mA Ambient Temperature ................ –40C to +85C Junction Temperature .............. –40C to +125C Thermal Resistance (4) θJB (3) θJA 12x15x4 QFN .... ……………2.5……14.0 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. 3) The device is not guaranteed to function outside of its operating conditions. 4) Measured on JESD51-7, 4-layer PCB. st 5) Need to get some test data from 1 sample for calibration and evaluation for MSL Level 2. MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 4 MPM3686 – 18V 20A STEP-DOWN POWER MODULE ELECTRICAL CHARACTERISTICS VIN = 12V, VOUT = 1.2V, Rtrim =10kΩ, Ctrim =560pF, TJ = 25C, unless otherwise noted. Parameters Input Voltage Range Symbol Input Voltage Range VIN Output Voltage Output Voltage Range 6) VOUT RANGE Output Voltage Accuracy (Load VOUT_DC_Load Regulation) 6) Output Voltage Accuracy (Line VOUT_DC_Line Regulation) 6) Quiescent Current Quiescent Current IIN Current Limit Output Current Limit ILIM Switching Frequency 6) Switching Frequency fSW Over-voltage and Under-voltage Protection VOVP_NONOVP Non-latch Threshold 7) Reference Voltage 8) Soft Start Time Timer 6) Minimum ON Time Minimum OFF Time Min 5V External VCC Max Units 2.5 4.5 18 18 V V 0.65 5 V COUT =5X47μF Ceramic, IOUT =0A to 20A COUT =5X47μF Ceramic, VIN =4.5V to 18V, IOUT =5A ±0.5 %Vout ±0.4 %Vout 860 1000 uA 20 25 30 A 400 500 600 kHz With negative current limit 117% 120% 123% VFB No negative current limit 127% 47% 130% 50% 133% 53% VFB VFB TJ = 0C to +70C 608 611 614 mV TJ = 0C to +120C 605 611 617 mV TJ = -40C to +125C 602 611 620 mV tSS 2 2.8 3.6 ms TON MIN TOFF MIN 20 200 30 360 40 420 ns ns VOVP TH VUVP VREF VEN =2V, VFB=0.65V Typ 700 LATCH OVP Threshold 6) UVP Threshold 6) Reference And Soft Start Condition IOUT=5A MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 5 MPM3686 – 18V 20A STEP-DOWN POWER MODULE ELECTRICAL CHARACTERISTICS VIN = 12V, VOUT = 1.2V, Rtrim =10kΩ, Ctrim =560pF, TJ = 25C, unless otherwise noted. Parameters Power Good Power Good Rising Threshold 7) Power Good Falling Threshold 7) Power Good Low to High Delay 7) Power Good Sink Current Capability 7) Power Good Leakage Current 7) Symbol PGVth-Hi Typ Max Units 87% 91% 94% VFB 80% VFB PGTd 2.5 ms IOL IPG_LEAK PG Low-Level Output Voltage VOL_10 Enable Input Current Min PGVth-Lo VOL_100 Enable 7) Enable Input Low Voltage Enable Hysteresis Condition VOL=600mV 12 VPG=3.3V VIN=0V, Pull PGood up to 3.3V through a 100KΩ resistor. VIN=0V, Pull PGood up to 3.3V through a 10KΩ resistor. 0.01 uA 500 550 600 mV 600 650 700 mV 1.1 1.3 250 1.5 V mV VILEN VEN-HYS IEN mA VEN = 2V 0 μA VCCVth 3.8 V VCCHYS 500 mV VCC 4.8 0.5 V % 25 °C °C VCC Regulator 7) VCC Under Voltage Lockout Threshold Rising VCC Under Voltage Lockout Threshold Hysteresis VCC Regulator VCC Load Regulation Icc=5mA Thermal Protection 6) Thermal Shutdown Thermal Shutdown Hysteresis TSD 150 Notes: 6) Guaranteed by design 7) 100% tested for internal IC prior to module assembly 8) Guaranteed by production test and/or characterization for internal IC prior to module assembly MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 6 MPM3686 – 18V 20A STEP-DOWN POWER MODULE PIN FUNCTIONS Pin # 1, 2, 55, 58, 60 3 4,6,23, 32, 44, 49 5 7- 22, 61, 62 24-31, 63 33- 43, 64 45-48, 65 50 51 52 53 54 56 57 59 Name Description AGND Analog/Signal Ground. It needs to be connected to GND on PCB layout. Output Voltage DC Trimming. Connect this pin to pin DC_trim> first, and then to the >DC_trim output voltage sense point through a resistor. The resistor value can be chosen based on equation 1. N/C Not connected. Keep these pins floating. Output Voltage AC Trimming. Connect these pins to the output through a capacitor. The capacitor value can be chosen based on equation 2. SW Switch Output. Keep them floating. VOUT Module voltage output node. System Power Ground. Reference ground of the regulated output voltage. PCB GND layout requires extra care. Connect using wide PCB traces. Supply Voltage. Supply power to the internal MOSFET and regulator. The MPM3686 operates from a +2.5V to +18V input rail with 5V external bias and from a +4.5V to VIN +18V input rail with internal bias. It requires input decoupling capacitors. Connect using wide PCB traces and multiple vias. Frequency Set In. An internal 430K frequency set resistor is used if connecting this >FREQ pin to Pin FREQ<. Keep this pin floating if values other than 300K are needed. Enable. Digital input that turns the regulator on or off. Drive EN high to turn on the EN regulator, drive it low to turn it off. Connect EN to IN through a pull-up resistor or a resistive voltage divider for automatic startup. Do not float this pin. Frequency Set Out. An internal 430K frequency set resistor is used if connecting this FREQ> pin to Pin FREQ>. If values other than 430K are needed, connect the resistor between this pin and pin VIN. Output Voltage DC Trimming. Connect this pin to pin >DC_trim first, and then to the DC_trim> output voltage sense point through a resistor. The resistor value can be chosen based on equation 1. Soft Start. Floating this pin has the default 3ms SS time. The SS time can be SS extended by connecting an external capacitor between SS and AGND pins. Power Good. The output is an open drain signal. Require a pull-up resistor to a DC PG voltage to indicate high if the output voltage exceeds 91% of the nominal voltage. There is a 2.5ms delay from FB ≥ 91% to PG goes high. Internal 4.8V LDO Output. Power the driver and control circuits. Keep this pin floating. VCC Applying a 5V external bias can disable the internal LDO to boost the efficiency. BST Bootstrap. Keep this pin floating. AC_trim MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 7 MPM3686 – 18V 20A STEP-DOWN POWER MODULE TYPICAL CHARACTERISTICS VIN=12V, VOUT=1.2V, TA=25˚C, unless otherwise noted. MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 8 MPM3686 – 18V 20A STEP-DOWN POWER MODULE TYPICAL CHARACTERISTICS VIN=12V, VOUT=1.2V, TA=25˚C, unless otherwise noted. MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 9 MPM3686 – 18V 20A STEP-DOWN POWER MODULE BLOCK DIAGRAM >FREQ IN 430K 5.7uF FREQ> VCC LDO VCC 1uF BST BST BIAS Minimum OFF Timer EN REFERENCE ON Timer HS Driver HS-FET LOGIC SS VOUT 30uF SOFT START/STOP VCC 300K AC_trim DC_trim> LS Driver FB Comparator ZCD Current Modulator PG LS-FET 1K >DC_trim 10K UV PGOOD Comparator AGND PGND UV Detect Comparator LS Current Limit OV OV Detect Comparator MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 10 MPM3686 – 18V 20A STEP-DOWN POWER MODULE OPERATION Power Module Operation The MPM3686 is a high performance single output synchronous switching mode DC-to-DC power supply. It can deliver 20A continuous output current. The MPM3686 can provide an output voltage from 0.65V to 5V over a 4.5V to 18V (or 2.5V to 18V with 5V external VCC bias) wide input voltage range. The MPM3686 is a complete power solution. It integrates a constant-on-time (COT) control DCto-DC regulator, power devices, an inductor, input/output capacitors and some other supporting resistors and small capacitors. It only needs as few as one external resistor and one external small capacitor to operate. The MPM3686 is controlled by both the VCC voltage and the EN signal. It can only be turned on when both voltages are higher than the thresholds. The switching frequency is determined by a frequency set resistor. The default switching frequency with the integrated resistor is shown in table 1. The default switching frequency increases with the output voltage. The switching frequency can also be programmed externally in the range of 200KHz to 1000KHz. The details can be found in the section of “SWITCHING FREQUENCY SETTING” on Page 12. The MPM3686 utilizes constant-on-time control. It has sufficient stability margin with simple loop compensation. And it provides very good transient response with a wide range of output capacitors, even with all ceramic output capacitors. The MPM3686 has a variable soft start timer to smooth-out the output voltage during start-up. The default (with SS pin floating) soft start timer is about 3ms. The soft-start time can be extended by adding a capacitor between SS pin and AGND pin. PWM Operation The MPM3686 uses Constant-on-time (COT) control to provide a fast transient response and ease loop stabilization. At the beginning of each cycle, the high-side MOSFET (HS-FET) turns ON when the feedback voltage (VFB) drops below the reference voltage (VREF), which indicates an insufficient output voltage. The input voltage and the frequency-set resistor determine the ON period as follows: TON (ns) 6.1 RFREQ (k ) VIN (V) 0.4 (1) After the ON period elapses, the HS-FET turns off. It turns ON again when VFB drops below VREF. By repeating this operation, the converter regulates the output voltage to the desired level. The integrated low-side MOSFET (LS-FET) turns on when the HS-FET is OFF to minimize the conduction loss. There is a dead short (or shootthrough) between input and GND if both HS-FET and LS-FET turn on at the same time. A deadtime (DT) internally generated between HS-FET OFF and LS-FETON, or LS-FET OFF and HSFET ON avoids shoot-through. Heavy-Load Operation Figure 2—Heavy Load Operation When the output current is high and the inductor current is always above zero amps, it is called continuous-conduction-mode (CCM). Figure 2 shows the CCM operation. When VFB is below VREF, HS-FET turns on for a fixed interval determined by the one-shot on-timer as per equation 1. When the HS-FET turns off, the LSFET turns on until the next period. In CCM operation, the switching frequency is fairly constant and is also called PWM mode. MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 11 MPM3686 – 18V 20A STEP-DOWN POWER MODULE Light-Load Operation As the load decreases, the inductor current decreases too. When the inductor current touches zero, the operation is transited from continuous-conduction-mode (CCM) to discontinuous-conduction-mode (DCM). Figure 3 shows the light load operation. When VFB drops below VREF, HS-FET turns on for a fixed interval determined by the one- shot ontimer as per equation 1. When the HS-FET turns off, the LS-FET turns on until the inductor current reaches zero. In DCM operation, the VFB does not reach VREF when the inductor current is approaching zero. The LS-FET driver turns into tri-state (high Z) whenever the inductor current reaches zero. A current modulator takes over the control of LS-FET and limits the inductor current less than -1mA. Hence, the output capacitors discharge slowly to GND through LS-FET. As a result, this mode improves the efficiency greatly at light load condition. At this condition, the HSFET does not turns ON as frequently as at heavy load condition. This is called pulse skip mode. At light load or no load condition, the output drops very slowly and the MPM3686 reduces the switching frequency naturally and then achieves high efficiency at light load. The IC turns into PWM mode once the output current exceeds the critical level. After that, the switching frequency stays fairly constant over the output current range. Switching Frequency Selecting the switching frequency requires trading off between efficiency and component size. Low frequency operation increases efficiency by reducing MOSFET switching losses, but requires larger inductor and capacitor values to minimize the output voltage ripple. The MPM3686 uses adaptive constant-on-time (COT) control to generate a fairly constant frequency at CCM condition, though the IC lacks a dedicated oscillator. The ON time of HSFET can be set by connecting a resistor between IN pin and FREQ pin. It’s input voltage adaptive. So for a fixed output voltage, the switching frequency stays fairly constant. The switching frequency can be set internally and externally. Figure 4 shows that the switching frequency is determined by the internal 430K resistor. The 430K resistor is connected to IN pin so that the input voltage is feed-forwarded to the one-shot ON-time timer. When operating in steady state at CCM, the duty ratio stays at VOUT/VIN, so the switching frequency is fairly constant over the input voltage range. The switching frequency can be determined by equation 3: Figure 3—Light Load Operation As the output current increases from the light load condition, the current modulator regulates the operating period that becomes shorter. The HS-FET turns ON more frequently. Hence, the switching frequency increases correspondingly. The output current reaches the critical level when the current modulator time decreases to zero. The critical output current level can be determined as follows: IOUT (VIN VOUT ) VOUT 2 L FSW VIN Where FSW is the switching frequency. (2) Figure 4 FSW (kHz) 106 6.1 430(k) VIN (V) T (ns) VIN (V) 0.4 VOUT (V) DELAY (3) Where TDELAY is the comparator delay of about 5ns. MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 12 MPM3686 – 18V 20A STEP-DOWN POWER MODULE Table 1 shows the switching frequency with different common output voltages: Vo (V) 1 1.2 1.5 1.8 fs(KHz) 400 500 600 700 determine the automatic start-up voltage: VINSTART 1.5 (RUP RDOWN ) (V) RDOWN (5) For example, for RUP=100kΩ and RDOWN=51kΩ, the VIN-START is set at 4.44V. To reduce noise, add a 10nF ceramic capacitor from EN to GND. Table 1 If a switching frequency other than those listed in Table 1 is desired, an external frequency set resistor can be connected as shown in figure 5: An internal zener diode on the EN pin clamps the EN pin voltage to prevent running away. The maximum pull up current (assuming the worst case 6V for the internal zener clamp) should be limited to 1mA or less. Therefore, when driving EN with an external logic signal, the driving voltage should be 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 of 1mA. If using a resistive voltage divider and VIN exceeds 6V, then the minimum resistance for the pull-up resistor RUP should meet: Figure 5 The switching frequency can be estimated through equation (4) as follows: FSW (kHz) 106 6.1 RFREQ (k) VIN (V) TDELAY (ns) VIN (V) 0.4 VOUT (V) (4) Where TDELAY is the comparator delay of about 5ns. Typically, the MPM3686 is set to 200kHz to 1MHz applications. Thanks to its monolithic structure, the MPM3686 is optimized to operate at high switching frequencies at high efficiency. High switching frequencies allow for physically smaller LC filter components to reduce the PCB footprint. Configuring the EN Control The power module turns on when EN goes high; conversely it turns off when EN goes low. Do not float the pin. For automatic start-up, pull the EN pin up to input voltage through a resistive voltage divider. 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 VIN 6V 6V 1mA RUP RDOWN (6) 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 () 1mA (7) A typical pull-up resistor is 100kΩ. VCC Power Supply The MPM3686 has an internal VCC LDO to supply the power to the internal circuits and drives the power devices. This VCC LDO is derived from the input supply. To ensure proper operation, the minimum input voltage should be 4.5V. An external 5V VCC bias can disable the internal LDO. In this case, Vin can be as low as 2.5V. The efficiency can be higher with external 5V VCC bias. Figure 6 shows the comparison. MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 13 MPM3686 – 18V 20A STEP-DOWN POWER MODULE on the soft-start capacitor exceeds the sensed output voltage at the FB pin. Figure 6 Soft Start The MPM3686 employs a soft start (SS) mechanism to ensure a smooth output during power-up. When the EN pin goes high, an internal current source (20μA) charges the SS capacitor. The SS capacitor voltage takes over the REF voltage to the PWM comparator. The output voltage smoothly ramps up with the SS voltage. Once the SS voltage reaches the REF voltage, it continues ramping up while VREF takes over the PWM comparator. At this point, soft start finishes and the device enters steady state operation. An internal 100nF SS capacitor is used. So the default (with SS pin floating) SS time can be estimated as: TSS (ms) 100(nF) VREF (V) ISS (uA) (8) So the default SS time is about 3ms. If longer SS time is needed, an external SS capacitor can be added between SS pin and AGND pin. The external capacitor value can be determined as follows: CSS (nF) TSS (ms) ISS (uA) 100(nF) VREF (V) (9) Pre-Bias Startup The MPM3686 has been designed for monotonic startup into pre-biased loads. If the output is prebiased to a certain voltage during startup, the IC will disable switching for both high-side and lowside switches until the voltage Power Good (PG) The MPM3686 has a power-good (PG) output. The PG pin is the open drain of a MOSFET. Connect it to VCC or some other voltage source that measures less than 5.5V through a pull-up resistor (typically 100kΩ). After applying the input voltage, the MOSFET turns on so that the PG pin is pulled to GND before the SS is ready. After the FB voltage reaches 91% of the REF voltage, the PG pin is pulled high after a 2.5ms delay. When the FB voltage drops to 80% of the REF voltage or exceeds 120% of the nominal REF voltage, the PG pin is pulled low. If the input supply fails to power the MPM3686, the PG pin is also pulled low even though this pin is tied to an external DC source through a pull-up resistor. Over-Current Protection (OCP) The MPM3686 features two current limit levels for over-current conditions: low-side valley current limit and low-side negative current limit. Low-Side Valley Current Limit: The device monitors the inductor current during the LS-FET ON state. If the LS-FET sourcing current is higher than the internal positive-valley-current limit, the HS-FET remains OFF and the LS-FET remains ON for the next ON time. When the LSFET sourcing current drops below the valley current limit, then the LS-FET turns off and the HS-FET turns on again. The MPM3686 enters OCP non-latch protection mode if the LS-FET sourcing valley current keeps exceeding the valley current limit for a certain period of time. During OCP, the device tries to recover from the over-current fault with hiccup mode: the chip disables the output power stage, discharges the soft-start capacitor and then automatically retries soft-start. The device repeats this operation cycle as long as the overcurrent condition still exists. When the overcurrent condition disappears, the MPM3686 initiates a new SS to rise back to regulation level. MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 14 MPM3686 – 18V 20A STEP-DOWN POWER MODULE Low-Side Negative Current Limit: If the sensed LS-FET negative current exceeds the negative current limit, the LS-FET turns off immediately and stays OFF for the remainder of the OFF period. In this situation, both MOSFETs are OFF until the end of a fixed interval. The HS-FET body diode conducts the inductor current for the fixed time. Over -Voltage Protection (OVP) The MPM3686 monitors the output voltage using the FB pin connected to the tap of a resistor divider to detect over-voltage. It provides nonlatch OVP mode. If the FB voltage exceeds the nominal REF voltage but remains lower than 120% of the REF voltage (0.611V), both MOSFETs are off. If the FB voltage exceeds 120% of the REF voltage but remains below 130%, the LS-FET turns on while the HS-FET remains off. The LSFET remains on until the FB voltage drops below 110% of the REF voltage or the low-side negative current limit is hit. If the FB voltage exceeds 130% of the REF voltage, it enters a non-latch mode. The LS-FET remains on until the FB voltage drops below 110% of the REF voltage, and the MPM3686 initiates a new SS to rise back to regulation level and operates normally again. IN RUP RDOWN EN Comparator EN Figure 7—Adjustable UVLO Threshold Thermal Shutdown The MPM3686 has thermal shutdown. The IC internally monitors the junction temperature. If the junction temperature exceeds the threshold value (minimum 150ºC), the converter shuts off. This is a non-latch protection. There is about 25ºC hysteresis. Once the junction temperature drops to about 125ºC, it initiates a soft startup. UVLO protection The MPM3686 has under-voltage lock-out protection (UVLO). When the VCC voltage exceeds the UVLO rising threshold, the MPM3686 powers up. It shuts off when the VCC voltage falls below the UVLO falling threshold voltage. This is non-latch protection. The MPM3686 is disabled when the VCC voltage falls below 3.3 V. If an application requires a higher UVLO threshold, use the two external resistors connected to the EN pin as shown in Figure 9 to adjust the startup input voltage. For best results, use the enable resistors to set the input voltage falling threshold (VSTOP) above 3.6 V. Set the rising threshold (VSTART) to provide enough hysteresis to account for any input supply variations. MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 15 MPM3686 – 18V 20A STEP-DOWN POWER MODULE APPLICATION INFORMATION Setting the Output Voltage-Small ESR Capacitors When the output capacitors are all ceramic capacitors or capacitors with small ESR, external RAMP is injected through the R/C network across the inductor. The circuit connection is as follows: light load conditions. The Ctrim is still recommended to boost the phase margin of the system. A value between 100pF and 2.2nF is recommended. The circuit connection can be made as the following: Figure 9 The Rtrim can be determined as follows to obtain the desired output voltage: Figure 8 Here is the procedure to find the values for Ctrim and Rtrim: a) Determine the Ton TON (ns) 5.3 RFREQ (K) VIN (V) 0.4 (10) b) Determine Ctrim. Choose a VRAMP around 10mV-30mV for most of the applications. CTRIM (pF) VIN ( V ) VOUT ( V ) TON (ns) R 3 (K) VRAMP ( V ) VRAMP (V) 2 VOUT ( V ) 1) 10(K) VFB _ AVG ( V ) R TRIM (K ) Setting the Capacitors RO (K) 300(K) 300(K ) RO (K) Output Voltage-Large (15) Input Capacitor The input current to the step-down power module is discontinuous, and therefore, it requires a capacitor to supply the AC current to the stepdown power module while maintaining the DC input voltage. Use ceramic capacitors for best performance. During layout, Place the input capacitors as close to the IN and GND pins as possible. The capacitance can vary significantly with temperature. Use capacitors with X5R or X7R ceramic dielectrics because they are fairly stable over a wide temperature range. (12) The capacitors must also have a ripple current rating that exceeds the converter’s maximum input ripple current. Estimate the input ripple current as follows: d) Calculate Rtrim to get the desired output voltage: R o (K) ( VOUT VREF 10 VREF (11) c) Find the average feedback voltage VFB VFB _ AVG (V) VREF (V) R TRIM (K) (13) (14) ESR ICIN IOUT VOUT V (1 OUT ) VIN VIN (16) The worst-case condition occurs at VIN = 2VOUT, where: I ICIN OUT (17) 2 If one or more piece of the output capacitors have large ESR, then there is no need of external RAMP. Otherwise, it’ll generate group pulses at MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 16 MPM3686 – 18V 20A STEP-DOWN POWER MODULE PCB Layout Recommendations For simplification, choose an input capacitor with an RMS current rating that exceeds half the maximum load current. 1. Place the input/output capacitors on the same side of the MPM3686, and as close to the MPM3686 package as possible. The input capacitance value determines the converter input voltage ripple. Select a capacitor value that meets any input voltage ripple requirements. 2. A solid system ground layer is required to be placed immediately below the surface layer with the MPM3686. Estimate the input voltage ripple as follows: V IOUT V (18) VIN OUT (1 OUT ) VIN FSW CIN VIN 3. Thermal VIAs (18 mil diameter and 8 mil hole size) are required to be placed underneath the GND, IN and VOUT pads, as well as the edges of the MPM3686 and the input/output capacitors. The worst-case condition occurs at VIN = 2VOUT, where: IOUT 1 (19) VIN 4 FSW CIN 4. Keep the DC_trim traces as short as possible. Ctrim Rtrim AGND AGND >DC_trim N/C N/C AC_trim SW SW SW SW SW SW SW SW SW SW SW SW AGND SW BST AGND SW SW SW VCC SW PG N/C AGND VOUT SS VOUT DC_trim> VOUT FREQ> VOUT EN VOUT VOUT GND IN >FERQ VOUT N/C VOUT VIN COUT2 CIN2 COUT3 CIN3 VIN CIN1 VIN VIN GND N/C GND GND GND GND GND GND GND GND GND GND N/C VOUT COUT1 Figure 10 MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 17 MPM3686 – 18V 20A STEP-DOWN POWER MODULE Typical Design Parameter Table The following table (Table 2) includes the recommended component values for typical designs. Ref Vin (V) 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 33 34 35 36 39 40 41 42 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 12 Vout (V) 1 1 1 1 1 1 1.2 1.2 1.2 1.2 1.2 1.2 1.5 1.5 1.5 1.5 1.5 1.5 1.8 1.8 1.8 1.8 1.8 1.8 2.5 2.5 2.5 2.5 2.5 2.5 3.3 3.3 3.3 3.3 5 5 5 5 Rtrim (KΩ) Ctrim (pF) Rfreq (KΩ) fs (KHz) 6.49 6.49 6.49 6.49 6.49 6.49 10 10 10 10 10 10 15 15 15 15 15.8 15.8 21 21 21 21 21 21 34 34 35.7 35.7 34 34 49.9 49.9 49.9 49.9 90.9 90.9 90.9 90.9 560 560 560 560 220 330 560 560 560 560 270 270 680 680 560 560 330 330 560 560 560 560 470 330 680 680 680 680 330 270 330 330 270 270 390 390 180 150 NS NS 300 300 178 178 649 649 NS NS 200 200 806 806 NS NS 243 243 750 750 NS NS 301 301 1000 1000 715 715 432 432 1000 1000 549 549 1500 1500 909 909 400 400 600 600 1000 1000 300 300 500 500 1000 1000 300 300 600 600 1000 1000 400 400 750 750 1000 1000 400 400 600 600 1000 1000 600 600 1000 1000 600 600 1000 1000 Cout (uF) 5X47 3X47 5X47 3X47 3X47 5X47 5X47 3X47 5X47 3X47 5X47 3X47 5X47 3X47 5X47 3X47 5X47 3X47 5X47 3X47 5X47 3X47 5X47 3X47 5X47 3X47 5X47 3X47 5X47 3X47 5X47 7X47 5X47 3X47 5X47 7X47 5X47 3X47 Ripple (mV) 11.6 16.4 5.0 7.6 3.8 2.2 24.0 38.4 11.2 14.8 3.2 4.6 32.8 46.0 8.4 11.6 5.8 7.0 25.4 49.6 7.6 9.4 8.8 12.4 34.2 46.4 18.8 25.2 9.8 13.0 31.6 21.2 6.0 10.2 49.2 36.0 20.8 28.8 Table 2: Typical Design Examples MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 18 MPM3686 – 18V 20A STEP-DOWN POWER MODULE PACKAGE INFORMATION QFN-65 (12mmx15mmx4mm) 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. MPM3686 Rev. 1.02 www.MonolithicPower.com 10/13/2016 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2016 MPS. All Rights Reserved. 19