MPM3840 The Future of Analog IC Technology 2.8V-5.5V, 4A, Power Module, Synchronous Step-Down Converter with Integrated Inductor DESCRIPTION FEATURES The MPM3840 is a DC/DC module that includes a monolithic, step-down, switch-mode converter with built-in, internal power MOSFETs and an inductor. The MPM3840 can provide 4A of continuous output current from a 2.8V to 5.5V input voltage with excellent load and line regulation. The MPM3840 is ideal for powering portable equipment that run on a single-cell Lithium-ion (Li+) battery. The output voltage can be regulated as low as 0.6V. Only input capacitors, output capacitors, and feedback (FB) resistors are required to complete the design. The constant-on-time (COT) control scheme provides a fast transient response, high light-load efficiency, and easy loop stabilization. Full protection features include cycle-by-cycle current limiting and thermal shutdown. The MPM3840 requires a minimal number of readily available, standard, external components and is available in an ultra-small QFN-20 (3mmx5mmx1.6mm) package. >80% Light-Load Efficiency Low IQ: 40μA Wide 2.8V to 5.5V Operating Input Range Output Voltage as Low as 0.6V 100% Duty Cycle in Dropout 4A Output Current 25mΩ and 12mΩ Internal Power MOSFETs 1.2MHz Frequency External Mode Control External Mode Control (PWM.PFM) and Dynamic Analog Voltage EN and Power Good for Power Sequencing Cycle-by-Cycle Over-Current Protection (OCP) 1.5ms Internal Soft-Start Time with PreBiased Start-Up Short-Circuit Protection (SCP) with Hiccup Mode Thermal Shutdown Stable with Low ESR Output Ceramic Capacitors Available in a QFN-20 (3mmx5mmx1.6mm) Package APPLICATIONS Networking/Servers Space-Constraint Applications Industrial Products 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 the MPS website under Quality Assurance. “MPS” and “The Future of Analog IC Technology” are registered trademarks of Monolithic Power Systems, Inc. TYPICAL APPLICATION Efficiency 100 VIN=5V 90 80 70 60 Vo=1V@PWM 50 Vo=1.5V@PWM 40 Vo=1V@PFM Vo=1.2V@PWM Vo=1.8V@PWM Vo=1.2V@PFM 30 Vo=1.5V@PFM Vo=1.8V@PFM 20 Vo=2.5V@PWM Vo=3.3V@PWM 10 0 0.001 Vo=2.5V@PFM Vo=3.3V@PFM 0.01 0.1 IOUT (A) MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 1 10 1 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR ORDERING INFORMATION Part Number* MPM3840GQV Package QFN-20 (3mmx5mmx1.6mm) Top Marking See Below * For Tape & Reel, add suffix –Z (e.g. MPM3840GQV–Z) TOP MARKING MP: MPS prefix Y: Year code W: Week code 3840: First four digits of the part number LLL: Lot number M: Module PACKAGE REFERENCE TOP VIEW GND GND SW VIN PG MODE 18 17 16 15 14 13 12 GND 1 GND 2 GND 3 10 FB SW 4 9 OUT SW 5 8 OUT SW 6 7 OUT 19 NC 20 EN 11 RAMP NC QFN-20 (3mmx5mmx1.6mm) MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 2 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR ABSOLUTE MAXIMUM RATINGS (1) Supply voltage (VIN) ...................................... 6V VSW ................................ -0.3V (-5V for <10ns) to 6V (10V for <10ns) All other pins ..................................... -0.3V to 6V Junction temperature ................................150°C Lead temperature .....................................260°C (2) Continuous power dissipation (TA = +25°C) ……….….. ................................................. 2.8W Storage temperature ................ -65°C to +150°C Recommended Operating Conditions (3) Supply voltage (VIN) ....................... 2.8V to 5.5V Operating junction temp. (TJ). .. -40°C to +125°C θJA θJC Thermal Resistance (4) QFN-20 (3mmx5mmx1.6mm) ... 46 .... 10 ... °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 produces an excessive die temperature, causing the regulator to 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. MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 3 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR ELECTRICAL CHARACTERISTICS VIN = 3.6V, VOUT = 1.2V, 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 Feedback current P-FET switch on resistance N-FET switch on resistance Dropout resistance Switch leakage VFB IFB RDSON RDSON RDR Condition 2.8V ≤ VIN ≤ 5.5V VFB = 0.65V Min Typ Max Units 0.594 0.600 50 25 12 47 0 0.606 1 V nA mΩ mΩ mΩ μA 5.5 6.5 A P N 100% on duty TJ = 25°C P-FET peak current limit 4.5 N-FET valley current limit 4 On time Switching frequency Minimum off time Minimum on time(5) Soft-start time PG UV threshold rising PG UV threshold falling PG OV threshold rising PG OV threshold falling Power good delay Power good sink current capability Power good logic-high voltage Power good internal pull-up resistor Under-voltage lockout threshold rising Under-voltage lockout threshold hysteresis EN input logic-low voltage fs TJ = 25°C 216 TJ = -40°C to 85°C 202 VOUT = 1.2V Sink 1mA VIN = 5V, VFB = 0.6V Supply current (shutdown) Supply current (quiescent) (5) Thermal shutdown Thermal hysteresis(5) Inductor L value Inductor DC resistance 338 0.4 4.9 2.4 500 2.55 2.7 300 1.2 VEN = 2V VEN = 0V VEN = 0V, TJ = 25°C VIN = 3.6V, VEN = 2V, VFB = 0.65V, TJ = 25°C ns kHz ns ns ms VFB VFB VFB VFB μs V V kΩ V mV 0.4 EN input logic-high voltage EN input current 324 1200 60 50 1.5 0.9 0.85 1.15 1.1 140 TMIN-OFF TMIN-On TSS-ON PGTH_Hi PGTH_Lo PGTH_Hi PGTH_Lo VPG LO VPG HI RPG 270 A V V 2 0 0.1 1 μA μA μA 40 60 μA 150 20 0.47 22 °C °C μH mΩ NOTE: 5) Guaranteed by design. MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 4 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR TYPICAL PERFORMANCE CHARACTERISTICS VIN = 5V, VOUT = 1.2V, COUT = 22μF*2, TA = +25°C, unless otherwise noted. Quiescent Current vs. Input Voltage No Switching 70 55 50 45 40 2.5 3 3.5 4 4.5 5 INPUT VOLTAGE(V) VIN=3.6V, No Switching 1 0.9 60 0.8 55 0.7 50 0.6 45 0.5 40 0.4 35 0.3 30 0.2 25 0.1 0 2.5 20 -40 -20 0 20 40 60 80 100120140 5.5 VEN=Low 65 Reference Voltage vs. Temperature 1 640 VIN=3.6V 7 0.9 EN THRESHOLD(V) 630 620 610 600 590 580 570 0.8 0.7 Rising Threshold 0.6 0.5 Falling Threshold 0.4 560 550 -40 -20 0 20 40 60 80 100120140 0.3 -40 -20 0 20 40 60 80 100120140 3 3.5 4 4.5 5 INPUT VOLTAGE(V) 5.5 Current Limit vs. Temperature EN Threshold vs. Temperature V =3.6V 650 IN REFERENCE VOLTAGE(mV) Shutdown Current vs. Input Voltage PWM CURRENT LIMIT(A) 60 Quiescent Current vs. Temperature VIN=3.6V 6.5 6 5.5 5 PMOS 4.5 4 3.5 NMOS 3 -40 -20 0 20 40 60 80 100120140 Current Limit vs. VIN VIN=3.6V PWM CURRENT LIMIT(A) 7 6.5 6 5.5 5 PMOS 4.5 4 3.5 3 2.5 NMOS 3 3.5 4 4.5 VIN (V) 5 5.5 MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 5 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN = 5V, VOUT = 1.2V, COUT = 22μF*2, TA = +25°C, unless otherwise noted. 100 Efficiency Efficiency VIN=5V VIN=3.3V 100 Load Regulation 0.50 90 90 0.40 80 80 0.30 70 70 60 Vo=1V@PWM 50 Vo=1.5V@PWM 40 Vo=1V@PFM 60 Vo=1.2V@PWM Vo=1.2V@PFM 30 Vo=1.5V@PFM Vo=1.8V@PFM 20 Vo=2.5V@PWM Vo=3.3V@PWM 10 Vo=2.5V@PFM Vo=3.3V@PFM 0 0.001 0.01 0.1 IOUT (A) 1 10 Vo=1.5V@PWM 0.00 40 Vo=1.8V@PWM -0.10 30 Vo=1V@PFM -0.20 20 Vo=1.2V@PFM -0.30 10 Vo=1.5V@PFM -0.40 Load Regulation 0 0.001 Vo=1.8V@PFM 0.01 0.1 IOUT (A) 1 10 0.50 0.40 0.40 0.40 0.30 0.30 0.00 0.00 -0.10 -0.20 -0.20 -0.30 -0.30 -0.40 -0.40 -0.40 -0.50 0 0.5 -0.50 0 0.5 PWM_Vo=1.2V -0.30 1 1.5 2 2.5 3 3.5 4 1.0 0.5 0.0 PWM_Io=0A 1 1.5 2 2.5 3 3.5 4 45 VOUT=3.3V 40 40 35 35 30 20 6 15 10 VIN=3.3V 0 4 20 VIN=5V 10 0 3 3.5 4 4.5 5 5.5 INPUT VOLTAGE (V) 3 3.5 25 5 -1.0 2 2.5 2 2.5 Case Temperature Rise 15 -0.5 1 1.5 Case Temperature Rise 25 PWM_Io=4A -0.50 0 0.5 OUTPUT CURRENT (A) 30 PWM_Io=2A PWM_Vo=1.2V OUTPUT CURRENT (A) OUTPUT CURRENT (A) Line Regulation PWM_Vo=1V 0.10 0.10 -0.20 4 VIN=3.3V 0.20 0.00 PFM_Vo=1.2V -0.10 -0.10 3 3.5 0.30 PFM_Vo=1V 0.20 PWM_Vo=2.5V 2 2.5 Load Regulation 0.50 0.10 1 1.5 OUTPUT CURRENT (A) Load Regulation PWM_Vo=1V PFM_Vo=2.5V -0.50 0 0.5 VIN=3.3V 0.50 0.20 PFM_Vo=1.2V 0.10 Vo=1.2V@PWM 50 Vo=1.8V@PWM PFM_Vo=1V 0.20 Vo=1V@PWM 1 2 3 IOUT(A) 5 4 5 0 0 1 2 3 IOUT(A) MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 4 5 6 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN = 5V, VOUT = 1.2V, COUT = 22μF*2, TA = +25°C, unless otherwise noted. 5 MAXIMUM OUTPUT CURRENT(A) MAXIMUM OUTPUT CURRENT(A) Power On 4 3 VIN=3.3V 2 VIN=5V 1 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 OUTPUT VOLTAGE(V) IOUT=0A, PWM Mode 5 4 3 V =5V,V IN OUT=3.3V VIN 2V/div. 2 1 VOUT 500mV/div. VIN=3.3V,VOUT=2.5V VSW 2V/div. IOUT 500mA/div. 0 -40 -20 0 20 40 60 80 100120140 Power On Power On Power On IOUT=0A, PFM Mode IOUT=4A, PWM Mode IOUT=4A, PFM Mode VOUT 500mV/div. VOUT 500mV/div. VOUT 500mV/div. VIN 2V/div. VIN 2V/div. VIN 2V/div. VSW 2V/div. VSW 2V/div. VSW 2V/div. IOUT 500mA/div. IOUT 5A/div. IOUT 5A/div. Power Off Power Off Power Off IOUT=0A, PWM Mode IOUT=0A, PFM Mode IOUT=4A, PWM Mode VOUT 500mV/div. VOUT 500mV/div. VOUT 500mV/div. VIN 2V/div. VSW 2V/div. VIN 2V/div. VSW 2V/div. VIN 2V/div. VSW 2V/div. IOUT 500mA/div. IOUT 500mA/div. IOUT 5A/div. MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 7 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN = 5V, VOUT = 1.2V, COUT = 22μF*2, TA = +25°C, unless otherwise noted. Power Off Enable Turn-On Enable Turn-On IOUT=4A, PFM Mode IOUT=0A, PWM Mode IOUT=0A, PFM Mode VOUT 500mV/div. VOUT 500mV/div. VOUT 500mV/div. VIN 2V/div. VEN 2V/div. VEN 2V/div. VSW 2V/div. VSW 2V/div. VSW 2V/div. IOUT 5A/div. IOUT 500mA/div. IOUT 500mA/div. Enable Turn-On Enable Turn-On Enable Turn-Off IOUT=4A, PWM Mode IOUT=4A, PFM Mode IOUT=0A, PWM Mode VOUT 500mV/div. VOUT 500mV/div. VOUT 500mV/div. VEN 2V/div. VEN 2V/div. VEN 2V/div. VSW 2V/div. VSW 2V/div. VSW 5V/div. IOUT 5A/div. IOUT 5A/div. IOUT 500mA/div. Enable Turn-Off Enable Turn-Off Enable Turn-Off IOUT=0A, PFM Mode IOUT=4A, PWM Mode IOUT=4A, PFM Mode VOUT 500mV/div. VOUT 500mV/div. VOUT 500mV/div. VEN 2V/div. VEN 2V/div. VEN 2V/div. VSW 2V/div. VSW 5V/div. VSW 2V/div. IOUT 500mA/div. IOUT 5A/div. IOUT 5A/div. MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 8 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN = 5V, VOUT = 1.2V, COUT = 22μF*2, TA = +25°C, unless otherwise noted. Steady State Steady State Steady State IOUT=0A, PWM Mode IOUT=4A, PWM/PFM Mode IOUT=0A, PFM Mode VOUT/AC 20mV/div. VOUT/AC 20mV/div. VOUT/AC 100mV/div. VIN 5V/div. VIN 5V/div. VSW 5V/div. VSW 5V/div. VSW 2V/div. IOUT 500mA/div. IOUT 5A/div. IOUT 500mA/div. VIN 5V/div. Steady State Response to Transient Load Response to Transient Load IOUT=0.1A, PFM Mode IOUT=0 to 2A, PWM Mode IOUT=0 to 4A, PWM Mode VOUT/AC 50mV/div. VOUT/AC 50mV/div. VOUT/AC 50mV/div. VIN 5V/div. VIN 5V/div. VIN 5V/div. VSW 2V/div. VSW 5V/div. VSW 5V/div. IOUT 2A/div. IOUT 5A/div. IOUT 500mA/div. Response to Transient Load Response to Transient Load Response to Transient Load IOUT=2A to 4A, PWM/PFM Mode IOUT=0 to 2A, PFM Mode IOUT=0 to 4A, PFM Mode VOUT/AC 50mV/div. VOUT/AC 50mV/div. VOUT/AC 50mV/div. VIN 5V/div. VIN 5V/div. VIN 5V/div. VSW 5V/div. VSW 5V/div. IOUT 2A/div. IOUT 5A/div. VSW 5V/div. IOUT 5A/div. MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 9 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN = 5V, VOUT = 1.2V, COUT = 22μF*2, TA = +25°C, unless otherwise noted. Power Good Power Bad Output Short Entry IOUT=0A IOUT=0A IOUT=0A, PFM Mode VOUT 500mV/div. VPG 2V/div. VIN 5V/div. VPG 2V/div. VOUT 500mV/div. VSW 5V/div. VOUT 500mV/div. VEN 2V/div. VEN 2V/div. IOUT 5A/div. Output Short Recovery Output Short Entry Output Short Recovery IOUT=0A, PFM Mode IOUT=0A, PWM Mode IOUT=0A, PWM Mode VOUT 500mV/div. VOUT 500mV/div. VOUT 500mV/div. VIN 5V/div. VIN 5V/div. VIN 5V/div. VSW 5V/div. VSW 5V/div. VSW 5V/div. IOUT 5A/div. IOUT 5A/div. IOUT 5A/div. MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 10 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR PIN FUNCTIONS Pin # 1, 2, 3, 17, 18 4, 5, 6, 16 7, 8, 9 Name GND SW OUT 10 FB 11 RAMP 12 EN 13 MODE 14 PG 15 VIN 19, 20 NC Description IC ground. Connect the GND pins to larger copper areas to the negative terminals of the input and output capacitors. Switch node. Connect SW to the inductor. SW also connects to the internal highside and low-side power MOSFET switches. Output voltage sense. Feedback. An external resistor divider from the output to GND tapped to FB sets the output voltage. External ramp. RAMP sets the ramp to optimize transient performance. Connect a ceramic capacitor (10pF to 47pF) between OUT and RAMP to improve transient performance. Enable. Set EN to a high voltage level to enable the MPM3840. For automatic startup, connect EN to VIN with a pull-up resistor. Multi-use pin. MODE is also denoted as VCON. For PWM and PFM selection: When VMODE is more than 1.2V, the MPM3840 enters PWM, and the internal reference is 0.6V. When VMODE is lower than 0.4V or is floating, the MPM3840 enters PFM. For analog voltage dynamic regulation: When VMODE is between 0.6V and 1.1V, the reference voltage can be controlled by VMODE, and the MPM3840 works in PWM. Avoid setting VMODE between 0.4V and 0.6V as the MPM3840 may operate in an unknown mode. Power good. PG has an internal, 500kΩ, pull-up resistor. PG is pulled up to VIN when the FB voltage is within 10% of the regulation level; otherwise, PG is low. There is a 140μs delay between the moment when VFB reaches the PG threshold and when PG goes high. Input supply. VIN requires a decoupling capacitor to ground to reduce switching spikes. Do not connect. NC must be left floating. MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 11 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR BLOCK DIAGRAM Figure 1: Functional Block Diagram MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 12 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR The MPM3840 uses a constant-on-time (COT) control with input voltage feed-forward to stabilize the switching frequency over the full input range. At light load, the MPM3840 employs a proprietary control of low-side switching and inductor current on the switching node to improve efficiency. The module has an integrated inductor that makes the schematic and layout design very simple. Only input capacitors, output capacitors, and FB resistors are required to complete the design. Constant-On-Time (COT) Control Compared to fixed-frequency PWM control, constant-on-time (COT) control offers a simpler control loop and faster transient response. By using an input voltage feed-forward, the MPM3840 maintains a nearly constant switching frequency across the input and output voltage ranges. The switching pulse on time can be estimated with Equation (1): t ON VOUT 0.83s VIN (1) To prevent inductor current runaway during the load transient, the MPM3840 has a constant minimum off-time of 60ns. This minimum off time limit will not affect operation in steady state in any way. Light-Load Operation During light loads, the MPM3840 uses a proprietary control scheme to save power and improve efficiency. A zero-current cross detection (ZCD) circuit is used to detect when the inductor current starts to reverse. The lowside MOSFET (LS-FET) turns off immediately when the inductor current starts to reverse and triggers ZCD in discontinuous conduction mode (DCM) operation. Considering the internal circuit propagation time, the typical delay is 50ns. This means that the inductor current continues falling after the ZCD is triggered in this delay time. If the inductor current falling slew rate is fast (VOUT is high or close to VIN), the LS-FET is turned off, and the inductor current may be negative. This prevents the MPM3840 from entering DCM operation. For example, if VIN is 3.6V, and VOUT is 3.3V, then the off time in CCM is 70ns. It is difficult to enter DCM at light load. Enable (EN) When the input voltage is greater than the under-voltage lockout (UVLO) threshold (typically 2.55V), the MPM3840 can be enabled by pulling EN higher than 1.2V. Leave EN floating or pull EN down to ground to disable the MPM3840. There is an internal 1MΩ resistor from EN to ground. MODE Selection and Analog Voltage Dynamic Regulation The MPM3840 has programmable pulse-width modulation (PWM) and pulse-frequency modulation (PFM) work modes. When the voltage on MODE (VMODE) is higher than 1.2V, the MPM3840 operates in PWM. When VMODE is lower than 0.4V or is floating, the MPM3840 operates in PFM, which can achieve high efficiency in light-load condition. PWM mode can maintain a constant switching frequency and small VOUT ripple, but has low efficiency at light load. 0.7 REFERENCE VOLTAGE (V) OPERATION 0.6 0.5 0.4 0.3 0.2 0.1 0 0.5 0.6 0.7 0.8 0.9 1 VCON (V) 1.1 1.2 Figure 2: Reference Voltage Change with VCON The MPM3840 can regulate the output voltage by dynamically changing the MODE voltage (VCON) to meet a situation where the output voltage must be adjusted directly. When VCON is an appropriate value (0.6V to 1.1V), the MPM3840 works in PWM, and the internal reference voltage changes smoothly as VCON changes to provide a new output voltage without changing the external resistor divider. When the VCON function is enabled, set the reference voltage (Vref) to be from 0.35V to 0.6V. The accuracy is typically 3%. When setting the Vref value from 0.1V to 0.35V, the accuracy is MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 13 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR typically 10%. The detailed VRef curve is shown in Figure 2. Calculate Vref with Equation (2): Ref(V)=0.985 VCON(V)-0.486 (2) Soft Start (SS) The MPM3840 has a built-in soft start (SS) that ramps up the output voltage at a constant slew rate to avoid overshooting at start-up. The softstart time is about 1.5ms, typically. Pre-Bias Start-Up The MPM3840 can start up with a pre-biased output voltage. If the internal SS voltage is lower than the FB voltage, the HS-FET and LSFET remain off until the SS voltage crosses the FB voltage. Power Good (PG) Indicator The MPM3840 has an open drain with a 500kΩ pull-up resistor as a power good (PG) indicator. Current Limit The MPM3840 has a 5.5A current limit for the HS-FET. When the HS-FET reaches its current limit, the MPM3840 enters hiccup mode until the current drops to prevent the inductor current from rising and damaging the components. Short Circuit and Recovery The MPM3840 enters short-circuit protection (SCP) mode when it reaches the current limit and attempts to recover with hiccup mode. The MPM3840 disables the output power stage, discharges the soft-start capacitor, and attempts to soft start. If the short-circuit condition remains after the soft start ends, the MPM3840 repeats this operation until the short circuit is removed and the output rises back to regulation levels. PG is pulled up to VIN when the FB voltage is within 10% of the regulation level; otherwise, PG is low. There is a 140μs delay between the moment when VFB reaches the PG threshold and when PG goes high. The MOSFET has a maximum RDS(ON) of 100Ω. MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 14 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR APPLICATION INFORMATION Setting the Output Voltage The external resistor divider sets the output voltage (see the Typical Application Circuit on page 17). Select the feedback resistor (R1) to reduce VOUT leakage current, typically between 40kΩ to 200kΩ. There is no strict requirement on the feedback resistor. R1 > 10kΩ is reasonable for most applications. R2 can be calculated with Equation (2): R2 R1 Vout 1 0.6 (2) The feedback circuit is shown in Figure 3. Selecting the Input Capacitor The input current to the step-down converter is discontinuous and therefore requires a capacitor to supply AC current to the step-down 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 values and small temperature coefficients. For most applications, a 22µF capacitor is sufficient. For higher output voltages, a 47µF capacitor may be needed to improve system stability. Since the input capacitor absorbs the input switching current, it requires an adequate ripple current rating. The RMS current in the input capacitor can be estimated with Equation (3): Vo ut IC1 ILOAD R1 FB Figure 3: Feedback Network Table 1 lists the recommended resistor values for common output voltages. Table 1: Resistor Values for Common Output Voltages R1 (kΩ) 200 (1%) 200 (1%) 200 (1%) 200 (1%) 200 (1%) (3) The worst-case condition occurs at VIN = 2VOUT, shown in Equation (4): R2 VOUT (V) 1.0 1.2 1.8 2.5 3.3 VOUT VOUT 1 VIN VIN R2 (kΩ) 300 (1%) 200 (1%) 100 (1%) 63.2 (1%) 44.2 (1%) IC1 ILOAD 2 (4) 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, use a small, high-quality, 0.1μF, ceramic capacitor placed as close to the IC as possible. When using ceramic capacitors, ensure that they have enough capacitance to prevent excessive voltage ripple at the input. The input voltage ripple caused by the capacitance can be estimated with Equation (5): VIN ILOAD V V OUT 1 OUT fS C1 VIN VIN MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. (5) 15 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR PCB Layout Guidelines Efficient PCB layout of the switching power supplies is critical for stable operation. Especially considering the high-switching converter, if the layout is not done carefully, the regulator could show poor performance. For best results, refer to Figure 3 and follow the guidelines below. 1. Place the input capacitor as close to VIN and GND as possible. 2. Place the FB resistor very close to FB and GND. Ensure that the trace is not wide. 3. Place the output capacitor close to chip. 4. Make the VIN, VOUT, and GND traces wide enough to carry a high current. 5. Places several vias on the GND copper for better thermal performance. Design Example Table 2 is a design example following the application guidelines for the specifications below. Table 2: Design Example 2.8V - 5.5V VIN 1.2V VOUT 0A - 4A IOUT The detailed application schematic is shown in Figure 4. The typical performance and circuit waveforms are shown in the Typical Performance Characteristics section. For more device applications, please refer to the related evaluation board datasheets. Top Layer Bottom Layer Figure 3: Recommended PCB Layout MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 16 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR GND SW TYPICAL APPLICATION CIRCUIT Figure 4: Application for 1.2V Output MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 17 MPM3840 – 4A, 2.8V-5.5V, POWER MODULE SYNCHRONOUS STEP-DOWN CONVERTERWITH INTEGRATED INDUCTOR PACKAGE INFORMATION QFN-20 (3mmx5mmx1.6mm) 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. MPM3840 Rev. 1.1 www.MonolithicPower.com 3/10/2017 MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2017 MPS. All Rights Reserved. 18