MP2496M 2.5A, 36V, Frequency Selectable Step-Down Converter with Single USB Charging Port The Future of Analog IC Technology DESCRIPTION FEATURES The MP2496M integrates a monolithic, stepdown, switch-mode converter and a single USB current-limit switch with charging port identification circuits. It achieves 2.5A of continuous output current with excellent load and line regulation over a wide input supply range. • • The output of the USB switch is current limited. The MP2496M provides a USB dedicated charging port (DCP) which supports battery charging specification 1.2 (BC1.2), divider mode, and 1.2V/1.2V mode without the need of outside user interaction. The output voltage has programmable line-drop compensation. Full protection features include hiccup current limiting, output over-voltage protection (OVP), and thermal shutdown. The MP2496M requires a minimum number of readily available, standard, external components and is available in a QFN-26 (4mmx4mm) package. EMI Reduction Technique Wide 7V to 36V Operating Input Voltage Range Fixed 5V Output Voltage with Line Drop Compensation Accurate USB Output Current Limit 40mΩ/32mΩ Low-RDS(ON) Internal Buck Power MOSFETs 24mΩ Low-RDS(ON) Internal USB Power MOSFET 350kHz/250kHz/150kHz Frequency Selectable Programmable Line Drop Compensation Output Over-Voltage Protection (OVP) Hiccup Current Limit Supports DCP Scheme for BC1.2, Divider Mode, and 1.2V/1.2V Mode ±8kV HBM ESD Rating for USB, DP, and DM Available in a QFN-26 (4mmx4mm) Package • • • • • • • • • • • APPLICATIONS • • • USB Dedicated Charging Port (DCP) Automotive Cigarette Lighter Adapters Power Supply for Linear Chargers 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 MP2496M Rev.1.0 10/10/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 1 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT ORDERING INFORMATION Part Number* MP2496MGR Package QFN-26 (4mmx4mm) Top Marking See Below * For Tape & Reel, add suffix –Z (eg. MP2496MGR–Z) TOP MARKING MPS: MPS prefix Y: Year code WW: Week code M2496M: Product code LLLLLL: Lot number PACKAGE REFERENCE TOP VIEW QFN-26 (4mmx4mm) MP2496M Rev.1.0 10/10/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 2 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT ABSOLUTE MAXIMUM RATINGS (1) Thermal Resistance Supply voltage (VIN) ..................................... 40V VSW ...................................................................... -0.3V (-5V for <10ns) to VIN + 0.3V (43V for <10ns) VBST ................................................... VSW + 6.5V (2) VEN ..............................................-0.3V to 10V All other pins ................................-0.3V to +6.5V (3) Continuous power dissipation (TA = +25°C) QFN-26 (4mmx4mm) ................................. 2.8W Junction temperature ................................150°C Lead temperature .....................................260°C Storage temperature ................ -65°C to +150°C QFN-26 (4mmx4mm).............. 44 ....... 9.... °C/W Recommended Operating Conditions (4) (5) θJA θJC NOTES: 1) Exceeding these ratings may damage the device. 2) For details on EN’s ABS MAX rating, please refer to the “Enable Control” section on page 11. 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 produces an excessive die temperature, causing the regulator to 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. Operation input voltage range ............7V to 36V Output current ................................2.5A for USB Operating junction temp. (TJ). .. -40°C to +125°C MP2496M Rev.1.0 10/10/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 3 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT ELECTRICAL CHARACTERISTICS VIN = 12V, VEN = 5V, TJ = -40°C to +125°C(6). Typical value is tested at TJ = +25°C, unless otherwise noted. Parameter Symbol Supply current (shutdown) IIN Supply current (quiescent) EN rising threshold EN hysteresis IQ_OL VEN_Rising VEN_Falling EN input current IEN Condition Min VEN = 0V,TJ = +25°C VEN = 0V,TJ = -40°C to +125°C No switching VEN = 2V, TJ = +25°C VEN = 2V,TJ = -40°C to +125°C VEN = 0V 1.33 110 1.1 0.8 Typ 1.6 1.43 140 1.8 1.8 0 Max 1 5 2.5 1.52 170 2.5 3 Units μA mA V mV μA Thermal shutdown(7) TSTD 165 °C Thermal hysteresis(7) TSTD_HYS 20 °C VCC regulator VCC load regulation Step-Down Converter VIN under-voltage lockout threshold rising VIN under-voltage lockout threshold hysteresis HS switch-on resistance LS switch-on resistance Output voltage VCC VCC_LOG ICC = 5mA VIN_UVLO TJ = +25°C 5.7 6.2 V mΩ mΩ 5 40 32 5.05 5.1 4.95 5.05 5.15 5.65 6 6.4 V 5.4 5.75 6.1 V 7V < VIN < 36V, no load, TJ = +25°C 7V < VIN < 36V, no load, TJ = -40°C to +125°C VOVP_F TJ = -40°C to +125°C Switch leakage SWLKG VEN = 0V, VSW = 36V or 0V, TJ = +25°C VEN = 0V, VSW = 36V or 0V, TJ = -40°C to +125°C Current limit(7) ILIMIT fSW1 fSW2 fSW3 MP2496M Rev.1.0 10/10/2015 5.2 RDSON_HS RDSON_LS OVP recovery Minimum on time V % V VOVP_R (7) 5.45 2 1 Output over-voltage protection Maximum duty cycle 5.1 1 VUVLO_HYS VOUT Oscillator frequency 4.75 DMAX TON_MIN Over 0-90% duty cycle FREQ = high, TJ = +25°C FREQ = high, TJ = -40°C to +125°C FREQ = low, TJ = +25°C FREQ = low, TJ = -40°C to +125°C FREQ = float, TJ = +25°C FREQ = float, TJ = -40°C to +125°C FREQ = 350kHz TJ = +25°C V 1 5 4 310 300 220 190 125 110 84 μA A 350 350 250 250 150 150 88 130 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 410 420 300 330 180 185 kHz % ns 4 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT ELECTRICAL CHARACTERISTICS (continued) VIN = 12V, VEN = 5V, TJ = -40°C to +125°C(6). Typical value is tested at TJ = +25°C, unless otherwise noted. Parameter Symbol Soft-start time tSS Condition Output from 10% to 90%,TJ = +25°C Output from 10% to 90%, TJ = -40°C to +125°C Min 1 Typ 1.65 Max 2.3 Units 0.9 1.65 2.4 TJ = +25°C TJ = -40°C to +125°C 3.8 3.75 4 4 4.3 4.33 V 220 270 320 mV ms USB Switch Under-voltage lockout threshold rising Under-voltage lockout threshold hysteresis Switch-on resistance Current limit Line drop compensation FREQ, VDROP high level FREQ, VDROP middle level FREQ, VDROP low level VBUS soft-start time Discharge resistance VUSB_UVR VUSB_UVHYS RDSON_SW ILimit VDROP_COM1 VDROP_COM2 VDROP_COM3 Off time of hiccup mode 2.6 300 VLOW RDCHG THICP_ON2 THICP_OFF VOUT = 5V, from 10% to 90%, TJ = +25°C VOUT = 5V, from 10% to 90%, TJ = -40°C to +125°C TJ = +25°C TJ = -40°C to +125°C VOUT = 5V, VBUS connected to GND VOUT = 5V, VBUS > 2V, OC TJ = +25°C VOUT = 5V, VBUS > 2V, OC TJ = -40°C to +125°C VOUT = 5V, VBUS connected to GND, TJ = +25°C VOUT = 5V, VBUS connected to GND, TJ = -40°C to +125°C mΩ A mV mV mV V 2.5 VMIDDLE TSS 2.9 500 VCC0.4V VHIGH THICP_ON1 On time of hiccup mode TJ = +25°C Max load 2.4A, VDROP = float, TJ = +25°C Max load 2.4A, VDROP = high Max load 2.4A, VDROP = GND 24 2.75 400 280 130 V 1 1.6 0.4 2.2 V 0.9 1.6 2.4 50 50 3(7) 70 75 Ω 3.5 5 6.5 ms 3 5 7 6.5 8.5 10.5 6 8.5 11 125 155 125 160 2.7 2.7 22 22 2.82 2.85 23 28 ms s BC1.2 DCP Mode DP and DM short resistance VDP = 0.8V, IDM = 1mA, TJ = +25°C RDP/DM_Short VDP = 0.8V, IDM = 1mA, TJ = -40°C to +125°C Ω Divider Mode DP/DM output voltage VDP/DM_Divider DP/DM output impedance RDP/DM_Divider MP2496M Rev.1.0 10/10/2015 VOUT = 5V, TJ = +25°C VOUT = 5V, TJ = -40°C to +125°C TJ = +25°C TJ = -40°C to +125°C 2.54 2.5 20 18 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. V kΩ 5 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT ELECTRICAL CHARACTERISTICS (continued) VIN = 12V, VEN = 5V, TJ = -40°C to +125°C(6). Typical value is tested at TJ = +25°C, unless otherwise noted. Parameter 1.2V/1.2V Mode Symbol DP/DM output voltage VDP/DM_1.2V DP/DM output impedance RDP/DM_1.2V Condition Min Typ Max Units VOUT = 5V, TJ = +25°C VOUT = 5V, TJ = -40°C to +125°C TJ = +25°C TJ = -40°C to +125°C 1.16 1.15 60 55 1.25 1.25 68 68 1.34 1.35 75 88 V kΩ NOTES: o 6) All min/max parameters are tested at TJ = 25 C. Limits over temperature are guaranteed by design, characterization, and correlation. 7) Guaranteed by design. MP2496M Rev.1.0 10/10/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 6 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT TYPICAL PERFORMANCE CHARACTERISTICS VIN = 12V, VOUT = 5V, L = 22µH, fS = 250kHz, TA = 25°C, unless otherwise noted. LINE DROP COMPENSATION (mV) Line Drop Compensation vs. Load Current 100 450 400 95 VDROP=Float 350 90 300 VIN=12V 85 250 200 80 VDROP=VCC 150 100 0.5 1 1.5 2 LOAD CURRENT (A) MP2496M Rev.1.0 10/10/2015 2.5 VIN=7V VIN=24V 75 VIN=36V 70 VDROP=GND 50 0 0 Efficiency vs. Load Current 65 0 0.5 1 1.5 2 LOAD CURRENT (A) 2.5 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 7 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT TYPICAL PERFORMANCE CHARACTERISTICS (continued) VIN = 12V, VOUT = 5V, L = 22µH, fS = 250kHz, TA = 25°C, unless otherwise noted. USB VOUT/AC 10mV/div. Buck VOUT 5V/div. VSW 10V/div. IL 500mA/div. USB VOUT/AC 10mV/div. Buck VOUT 5V/div. USB VOUT 2V/div. Buck VOUT 5V/div. VSW 10V/div. VSW 10V/div. IL 2A/div. USB VOUT 2V/div. Buck VOUT 5V/div. USB VOUT 2V/div. Buck VOUT 5V/div. USB VOUT 2V/div. Buck VOUT 5V/div. VSW 10V/div. VSW 5V/div. VSW 5V/div. USB IOUT 2A/div. USB VOUT 2V/div. USB IOUT 2A/div. MP2496M Rev.1.0 10/10/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 8 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT PIN FUNCTIONS QFN-26 Pin # Name 1, 2 USB 3, 15, 25 4, 14 5, 6, 12, 13 7 8 9, 10, 26 11 16, 17 18 19 20 21, 22 23 24 MP2496M Rev.1.0 10/10/2015 Description USB output. Buck output. OUT is the USB’s power input. Internal circuits sense the OUT OUT voltage and regulate it to 5V. Supply voltage. The MP2496M operates on a 7V to 36V input voltage. CIN is needed to prevent large voltage spikes at the input. Place CIN as close to the IC IN as possible. IN is the drain of the internal power device and the power supply for the whole chip. Power ground. PGND is the reference ground of the regulated output voltage. PGND PGND requires extra care during PCB layout. Connect to GND with copper traces and vias. Frequency selection. Float FREQ to set the frequency to 150kHz. Pull FREQ FREQ to ground to set the frequency to 250kHz. Pull FREQ to high to set the frequency to 350kHz. EN On/Off control input. SW Switch output. Connect using a wide PCB trace. Bootstrap. Requires a 0.1µF capacitor between SW and BST to form a floating BST supply across the high-side switch driver. NC No connection. NC can be connected to OUT for better thermal dissipation. AGND Analog ground. Connect AGND to PGND. VCC Internal 5V LDO regulator output. Decouple VCC with a 0.22µF capacitor. Line drop compensation selection. Refer to the EC table for detailed VDROP specifications. NC No connection. NC must be left floating. D+ data line to the USB connector. Input/output used for handshaking with DP portable devices. D- data line to the USB connector. Input/output used for handshaking with DM portable devices. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 9 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT FUNCTIONAL BLOCK DIAGRAM IN EN 12KΩ 1MΩ Current Sense Amplifier VCC Regulator 7.6V VCC Oscillator Σ Reference Bootstrap Regulator FREQ HS Driver Current Limit Comparator Control Logic OUT Rtop SS Rbot VCC SW LS Driver PGND Error Amplifier Line Drop Compensation VDROP BST OVP Comparator PWM Comparator Curent Sense USB Discharge Charge Pump UVLO Current Limit Control Logic Thermal Sense Discharge 2.7V AGND 1.2V DP Auto Detect DM NC Figure 1: Functional Block Diagram MP2496M Rev.1.0 10/10/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 10 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT OPERATION BUCK CONVERTER SECTION: The MP2496M integrates a monolithic, synchronous, rectified, step-down, switch-mode converter with internal power MOSFETs and a USB current-limit switch with charging port autodetection. It offers a very compact solution that achieves 2.5A of continuous output current with excellent load and line regulation over a wide input supply range. The MP2496M operates in a fixed-frequency, peak current-mode control to regulate the output voltage. The internal clock initiates the PWM cycle, turning on the integrated high-side power MOSFET (HS-FET). The HS-FET remains on until its current reaches the value set by VCOMP. If the power switch is off, it remains off until the next clock cycle starts. If the duty cycle reaches 88% (350kHz switching frequency) in one PWM period, the current in the power MOSFET does not reach the value set by VCOMP and is forced off. Error Amplifier (EA) The error amplifier compares the internal feedback voltage against the internal 1V reference (REF) and outputs the COMP voltage, which controls the power MOSFET current. The optimized internal compensation network minimizes the external component count and simplifies the control loop design. VCC Regulator The 5V internal regulator powers most of the internal circuitries. This regulator takes the VIN input and operates in the full VIN range. When VIN is greater than 5.0V, the output of the regulator is in full regulation. When VIN is lower than 5.0V, the output voltage decreases with VIN. An external 0.22µF ceramic capacitor is required for decoupling. Enable Control (EN) The MP2496M has an enable control (EN). Pulling EN high enables the IC; pulling EN low disables the IC. Connect EN to VIN through a resistor for automatic start-up. An internal 1MΩ resistor connected from EN to GND allows EN to float to shut down the IC. MP2496M Rev.1.0 10/10/2015 EN is clamped internally using a 7.6V series Zener diode (see Figure 2). Connecting the EN input through a pull-up resistor to the voltage on VIN limits the EN input current to less than 230μA and the amplitude of the voltage source below 10V, preventing damage to the Zener diode. For example, connect 36V to VIN, RPULLUP ≥ (36V – 10V)/230µA = 113kΩ. Figure 2: Zener Diode between EN and GND Under-Voltage Lockout (UVLO) Under-voltage lockout (UVLO) protects the chip from operating at an insufficient supply voltage. The MP2496M’s UVLO comparator monitors the input voltage. The UVLO rising threshold is 5.7V while its falling threshold is 4.7V. Internal Soft Start (SS) The soft start prevents the converter output voltage from overshooting during start-up. When the chip starts, the internal circuitry generates a soft-start voltage (SS) that ramps up from 0V to 5V. When SS is lower than REF, the error amplifier uses SS as the reference. When SS is higher than REF, the error amplifier uses REF as the reference. The SS time is internally set to 1.65ms. If the output of the MP2496M is pre-biased to a certain voltage during start-up, the IC disables the switching of both the high-side and low-side switches until the voltage on the internal soft-start capacitor exceeds the internal feedback voltage. Buck Over-Current Protection (OCP) The MP2496M has a cycle-by-cycle, over-current limit for when the inductor peak current exceeds the current limit threshold and FB voltage drops below the under-voltage (UV) threshold, typically 70% below the reference. Once UV is triggered, the MP2496M enters hiccup mode to restart the part periodically. This protection mode is especially useful when the output is dead-shorted to ground. The average short-circuit current is greatly reduced to alleviate thermal issues and protect the regulator. The MP2496M exits hiccup mode once the over-current condition is removed. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 11 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT Buck Output Over-Voltage Protection (OVP) The MP2496M buck converter has output overvoltage protection (OVP). If the output is higher than 6V, the high-side switch stops turning on, and the low-side switch turns on to discharge the output voltage until the output decreases to 5.75V. The chip then resumes normal operation. If the output over-voltage can’t be discharged to 5.75V, the low-side switch turns off after the inductor current reaches a negative current limit and remains off until the next clock cycle is triggered. Floating Driver and Bootstrap Charging An external bootstrap capacitor powers the floating power MOSFET driver. This floating driver has its own UVLO protection. The UVLO’s rising threshold is 2.2V with a hysteresis of 150mV. The bootstrap capacitor voltage is regulated internally by VIN through D1, M1, C4, L1, and C2 (see Figure 3). If VBST-VSW exceeds 5V, U1 regulates M1 to maintain a 5V BST voltage across C4. Start-Up and Shutdown If both VIN and EN exceed their respective thresholds, the chip is enabled. The reference block starts first, generating stable reference voltages and currents, and then the internal regulator is enabled. The regulator provides a stable supply for the remaining circuitries. Three events can shut down the chip: EN low, VIN low, and thermal shutdown. During the shutdown procedure, the signaling path is blocked first to avoid any fault triggering. The COMP voltage and the internal supply rail are then pulled down. The floating driver is not subject to this shutdown command. Buck Output Discharge The buck portion uses a discharge function to provide a resistive discharge path for the external output capacitor. The function is active when the part is disabled (input voltage is under UVLO, enable off) and is done in a very limited amount of time. After VCC is discharged below 1V, the buck output discharge resistor disconnects. D1 VIN M1 BST 5V U1 C4 VOUT SW L1 C2 Figure 3: Internal Bootstrap Charging Circuit MP2496M Rev.1.0 10/10/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 12 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT USB CURRENT-LIMIT SWITCH SECTION: Current-Limit Switch The MP2496M has a single-channel, USB, current-limit switch. It provides built-in, soft-start circuitry that controls the rising slew rate of the output voltage to limit inrush current and voltage surges. When the load current reaches the current limit threshold (typically 2.75A), the USB power MOSFET switches into a foldback current limit mode, 70% of the current limit (see Figure 4). If the over-current limit condition lasts for more than 3ms, the chip enters hiccup mode with 3ms of on-time and 8.5s of off-time. Vout(V) Iout(A) Current Limit 5 Fold-back Current Limit 0 3ms t Figure 4: Over-Current Limit During VIN or EN start-up, the CC load current does not exceed 70% of the current limit to avoid triggering the foldback current limit and start-up failure. Output Line Drop Compensation The MP2496M is capable of compensating for an output voltage drop (such as a high impedance caused by a long trace) to keep a fairly constant 5V load-side voltage. The MP2496M uses the internal current sense output voltage of the current-limit switch to compensate for the line drop voltage. Since the trace resistance varies for different cables, the MP2496M provides selectable line drop compensation through VDROP. The line drop compensation amplitude increases linearly as the load current increases and also has an upper limitation. MP2496M Rev.1.0 10/10/2015 USB Output Over-Voltage Protection (OVP) In order to protect the device at the cable terminal, the USB switch’s output has a dynamic overvoltage protection threshold. The MP2496M adjusts the OVP threshold based on different USB loading currents. The MP2496M has intelligent line drop compensation and a dynamic overvoltage protection control scheme to ensure the voltage at the cable terminal meets the 4.75V5.25V specification. USB Output Discharge Each USB portion involves a discharge function that provides a resistive discharge path for the external output capacitor. The function is active when the part is disabled (input voltage is under UVLO, enable off) and is done in a very limited amount of time. Auto-Detection The MP2496M integrates the USB dedicated charging port auto-detect function, which recognizes most mainstream portable devices. It supports the following charging schemes: • USB battery charging specification BC1.2/ Chinese Telecommunications Industry Standard YD/T 1591-2009 • Divider mode • 1.2V/1.2V mode The auto-detect function is a state machine that supports all of the above DCP charging schemes. Thermal Shutdown Thermal shutdown prevents the chip from operating at exceedingly high temperatures. When the silicon die temperature exceeds 165°C, the entire chip shuts down. When the temperature falls below its lower threshold, typically 145°C, the chip is enabled again. www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 13 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT APPLICATION INFORMATION Selecting the Inductor Use an inductor with a DC current rating at least 25% higher than the maximum load current for most applications. Select an inductor with a small DC resistance for best efficiency. The inductor value for most designs can be estimated with Equation (1): L1 = VOUT × (VIN − VOUT ) VIN × ΔIL × fOSC (1) Where ΔIL is the inductor ripple current. Choose the inductor ripple current to be approximately 30% of the maximum load current. The maximum inductor peak current is calculated with Equation (2): IL(MAX ) = ILOAD ΔI + L 2 (2) A 22μH inductance is recommended to improve EMI. Selecting the Buck 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. For best performance, use low ESR capacitors. Ceramic capacitors with X5R or X7R dielectrics are recommended highly because of their low ESR and small temperature coefficients. For CLA applications, a low ESR 100μF electrolytic capacitor and twopiece 10μF ceramic capacitors are recommended for EMI reduction. The input capacitor can be electrolytic, tantalum, or ceramic. When using electrolytic capacitors, place two high-quality ceramic capacitors as close to the IC’s IN as possible. The input voltage ripple caused by the capacitance can be estimated with Equation (5): ΔVIN = ⎛ ⎞ ILOAD V V × OUT × ⎜ 1 − OUT ⎟ fS × C1 VIN ⎝ VIN ⎠ (5) Selecting the Buck Output Capacitor The device requires an output capacitor (C2) to maintain the DC output voltage. Estimate the output voltage ripple with Equation (6): ΔVOUT = ⎞ (6) VOUT ⎛ VOUT ⎞ ⎛ 1 × ⎜1 − ⎟ ⎟ × ⎜ RESR + fS × L1 ⎝ VIN ⎠ ⎝ 8 × fS × C2 ⎠ Where L1 is the inductor value and RESR is the equivalent series resistance (ESR) value of the output capacitor. For tantalum or electrolytic capacitors, ESR dominates the impedance at the switching frequency. For simplification, the output ripple can be approximated with Equation (7): ΔVOUT = VOUT ⎛ V ⎞ × ⎜ 1 − OUT ⎟ × RESR fS × L1 ⎝ VIN ⎠ (7) The characteristics of the output capacitor affect the stability of the regulation system. Low ESR electrolytic capacitors are recommended for a low output ripple and good control loop stability. For CLA applications, a 270µF polymer capacitor or an electrolytic capacitor with ~20mΩ ESR, and one 1µF ceramic capacitor are recommended. Since the input capacitor (C1) 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): I C1 = ILOAD × VOUT ⎛⎜ VOUT × 1− VIN ⎜⎝ VIN ⎞ ⎟ ⎟ ⎠ (3) The worse-case condition occurs at VIN = 2VOUT, shown in Equation (4): IC1 = ILOAD 2 (4) For simplification, choose an input capacitor with an RMS current rating greater than half of the maximum load current. MP2496M Rev.1.0 10/10/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 14 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT PCB Layout Guidelines(8) Efficient PCB layout is critical for stable operation and thermal dissipation. For best results, refer to Figure 5 and follow the guidelines below. 1. Connect the IC’s OUT with short, direct, and wide traces. It is highly recommended to add vias under the IC and route the OUT trace on both PCB layers. 2. Use a large copper plane for PGND. Multiple vias should be added for better thermal dissipation. 3. Connect AGND to PGND. 4. Use a large copper plane for SW and USB. 5. Place the USB output capacitor close to USB. 6. Place two ceramic input decoupling capacitors as close to IN and PGND as possible to improve EMI performance. 7. Place the VCC decoupling capacitor as close to VCC as possible. NOTE: (8) The recommended layout is based on Figure 6: Typical Application Circuit on the next page. (4.78cmх1.38cm) Figure 5: Recommended Layout MP2496M Rev.1.0 10/10/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 15 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT TYPICAL APPLICATION CIRCUIT C4 100nF L2 2.2µH C1C 10μF L1 22μH 11 VIN 12V 9,10,26 4,14 C1 100μF + C1A 10μF C1B 10μF 3,15,25 R1 300kΩ 8 C2A 1μF 16,17 C2 270μF 20mΩ ESR + 1,2 C5 10μF 24 D- 23 D+ U S B USB, 2.5A 20 Float 21,22 7 19 5,6,12,13 18 C3 220nF Figure 6: VIN = 12V, USB = 5V/2.5A MP2496M Rev.1.0 10/10/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 16 MP2496M – STEP-DOWN CONVERTER WITH SINGLE USB CHARGING PORT PACKAGE INFORMATION 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. MP2496M Rev.1.0 10/10/2015 www.MonolithicPower.com MPS Proprietary Information. Patent Protected. Unauthorized Photocopy and Duplication Prohibited. © 2015 MPS. All Rights Reserved. 17