EVALUATION KIT AVAILABLE MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation General Description The MAX17503/MAX17503S high-efficiency, highvoltage, synchronously rectified step-down converter with dual integrated MOSFETs operates over a 4.5V to 60V input. It delivers up to 2.5A and 0.9V to 90%VIN output voltage. Built-in compensation across the output voltage range eliminates the need for external components. The feedback (FB) regulation accuracy over -40C to +125C is 1.1%. The device is available in a compact (4mm x 4mm) TQFN lead(Pb)-free package with an exposed pad. Simulation models are available. The device features a peak-current-mode control architecture with a MODE feature that can be used to operate the device in pulse-width modulation (PWM), pulse-frequency modulation (PFM), or discontinuousconduction mode (DCM) control schemes. PWM operation provides constant frequency operation at all loads, and is useful in applications sensitive to switching frequency. PFM operation disables negative inductor current and additionally skips pulses at light loads for high efficiency. DCM features constant frequency operation down to lighter loads than PFM mode by not skipping pulses, but only disabling negative inductor current at light loads. DCM operation offers efficiency performance that lies between PWM and PFM modes. The MAX17503S offers a lower minimum on-time that allows for higher switching frequencies and a smaller solution size. A programmable soft-start feature allows users to reduce input inrush current. The device also incorporates an output enable/undervoltage lockout pin (EN/UVLO) that allows the user to turn on the part at the desired inputvoltage level. An open-drain RESET pin provides a delayed power-good signal to the system upon achieving successful regulation of the output voltage. Benefits and Features Eliminates External Components and Reduces Total Cost * No Schottky-Synchronous Operation for High Efficiency and Reduced Cost * Internal Compensation for Stable Operation at Any Output Voltage * All-Ceramic Capacitor Solution: Ultra-Compact Layout with as Few as Eight External Components Reduces Number of DC-DC Regulators to Stock * Wide 4.5V to 60V Input Voltage Range * 0.9V to 90%VIN Output Voltage * Delivers up to 2.5A Over Temperature * 100kHz to 2.2MHz Adjustable Frequency with External Synchronization * MAX17503S Allows Higher Frequency of Operation * Available in a 20-Pin, 4mm x 4mm TQFN Package Reduces Power Dissipation * Peak Efficiency > 90% * PFM and DCM Modes for High Light-Load Efficiency * Shutdown Current = 2.8A (typ) Operates Reliably * Hiccup-Mode Current Limit and Autoretry Startup * Built-In Output-Voltage Monitoring (Open-Drain RESET Pin) * Resistor-Programmable EN/UVLO Threshold * Adjustable Soft-Start and Prebiased Power-Up * High Industrial -40C to +125C Ambient Operating Temperature Range/-40C to +150C Junction Temperature Range Applications Industrial Power Supplies Distributed Supply Regulation Base Station Power Supplies Wall Transformer Regulation High-Voltage Single-Board Systems General-Purpose Point-of-Load 19-6669; Rev 3; 4/17 Ordering Information appears at end of data sheet. MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Absolute Maximum Ratings (Note 1) VIN to PGND..........................................................-0.3V to +65V EN/UVLO to SGND................................................-0.3V to +65V LX to PGND................................................-0.3V to (VIN + 0.3V) BST to PGND.........................................................-0.3V to +70V BST to LX..............................................................-0.3V to +6.5V BST to VCC............................................................-0.3V to +65V CF, RESET, SS, MODE, SYNC, RT to SGND......................................................-0.3V to +6.5V FB to SGND..........................................................-0.3V to +1.5V VCC to SGND........................................................-0.3V to +6.5V SGND to PGND.....................................................-0.3V to +0.3V LX Total RMS Current............................................................4A Output Short-Circuit Duration.....................................Continuous Continuous Power Dissipation (TA = +70C) (multilayer board) TQFN (derate 30.3mW/C above TA = +70C).......2424.2mW Junction Temperature....................................................... +150C Storage Temperature Range..............................-65NC to +160C Lead Temperature (soldering, 10s).................................. +300C Soldering Temperature (reflow)........................................ +260C Stresses beyond those listed under "Absolute Maximum Ratings" may cause permanent damage to the device. These are stress ratings only; functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. Note 1: Junction temperature greater than +125C degrades operating lifetimes. Package Information PACKAGE TYPE: 20 TQFN Package Code T2044+4 Outline Number 21-0139 Land Pattern Number 90-0409 THERMAL RESISTANCE, FOUR-LAYER BOARD Junction to Ambient (JA) 33C/W Junction to Case (JC) 2C/W Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial. For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. Electrical Characteristics (VIN = VEN/UVLO = 24V, RRT = 40.2kI (500kHz), CVCC = 2.2F, VPGND = VSGND = VMODE = VSYNC = 0V, LX = SS = RESET = open, VBST to VLX = 5V, VFB = 1V, TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C. All voltages are referenced to SGND, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 60 V 2.8 4.5 INPUT SUPPLY (VIN) Input Voltage Range Input Shutdown Current VIN IIN-SH VFB = 1V, MODE = RT = open 118 VFB = 1V, MODE = open 162 IQ-DCM DCM mode, VLX = 0.1V 1.16 IQ_PWM Normal switching mode, fSW = 500kHz, VFB = 0.8V 9.5 IQ_PFM Input Quiescent Current www.maximintegrated.com 4.5 VEN/UVLO = 0V (shutdown mode) A 1.8 mA Maxim Integrated 2 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Electrical Characteristics (continued) (VIN = VEN/UVLO = 24V, RRT = 40.2kI (500kHz), CVCC = 2.2F, VPGND = VSGND = VMODE = VSYNC = 0V, LX = SS = RESET = open, VBST to VLX = 5V, VFB = 1V, TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C. All voltages are referenced to SGND, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS ENABLE/UVLO (EN/UVLO) EN/UVLO Threshold EN/UVLO Input Leakage Current VENR VEN/UVLO rising 1.19 1.215 1.26 VENF VEN/UVLO falling 1.068 1.09 1.131 -50 0 +50 nA 4.75 5 5.25 V 26.5 54 100 mA IEN VEN/UVLO = 0V, TA = +25C V LDO VCC Output Voltage Range VCC VCC Current Limit IVCC-MAX VCC Dropout VCC-DO 6V < VIN < 60V, IVCC = 1mA 1mA IVCC 25mA VCC = 4.3V, VIN = 6V VIN = 4.5V, IVCC = 20mA 4.2 VCC_UVR VCC rising 4.05 4.2 4.3 VCC_UVF VCC falling 3.65 3.8 3.9 High-Side nMOS On-Resistance RDS-ONH ILX = 0.3A 165 325 mI Low-Side nMOS On-Resistance RDS-ONL ILX = 0.3A 80 150 mI LX Leakage Current ILX_LKG VLX = VIN - 1V, VLX = VPGND + 1V, TA = +25C -2 +2 A VSS = 0.5V 4.7 5 5.3 A -40C TA +125C 0.89 0.9 0.91 V 0 < VFB < 1V, TA = +25C -50 +50 nA VCC UVLO V V POWER MOSFET AND BST DRIVER SOFT-START (SS) Charging Current ISS FEEDBACK (FB) FB Regulation Voltage VFB_REG FB Input Bias Current IFB MODE VCC 1.6 VM-DCM MODE = VCC (DCM mode) VM-PFM MODE = open (PFM mode) VM-PWM MODE = GND (PWM mode) FB Threshold for Entering Hibernate Mode VFB_HBR VFB rising 100.8 102.3 103.5 % FB Threshold for Exiting Hibernate Mode VFB_HBF VFB falling 100 101.1 102.3 % 3.2 3.7 4.3 A 3.7 4.3 5 A -0.16 0 +0.16 MODE Threshold V VCC / 2 1.4 PFM/HIBERNATE MODE CURRENT LIMIT Peak Current-Limit Threshold Runaway Current-Limit Threshold IPEAK-LIMIT IRUNAWAY-LIMIT Valley Current-Limit Threshold ISINK-LIMIT PFM Current-Limit Threshold IPFM www.maximintegrated.com MODE = open/VCC MODE = GND MODE = open -1.8 0.6 0.75 0.9 A A Maxim Integrated 3 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Electrical Characteristics (continued) (VIN = VEN/UVLO = 24V, RRT = 40.2kI (500kHz), CVCC = 2.2F, VPGND = VSGND = VMODE = VSYNC = 0V, LX = SS = RESET = open, VBST to VLX = 5V, VFB = 1V, TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C. All voltages are referenced to SGND, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX RRT = 210k 90 100 110 RRT = 102k 180 200 220 UNITS RT AND SYNC Switching Frequency fSW SYNC Frequency Capture Range RRT = 40.2k 475 500 525 RRT = 8.06k 1950 2200 2450 RRT = open 460 500 540 fSW set by RRT 1.1 x fSW SYNC Pulse Width SYNC Threshold FB Undervoltage Trip Level to Cause Hiccup 1.4 x fSW 50 VIH VIL 0.8 Hiccup Timeout 0.56 (Note 3) Minimum On-Time tON-MIN Minimum Off-Time tOFF-MIN 0.58 0.65 32,768 MAX17503 MAX17503S 55 140 LX Dead Time RESET Output Level Low IRESET = 10mA RESET Output Leakage Current TA = TJ = +25C, VRESET = 5.5V -0.1 V V Cycles 135 ns 80 ns 160 ns 5 RESET kHz ns 2.1 VFB-HICF kHz ns 0.4 V +0.1 A FB Threshold for RESET Assertion VFB-OKF VFB falling 90.5 92 94.6 %VFB- FB Threshold for RESET Deassertion VFB-OKR VFB rising 93.8 95 97.8 %VFB- RESET Deassertion Delay After FB Reaches 95% Regulation REG REG 1024 Cycles 165 C 10 C THERMAL SHUTDOWN Thermal-Shutdown Threshold Temperature rising Thermal-Shutdown Hysteresis Note 2: All limits are 100% tested at +25C. Limits over temperature are guaranteed by design. Note 3: See the Overcurrent Protection/Hiccup Mode Section for more details. www.maximintegrated.com Maxim Integrated 4 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Typical Operating Characteristics (VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2F, CBST = 0.1F, CSS = 5600pF, RT = MODE = open, TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C. All voltages are referenced to GND, unless otherwise noted.) VIN = 36V VIN = 24V 70 VIN = 48V VIN = 12V 60 90 EFFICIENCY (%) 80 VIN = 24V 60 VIN = 48V VIN = 36V VIN = 12V 80 VIN = 36V VIN = 24V 70 VIN = 48V VIN = 12V 60 500 1000 1500 2000 LOAD CURRENT (mA) 50 30 2500 0 500 1000 1500 2000 2500 VIN = 12V 95 VIN = 24V 90 VIN = 48V VIN = 12V 50 40 80 75 30 65 MODE = SGND 0 500 1000 1500 2000 60 2500 VIN = 36V 1 10 LOAD CURRENT (mA) 30 MODE = OPEN 10 100 1000 2500 LOAD CURRENT (mA) MAX17503S, 3.3VOUTPUT, PFM MODE, FIGURE 4d CIRCUIT, EFFICIENCY vs. LOADCURRENT 80 85 80 75 70 65 VIN = 48V 60 VIN = 36V MODE = OPEN 55 50 40 90 EFFICIENCY (%) EFFICIENCY (%) VIN = 24V VIN = 24V VIN = 12V VIN = 36V 50 1000 2500 100 MAX17503 toc04 VIN = 12V 90 VIN = 48V 60 toc04a 100 95 70 LOAD CURRENT (mA) MAX17503, 3.3V OUTPUT, PFM MODE, FIGURE 4b CIRCUIT EFFICIENCY vs. LOAD CURRENT 2500 80 MODE = OPEN 100 2000 90 VIN = 48V 70 1500 MAX17503S, 5VOUTPUT, PFM MODE, FIGURE 4c CIRCUIT, EFFICIENCY vs. LOADCURRENT 100 EFFICIENCY (%) EFFICIENCY (%) VIN = 36V 85 1000 LOAD CURRENT (mA) toc03a toc02a 100 80 VIN = 24V 500 0 MAX17503, 5V OUTPUT, PFM MODE, FIGURE 4a CIRCUIT EFFICIENCY vs. LOAD CURRENT 90 60 40 LOAD CURRENT (mA) MAX17503S, 3.3VOUTPUT, PWM MODE, FIGURE 4d CIRCUIT, EFFICIENCY vs. LOADCURRENT 70 MODE = SGND MODE = SGND MAX17503 toc03 0 100 EFFICIENCY (%) 70 40 MODE = SGND 20 80 90 50 50 40 100 MAX17503 toc02 MAX17503 toc01 90 EFFICIENCY (%) 100 MAX17503, 3.3V OUTPUT, PWM MODE, FIGURE 4b CIRCUIT EFFICIENCY vs. LOAD CURRENT toc01a 100 MAX17503S, 5VOUTPUT, PWMMODE, FIGURE 4c CIRCUIT, EFFICIENCY vs. LOADCURRENT EFFICIENCY (%) MAX17503, 5V OUTPUT, PWM MODE, FIGURE 4a CIRCUIT EFFICIENCY vs. LOAD CURRENT 1 10 100 LOAD CURRENT (mA) www.maximintegrated.com 1000 2500 70 VIN = 48V 60 50 VIN = 12V VIN = 24V VIN = 36V 40 30 MODE = OPEN 10 100 1000 2500 LOAD CURRENT (mA) Maxim Integrated 5 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Typical Operating Characteristics (continued) (VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2F, CBST = 0.1F, CSS = 5600pF, RT = MODE = open, TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C. All voltages are referenced to GND, unless otherwise noted.) MAX17503S, 5VOUTPUT, DCM MODE, FIGURE 4c CIRCUIT, EFFICIENCY vs. LOADCURRENT VIN = 48V VIN = 24V 50 70 60 40 10 100 0 1000 2500 LOAD CURRENT (mA) VIN = 24V VIN = 12V 50 10 100 40 5.04 5.03 10 100 4.99 VIN = 48V 4.95 1000 500 0 MAX17503 toc08 3.33 3.32 3.31 3.30 3.29 VIN = 12V VIN = 24V VIN = 36V VIN = 48V 3.26 3.25 MODE = SGND 0 www.maximintegrated.com 500 1000 1500 2000 LOAD CURRENT (mA) 2500 4.98 4.97 4.96 4.95 VIN = 36V VIN = 12V 4.94 0 500 1000 1500 2000 2500 LOAD CURRENT (mA) MAX17503S, 3.3VOUTPUT, PWM MODE, FIGURE 4d CIRCUIT, LOAD AND LINE REGULATION 3.50 3.45 3.40 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 3.34 VIN = 24V toc08a 3.35 VIN = 48V 4.99 4.92 2500 1000 1500 2000 LOAD CURRENT (mA) 1000 2500 4.93 MODE = SGND MAX17503, 3.3V OUTPUT, PWM MODE, FIGURE 4b CIRCUIT LOAD AND LINE REGULATION 3.27 5.00 VIN = 12V VIN = 24V VIN = 36V 4.98 100 5.01 5.00 LOAD CURRENT (mA) 3.28 10 MAX17503S, 5VOUTPUT, PWM MODE, FIGURE 4c CIRCUIT, LOAD AND LINE REGULATION 5.02 5.01 4.96 MODE = VCC 1 MODE = VCC 1 LOAD CURRENT (mA) 5.02 4.97 30 20 1000 5.05 OUTPUT VOLTAGE (V) EFFICIENCY (%) 70 60 1 20 toc07a VIN = 36V 80 VIN = 36V MAX17503, 5V OUTPUT, PWM MODE, FIGURE 4a CIRCUIT LOAD AND LINE REGULATION toc06a VIN = 48V 90 VIN = 24V 50 LOAD CURRENT (mA) MAX17503S, 3.3VOUTPUT, DCM MODE, FIGURE 4d CIRCUIT, EFFICIENCY vs. LOADCURRENT 100 MODE = VCC OUTPUT VOLTAGE (V) 1 VIN = 48V 60 30 10 MODE = VCC 70 40 20 VIN = 36V 30 10 VIN = 12V 50 VIN = 12V 80 VIN = 24V 30 40 20 90 VIN = 36V 80 EFFICIENCY (%) 60 100 MAX17503 toc07 EFFICIENCY (%) 70 VIN = 48V 90 EFFICIENCY (%) VIN = 12V 80 100 MAX17503 toc05 90 toc05a 100 MAX17503, 3.3V OUTPUT, DCM MODE, FIGURE 4b CIRCUIT EFFICIENCY vs. LOAD CURRENT MAX17503 toc06 MAX17503 5V OUTPUT, DCM MODE, FIGURE 4a CIRCUIT EFFICIENCY vs. LOAD CURRENT VIN = 48V VIN = 24V 3.35 3.30 3.25 VIN = 12V VIN = 36V 3.20 3.15 3.10 0 500 1000 1500 2000 2500 LOAD CURRENT (mA) Maxim Integrated 6 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Typical Operating Characteristics (continued) (VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2F, CBST = 0.1F, CSS = 5600pF, RT = MODE = open, TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C. All voltages are referenced to GND, unless otherwise noted.) MAX17503S, 5VOUTPUT, PFM MODE, FIGURE 4c CIRCUIT, LOAD AND LINE REGULATION MAX17503 toc09 5.1 5.0 4.9 VIN = 36V 4.8 4.7 5 4.95 VIN = 24V 4.9 500 2500 1000 1500 2000 LOAD CURRENT (mA) 0 500 toc10a 3.30 3.20 VIN = 24V VIN = 36V 3.10 0 500 1000 3.2 1000 1500 1500 2000 2500 LOAD CURRENT (mA) VIN = 36V 2000 2500 2400 2200 2000 1800 1600 1400 1200 1000 800 600 400 200 0 VOUT 2V/div IOUT 1A/div VRESET 5V/div 1ms/div 500 1000 1500 2000 LOAD CURRENT (mA) 2500 SWITCHING FREQUENCY vs. RT RESISTANCE 0 10 20 30 40 50 60 70 80 90 100 RRT (k) toc12a MAX17503 toc12 VEN/UVLO 2V/div MODE = OPEN 0 MAX17503S, SOFT-START/ SHUTDOWNFROM EN/UVLO, 5V OUTPUT, 2.5A LOADCURRENT, FIGURE 4c CIRCUIT) MAX17503, SOFT-START/SHUTDOWN FROM EN/UVLO 5V OUTPUT, 2.5A LOAD CURRENT, FIGURE 4a CIRCUIT www.maximintegrated.com VIN = 24V 3.1 3.0 VIN = 12V 3.40 VIN = 48V 3.3 LOAD CURRENT (mA) VIN = 48V 3.50 OUTPUT VOLTAGE (V) 4.75 MAX17503S, 3.3VOUTPUT, PFM MODE,FIGURE 4d CIRCUIT, LOAD AND LINE REGULATION 3.60 3.00 VIN = 36V 3.4 4.8 MODE = OPEN 0 VIN = 12V 4.85 VIN = 48V 4.6 4.5 VIN = 12V 5.1 5.05 VIN = 12V 3.5 VIN = 48V 5.15 MAX17503 toc11 5.2 3.6 OUTPUT VOLTAGE (V) VIN = 24V 5.2 SWITCHING FREQUENCY (kHz) 5.3 5.25 OUTPUT VOLTAGE (V) OUTPUT VOLTAGE (V) 5.4 toc09a 5.5 MAX17503, 3.3V OUTPUT, PFM MODE, FIGURE 4b CIRCUIT LOAD AND LINE REGULATION MAX17503 toc10 MAX17503, 5V OUTPUT, PFM MODE, FIGURE 4a CIRCUIT LOAD AND LINE REGULATION VEN/UVLO 5V/div VOUT 2V/div IOUT 1A/div VRESET 5V/div 1ms/div Maxim Integrated 7 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Typical Operating Characteristics (continued) (VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2F, CBST = 0.1F, CSS = 5600pF, RT = MODE = open, TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C. All voltages are referenced to GND, unless otherwise noted.) MAX17503S, SOFT-START/ SHUTDOWNFROM EN/UVLO, 3.3V OUTPUT, 2.5A LOADCURRENT, FIGURE 4d CIRCUIT) MAX17503 SOFT-START/SHUTDOWN FROM EN/UVLO 3.3V OUTPUT, 2.5A LOAD CURRENT, FIGURE 4b CIRCUIT toc13a MAX17503 toc13 VEN/UVLO 2V/div VEN/UVLO VOUT 2V/div VOUT IOUT 1A/div IOUT 1A/div VRESET 5V/div VRESET 5V/div 5V/div 2V/div 1mS/div 1ms/div MAX17503 SOFT-START/SHUTDOWN FROM EN/UVLO 5V OUTPUT, PFM MODE, 5mA LOAD CURRENT, FIGURE 4a CIRCUIT MAX17503S, SOFT-START/SHUTDOWN FROMEN/UVLO, 5V OUTPUT, PFM MODE 5MA LOAD CURRENT, FIGURE 4c CIRCUIT) toc14a MAX17503 toc14 MODE = OPEN VEN/UVLO 2V/div VOUT 1V/div VRESET 5V/div 5V/div VEN/UVLO 1V/div VOUT VRESET 5V/div 2mS/div 2ms/div MAX17503 SOFT-START/SHUTDOWN FROM EN/UVLO, 3.3V OUTPUT, PFM MODE, 5mA LOAD CURRENT, FIGURE 4b CIRCUIT MAX17503 toc15 MAX17503S, SOFT-START/SHUTDOWN FROMEN/UVLO, 3.3V OUTPUT,PFMMODE 5MA LOAD CURRENT, FIGURE 4d CIRCUIT) toc15a MODE = OPEN VEN/UVLO 2V/div VOUT 1V/div VRESET 5V/div 2ms/div www.maximintegrated.com 5/div VEN/UVLO VOUT 1V/div VRESET 5V/div 2mS/div Maxim Integrated 8 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Typical Operating Characteristics (continued) (VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2F, CBST = 0.1F, CSS = 5600pF, RT = MODE = open, TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C. All voltages are referenced to GND, unless otherwise noted.) MAX17503 5V OUTPUT, PWM MODE SOFT-START WITH 2.5V PREBIAS, FIGURE 4a CIRCUIT MAX17503S, SOFT-START WITH2.5VPREBIAS, 5V OUTPUT, PWM MODE, FIGURE 4c CIRCUIT toc16a MAX17503 toc16 MODE = SGND 5V/div VEN/UVLO 2V/div VEN/UVLO 2V/div VOUT 2V/div VOUT VRESET 5V/div VRESET 5V/div 1ms/div 1mS/div MAX17503 3.3V OUTPUT, PFM MODE SOFT-START WITH 2.5V PREBIAS, FIGURE 4b CIRCUIT MAX17503S, SOFT-START WITH2.5VPREBIAS, 3.3V OUTPUT, PWM MODE, FIGURE 4d CIRCUIT toc17a MAX17503 toc17 MODE = OPEN VEN/UVLO 2V/div VEN/UVLO 5V/div 1V/div VOUT 1V/div VOUT VRESET 5V/div VRESET 5V/div 1ms/div 1mS/div MAX17503 5V OUTPUT, 2.5A LOAD CURRENT STEADY-STATE SWITCHING WAVEFORMS, FIGURE 4a CIRCUIT MAX17503S, STEADY-STATE SWITCHING WAVEFORMS, 5VOUTPUT, 2.5A LOADCURRENT, FIGURE 4c CIRCUIT toc18a MAX17503 toc18 VOUT (AC) 50mV/div VOUT (AC) VLX 10V/div VLX 10V/div ILX 2A/div ILX 1A/div 1s/div www.maximintegrated.com 50mV/div 400nS/div Maxim Integrated 9 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Typical Operating Characteristics (continued) (TA = +25C, unless otherwise noted.) MAX17503 5V OUTPUT, PWM MODE, NO LOAD STEADY-STATE SWITCHING WAVEFORMS, FIGURE 4a CIRCUIT MAX17503S, STEADY-STATE SWITCHING WAVEFORMS, 5VOUTPUT, NO LOAD CURRENT, FIGURE 4c CIRCUIT toc19a MAX17503 toc19 VOUT (AC) 50mV/div MODE = SGND VLX 10V/div ILX 500mA/div VOUT (AC) 50mV/div VLX 10V/div ILX 500mA/div 400ns/div 1s/div MAX17503 5V OUTPUT, PFM MODE, 25mA LOAD STEADY-STATE SWITCHING WAVEFORMS, FIGURE 4a CIRCUIT MAX17503S, STEADY-STATE SWITCHING WAVEFORMS, 5VOUTPUT, PFMMODE, 25mA LOAD CURRENT, FIGURE 4c CIRCUIT toc20a MAX17503 toc20 VOUT (AC) VOUT (AC) 100mV/div VLX 10V/div ILX 500mA/div ILX MODE = OPEN MAX17503 toc21 VOUT (AC) 20mV/div VLX 10V/div 500mA/div 4s/div MAX17503 5V OUTPUT, DCM MODE, 25mA LOAD STEADY-STATE SWITCHING WAVEFORMS, FIGURE 4a CIRCUIT MAX17503S, STEADY-STATE SWITCHING WAVEFORMS, 5VOUTPUT, DCM MODE, 25mA LOAD CURRENT, FIGURE 4c CIRCUIT toc21a VOUT (AC) 20mV/div VLX 10V/div ILX 200mA/div MODE = VCC 1s/div www.maximintegrated.com 10V/div VLX 10s/div ILX 200mA/div 100mV/div 1s/div Maxim Integrated 10 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Typical Operating Characteristics (continued) (VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2F, CBST = 0.1F, CSS = 5600pF, RT = MODE = open, TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C. All voltages are referenced to GND, unless otherwise noted.) MAX17503 5V OUTPUT, PWM MODE (LOAD CURRENT STEPPED FROM 1A TO 2A), FIGURE 4a CIRCUIT MAX17503S, 5VOUTPUT, PWM MODE, FIGURE 4c CIRCUIT (LOAD CURRENT STEPPED FROM 1A TO2A) toc22a MAX17503 toc22 MODE = SGND VOUT (AC) 100mV/div VOUT AC IOUT 1A/div ILX 100mV/div 1A/div 40S/div 40s/div MAX17503 3.3V OUTPUT, PWM MODE (LOAD CURRENT STEPPED FROM 1A TO 2A), FIGURE 4b CIRCUIT MAX17503S, 3.3VOUTPUT, PWM MODE, FIGURE 4d CIRCUIT (LOAD CURRENT STEPPED FROM 1A TO2A) toc23a MAX17503 toc23 MODE = SGND VOUT (AC) 50mV/div VOUT AC IOUT 1A/div 50mV/div ILX 2A/div 40S/div 40s/div MAX17503 5V OUTPUT, PWM MODE (LOAD CURRENT STEPPED FROM NO-LOAD TO 1A), FIGURE 4a CIRCUIT MAX17503S, 5V OUTPUT, PWM MODE, FIGURE 4c CIRCUIT (LOAD CURRENT STEPPED FROM NO LOAD TO 1A) toc24a MAX17503 toc24 MODE = SGND VOUT (AC) 100mV/div VOUT AC IOUT 1A/div ILX 40s/div www.maximintegrated.com 100mV/div 1A/div 40S/div Maxim Integrated 11 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Typical Operating Characteristics (continued) (TA = +25C, unless otherwise noted.) MAX17503 3.3V OUTPUT, PWM MODE (LOAD CURRENT STEPPED FROM NO-LOAD TO 1A), FIGURE 4b CIRCUIT MAX17503S, 3.3V OUTPUT, PWM MODE, FIGURE 4d CIRCUIT (LOAD CURRENT STEPPED FROM NO LOAD TO 1A) toc25a MAX17503 toc25 MODE = SGND VOUT (AC) 50mV/div VOUT AC IOUT 1A/div ILX 50mV/div 1A/div 40S/div 40s/div MAX17503 5V OUTPUT, PFM MODE (LOAD CURRENT STEPPED FROM 5mA TO 1A), FIGURE 4a CIRCUIT MAX17503 toc26 MODE = OPEN VOUT (AC) 100mV/div IOUT 500mA/div 2ms/div MAX17503 3.3V OUTPUT, PFM MODE (LOAD CURRENT STEPPED FROM 5mA TO 1A), FIGURE 4b CIRCUIT MAX17503 toc27 MODE = OPEN VOUT (AC) 50mV/div IOUT 500mA/div 2ms/div www.maximintegrated.com Maxim Integrated 12 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Typical Operating Characteristics (continued) (VIN = VEN/UVLO = 24V, VPGND = VSGND = 0V, CVIN = CVCC = 2.2F, CBST = 0.1F, CSS = 5600pF, RT = MODE = open, TA = -40C to +125C, unless otherwise noted. Typical values are at TA = +25C. All voltages are referenced to GND, unless otherwise noted.) MAX17503 5V OUTPUT, DCM MODE (LOAD CURRENT STEPPED FROM 50mA TO 1A), FIGURE 4a CIRCUIT MAX17503S, 5VOUTPUT, DCM MODE (LOAD CURRENT STEPPED FROM 50mATO1A) FIGURE 4c CIRCUIT toc28a MAX17503 toc28 MODE = VCC VOUT (AC) 100mV/div IOUT 500mA/div VOUT (AC) 100mV/div IOUT 500mA/div 200s/div 200s/div MAX17503 3.3V OUTPUT, DCM MODE (LOAD CURRENT STEPPED FROM 50mA TO 1A), FIGURE 4b CIRCUIT MAX17503S, 3.3VOUTPUT, DCM MODE (LOAD CURRENT STEPPED FROM 50mATO1A) FIGURE 4d CIRCUIT toc29a MAX17503 toc29 MODE = VCC VOUT (AC) 100mV/div IOUT 500mA/div VOUT (AC) 100mV/div IOUT 500mA/div 200s/div 200s/div MAX17503 5V OUTPUT, OVERLOAD PROTECTION, FIGURE 4a CIRCUIT MAX17503S, OVERLOADPROTECTION 5V OUTPUT, FIGURE 4c CIRCUIT MAX17503 toc30 toc30a VOUT 500mV/div VOUT IOUT 1A/div IOUT 20ms/div www.maximintegrated.com 200mV/div 1A/div 10ms/div Maxim Integrated 13 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Typical Operating Characteristics (continued) (TA = +25C, unless otherwise noted.) MAX17503 5V OUTPUT, APPLICATION OF EXTERNAL CLOCK AT 700kHz, FIGURE 4a CIRCUIT MAX17503S, APPLICATIONOF EXTERNAL CLOCKAT 1.2MHz, 5V OUTPUT, FIGURE 4c CIRCUIT MAX17503 toc31 VLX 10V/div toc31a VLX VSYNC 2V/div 10V/div VSYNC 2V/div MODE = SGND 2s/div 2s/div MAX17503 5V OUTPUT, 2.5A LOAD CURRENT BODE PLOT, FIGURE 4a CIRCUIT MAX17503 toc32 50 PHASE 40 80 60 30 40 GAIN 10 20 0 0 -10 -20 CROSSOVER FREQUENCY = 58.2kHz -30 PHASE MARGIN = 63.4 -40 2 1k 4 6 81 2 -20 PHASE () GAIN (dB) 20 -50 100 -40 -60 4 6 81 2 100k 10k -80 -100 FREQUENCY (Hz) MAX17503S, 3.3VOUTPUT, 2.5A LOAD CURRENT, BODE PLOT, FIGURE 4cCIRCUIT MAX17503 5V OUTPUT, 2.5A LOAD CURRENT BODE PLOT, FIGURE 4b CIRCUIT MAX17503 toc33 100 80 30 60 20 40 GAIN 10 20 0 -10 CROSSOVER FREQUENCY = 62.5kHz -20 PHASE MARGIN = 61.2 -30 -40 2 1k 4 6 81 2 0 -20 -40 4 6 81 10k FREQUENCY (Hz) www.maximintegrated.com 100k 2 -60 PHASE GAIN PHASE () PHASE 40 GAIN (dB) GAIN (dB) 50 toc33a 120 PHASE () 60 CROSSOVER FREQUENCY = 77.5kHz, PHASE MARGIN = 64.7 -80 FREQUENCY (Hz) Maxim Integrated 14 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation PGND SGND VCC MODE TOP VIEW PGND Pin Configuration 15 14 13 12 11 PGND 16 LX 17 MAX17503/ MAX17503 MAX17503S LX 18 LX 19 2 3 4 5 EN/UVLO RESET VIN 1 VIN + VIN BST 20 10 RT 9 FB 8 CF 7 SS 6 SYNC TQFN 4mm x 4mm * EXPOSED PAD (CONNECT TO GROUND). Pin Description PIN NAME 1-3 VIN Power-Supply Input. 4.5V to 60V input supply range. Connect the VIN pins together. Decouple to PGND with a 2.2F capacitor; place the capacitor close to the VIN and PGND pins. Refer to the MAX17503/ MAX17503S EV kit data sheets for a layout example. 4 EN/UVLO Enable/Undervoltage Lockout. Drive EN/UVLO high to enable the output voltage. Connect to the center of the resistor-divider between VIN and SGND to set the input voltage at which the device turns on. Pull up to VIN for always-on operation. 5 RESET 6 SYNC 7 SS Soft-Start Input. Connect a capacitor from SS to SGND to set the soft-start time. 8 CF At switching frequencies lower than 500kHz, connect a capacitor from CF to FB. Leave CF open if switching frequency is equal or more than 500kHz. See the Loop Compensation section for more details. 9 FB Feedback Input. Connect FB to the center tap of an external resistor-divider from the output to GND to set the output voltage. See the Adjusting Output Voltage section for more details. 10 RT Connect a resistor from RT to SGND to set the regulator's switching frequency. Leave RT open for the default 500kHz frequency. See the Setting the Switching Frequency (RT) section for more details. MODE MODE pin configures the device to operate either in PWM, PFM, or DCM modes of operation. Leave MODE unconnected for PFM operation (pulse skipping at light loads). Connect MODE to SGND for constant-frequency PWM operation at all loads. Connect MODE to VCC for DCM operation. See the Mode Selection (MODE) section for more details. 11 www.maximintegrated.com FUNCTION Open-Drain RESET Output. The RESET output is driven low if FB drops below 92% of its set value. RESET goes high 1024 clock cycles after FB rises above 95% of its set value. The device can be synchronized to an external clock using this pin. See the External Frequency Synchronization (SYNC) section for more details. Maxim Integrated 15 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Pin Description (continued) PIN NAME FUNCTION 12 VCC 13 SGND 5V LDO Output. Bypass VCC with 2.2F ceramic capacitance to SGND. Analog Ground 14-16 PGND Power Ground. Connect the PGND pins externally to the power ground plane. Connect the SGND and PGND pins together at the ground return path of the VCC bypass capacitor. Refer to the MAX17503/ MAX17503S EV kit data sheets for a layout example. 17-19 LX 20 BST -- EP Switching Node. Connect LX pins to the switching side of the inductor. Refer to the MAX17503/ MAX17503S EV kit data sheets for a layout example. Boost Flying Capacitor. Connect a 0.1F ceramic capacitor between BST and LX. Exposed pad. Connect to the SGND pin. Connect to a large copper plane below the IC to improve heat dissipation capability. Add thermal vias below the exposed pad. Refer to the MAX17503/MAX17503S EV kit data sheets for a layout example. Block Diagram VCC 5V BST MAX17503/MAX17503S LDO VIN SGND CURRENT-SENSE LOGIC EN/UVLO HICCUP 1.215V PWM/ PFM/ HICCUP LOGIC AND DRIVERS LX RT PGND OSCILLATOR SYNC CF FB VCC SS SWITCHOVER LOGIC VBG = 0.9V SLOPE COMPENSATION 5A FB HICCUP www.maximintegrated.com MODE SELECTION LOGIC ERROR AMPLIFIER/ LOOP COMPENSATION EN/UVLO MODE RESET RESET LOGIC Maxim Integrated 16 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Detailed Description The MAX17503/MAX17503S high-efficiency, highvoltage, synchronously rectified step-down converter with dual integrated MOSFETs operates over a 4.5V to 60V input. It delivers up to 2.5A and 0.9V to 90%VIN output voltage. Built-in compensation across the output voltage range eliminates the need for external components. The feedback (FB) regulation accuracy over -40NC to +125NC is 1.1%. The device features a peak-current-mode control architecture. An internal transconductance error amplifier produces an integrated error voltage at an internal node, which sets the duty cycle using a PWM comparator, a highside current-sense amplifier, and a slope-compensation generator. At each rising edge of the clock, the highside MOSFET turns on and remains on until either the appropriate or maximum duty cycle is reached, or the peak current limit is detected. During the high-side MOSFET's on-time, the inductor current ramps up. During the second half of the switching cycle, the high-side MOSFET turns off and the low-side MOSFET turns on. The inductor releases the stored energy as its current ramps down and provides current to the output. The device features a MODE pin that can be used to operate the device in PWM, PFM, or DCM control schemes. The device integrates adjustable-input undervoltage lockout, adjustable soft-start, open RESET, and external frequency synchronization features. The MAX17503S offers a lower Minimum On-Time that allows for higher switching frequencies and a smaller solution size. Mode Selection (MODE) The logic state of the MODE pin is latched when VCC and EN/UVLO voltages exceed the respective UVLO rising thresholds and all internal voltages are ready to allow LX switching. If the MODE pin is open at power-up, the device operates in PFM mode at light loads. If the MODE pin is grounded at power-up, the device operates in constant-frequency PWM mode at all loads. Finally, if the MODE pin is connected to VCC at power-up, the device operates in constant-frequency DCM mode at light loads. State changes on the MODE pin are ignored during normal operation. www.maximintegrated.com PWM Mode Operation In PWM mode, the inductor current is allowed to go negative. PWM operation provides constant frequency operation at all loads, and is useful in applications sensitive to switching frequency. However, the PWM mode of operation gives lower efficiency at light loads compared to PFM and DCM modes of operation. PFM Mode Operation PFM mode of operation disables negative inductor current and additionally skips pulses at light loads for high efficiency. In PFM mode, the inductor current is forced to a fixed peak of 750mA every clock cycle until the output rises to 102.3% of the nominal voltage. Once the output reaches 102.3% of the nominal voltage, both the high-side and low-side FETs are turned off and the device enters hibernate operation until the load discharges the output to 101.1% of the nominal voltage. Most of the internal blocks are turned off in hibernate operation to save quiescent current. After the output falls below 101.1% of the nominal voltage, the device comes out of hibernate operation, turns on all internal blocks, and again commences the process of delivering pulses of energy to the output until it reaches 102.3% of the nominal output voltage. The advantage of the PFM mode is higher efficiency at light loads because of lower quiescent current drawn from supply. The disadvantage is that the output-voltage ripple is higher compared to PWM or DCM modes of operation and switching frequency is not constant at light loads. DCM Mode Operation DCM mode of operation features constant frequency operation down to lighter loads than PFM mode, by not skipping pulses but only disabling negative inductor current at light loads. DCM operation offers efficiency performance that lies between PWM and PFM modes. Linear Regulator (VCC) An internal linear regulator (VCC) provides a 5V nominal supply to power the internal blocks and the low-side MOSFET driver. The output of the linear regulator (VCC) should be bypassed with a 2.2F ceramic capacitor to SGND. The device employs an undervoltage lockout circuit that disables the internal linear regulator when VCC falls below 3.8V (typ). Maxim Integrated 17 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Setting the Switching Frequency (RT) The switching frequency of the device can be programmed from 100kHz to 2.2MHz by using a resistor connected from the RT pin to SGND. The switching frequency (fSW) is related to the resistor connected at the RT pin (RRT) by the following equation: R RT 21x 10 3 - 1.7 f SW where RRT is in k and fSW is in kHz. Leaving the RT pin open causes the device to operate at the default switching frequency of 500kHz. See Table 1 for RT resistor values for a few common switching frequencies. To operate the MAX17503/MAX17503S at switching frequencies lower than 200kHz, an R-C network has to be connected in parallel to the resistor connected from RT to SGND, as shown in Figure 1. The values of the components R8 and C13 are 90.9kW and 220pF, respectively. Operating Input Voltage Range The minimum and maximum operating input voltages for a given output voltage should be calculated as follows: VIN(MIN) = VOUT + (I OUT(MAX) x (R DCR + 0.15)) 1- (f SW(MAX) x t OFF(MAX) ) + (I OUT(MAX) x 0.175) VIN(MAX) = VOUT f SW(MAX) x t ON(MIN) where VOUT is the steady-state output voltage, IOUT (MAX) is the maximum load current, RDCR is the DC resistance of the inductor, fSW(MAX) is the maximum switching frequency, tOFF-MAX is the worst-case minimum switch off-time (160ns), and tON-MIN is the worst-case minimum switch on-time (135ns for the MAX17503, 80ns for the MAX17503S). Table 1. Switching Frequency vs. RT Resistor SWITCHING FREQUENCY (kHz) RT RESISTOR (k) 500 Open 100 210 200 102 400 49.9 1000 19.1 2200 8.06 www.maximintegrated.com External Frequency Synchronization (SYNC) The internal oscillator of the device can be synchronized to an external clock signal on the SYNC pin. The external synchronization clock frequency must be between 1.1 x fSW and 1.4 x fSW, where fSW is the frequency programmed by the RT resistor. The minimum external clock pulse-width high should be greater than 50ns. See the RT AND SYNC section in the Electrical Characteristics table for details. Overcurrent Protection/Hiccup Mode The device is provided with a robust overcurrent protection scheme that protects the device under overload and output short-circuit conditions. A cycle-by-cycle peak current limit turns off the high-side MOSFET whenever the high-side switch current exceeds an internal limit of 3.7A (typ). A runaway current limit on the high-side switch current at 4.3A (typ) protects the device under high input voltage, short-circuit conditions when there is insufficient output voltage available to restore the inductor current that was built up during the on-period of the step-down converter. One occurrence of the runaway current limit triggers a hiccup mode. In addition, if due to a fault condition, feedback voltage drops to 0.58V (typ) any time after soft-start is complete, and hiccup mode is triggered. In hiccup mode, the converter is protected by suspending switching for a hiccup timeout period of 32,768 clock cycles. Once the hiccup timeout period expires, soft-start is attempted again. Note that when softstart is attempted under overload condition, if feedback voltage does not exceed 0.58V, the device switches at half the programmed switching frequency. Hiccup mode of operation ensures low power dissipation under output short-circuit conditions. R5 R8 C13 Figure 1. Setting the Switching Frequency Maxim Integrated 18 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation RESET Output The device includes a RESET comparator to monitor the output voltage. The open-drain RESET output requires an external pullup resistor. RESET goes high (high impedance) 1024 switching cycles after the regulator output increases above 95% of the designed nominal regulated voltage. RESET goes low when the regulator output voltage drops to below 92% of the nominal regulated voltage. RESET also goes low during thermal shutdown. Prebiased Output When the device starts into a prebiased output, both the high-side and the low-side switches are turned off so that the converter does not sink current from the output. Highside and low-side switches do not start switching until the PWM comparator commands the first PWM pulse, at which point switching commences. The output voltage is then smoothly ramped up to the target value in alignment with the internal reference. Thermal-Shutdown Protection Thermal-shutdown protection limits total power dissipation in the device. When the junction temperature of the device exceeds +165C, an on-chip thermal sensor shuts down the device, allowing the device to cool. The thermal sensor turns the device on again after the junction temperature cools by 10C. Soft-start resets during thermal shutdown. Carefully evaluate the total power dissipation (see the Power Dissipation section) to avoid unwanted triggering of the thermal shutdown in normal operation. Applications Information Input Capacitor Selection The input filter capacitor reduces peak currents drawn from the power source and reduces noise and voltage ripple on the input caused by the circuit's switching. The input capacitor RMS current requirement (IRMS) is defined by the following equation: = IRMS I OUT(MAX) x VOUT x (VIN - VOUT ) VIN where, IOUT(MAX) is the maximum load current. IRMS has a maximum value when the input voltage equals twice the output voltage (VIN = 2 x VOUT), so IRMS(MAX) = IOUT(MAX)/2. Choose an input capacitor that exhibits less than +10C temperature rise at the RMS input current for optimal long-term reliability. Use low-ESR ceramic capacitors with high-ripple-current capability at the input. X7R capacitors are recommended in industrial applications for their www.maximintegrated.com temperature stability. Calculate the input capacitance using the following equation: C IN = I OUT(MAX) x D x (1- D) x f SW x VIN where D = VOUT/VIN is the duty ratio of the controller, fSW is the switching frequency, VIN is the allowable input voltage ripple, and E is the efficiency. In applications where the source is located distant from the device input, an electrolytic capacitor should be added in parallel to the ceramic capacitor to provide necessary damping for potential oscillations caused by the inductance of the longer input power path and input ceramic capacitor. Inductor Selection Three key inductor parameters must be specified for operation with the device: inductance value (L), inductor saturation current (ISAT), and DC resistance (RDCR). The switching frequency and output voltage determine the inductor value as follows: L= VOUT f SW where VOUT, and fSW are nominal values. Select a low-loss inductor closest to the calculated value with acceptable dimensions and having the lowest possible DC resistance. The saturation current rating (ISAT) of the inductor must be high enough to ensure that saturation can occur only above the peak current-limit value of 3.7A. Output Capacitor Selection X7R ceramic output capacitors are preferred due to their stability over temperature in industrial applications. The output capacitors are usually sized to support a step load of 50% of the maximum output current in the application, so the output voltage deviation is contained to 3% of the output voltage change. The minimum required output capacitance can be calculated as follows: C OUT= 1 I STEP x t RESPONSE x 2 VOUT t RESPONSE ( 0.33 1 + ) fC f sw where ISTEP is the load current response time of the controller, output-voltage deviation, fC is crossover frequency, and fSW is step, tRESPONSE is the DVOUT is the allowable the target closed-loop the switching frequency. Maxim Integrated 19 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation VOUT VIN R3 R1 FB EN/UVLO R2 R4 SGND SGND Figure 2. Setting the Input Undervoltage Lockout Figure 3. Setting the Output Voltage Table 2. C6 Capacitor Value at Various Switching Frequencies For example, to program a 1ms soft-start time, a 5.6nF capacitor should be connected from the SS pin to SGND. SWITCHING FREQUENCY RANGE (kHz) C6 (pF) 200 to 300 2.2 300 to 400 1.2 400 to 500 0.75 For the MAX17503, select fC to be 1/9th of fSW if the switching frequency is less than or equal to 500kHz. If the switching frequency is more than 500kHz, select fC to be 55kHz. For the MAX17503S, select fC to be 1/10th of fSW if the switching frequency is less than or equal to 1MHz. If the switching frequency is more than 1MHz, select fC to be 100kHz. Derating of ceramic capacitors with DC-voltage must be considered while selecting the output capacitor. Derating curves are available from all major ceramic capacitor vendors. Soft-Start Capacitor Selection The device implements adjustable soft-start operation to reduce inrush current. A capacitor connected from the SS pin to SGND programs the soft-start time. The selected output capacitance (CSEL) and the output voltage (VOUT) determine the minimum required soft-start capacitor as follows: C SS 28 x 10 -6 x C SEL x VOUT The soft-start time (tSS) is related to the capacitor connected at SS (CSS) by the following equation: C SS t SS = 5.55 x 10 -6 www.maximintegrated.com Setting the Input Undervoltage-Lockout Level The device offers an adjustable input undervoltage-lockout level. Set the voltage at which the device turns on with a resistive voltage-divider connected from VIN to SGND. Connect the center node of the divider to EN/UVLO. Choose R1 to be 3.3MI and then calculate R2 as follows: R2 = R1x 1.215 (VINU - 1.215) where VINU is the voltage at which the device is required to turn on. Ensure that VINU is higher than 0.8 x VOUT. If the EN/UVLO pin is driven from an external signal source, a series resistance of minimum 1k is recommended to be placed between the signal source output and the EN/ UVLO pin, to reduce voltage ringing on the line. Loop Compensation The device is internally loop compensated. However, if the switching frequency is less than 500kHz, connect a 0402 capacitor C6 between the CF pin and the FB pin. Use Table 2 to select the value of C6. If the switching frequency is less than 200kHz, connect an additional R-C network in parallel to the top resistor of the feedback divider (R3). See Figure 5 to calculate the values of the components R7, C12, and C6. Maxim Integrated 20 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Adjusting Output Voltage Set the output voltage with a resistive voltage-divider connected from the positive terminal of the output capacitor (VOUT) to SGND (see Figure 3). Connect the center node of the divider to the FB pin. Use the following procedure to choose the resistive voltage-divider values: Calculate resistor R3 from the output to the FB pin as follows: 216 x 10 3 R3 = f C x C OUT where R3 is in k, crossover frequency fC is in kHz, and the output capacitor COUT is in F. For the MAX17503, choose fC to be 1/9th of the switching frequency, fSW, if the switching frequency is less than or equal to 500kHz. If the switching frequency is more than 500kHz, select fC to be 55kHz. For the MAX17503S, select fC to be 1/10th of fSW if the switching frequency is less than or equal to 1MHz. If the switching frequency is more than 1MHz, select fC to be 100kHz. Calculate resistor R4 from the FB pin to SGND as follows: R4 = R3 x 0.9 (VOUT - 0.9) Power Dissipation At a particular operating condition, the power losses that lead to temperature rise of the part are estimated as follows: ( 1 PLOSS = (POUT x ( - 1)) - I OUT 2 x R DCR ) P= OUT VOUT x I OUT where POUT is the total output power, is the efficiency of the converter, and RDCR is the DC resistances of the inductor. (See the Typical Operating Characteristics for more information on efficiency at typical operating conditions.) For a multilayer board, the thermal performance metrics for the package are given below: JA = 33C W JC =2C W If the application has a thermal management system that ensures that the exposed pad of the device is maintained at a given temperature (TEP_MAX) by using proper heat sinks, then the junction temperature of the device can be estimated at any given maximum ambient temperature from the equation below: T= J_MAX TEP_MAX + ( JC x PLOSS ) Junction temperature greater than +125C degrades operating lifetimes. PCB Layout Guidelines All connections carrying pulsed currents must be very short and as wide as possible. The inductance of these connections must be kept to an absolute minimum due to the high di/dt of the currents. Since inductance of a current carrying loop is proportional to the area enclosed by the loop, if the loop area is made very small, inductance is reduced. Additionally, small-current loop areas reduce radiated EMI. A ceramic input filter capacitor should be placed close to the VIN pins of the IC. This eliminates as much trace inductance effects as possible and gives the IC a cleaner voltage supply. A bypass capacitor for the VCC pin also should be placed close to the pin to reduce effects of trace impedance. When routing the circuitry around the IC, the analog small-signal ground and the power ground for switching currents must be kept separate. They should be connected together at a point where switching activity is at a minimum, typically the return terminal of the VCC bypass capacitor. This helps keep the analog ground quiet. The ground plane should be kept continuous/unbroken as far as possible. No trace carrying high switching current should be placed directly over any ground plane discontinuity. PCB layout also affects the thermal performance of the design. A number of thermal vias that connect to a large ground plane should be provided under the exposed pad of the part, for efficient heat dissipation. For a sample layout that ensures first pass success, refer to the MAX17503 evaluation kit layout available at www.maximintegrated.com. The junction temperature of the device can be estimated at any given maximum ambient temperature (TA_MAX) from the equation below: TJ_MAX = T A _MAX + ( JA x PLOSS ) www.maximintegrated.com Maxim Integrated 21 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Recommended Component Placement for MAX17503/MAX17503S VOUT PLANE PGND PLANE L1 LX PLANE C1 C4 C5 LX PLANE PGND PLANE VIN PLANE MAX17503/ MAX17503S SGND C2 R1 R2 MODE R6 SYNC C3 C6 R3 R5 R4 SGND PLANE www.maximintegrated.com Maxim Integrated 22 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Recommended Component Placement for MAX17503/MAX17503S (continued) VOUT PLANE PGND PLANE L1 LX PLANE C1 C4 C5 LX PLANE PGND PLANE VIN PLANE MAX17503/ MAX17503S SGND C2 R1 R2 MODE R6 SYNC C3 C6 R3 R5 R4 SGND PLANE www.maximintegrated.com Maxim Integrated 23 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation VIN (6.5V TO 60V) C1 2.2F VIN EN/UVLO RT VIN VIN BST SYNC LX MAX17503 MODE C2 2.2F C5 0.1F L1 10H VOUT 5V, 2.5A C4 22F LX LX VCC R3 178k FB SGND R4 39k RESET CF SS PGND PGND PGND C3 5.6nF fSW = 500kHz a) 5V Output, 500kHz Switching Frequency VIN (6.5V TO 60V) C1 2.2uF VIN VIN EN/UVLO RT VIN VIN BST SYNC LX MODE C2 2.2F C5 0.1F L1 6.8H C4 47F LX MAX17503 LX VCC VOUT 3.3V, 2.5A R3 127k FB SGND CF R4 47.5k RESET SS PGND PGND C3 5600pF PGND fSW = 500kHz b) 3.3V Output, 500kHz Switching Frequency Figure 4. MAX17503/MAX17503S Typical Application Circuits www.maximintegrated.com Maxim Integrated 24 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation VIN C1 2.2F R5 EN/UVLO RT VIN VIN VIN BST 19.1K SYNC C5 0.1F LX VOUT 5V,2.5A C4 10F LX MAX17503S MODE L1 4.7H LX C2 2.2F VCC R3 196K FB SGND R4 43.2K RESET CF SS PGND PGND PGND C3 5.6nF fSW = 1MHz L1 = 4.7H (XAL4030, 4mm x 4mm) C) 5V Output, 1MHz Switching Frequency VIN C1 2.2F R5 EN/UVLO RT VIN VIN VIN BST 19.1K SYNC LX LX MAX17503S MODE C5 0.1F L1 3.3H VOUT 3.3V,2.5A C4 22F LX C2 2.2F VCC R3 115K FB SGND R4 43.2K RESET CF SS PGND PGND PGND C3 5.6nF fSW = 1MHz L1 = 3.3H (XAL4030, 4mm x 4mm) d) 3.3V Output, 1MHz Switching Frequency Figure 4. MAX17503/MAX17503S Typical Application Circuits (continued) www.maximintegrated.com Maxim Integrated 25 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation VIN C1 C13 220pF 2.2F C8 2.2F R8 EN/UVLO 90.9k R5 VIN VIN VIN RT BST C5 0.1F 210k SYNC MODE MAX17503 LX L1 LX 33H VOUT 3.3V, 2.5A C4 100F C9 C12 100F LX R3 97.6k VCC C2 R7 2.2F 47pF 1k FB SGND CF RESETB SS C3 PGND PGND 33000pF C6 15pF R4 36.5k PGND Fsw = 100kHz C12 = 0.8/ (R5 X Fsw) R7 = R5/100 C6 = 14/Fsw Figure 5. MAX17503/MAX17503S Typical Application Circuit--3.3V Output, 100kHz Switching Frequency Ordering Information PART MAX17503ATP+ MAX17503SATP+ Chip Information PIN-PACKAGE PROCESS: BiCMOS 20 TQFN 4mm x 4 mm 20 TQFN-EP* 4mm x 4 mm Note: All devices operate over the -40C to +125C temperature range, unless otherwise noted. +Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. www.maximintegrated.com Maxim Integrated 26 MAX17503 4.5V-60V, 2.5A, High-Efficiency, Synchronous Step-Down DC-DC Converter With Internal Compensation Revision History REVISION NUMBER REVISION DATE 0 8/13 Initial release 1 4/14 Added description and schematic for operation at 100kHz frequency 2 10/16 Added MAX17503S to data sheet, updated junction temperature, and added TOCs 3 4/17 Updated data sheet title 3.1 PAGES CHANGED DESCRIPTION Corrected typos -- 1-9, 12-13, 15, 18 1-17 1-27 15, 17-18, 21 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maximintegrated.com. Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. (c) 2017 Maxim Integrated Products, Inc. 27 Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: Maxim Integrated: MAX17503ATP+ MAX17503EVKITB# MAX17503ATP+T MAX17503SATP+ MAX17503SATP+T