19-6244; Rev 0; 5/12 EVALUATION KIT AVAILABLE MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter General Description The MAX17501 high-efficiency, high-voltage, synchronous step-down DC-DC converter operates over a 4.5V to 60V input voltage range and is designed for a wide range of applications. The ultra-wide-input operation makes it ideal for not only industrial control and building automation, but also base stations, telecom, home entertainment and automotive applications. It delivers output currents up to 500mA, at output voltages of 3.3V and 5V. The output voltage is accurate within Q1.6% over temperature. The device operates over the -40NC to +125NC industrial temperature range and is available in a tiny, 10-pin (3mm x 2mm) TDFN with an exposed pad. The device features peak-current-mode control with pulse-width modulation (PWM). The PWM operation ensures constant switching frequency at all operating conditions. The low-resistance, on-chip, pMOS/nMOS switches ensure high efficiency at full load while minimizing the critical inductances, making the layout a much simpler task compared to discrete solutions. The device offers fixed switching frequency of 600kHz. To reduce input inrush current, the device offers an adjustable voltage soft-start feature with an external capacitor from the SS pin to ground. The device also incorporates an output enable/undervoltage lockout pin (EN/UVLO) that allows the user to turn on the part at the desired input-voltage level. An open-drain RESET pin provides a delayed power-good signal to the system upon achieving successful regulation of the output voltage. The device supports hiccup-mode current-limit protection for low power dissipation under overload and output short-circuit conditions. Applications Industrial Process Control Benefits and Features S Eliminate External Components and Reduce Total Cost No Schottky-Synchronous Operation for High Efficiency and Reduced Cost Internal Compensation for Ultra-Compact Layout All-Ceramic Capacitors S Reduce Number of DC-DC Regulators to Stock Wide 4.5V to 60V Operating-Voltage Range Fixed 3.3V and 5V Output Delivers Up to 500mA Over Temperature 600kHz Switching Frequency S Reduce Power Dissipation Peak Efficiency > 90% Shutdown Current = 1µA (typ) S Operate Reliably in Adverse Industrial Environments Hiccup-Mode Current Limit and Autoretry Startup Built-In Output-Voltage Monitoring (Open-Drain RESET Pin) Resistor-Programmable UVLO Threshold Increased Safety with Adjustable Soft-Start and Prebiased Power-Up Optional Adjustable Output and PFM (Available Upon Factory Request) -40NC to +125NC Industrial Temperature Range Typical Operating Circuit VIN 24V ±20% L1 47µH C1 1µF 1206 HVAC and Building Control 1 JU1 2 3 General-Purpose Point-of-Load Base Station, VOIP, Telecom Home Theater Automotive LX VIN R1 3.32MI EN/UVLO R2 866kI C4 10µF, 6.3V 1206 VOUT 5V, 500mA PGND MAX17501F GND VCC C2 1µF C3 3300pF SS N.C. FB/VO RESET RESET Battery-Powered Equipment Ordering Information appears at end of data sheet. For related parts and recommended products to use with this part, refer to www.maxim-ic.com/MAX17501.related. ����������������������������������������������������������������� Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter ABSOLUTE MAXIMUM RATINGS VIN to GND.............................................................-0.3V to +70V EN/UVLO to GND.......................................... -0.3V to VIN + 0.3V LX to PGND............................................................-0.3V to +70V FB, RESET, COMP, SS to GND.................................. -0.3V to 6V VCC to GND..............................................................-0.3V to +6V GND to PGND.......................................................-0.3V to +0.3V LX Total RMS Current......................................................... Q1.6A Output Short-Circuit Duration.....................................Continuous Continuous Power Dissipation (TA = +70NC) 10-Pin TDFN (derate 14.9mW/NC above +70NC) (multilayer board)....................................................1188.7mW Operating Temperature Range......................... -40NC to +125NC Junction Temperature......................................................+150NC Storage Temperature Range............................. -65NC to +160NC Lead Temperature (soldering, 10s).................................+300NC Soldering Temperature (reflow).......................................+260NC Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and 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. PACKAGE THERMAL CHARACTERISTICS (Note 1) Thermal Resistance TDFN Junction-to-Ambient Thermal Resistance (BJA)........67.3NC/W Junction-to-Case Thermal Resistance (BJC).............18.2NC/W Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.com/thermal-tutorial. ELECTRICAL CHARACTERISTICS (VIN = 24V, VGND = VPGND = 0V, CVIN = CVCC = 1FF, VEN = 1.5V, CSS = 3300pF, VFB = 0.98 x VOUT, LX = unconnected, RESET = unconnected. TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC. All voltages are referenced to GND, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 60 V 0.9 3.5 FA VIN = 12V 3.7 5.2 VIN = 24V 5 6.75 INPUT SUPPLY (VIN) Input Voltage Range Input Supply Current VIN 4.5 IIN-SH VEN = 0V, shutdown mode IIN-SW Normal switching mode, VCOMP = 0.8V VENR VEN rising 1.194 1.218 1.236 VENF VEN falling 1.114 1.135 1.156 V 7 200 nA 4.65 5 5.35 V 40 80 mA mA ENABLE/UVLO (EN/UVLO) EN Threshold VEN-TRUESD EN Input Leakage Current VEN falling, true shutdown 0.75 IEN LDO VCC Output Voltage Range VCC Current Limit VCC Dropout VCC UVLO VCC 6V < VIN < 12V, 0mA < IVCC < 10mA, 12V < VIN < 60V, 0mA < IVCC < 2mA IVCC-MAX VCC = 4.3V, VIN = 12V 17 VCC-DO VIN = 4.5V, IVCC = 5mA 4.1 VCC-UVR VCC rising 3.85 4 4.15 VCC-UVF VCC falling 3.55 3.7 3.85 V V ����������������������������������������������������������������� Maxim Integrated Products 2 MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter ELECTRICAL CHARACTERISTICS (continued) (VIN = 24V, VGND = VPGND = 0V, CVIN = CVCC = 1FF, VEN = 1.5V, CSS = 3300pF, VFB = 0.98 x VOUT, LX = unconnected, RESET = unconnected. TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC. All voltages are referenced to GND, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS 1 FA LX LX Leakage Current ILX_LKG VEN = 0V, TA = +25NC, VLX = (VPGND + 1V) to (VIN - 1V) SOFT-START (SS) Switchover to Internal ReferenceVoltage Threshold Charging Current VSS-TH ISS 863 880 898 mV 4.7 5 5.3 FA MAX17501E, VFB = 3.3V 6.8 12 17 FA MAX17501F, VFB = 5V 6.8 12 17 FA MAX17501E only 3.248 3.3 3.352 MAX17501F only 4.922 5 5.08 VSS = 0.5V FEEDBACK (FB) FB Input Bias Current IFB TA = +25NC OUTPUT VOLTAGE (VOUT) Output Voltage Range CURRENT LIMIT Peak-Current-Limit Threshold IPEAK-LIMIT 0.585 0.685 0.795 A Runaway-Current-Limit Threshold IRUNAWAY- 0.73 0.865 1 A Valley Current-Limit Threshold ISINK-LIMIT 0.3 0.35 0.4 A 560 600 640 280 300 320 LIMIT TIMING Switching Frequency fSW VFB > VOUT-HICF VFB < VOUT-HICF MAX17501E/F kHz Events to Hiccup After Crossing Runaway-Current Limit VOUT Undervoltage Trip Level to Cause Hiccup 1 VOUT-HICF VSS > 0.95V (soft-start is done) 69.14 HICCUP Timeout 73.14 32,768 Minimum On-Time Maximum Duty Cycle LX Dead Time 71.14 tON_MIN DMAX VFB = 0.98 x VFBREG MAX17501E/F 92 % Cycles 85 120 ns 94 96 % 5 ns ����������������������������������������������������������������� Maxim Integrated Products 3 MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter ELECTRICAL CHARACTERISTICS (continued) (VIN = 24V, VGND = VPGND = 0V, CVIN = CVCC = 1FF, VEN = 1.5V, CSS = 3300pF, VFB = 0.98 x VOUT, LX = unconnected, RESET = unconnected. TA = TJ = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC. All voltages are referenced to GND, unless otherwise noted.) (Note 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS RESET RESET Output Level Low IRESET = 1mA 0.02 V RESET Output Leakage Current High VFB = 1.01 x VOUT, TA = +25NC 0.45 FA VOUT Threshold for RESET Assertion VOUT-OKF VFB falling 90.5 92.5 94.5 % VOUT Threshold for RESET Deassertion VOUT-OKR VFB rising 93.5 95.5 97.5 % RESET Deassertion Delay After FB Reaches 95% Regulation 1024 Cycles 165 NC 10 NC THERMAL SHUTDOWN Thermal-Shutdown Threshold Temperature rising Thermal-Shutdown Hysteresis Note 2: All limits are 100% tested at +25NC. Limits over temperature are guaranteed by design. Note 3: Guaranteed by design, not production tested. ����������������������������������������������������������������� Maxim Integrated Products 4 MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter Typical Operating Characteristics (VIN = 24V, VGND = VPGND = 0V, CVIN = CVCC = 1FF, VEN = 1.5V, CSS = 3300pF, VFB = 0.98 x VOUT, unless otherwise noted.) EFFICIENCY vs. LOAD CURRENT (MAX17501F) VIN = 48V VIN = 36V VIN = 48V VIN = 24V 75 VIN = 36V 65 70 VIN = 12V 55 3.290 5.005 5.000 4.995 VIN = 36V VIN = 12V 1.10 1.05 4.990 1.00 0.95 0.90 0.85 0.80 0.75 -40 -20 EN/UVLO THRESHOLD VOLTAGE vs. TEMPERATURE 1.21 1.20 RISING THRESHOLD 1.19 1.18 1.17 1.16 FALLING THRESHOLD 1.15 1.14 40 60 -40 -20 0 20 40 60 TEMPERATURE (°C) 80 100 120 4.85 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) OUTPUT VOLTAGE vs. TEMPERATURE (MAX17501E) OUTPUT VOLTAGE vs. TEMPERATURE (MAX17501F) 3.310 3.305 3.300 NO LOAD 3.295 FULL LOAD 3.290 5.05 5.04 5.03 5.02 NO LOAD 5.01 5.00 4.99 4.98 FULL LOAD 4.97 4.96 3.280 1.12 4.90 TEMPERATURE (°C) 3.285 1.13 4.95 4.80 80 100 120 3.315 OUTPUT VOLTAGE (V) 1.22 20 3.320 MAX17501 toc07 1.23 0 OUTPUT VOLTAGE (V) 50 100 150 200 250 300 350 400 450 500 LOAD CURRENT (mA) MAX17501 toc08 0 50 100 150 200 250 300 350 400 450 500 LOAD CURRENT (mA) 5.00 0.70 4.985 EN/UVLO THRESHOLD VOLTAGE (V) 0 NO-LOAD SWITCHING CURRENT vs. TEMPERATURE MAX17501 toc05 MAX17501 toc04 VIN = 48V VIN = 24V VIN = 12V 3.296 SHUTDOWN CURRENT vs. TEMPERATURE SHUTDOWN CURRENT (µA) OUTPUT VOLTAGE (V) 5.010 VIN = 24V 3.298 100 150 200 250 300 350 400 450 500 LOAD CURRENT (mA) OUTPUT VOLTAGE vs. LOAD CURRENT (MAX17501F) 5.015 3.300 3.292 65 100 150 200 250 300 350 400 450 500 LOAD CURRENT (mA) 3.302 3.294 VIN = 12V NO-LOAD SWITCHING CURRENT (mA) 60 3.304 MAX17501 toc06 VIN = 24V 80 VIN = 36V 3.306 MAX17501 toc09 70 85 VIN = 48V 3.308 OUTPUT VOLTAGE (V) 80 75 90 EFFICIENCY (%) 85 3.310 MAX17501 toc02 90 EFFICIENCY (%) 95 MAX17501 toc01 95 OUTPUT VOLTAGE vs. LOAD CURRENT (MAX17501E) MAX17501 toc03 EFFICIENCY vs. LOAD CURRENT (MAX17501E) 4.95 -40 -20 0 20 40 60 TEMPERATURE (°C) 80 100 120 -40 -20 0 20 40 60 80 100 120 TEMPERATURE (°C) ����������������������������������������������������������������� Maxim Integrated Products 5 MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter Typical Operating Characteristics (continued) (VIN = 24V, VGND = VPGND = 0V, CVIN = CVCC = 1FF, VEN = 1.5V, CSS = 3300pF, VFB = 0.98 x VOUT, unless otherwise noted.) RUNAWAY CURRENT LIMIT vs. TEMPERATURE 0.8 0.7 0.6 0.9 0.8 0.7 0.6 700 MAX17501 toc12 MAX17501 toc11 MAX17501 toc10 0.9 1.0 RUNAWAY CURRENT LIMIT (A) PEAK CURRENT LIMIT (A) 1.0 SWITCHING FREQUENCY vs. TEMPERATURE 680 SWITCHING FREQUENCY (kHz) PEAK CURRENT LIMIT vs. TEMPERATURE 660 640 620 600 580 560 540 520 0.5 0.5 -40 -20 0 20 40 60 100 120 80 500 -40 -20 0 20 40 60 80 100 120 -40 -20 0 20 40 60 100 120 80 TEMPERATURE (°C) TEMPERATURE (°C) TEMPERATURE (°C) SOFT-START/SHUTDOWN FROM EN/EVLO (MAX17501E) SOFT-START/SHUTDOWN FROM EN/EVLO (MAX17501F) SOFT-START FROM VIN (MAX17501E) MAX17501 toc13 EN/UVLO 2V/div VOUT 1V/div IOUT 200mA/div EN/UVLO 2V/div VIN 20V/div VOUT 2V/div IOUT 200mA/div IOUT 200mA/div VOUT 1V/div RESET 5V/div RESET 2V/div MAX17501 toc15 MAX17501 toc14 RESET 2V/div 1ms/div 1ms/div 400µs/div SOFT-START FROM VIN (MAX17501F) SOFT-START WITH 2V PREBIAS (MAX17501E) SOFT-START WITH 2.5V PREBIAS (MAX17501F) MAX17501 toc16 VIN 20V/div IOUT 200mA/div VOUT 2V/div RESET 5V/div 400µs/div MAX17501 toc18 MAX17501 toc17 EN/UVLO 2V/div EN/UVLO 2V/div VOUT 1V/div VOUT 1V/div RESET 2V/div RESET 5V/div 400µs/div 400µs/div ����������������������������������������������������������������� Maxim Integrated Products 6 MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter Typical Operating Characteristics (continued) (VIN = 24V, VGND = VPGND = 0V, CVIN = CVCC = 1FF, VEN = 1.5V, CSS = 3300pF, VFB = 0.98 x VOUT, unless otherwise noted.) LOAD TRANSIENT RESPONSE OF MAX17501E (LOAD CURRENT STEPPED FROM NO LOAD TO 250mA) LOAD TRANSIENT RESPONSE OF MAX17501F (LOAD CURRENT STEPPED FROM NO LOAD TO 250mA) LOAD TRANSIENT RESPONSE OF MAX17501E (LOAD CURRENT STEPPED FROM 250mA TO 500mA) MAX17501 toc20 MAX17501 toc21 MAX17501 toc19 VOUT (AC) 100mV/div VOUT (AC) 50mV/div VOUT (AC) 50mV/div IOUT 200mA/div IOUT 200mA/div IOUT 100mA/div 20µs/div 20µs/div 20µs/div LOAD TRANSIENT RESPONSE OF MAX17501F (LOAD CURRENT STEPPED FROM 250mA TO 500mA) SWITCHING WAVEFORMS OF MAX17501F AT 500mA LOAD OUTPUT OVERLOAD PROTECTION OF MAX17501F MAX17501 toc23 MAX17501 toc22 MAX17501 toc24 VOUT (AC) 50mV/div VOUT (AC) 100mV/div VOUT 2V/div ILX 500mA/div IOUT 200mA/div LX 10V/div 2µs/div 20µs/div BODEPLOT OF MAX17501E AT 500mA LOAD MAX17501 toc25 BW = 62kHz PM = 59° 4 5 6 7 8 91 IOUT 200mA/div 20ms/div BODEPLOT OF MAX17501F AT 500mA LOAD MAX17501 toc26 BW = 35kHz PM = 73° 2 3 4 5 6 7 891 2 4 5 6 7 8 91 2 3 4 5 6 7 891 2 ����������������������������������������������������������������� Maxim Integrated Products 7 MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter Pin Configuration TOP VIEW MAX17501 10 LX 2 9 GND EN/UVLO 3 8 RESET VCC 4 7 N.C. FB 5 6 SS PGND 1 VIN + EP* TDFN (3mm x 2mm) *EP = EXPOSED PAD, CONNECTED TO GND Pin Description PIN NAME FUNCTION Power Ground. Connect PGND externally to the power ground plane. Connect GND and PGND pins together at the ground return path of the VCC bypass capacitor. 1 PGND 2 VIN 3 EN/UVLO 4 VCC 5 FB 5V LDO Output. Bypass VCC with 1FF ceramic capacitance to GND. Feedback Input. Directly connect FB to the output. 6 SS Soft-Start Input. Connect a capacitor from SS to GND to set the soft-start time. 7 N.C. 8 RESET 9 GND 10 LX Switching Node. Connect LX to the switching side of the inductor. LX is high impedance when the device is in shutdown mode. — EP Exposed Pad. Connect to the GND pin of the IC. Connect to a large copper plane below the IC to improve heat dissipation capability. Power-Supply Input. The input supply range is from 4.5V to 60V. Enable/Undervoltage Lockout Input. Drive EN/UVLO high to enable the output voltage. Connect to the center of resistive divider between VIN and GND to set the input voltage (undervoltage threshold) at which the device turns on. Pull up to VIN for always on. No Connection. Leave unconnected. Open-Drain RESET Output. The RESET output is driven low if FB drops below 92.5% of its set value. RESET goes high 1024 clock cycles after FB rises above 95.5% of its set value. Analog Ground ����������������������������������������������������������������� Maxim Integrated Products 8 MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter Block Diagram VCC PGND N DRIVER 5µA SS LX MAX17501 HICCUP SS P DRIVER VIN CURRENT SENSE VCC PWM COMPARATOR LDO CLK PWM LOGIC OSC COMP HICCUP SLOPE COMPENSATION START EN/UVLO RESET LOGIC SS 900mV RESET COMP REFERENCE SWITCHOVER LOGIC GM FB INTERNAL COMPENSATION GND ����������������������������������������������������������������� Maxim Integrated Products 9 MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter Detailed Description The MAX17501 step-down regulator operates from 4.5V to 60V and delivers up to 500mA load current. Output voltage regulation accuracy meets Q1.6% over load, line, and temperature. The device uses a peak-current-mode-control scheme. It employs synchronous rectification. An internal transconductance error amplifier produces an integrated error voltage. The error voltage sets the duty cycle using a PWM comparator, a high-side current-sense amplifier, and a slope-compensation generator. At each rising edge of the clock, the high-side p-channel 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 n-channel MOSFET turns on. The inductor releases the stored energy as its current ramps down, and provides current to the output (the internal low RDSON pMOS/ nMOS switches ensure high efficiency at full load). This device also integrates enable/undervoltage lockout (EN/UVLO), adjustable soft-start time (SS), and opendrain reset output (RESET) functionality. 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 VCC linear regulator should be bypassed with a 1FF ceramic capacitor to GND. The device employs an undervoltage-lockout circuit that disables the internal linear regulator when VCC falls below 3.7V (typ). The 300mV UVLO hysteresis prevents chattering on power-up/power-down. The internal VCC linear regulator can source up to 40mA (typ) to supply the device and to power the low-side gate driver. Switching Frequency The devices have a fixed 600kHz switching frequency. The minimum duty ratio at which the devices can operate is 7.7%. Overcurrent Protection/Hiccup Mode The device is provided with a robust overcurrentprotection 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 800mA (typ). A runaway-current limit on the highside switch current at 900mA (typ) protects the device under high input voltage, short-circuit conditions when there is insufficient output voltage available to restore the inductor current that built up during the on period of the step-down converter. One occurrence of the runawaycurrent limit triggers a hiccup mode. In addition, if due to a fault condition, output voltage drops to 71.1% (typ) of its nominal value 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. RESET Output The device includes a RESET comparator to monitor the output voltage. The open-drain RESET output requires an external pullup resistor. RESET can sink 2mA of current while low. RESET goes high (high impedance) 1024 switching cycles after the regulator output increases above 95.5% of the designed nominal regulated voltage. RESET goes low when the regulator output voltage drops to below 92.5% of the nominal regulated voltage. RESET goes low during thermal shutdown. Prebiased Output When the device starts into a prebiased output, both the high-side and 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 first with the high-side switch. The output voltage is then smoothly ramped up to the target value in alignment with the internal reference. Thermal-Overload Protection Thermal-overload protection limits total power dissipation in the device. When the junction temperature of the device exceeds +165NC, 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 10NC. Soft-start resets during thermal shutdown. Carefully evaluate the total power dissipation (see the Power Dissipation section) to avoid unwanted triggering of the thermal-overload protection in normal operation. ���������������������������������������������������������������� Maxim Integrated Products 10 MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter Applications Information Input Capacitor Selection The discontinuous input-current waveform of the buck converter causes large ripple currents in the input capacitor. The switching frequency, peak inductor current, and the allowable peak-to-peak voltage ripple that reflects back to the source dictate the capacitance requirement. The device’s high switching frequency allows the use of smaller value input capacitors. X7R capacitors are recommended in industrial applications for their temperature stability. A minimum value of 1FF should be used for the input capacitor. Higher values help reduce the ripple on the input DC bus further. In applications where the source is located distant from the device input, an electrolytic capacitor should be added in parallel to the 1FF ceramic capacitor to provide necessary damping for potential oscillations caused by 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). To determine the inductance value, select the ratio of inductor peak-to-peak ripple current to the DC average current (LIR). For LIR values that are too high, the RMS currents are high, and therefore the inductor I2R losses are high. For LIR values that are too low, the inductance values are high and consequently the inductor DC resistance is also high, and therefore inductor I2R losses are high as well. A good compromise between size and loss is a 30% peak-to-peak ripple current to average-current ratio (LIR = 0.3). The switching frequency, input voltage, output voltage, and selected LIR determine the inductor value as follows: L= VOUT × (VIN - VOUT ) where VIN, VOUT, and IOUT are nominal values. The switching frequency is 600kHz for the MAX17501E/ MAX17501F. 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 (IPEAK-LIMIT (typ) = 0.8A for the device). A variety of inductors from different suppliers are available to meet this requirement (e.g., inductors from the Coilcraft LPS6235 series). See Table 1 to select inductors for 5V and 3.3V fixed output-voltage applications based on the MAX17501E/ MAX17501F. Output Capacitor Selection X7R ceramic output capacitors are preferred due to their stability over temperature in industrial applications. The output capacitor is usually sized to support a step load of 50% of the maximum output current in the application, such that the output-voltage deviation is contained to 3% of the output-voltage change. The output capacitance can be calculated as follows: C OUT= 1 I STEP × t RESPONSE × ∆VOUT 2 t RESPONSE ≅ ( 0.33 fC + 1 fSW ) where ISTEP is the load current step, tRESPONSE is the response time of the controller, DVOUT is the allowable output-voltage deviation, fC is the target closed-loop crossover frequency, and fSW is the switching frequency. fC is generally chosen to be 1/8 to 1/10 of fSW. Use Table 2 to select output capacitors for fixed 5V and 3.3V output-voltage applications based on the MAX17501E/MAX17501F. VIN × fSW × IOUT × LIR Table 1. Inductor Selection VOUT (V) IOUT (max) (mA) L (µH) MINIMUM ISAT (mA) SUGGESTED PART 5 500 47 800 Coilcraft LPS6235-473ML_ 3.3 500 33 800 Coilcraft LPS6235-333ML_ ���������������������������������������������������������������� Maxim Integrated Products 11 MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter Table 2. Output Capacitor Selection VOUT (V) IOUT (max) (mA) TYPE VOLTAGE RATING (V) 5 500 10FF/1206/X7R 6.3 Murata GRM31CR70J106KA01L 3.3 500 10FF/1206/X7R 6.3 Murata GRM31CR70J106KA01L Soft-Start Capacitor Selection The device implements adjustable soft-start operation for the synchronous step-down converter. A capacitor connected from the SS pin to GND programs the soft-start period. The soft-start time (tSS) is related to the capacitor connected at SS (CSS) by the following equation: C= SS 5.55 × t SS where tSS is in milliseconds and CSS is in nanofarads. For example, to have a 1.8ms soft-start time, a 10nF capacitor should be connected from the SS pin to GND. Setting the Input Undervoltage Lockout Level The device offers an adjustable input undervoltagelockout level. Set the voltage at which the device turns on with a resistive voltage-divider connected from VIN to GND (see Figure 1). Connect the center node of the divider to EN/UVLO. Choose R1 to be 3.3MI, and then calculate R2 as follows: R2 = R1× 1.218 (VINU -1.218) where VINU is the voltage at which the device is required to turn on. VIN SUGGESTED PART Power Dissipation It should be ensured that the junction temperature of the device does not exceed +125NC under the operating conditions specified for the power supply. At a particular operating condition, the power losses that lead to temperature rise of the device are estimated as follows: ( 1 2 PLOSS =× POUT -1 - IOUT × R DCR η P= OUT VOUT × IOUT ) where POUT is the output power, E is is the efficiency of the device, and RDCR is the DC resistance of the output Inductor (see the Typical Operating Characteristics for more information on efficiency at typical operating conditions). The maximum power that can be dissipated in the device’s 10-pin TDFN-EP package is 1188.7mW at +70NC temperature. The power dissipation capability should be derated as the temperature goes above +70NC at 14.9mW/NC. For a multilayer board, the thermal performance metrics for the package are given below: BJA = 67.3NC/W BJC = 18.2NC/W The junction temperature of the device can be estimated at any given maximum ambient temperature (TA_MAX) from the following equation: TJ_MAX = TA_MAX + (θ JA × PLOSS ) R1 EN/UVLO R2 GND Figure 1. Adjustable EN/UVLO Network 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 + (θ JC × PLOSS ) ���������������������������������������������������������������� Maxim Integrated Products 12 MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter 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 pin of the device. This eliminates as much trace inductance effects as possible and gives the device a cleaner voltage supply. The bypass capacitor for the VCC pin should also be placed close to the pin to reduce effects of trace impedance. The feedback trace should be routed as far as possible from the inductor. When routing the circuitry around the device, 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 minimum, typically the return terminal of the VCC bypass capacitor. This helps to keep the analog ground quiet. The ground plane should be kept continuous/ unbroken as much 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 device, for efficient heat dissipation. Several vias in parallel have lower impedance than a single via. For a sample layout that ensures first-pass success, refer to the MAX17501 evaluation kit layout available at www.maxim-ic.com. ���������������������������������������������������������������� Maxim Integrated Products 13 MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter Typical Applications Circuits VIN 24V ±20% L1 47µH LX VIN C1 1µF 1206 C4 10µF, 6.3V 1206 R1 3.32MI 1 JU1 2 3 PGND EN/UVLO R2 866kI VOUT 5V, 500mA MAX17501F GND VCC C2 1µF FB SS C3 3300pF N.C. RESET RESET Figure 2. MAX17501F Application Circuit (5V Output, 500mA Maximum Load Current, 600kHz Switching Frequency) VIN 24V ±20% L1 33µH LX VIN C1 1µF 1206 1 JU1 2 3 C4 10µF, 6.3V 1206 R1 3.32MI EN/UVLO R2 866kI VOUT 3.3V, 500mA PGND MAX17501E GND VCC C2 1µF C3 3300pF SS N.C. FB RESET RESET Figure 3. MAX17501E Application Circuit (3.3V Output, 500mA Maximum Load Current, 600kHz Switching Frequency) ���������������������������������������������������������������� Maxim Integrated Products 14 MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter Ordering Information /Selector Guide PART PIN-PACKAGE OUTPUT VOLTAGE SWITCHING FREQUENCY PEAK-CURRENT-MODE CONTROL SCHEME OUTPUT CURRENT MAX17501EATB+ 10 TDFN-EP* 3.3V 600kHz Forced PWM 500mA MAX17501FATB+ 10 TDFN-EP* 5V 600kHz Forced PWM 500mA Note: All devices are specified over the -40°C to +125°C operating temperature range. Optional variants available to support adjustable output and PFM. Contact your Maxim sales representative for more information. +Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. Chip Information PROCESS: BiCMOS Package Information For the latest package outline information and land patterns (footprints), go to www.maxim-ic.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. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 10 TDFN-EP T1032N+1 21-0429 90-0082 ���������������������������������������������������������������� Maxim Integrated Products 15 MAX17501 60V, 500mA, Ultra-Small, High-Efficiency, Synchronous Step-Down DC-DC Converter Revision History REVISION NUMBER REVISION DATE 0 5/12 DESCRIPTION Initial release PAGES CHANGED — 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 Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2012 Maxim Integrated Products 16 Maxim is a registered trademark of Maxim Integrated Products, Inc.