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19-2988; Rev 2; 5/04 MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter General Description The MAX5035 easy-to-use, high-efficiency, high-voltage, step-down DC-DC converter operates from an input voltage up to 76V and consumes only 270µA quiescent current at no load. This pulse-width modulated (PWM) converter operates at a fixed 125kHz switching frequency at heavy loads, and automatically switches to pulse-skipping mode to provide low quiescent current and high efficiency at light loads. The MAX5035 includes internal frequency compensation simplifying circuit implementation. The device uses an internal lowon-resistance, high-voltage, DMOS transistor to obtain high efficiency and reduce overall system cost. This device includes undervoltage lockout, cycle-by-cycle current limit, hiccup mode output short-circuit protection, and thermal shutdown. The MAX5035 delivers up to 1A output current. The output current may be limited by the maximum power dissipation capability of the package. External shutdown is included, featuring 10µA (typ) shutdown current. The MAX5035A/B/C versions have fixed output voltages of 3.3V, 5V, and 12V, respectively, while the MAX5035D features an adjustable output voltage from 1.25V to 13.2V. The MAX5035 is available in space-saving 8-pin SO and 8-pin plastic DIP packages and operates over the automotive (-40°C to +125°C) temperature range. Automotive Consumer Electronics Industrial Distributed Power Applications Typical Operating Circuit VIN 7.5V TO 76V 68µF VIN BST R1 ON R2 OFF MAX5035 LX ON/OFF SGND FB VD GND 0.1µF 100µH D1 50SQ100 0.1µF VOUT 5V 68µF Features ♦ Wide 7.5V to 76V Input Voltage Range ♦ Fixed (3.3V, 5V, 12V) and Adjustable (1.25V to 13.2V) Versions ♦ 1A Output Current ♦ Efficiency Up to 94% ♦ Internal 0.4Ω High-Side DMOS FET ♦ 270µA Quiescent Current at No Load, 10µA Shutdown Current ♦ Internal Frequency Compensation ♦ Fixed 125kHz Switching Frequency ♦ Thermal Shutdown and Short-Circuit Current Limit ♦ 8-Pin SO and PDIP Packages Ordering Information PART MAX5035AUSA MAX5035AUPA MAX5035AASA MAX5035BUSA MAX5035BUPA MAX5035BASA MAX5035CUSA MAX5035CUPA MAX5035CASA MAX5035DUSA MAX5035DUPA MAX5035DASA TEMP RANGE PINPACKAGE OUTPUT VOLTAGE (V) 0°C to +85°C 8 SO 0°C to +85°C 8 PDIP 3.3 -40°C to +125°C 8 SO 0°C to +85°C 8 SO 0°C to +85°C 8 PDIP 5.0 -40°C to +125°C 8 SO 0°C to +85°C 8 SO 0°C to +85°C 8 PDIP 12 -40°C to +125°C 8 SO 0°C to +85°C 8 SO 0°C to +85°C 8 PDIP ADJ -40°C to +125°C 8 SO Pin Configuration TOP VIEW BST 1 VD 2 SGND 3 FB 4 MAX5035 SO/PDIP 8 LX 7 VIN 6 GND 5 ON/OFF ________________________________________________________________ Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter MAX5035 ABSOLUTE MAXIMUM RATINGS (Voltages referenced to GND, unless otherwise specified.) VIN .........................................................................-0.3V to +80V SGND ....................................................................-0.3V to +0.3V LX.................................................................-0.8V to (VIN + 0.3V) BST ...............................................................-0.3V to (VIN + 10V) BST (transient < 100ns) ................................-0.3V to (VIN + 15V) BST to LX................................................................-0.3V to +10V BST to LX (transient < 100ns) ................................-0.3V to +15V ON/OFF........................................................-0.3V to (VIN + 0.3V) VD...........................................................................-0.3V to +12V FB MAX5035A/MAX5035B/MAX5035C ...................-0.3V to +15V MAX5035D .........................................................-0.3V to +12V VOUT Short-Circuit Duration...........................................Indefinite VD Short-Circuit Duration ..............................................Indefinite Continuous Power Dissipation (TA = +70°C) 8-Pin PDIP (derate 9.1mW/°C above +70°C)...............727mW 8-Pin SO (derate 5.9mW/°C above +70°C)..................471mW Operating Temperature Range MAX5035_U_ _ ...................................................0°C to +85°C MAX5035_A_ _ ..............................................-40°C to +125°C Storage Temperature Range .............................-65°C to +150°C Junction Temperature ......................................................+150°C Lead Temperature (soldering, 10s) .................................+300°C 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. ELECTRICAL CHARACTERISTICS (MAX5035_U_ _) (VIN = +12V, VON/OFF = +12V, IOUT = 0, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Application Circuit.) PARAMETER Input Voltage Range Undervoltage Lockout Output Voltage Feedback Voltage Efficiency Quiescent Supply Current Shutdown Current Peak Switch Current Limit Switch Leakage Current Switch On-Resistance SYMBOL VIN UVLO VOUT VFB η IQ ISHDN ILIM IOL RDS(ON) MAX5035A MAX5035B MAX5035C MAX5035D CONDITIONS MAX5035A VIN = 7.5V to 76V, IOUT = 20mA to 1A MAX5035B VIN = 7.5V to 76V, IOUT = 20mA to 1A MAX5035C VIN = 15V to 76V, IOUT = 20mA to 1A VIN = 7.5V to 76V, MAX5035D VIN = 12V, ILOAD = 0.5A, MAX5035A VIN = 12V, ILOAD = 0.5A, MAX5035B VIN = 24V, ILOAD = 0.5A, MAX5035C VIN = 12V, VOUT = 5V, ILOAD = 0.5A, MAX5035D VFB = 3.5V, VIN = 7.5V to 76V, MAX5035A VFB = 5.5V, VIN = 7.5V to 76V, MAX5035B VFB = 13V, VIN = 15V to 76V, MAX5035C VFB = 1.3V, MAX5035D VON/OFF = 0V, VIN = 7.5V to 76V (Note 1) VIN = 76V, VON/OFF = 0V, VLX = 0V ISWITCH = 1A MIN 7.5 7.5 15 7.5 3.185 TYP 5.2 3.3 MAX 76.0 76.0 76 76.0 UNITS V V 3.415 4.85 5.0 5.15 V 11.64 12 12.36 1.192 1.221 1.250 V 86 90 94 % 90 270 440 270 440 µA 270 440 270 440 10 45 µA 1.30 1.80 2.50 A 1 µA 0.40 0.80 Ω 2 _______________________________________________________________________________________ MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter ELECTRICAL CHARACTERISTICS (continued) (MAX5035_U_ _) (VIN = +12V, VON/OFF = +12V, IOUT = 0, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Application Circuit.) PARAMETER SYMBOL CONDITIONS PFM Threshold FB Input Bias Current ON/OFF CONTROL INPUT ON/OFF Input-Voltage Threshold ON/OFF Input-Voltage Hysteresis ON/OFF Input Current OSCILLATOR IPFM IB Minimum switch current in any cycle MAX5035D VON/OFF VHYST ION/OFF Rising trip point VON/OFF = 0V to VIN Oscillator Frequency Maximum Duty Cycle VOLTAGE REGULATOR fOSC DMAX MAX5035D Regulator Output Voltage VD Dropout Voltage Load Regulation ∆VD/∆IVD PACKAGE THERMAL CHARACTERISTICS VIN = 8.5V to 76V, IL = 0 7.5V ≤ VIN ≤ 8.5V, IL = 1mA 0 to 5mA Thermal Resistance (Junction to Ambient) SO package (JEDEC 51) θJA DIP package (JEDEC 51) THERMAL SHUTDOWN Thermal-Shutdown Junction Temperature TSH Thermal-Shutdown Hysteresis THYST MIN 55 -150 TYP 85 +0.01 MAX 130 +150 UNITS mA nA 1.53 1.69 1.85 V 100 mV 10 150 nA 109 125 135 kHz 95 % 6.9 7.8 8.8 V 2.0 V 150 Ω 170 °C/W 110 +160 °C 20 °C ELECTRICAL CHARACTERISTICS (MAX5035_A_ _) (VIN = +12V, VON/OFF = +12V, IOUT = 0, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Application Circuit.) (Note 2) PARAMETER Input Voltage Range Undervoltage Lockout Output Voltage Feedback Voltage SYMBOL VIN UVLO VOUT VFB MAX5035A MAX5035B MAX5035C MAX5035D CONDITIONS MAX5035A VIN = 7.5V to 76V, IOUT = 20mA to 1A MAX5035B VIN = 7.5V to 76V, IOUT = 20mA to 1A MAX5035C VIN = 15V to 76V, IOUT = 20mA to 1A VIN = 7.5V to 76V, MAX5035D MIN 7.5 7.5 15 7.5 3.185 TYP 5.2 3.3 MAX 76.0 76.0 76 76.0 UNITS V V 3.415 4.825 5.0 5.175 V 11.58 12 12.42 1.192 1.221 1.250 V _______________________________________________________________________________________ 3 MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter ELECTRICAL CHARACTERISTICS (MAX5035_A_ _) (VIN = +12V, VON/OFF = +12V, IOUT = 0, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Application Circuit.) (Note 2) PARAMETER Efficiency SYMBOL η Quiescent Supply Current IQ Shutdown Current Peak Switch Current Limit Switch Leakage Current Switch On-Resistance PFM Threshold FB Input Bias Current ON/OFF CONTROL INPUT ON/OFF Input-Voltage Threshold ON/OFF Input-Voltage Hysteresis ON/OFF Input Current OSCILLATOR ISHDN ILIM IOL RDS(ON) IPFM IB VON/OFF VHYST ION/OFF Oscillator Frequency Maximum Duty Cycle VOLTAGE REGULATOR fOSC DMAX Regulator Output Voltage VD Dropout Voltage Load Regulation ∆VD/∆IVD PACKAGE THERMAL CHARACTERISTICS Thermal Resistance (Junction to Ambient) θJA THERMAL SHUTDOWN Thermal-Shutdown Junction Temperature TSH Thermal-Shutdown Hysteresis THYST CONDITIONS VIN = 12V, ILOAD = 0.5A, MAX5035A VIN = 12V, ILOAD = 0.5A, MAX5035B VIN = 24V, ILOAD = 0.5A, MAX5035C VIN = 12V, VOUT = 5V, ILOAD = 0.5A, MAX5035D VFB = 3.5V, VIN = 7.5V to 76V, MAX5035A VFB = 5.5V, VIN = 7.5V to 76V, MAX5035B VFB = 13V, VIN = 15V to 76V, MAX5035C VFB = 1.3V, MAX5035D VON/OFF = 0V, VIN = 7.5V to 76V (Note 1) VIN = 76V, VON/OFF = 0V, VLX = 0V ISWITCH = 1A Minimum switch current in any cycle MAX5035D Rising trip point VON/OFF = 0V to VIN MAX5035D VIN = 8.5V to 76V, IL = 0 7.5V ≤ VIN ≤ 8.5V, IL = 1mA 0 to 5mA SO package (JEDEC 51) DIP package (JEDEC 51) Note 1: Switch current at which current limit is activated. Note 2: All limits at -40°C are guaranteed by design, not production tested. MIN 1.30 55 -150 TYP MAX 86 90 94 90 270 270 270 270 10 1.80 1 0.40 85 +0.01 440 440 440 440 45 2.50 0.80 130 +150 UNITS % µA µA A µA Ω mA nA 1.50 1.69 1.85 V 100 mV 10 150 nA 105 125 137 kHz 95 % 6.5 7.8 9.0 V 2.0 V 150 Ω 170 °C/W 110 +160 °C 20 °C 4 _______________________________________________________________________________________ MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter Typical Operating Characteristics (VIN = 12V, VON/OFF = 12V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Application Circuit, if applicable.) MAX5035 toc03 VOUT (V) VOUT vs. TEMPERATURE (MAX5035AASA, VOUT = 3.3V) 3.40 IOUT = 0.1A 3.36 IOUT = 1A 3.32 3.28 3.24 3.20 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (°C) MAX5035 toc01 VOUT (V) VOUT vs. TEMPERATURE (MAX5035DASA, VOUT = 5V) 5.20 5.15 5.10 5.05 IOUT = 0.1A 5.00 4.95 IOUT = 1A 4.90 4.85 4.80 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (°C) MAX5035 toc02 OUTPUT VOLTAGE (V) LINE REGULATION (MAX5035AASA, VOUT = 3.3V) 3.40 IOUT = 0.1A 3.36 IOUT = 1A 3.32 3.28 3.24 3.20 5 20 35 50 65 80 INPUT VOLTAGE (V) OUTPUT VOLTAGE (V) LINE REGULATION (MAX5035DASA, VOUT = 5V) 5.20 5.15 5.10 5.05 IOUT = 0.1A 5.00 4.95 IOUT = 1A 4.90 4.85 4.80 5 20 35 50 65 80 INPUT VOLTAGE (V) MAX5035 toc04 VOUT (V) MAX5035 toc05 LOAD REGULATION (MAX5035AASA, VOUT = 3.3V) 3.40 VIN = 76V 3.36 VIN = 7.5V, 24V 3.32 3.28 3.24 3.20 0 200 400 600 800 1000 ILOAD (mA) VOUT (V) LOAD REGULATION (MAX5035DASA, VOUT = 5V) 5.10 MAX5035 toc06 5.05 VIN = 24V VIN = 7.5V 5.00 VIN = 76V 4.95 4.90 0 200 400 600 800 1000 ILOAD (mA) _______________________________________________________________________________________ 5 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter MAX5035 EFFICIENCY (%) Typical Operating Characteristics (continued) (VIN = 12V, VON/OFF = 12V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Application Circuit, if applicable.) EFFICIENCY vs. LOAD CURRENT (MAX5035AASA, VOUT = 3.3V) 100 90 80 70 60 VIN = 7.5V 50 VIN = 12V 40 VIN = 24V 30 VIN = 48V 20 VIN = 76V 10 0 0 200 400 600 800 1000 LOAD CURRENT (mA) OUTPUT CURRENT LIMIT vs. TEMPERATURE 2.0 MAX5035 toc07 EFFICIENCY (%) EFFICIENCY vs. LOAD CURRENT (MAX5035DASA, VOUT = 5V) 100 90 80 70 60 VIN = 7.5V 50 VIN = 12V 40 VIN = 24V 30 VIN = 48V 20 VIN = 76V 10 0 0 200 400 600 800 1000 LOAD CURRENT (mA) OUTPUT CURRENT LIMIT vs. INPUT VOLTAGE 2.0 MAX5035 toc08 EFFICIENCY (%) EFFICIENCY vs. LOAD CURRENT (MAX5035DASA, VOUT = 12V) 100 MAX5035 toc09 90 80 70 VIN = 15V 60 VIN = 24V 50 40 VIN = 48V 30 VIN = 76V 20 10 0 0 200 400 600 800 1000 LOAD CURRENT (mA) QUIESCENT SUPPLY CURRENT vs. TEMPERATURE 350 MAX5035 toc12 MAX5035 toc11 QUIESCENT SUPPLY CURRENT (µA) MAX5035 toc10 OUTPUT CURRENT LIMIT (A) OUTPUT CURRENT LIMIT (A) 1.5 1.0 0.5 0 -50 -25 MAX5035DASA VOUT = 5V 5% DROP IN VOUT 0 25 50 75 100 125 150 TEMPERATURE (°C) QUIESCENT SUPPLY CURRENT vs. INPUT VOLTAGE 350 1.7 1.4 1.1 0.8 0.5 5 25 MAX5035DASA VOUT = 5V 5% DROP IN VOUT 20 35 50 65 80 INPUT VOLTAGE (V) SHUTDOWN CURRENT vs. TEMPERATURE 320 290 260 230 200 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (°C) SHUTDOWN CURRENT vs. INPUT VOLTAGE 20 MAX5035 toc15 MAX5035 toc14 SHUTDOWN CURRENT (µA) MAX5035 toc13 SHUTDOWN CURRENT (µA) QUIESCENT SUPPLY CURRENT (µA) 320 20 16 290 15 12 260 10 8 230 5 4 200 6 16 26 36 46 56 66 76 INPUT VOLTAGE (V) 0 -50 -25 0 25 50 75 100 125 150 TEMPERATURE (°C) 0 6 16 26 36 46 56 66 76 INPUT VOLTAGE (V) 6 _______________________________________________________________________________________ MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter Typical Operating Characteristics (continued) (VIN = 12V, VON/OFF = 12V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Application Circuit, if applicable.) VOUT (V) MAX5035 toc16 OUTPUT VOLTAGE vs. INPUT VOLTAGE 15 MAX5035DASA VOUT = 12V 12 VON/OFF = VIN 9 MAX5035DASA LOAD-TRANSIENT RESPONSE MAX5035 toc17 VOUT = 5V A MAX5035DASA LOAD-TRANSIENT RESPONSE MAX5035 toc18 VOUT = 5V A 6 IOUT = 1A 3 IOUT = 0.3A B B IOUT = 0 0 0 3 6 9 12 15 VIN (V) 400µs/div A: VOUT, 200mV/div, AC-COUPLED B: IOUT, 500mA/div, 0.1A TO 1A 400µs/div A: VOUT, 200mV/div, AC-COUPLED B: IOUT, 500mA/div, 0.5A TO 1A MAX5035DASA LOAD-TRANSIENT RESPONSE MAX5035 toc19 VOUT = 5V A MAX5035DASA LX WAVEFORMS MAX5035 toc20 A 0 400µs/div A: VOUT, 200mV/div, AC-COUPLED B: IOUT, 500mA/div, 0.1A TO 0.5A B B 0 4µs/div A: SWITCH VOLTAGE (LX PIN), 20V/div (VIN = 48V) B: INDUCTOR CURRENT, 500mA/div (IOUT = 1A) MAX5035DASA LX WAVEFORMS MAX5035 toc21 A 0 B 0 4µs/div A: SWITCH VOLTAGE (LX PIN), 20V/div (VIN = 48V) B: INDUCTOR CURRENT, 200mA/div (IOUT = 100mA) _______________________________________________________________________________________ 7 MAX5035 PEAK SWITCH CURRENT LIMIT (A) MAX5035 toc25 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter Typical Operating Characteristics (continued) (VIN = 12V, VON/OFF = 12V, TA = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Application Circuit, if applicable.) MAX5035DASA LX WAVEFORMS MAX5035 toc22 MAX5035DASA STARTUP WAVEFORM (IO = 0) MAX5035 toc23 A 0 B 0 4µs/div A: SWITCH VOLTAGE (LX PIN), 20V/div (VIN = 48V) B: INDUCTOR CURRENT, 200mA/div (IOUT = 0) A 0 B 0 A: VON/OFF, 2V/div B: VOUT, 2V/div 1ms/div MAX5035DASA STARTUP WAVEFORM (IO = 1A) MAX5035 toc24 A 0 B 0 A: VON/OFF, 2V/div B: VOUT, 2V/div 1ms/div PEAK SWITCH CURRENT LIMIT vs. INPUT VOLTAGE 3.0 2.5 2.0 1.5 1.0 0.5 6 MAX5035DASA VOUT = 5V 5% DROP IN VOUT 16 26 36 46 56 66 76 INPUT VOLTAGE (V) 8 _______________________________________________________________________________________ MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter Pin Description PIN NAME FUNCTION 1 BST Boost Capacitor Connection. Connect a 0.1µF ceramic capacitor from BST to LX. 2 VD Internal Regulator Output. Bypass VD to GND with a 0.1µF ceramic capacitor. 3 SGND Internal Connection. SGND must be connected to GND. Output Sense Feedback Connection. For fixed output voltage (MAX5035A, MAX5035B, MAX5035C), 4 FB connect FB to VOUT. For adjustable output voltage (MAX5035D), use an external resistive voltage-divider to set VOUT. VFB regulating set point is 1.22V. 5 ON/OFF Shutdown Control Input. Pull ON/OFF low to put the device in shutdown mode. Drive ON/OFF high for normal operation. 6 GND Ground 7 VIN Input Voltage. Bypass VIN to GND with a low ESR capacitor as close to the device as possible. 8 LX Source Connection of Internal High-Side Switch ON/OFF Block Diagram VIN 1.69V VD ENABLE REGULATOR (FOR ANALOG) REGULATOR (FOR DRIVER) VREF OSC RAMP CPFM CILIM IREF-PFM HIGH-SIDE CURRENT SENSE IREF-LIM BST MAX5035 FB Rh RAMP CLK CONTROL LOGIC x1 TYPE 3 COMPENSATION Rl VREF EAMP CPWM THERMAL SHUTDOWN GND LX SGND _______________________________________________________________________________________ 9 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter MAX5035 Detailed Description The MAX5035 step-down DC-DC converter operates from a 7.5V to 76V input voltage range. A unique voltage-mode control scheme with voltage feed-forward and an internal switching DMOS FET provides high efficiency over a wide input voltage range. This pulsewidth modulated converter operates at a fixed 125kHz switching frequency. The device also features automatic pulse-skipping mode to provide low quiescent current and high efficiency at light loads. Under no load, the MAX5035 consumes only 270µA, and in shutdown mode, consumes only 10µA. The MAX5035 also features undervoltage lockout, hiccup mode output shortcircuit protection, and thermal shutdown. Shutdown Mode Drive ON/OFF to ground to shut down the MAX5035. Shutdown forces the internal power MOSFET off, turns off all internal circuitry, and reduces the VIN supply current to 10µA (typ). The ON/OFF rising threshold is 1.69V (typ). Before any operation begins, the voltage at ON/OFF must exceed 1.69V (typ). The ON/OFF input has 100mV hysteresis. Undervoltage Lockout (UVLO) Use the ON/OFF function to program the UVLO threshold at the input. Connect a resistive voltage-divider from VIN to GND with the center node to ON/OFF as shown in Figure 1. Calculate the threshold value by using the following formula: VUVLO(TH) = 1 + R1 R2  × 1.85V The minimum recommended VUVLO(TH) is 6.5V, 7.5V, and 13V for the output voltages of 3.3V, 5V, and 12V, respectively. The recommended value for R2 is less than 1MΩ. If the external UVLO threshold-setting divider is not used, an internal undervoltage-lockout feature monitors the supply voltage at VIN and allows operation to start when VIN rises above 5.2V (typ). This feature can be used only when VIN rise time is faster than 2ms. For slower VIN rise time, use the resistive-divider at ON/OFF. Boost High-Side Gate Drive (BST) Connect a flying bootstrap capacitor between LX and BST to provide the gate-drive voltage to the high-side N-channel DMOS switch. The capacitor is alternately charged from the internally regulated output voltage VD and placed across the high-side DMOS driver. Use a 0.1µF, 16V ceramic capacitor located as close to the device as possible. On startup, an internal low-side switch connects LX to ground and charges the BST capacitor to VD. Once the BST capacitor is charged, the internal low-side switch is turned off and the BST capacitor voltage provides the necessary enhancement voltage to turn on the high-side switch. Thermal-Overload Protection The MAX5035 features integrated thermal overload protection. Thermal overload protection limits total power dissipation in the device, and protects the device in the event of a fault condition. When the die temperature exceeds +160°C, an internal thermal sensor signals the shutdown logic, turning off the internal power MOSFET and allowing the IC to cool. The thermal sensor turns the internal power MOSFET back on after the IC’s die temperature cools down to +140°C, resulting in a pulsed output under continuous thermal overload conditions. Applications Information Setting the Output Voltage The MAX5035A/B/C have preset output voltages of 3.3V, 5.0V, and 12V, respectively. Connect FB to the preset output voltage (see the Typical Operating Circuit). The MAX5035D offers an adjustable output voltage. Set the output voltage with a resistive voltage-divider connected from the circuit’s output to ground (Figure 1). Connect the center node of the divider to FB. Choose R4 less than 15kΩ, then calculate R3 as follows: R3 = (VOUT −1.22) × R4 1.22 VIN 7.5V TO 76V 68µF R1 R2 VIN LX ON/OFF BST MAX5035D FB VD SGND GND 100µH 0.1µF D1 50SQ100 R3 41.2kΩ 0.1µF R4 13.3kΩ VOUT 5V COUT 68µF Figure 1. Adjustable Output Voltage 10 ______________________________________________________________________________________ 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter MAX5035 The MAX5035 features internal compensation for optimum closed-loop bandwidth and phase margin. With the preset compensation, it is strongly advised to sense the output immediately after the primary LC. Inductor Selection The choice of an inductor is guided by the voltage difference between VIN and VOUT, the required output current, and the operating frequency of the circuit. Use an inductor with a minimum value given by: L = (VIN − VOUT) × D 0.3 × IOUTMAX × fSW where: D = VOUT VIN IOUTMAX is the maximum output current required, and fSW is the operating frequency of 125kHz. Use an inductor with a maximum saturation current rating equal to at least the peak switch current limit (ILIM). Use inductors with low DC resistance for higher efficiency. Selecting a Rectifier The MAX5035 requires an external Schottky rectifier as a freewheeling diode. Connect this rectifier close to the device using short leads and short PC board traces. Choose a rectifier with a continuous current rating greater than the highest expected output current. Use a rectifier with a voltage rating greater than the maximum expected input voltage, VIN. Use a low forward-voltage Schottky rectifier for proper operation and high efficiency. Avoid higher than necessary reverse-voltage Schottky rectifiers that have higher forward-voltage drops. Use a Schottky rectifier with forward-voltage Table 1. Diode Selection VIN (V) DIODE PART NUMBER 15MQ040N 7.5 to 36 B240A B240 MBRS240, MBRS1540 30BQ060 7.5 to 56 B360A CMSH3-60 MBRD360, MBR3060 7.5 to 76 50SQ100, 50SQ80 MBRM5100 MANUFACTURER IR Diodes, Inc. Central Semiconductor ON Semiconductor IR Diodes, Inc. Central Semiconductor ON Semiconductor IR Diodes, Inc. drop (VFB) less than 0.45V at +25°C and maximum load current to avoid forward biasing of the internal body diode (LX to ground). Internal body diode conduction may cause excessive junction temperature rise and thermal shutdown. Use Table 1 to choose the proper rectifier at different input voltages and output current. Input Bypass Capacitor 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 MAX5035 high switching frequency allows the use of smaller-value input capacitors. The input ripple is comprised of ∆VQ (caused by the capacitor discharge) and ∆VESR (caused by the ESR of the capacitor). Use low-ESR aluminum electrolytic capacitors with high ripple-current capability at the input. Assuming that the contribution from the ESR and capacitor discharge is equal to 90% and 10%, respectively, calculate the input capacitance and the ESR required for a specified ripple using the following equations: ESRIN = ∆VESR  IOUT + ∆IL 2   where CIN = IOUT × ∆ VQ D × (1− D) fSW ∆IL = (VIN − VOUT) × VOUT , VIN × fSW × L D = VOUT VIN IOUT is the maximum output current of the converter and fSW is the oscillator switching frequency (125kHz). For example, at VIN = 48V, VOUT = 3.3V, the ESR and input capacitance are calculated for the input peak-topeak ripple of 100mV or less yielding an ESR and capacitance value of 80mΩ and 51µF, respectively. Low-ESR, ceramic, multilayer chip capacitors are recommended for size-optimized application. For ceramic capacitors, assume the contribution from ESR and capacitor discharge is equal to 10% and 90%, respectively. The input capacitor must handle the RMS ripple current without significant rise in temperature. The maximum capacitor RMS current occurs at about 50% duty cycle. ______________________________________________________________________________________ 11 MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter Ensure that the ripple specification of the input capacitor exceeds the worst-case capacitor RMS ripple current. Use the following equations to calculate the input capacitor RMS current: where ICRMS = IPRMS2 − IAVGIN2 ( ) IPRMS = IPK2 + IDC2 + IPK × IDC   × D 3 IAVGIN = VOUT × IOUT VIN × η IPK = IOUT + ∆IL 2 , IDC = IOUT − ∆ IL 2 and D = VOUT VIN IPRMS is the input switch RMS current, IAVGIN is the input average current, and η is the converter efficiency. The ESR of aluminum electrolytic capacitors increases significantly at cold temperatures. Use a 1µF or greater value ceramic capacitor in parallel with the aluminum electrolytic input capacitor, especially for input voltages below 8V. Output Filter Capacitor The worst-case peak-to-peak and RMS capacitor ripple current, allowable peak-to-peak output ripple voltage, and the maximum deviation of the output voltage during load steps determine the capacitance and the ESR requirements for the output capacitors. The output capacitance and its ESR form a zero, which improves the closed-loop stability of the buck regulator. Choose the output capacitor so the ESR zero frequency (fZ) occurs between 20kHz to 40kHz. Use the following equation to verify the value of fZ. Capacitors with 100mΩ to 250mΩ ESR are recommended to ensure the closedloop stability, while keeping the output ripple low. fZ = 2 × π × 1 COUT × ESROUT The output ripple is comprised of ∆VOQ (caused by the capacitor discharge) and ∆VOESR (caused by the ESR of the capacitor). Use low-ESR tantalum or aluminum electrolytic capacitors at the output. Assuming that the contributions from the ESR and capacitor discharge equal 80% and 20% respectively, calculate the output capacitance and the ESR required for a specified ripple using the following equations: ESROUT = ∆VOESR ∆ IL COUT ≈ 2.2 × ∆IL ∆VOQ × fSW The MAX5035 has an internal soft-start time (tSS) of 400µs. It is important to keep the output rise time at startup below tSS to avoid output overshoot. The output rise time is directly proportional to the output capacitor. Use 68µF or lower capacitance at the output to control the overshoot below 5%. In a dynamic load application, the allowable deviation of the output voltage during the fast-transient load dictates the output capacitance value and the ESR. The output capacitors supply the step load current until the controller responds with a greater duty cycle. The response time (tRESPONSE) depends on the closedloop bandwidth of the converter. The resistive drop across the capacitor ESR and capacitor discharge cause a voltage droop during a step load. Use a combination of low-ESR tantalum and ceramic capacitors for better transient load and ripple/noise performance. Keep the maximum output-voltage deviation above the tolerable limits of the electronics being powered. Assuming a 50% contribution each from the output capacitance discharge and the ESR drop, use the following equations to calculate the required ESR and capacitance value: ESROUT = ∆VOESR ISTEP COUT = ISTEP × tRESPONSE ∆VOQ where ISTEP is the load step and tRESPONSE is the response time of the controller. Controller response time is approximately one-third of the reciprocal of the closed-loop unity-gain bandwidth, 20kHz typically. PC Board Layout Considerations Proper PC board layout is essential. Minimize ground noise by connecting the anode of the Schottky rectifier, the input bypass capacitor ground lead, and the output filter capacitor ground lead to a single point (“star” 12 ______________________________________________________________________________________ MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter ground configuration). A ground plane is required. Minimize lead lengths to reduce stray capacitance, trace resistance, and radiated noise. In particular, place the Schottky rectifier diode right next to the device. Also, place BST and VD bypass capacitors very close to the device. Use the PC board copper plane connecting to VIN and LX for heatsinking. Application Circuits VIN R1 R2 CIN VIN BST LX MAX5035 ON/OFF FB VD SGND GND 0.1µF L1 D1 0.1µF VOUT COUT Figure 2. Fixed Output Voltages Table 2. Typical External Components Selection (Circuit of Figure 2) VIN (V) 7.5 to 76 7.5 to 76 7.5 to 76 7.5 to 76 VOUT (V) 3.3 3.3 5 5 IOUT (A) 0.5 1 0.5 1 EXTERNAL COMPONENTS CIN = 68µF, Panasonic, EEVFK2A680Q COUT = 68µF, Vishay Sprague, 594D686X_010C2T CBST = 0.1µF, 0805 R1 = 1MΩ ±1%, 0805 R2 = 384kΩ ±1%, 0805 D1 = 50SQ100, IR L1 = 100µH, Coilcraft Inc., DO5022P-104 CIN = 68µF, Panasonic, EEVFK2A680Q COUT = 68µF, Vishay Sprague, 594D68X_010C2T CBST = 0.1µF, 0805 R1 = 1MΩ ±1%, 0805 R2 = 384kΩ ±1%, 0805 D1 = 50SQ100, IR L1 = 100µH, Coilcraft Inc., DO5022P-104 15 to 76 12 CIN = 68µF, Panasonic, EEVFK2A680Q COUT = 15µF, Vishay Sprague, 594D156X0025C2T CBST = 0.1µF, 0805 1 R1 = 1MΩ ±1%, 0805 R2 = 139kΩ ±1%, 0805 D1 = 50SQ100, IR L1 = 220µH, Coilcraft Inc., DO5022P-224 ______________________________________________________________________________________ 13 MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter Table 2. Typical External Components Selection (Circuit of Figure 2) (continued) VIN (V) 9 to 14 VOUT (V) 3.3 5 IOUT (A) 1 1 EXTERNAL COMPONENTS CIN = 220µF, Panasonic, EEVFK1E221P COUT = 68µF, Vishay Sprague, 594D686X_010C2T CBST = 0.1µF, 0805 R1 = 1MΩ ±1%, 0805 R2 = 274kΩ ±1%, 0805 D1 = B220, Diodes Inc. L1 = 100µH, Coilcraft Inc., DO5022P-104 CIN = 220µF, Panasonic, EEVFK1E221P COUT = 68µF, Vishay Sprague, 594D686X_010C2T CBST = 0.1µF, 0805 R1 = 1MΩ ±1%, 0805 R2 = 274kΩ ±1%, 0805 D1 = B220, Diodes Inc. L1 = 100µH, Coilcraft Inc., DO5022P-104 CIN = 220µF, Panasonic, EEVFK1H221P COUT = 68µF, Vishay Sprague, 594D686X_010C2T CBST = 0.1µF, 0805 3.3 1 R1 = 1MΩ ±1%, 0805 R2 = 130kΩ ±1%, 0805 D1 = MBRS2040, ON Semiconductor L1 = 100µH, Coilcraft Inc., DO5022P-104 18 to 36 5 CIN = 220µF, Panasonic, EEVFK1H221P COUT = 68µF, Vishay Sprague, 594D686X_010C2T CBST = 0.1µF, 0805 1 R1 = 1MΩ ±1%, 0805 R2 = 130kΩ ±1%, 0805 D1 = MBRS2040, ON Semiconductor L1 = 100µH, Coilcraft Inc., DO5022P-104 CIN = 220µF, Panasonic, EEVFK1H221P COUT = 15µF, Vishay Sprague, 594D156X_0025C2T CBST = 0.1µF, 0805 12 1 R1 = 1MΩ ±1%, 0805 R2 = 130kΩ ±1%, 0805 D1 = MBRS2040, ON Semiconductor L1 = 220µH, Coilcraft Inc., DO5022P-224 14 ______________________________________________________________________________________ MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter Table 3. Component Suppliers SUPPLIER AVX Coilcraft Diodes Incorporated Panasonic Sanyo TDK Vishay PHONE 843-946-0238 847-639-6400 805-446-4800 714-373-7366 619-661-6835 847-803-6100 402-563-6866 FAX 843-626-3123 847-639-1469 805-446-4850 714-737-7323 619-661-1055 847-390-4405 402-563-6296 WEBSITE www.avxcorp.com www.coilcraft.com www.diodes.com www.panasonic.com www.sanyo.com www.component.tdk.com www.vishay.com PTC* VIN 12V CIN 68µF MAX5035 FB BST ON/OFF VIN LX Ct Rt VD SGND GND 0.1µF L1 0.1µF 100µH D1 B240 VOUT 5V AT 1A COUT 68µF *LOCATE PTC AS CLOSE TO HEAT-DISSIPATING COMPONENTS AS POSSIBLE. Figure 3. Load Temperature Monitoring with ON/OFF (Requires Accurate VIN) ______________________________________________________________________________________ 15 MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter VIN 7.5V TO 36V R1 CIN 68µF MAX5035B FB BST ON/OFF VIN LX Ct Rt VD SGND GND 0.1µF L1 0.1µF 220µH D1 B240 VOUT 5V COUT 68µF R1' C'IN 68µF MAX5035A FB BST ON/OFF VIN LX Ct' Rt' VD SGND GND 0.1µF L1' 0.1µF 100µH D1' B240 V'OUT 3.3V C'OUT 68µF Figure 4. Dual-Sequenced DC-DC Converters (Startup Delay Determined by R1/R1’, Ct/Ct’ and Rt/Rt’) Chip Information TRANSISTOR COUNT: 4344 PROCESS: BiCMOS 16 ______________________________________________________________________________________ MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) SOICN .EPS N 1 TOP VIEW EH D A e B A1 FRONT VIEW INCHES DIM MIN MAX A 0.053 0.069 A1 0.004 0.010 B 0.014 0.019 C 0.007 0.010 e 0.050 BSC E 0.150 0.157 H 0.228 0.244 L 0.016 0.050 MILLIMETERS MIN MAX 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 1.27 BSC 3.80 4.00 5.80 6.20 0.40 1.27 VARIATIONS: INCHES DIM MIN D 0.189 D 0.337 D 0.386 MAX 0.197 0.344 0.394 MILLIMETERS MIN 4.80 8.55 9.80 MAX 5.00 8.75 10.00 N MS012 8 AA 14 AB 16 AC C 0∞-8∞ L SIDE VIEW PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE, .150" SOIC APPROVAL DOCUMENT CONTROL NO. 21-0041 REV. 1 B1 ______________________________________________________________________________________ 17 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) MAX5035 PDIPN.EPS 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. 18 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2004 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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