19-2988; Rev 0; 9/03 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter The MAX5035 delivers up to 1A output current. 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 industrial (0°C to +85°C) temperature range. Applications 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 ♦ 350µA 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 TEMP RANGE PINPACKAGE MAX5035AUSA 0°C to +85°C 8 SO MAX5035AUPA 0°C to +85°C 8 PDIP MAX5035BUSA 0°C to +85°C 8 SO Consumer Electronics MAX5035BUPA 0°C to +85°C 8 PDIP Industrial MAX5035CUSA 0°C to +85°C 8 SO Distributed Power MAX5035CUPA 0°C to +85°C 8 PDIP MAX5035DUSA 0°C to +85°C 8 SO MAX5035DUPA 0°C to +85°C 8 PDIP OUTPUT VOLTAGE (V) 3.3 5.0 12 ADJ Typical Operating Circuit Pin Configuration VIN 7.5V TO 76V VIN 68µF BST 0.1µF 100µH MAX5035 LX R1 D1 50SQ100 ON/OFF 68µF ON FB R2 OFF VOUT 5V TOP VIEW BST 1 8 LX VD 2 7 VIN SGND 3 6 GND FB 4 5 ON/OFF MAX5035 VD SGND GND 0.1µF SO/PDIP ________________________________________________________________ Maxim Integrated Products 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. 1 MAX5035 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 350µA 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. MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter 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 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 (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 2 SYMBOL VIN CONDITIONS MIN VFB η IQ MAX 7.5 76.0 MAX5035B 7.5 76.0 MAX5035C 15 76 MAX5035D 7.5 76.0 UVLO VOUT TYP MAX5035A 5.2 MAX5035A 3.185 3.3 3.415 MAX5035B VIN = 7.5V to 76V, IOUT = 20mA to 1A 4.85 5.0 5.15 MAX5035C VIN = 15V to 76V, IOUT = 20mA to 1A 11.64 12 12.36 1.192 1.221 1.250 VIN = 12V, ILOAD = 0.5A, MAX5035A 86 VIN = 12V, ILOAD = 0.5A, MAX5035B 90 V V % VIN = 24V, ILOAD = 0.5A, MAX5035C 94 VIN = 12V, VOUT = 5V, ILOAD = 0.5A, MAX5035D 90 VFB = 3.5V, VIN = 7.5V to 76V, MAX5035A 350 VFB = 5.5V, VIN = 7.5V to 76V, MAX5035B 350 460 VFB = 13V, VIN = 15V to 76V, MAX5035C 350 460 VFB = 1.3V, MAX5035D 350 460 _______________________________________________________________________________________ V V VIN = 7.5V to 76V, IOUT = 20mA to 1A VIN = 7.5V to 76V, MAX5035D UNITS 460 µA 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter (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 Shutdown Current SYMBOL ISHDN CONDITIONS VON/OFF = 0V, VIN = 7.5V to 76V Peak Switch Current Limit ILIM (Note 1) Switch Leakage Current IOL VIN = 76V, VON/OFF = 0V, VLX = 0V Switch On-Resistance PFM Threshold RDS(ON) IPFM FB Input Bias Current IB MIN TYP MAX UNITS 10 45 µA 1.80 2.40 1 A µA 0.40 0.80 Ω Minimum switch current in any cycle 55 85 110 mA MAX5035D -12 +0.01 +12 nA Rising trip point 1.53 1.69 1.85 ISWITCH = 1A ON/OFF CONTROL INPUT ON/OFF Input-Voltage Threshold VON/OFF ON/OFF Input-Voltage Hysteresis VHYST ON/OFF Input Current ION/OFF 100 VON/OFF = 0V to VIN V mV 10 150 nA 125 135 kHz OSCILLATOR Oscillator Frequency fOSC Maximum Duty Cycle DMAX 109 MAX5035D 95 % VOLTAGE REGULATOR Regulator Output Voltage VD Dropout Voltage ∆VD/∆IVD Load Regulation VIN = 8.5V to 76V, IL = 0mA 6.9 7.8 8.8 V 7.5V ≤ VIN ≤ 8.5V, IL = 1mA 2.0 V 0 to 5mA 150 mV/mA SO package (JEDEC 51) 170 DIP package (JEDEC 51) 110 PACKAGE THERMAL CHARACTERISTICS Thermal Resistance (Junction to Ambient) θJA °C/W THERMAL SHUTDOWN Thermal-Shutdown Junction Temperature Thermal-Shutdown Hysteresis TSH +160 °C THYST 20 °C Note 1: Switch current at which current limit is activated. _______________________________________________________________________________________ 3 MAX5035 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VIN = 12V, VON/OFF = 12V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Application Circuit, if applicable.) OUTPUT VOLTAGE vs. TEMPERATURE (MAX5035DUSA, VOUT = 5V) IOUT = 0.1A 3.36 5.15 VOUT (V) VOUT (V) 3.32 3.28 IOUT = 0.1A 5.05 5.00 4.95 IOUT = 0.1A 3.36 OUTPUT VOLTAGE (V) 5.10 IOUT = 1A 3.40 MAX5035 toc02 5.20 MAX5035 toc01 3.40 LINE REGULATION (MAX5035AUSA, VOUT = 3.3V) IOUT = 1A 4.90 3.24 MAX5035 toc03 OUTPUT VOLTAGE vs. TEMPERATURE (MAX5035AUSA, VOUT = 3.3V) IOUT = 1A 3.32 3.28 3.24 4.85 3.20 4.80 25 75 50 100 3.20 0 25 75 50 100 5 35 50 65 TEMPERATURE (°C) INPUT VOLTAGE (V) LINE REGULATION (MAX5035DUSA, VOUT = 5V) LOAD REGULATION (MAX5035AUSA, VOUT = 3.3V) LOAD REGULATION (MAX5035DUSA, VOUT = 5V) 5.15 VIN = 76V 3.36 5.10 5.10 5.05 VIN = 7.5V, 24V 5.00 VIN = 7.5V 5.00 3.28 IOUT = 1A 4.95 VIN = 24V 3.32 VOUT (V) VOUT (V) IOUT = 0.1A 80 MAX5035 toc06 3.40 MAX5035 toc04 5.20 5.05 20 TEMPERATURE (°C) MAX5035 toc05 0 OUTPUT VOLTAGE (V) MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter VIN = 76V 4.90 4.95 3.24 4.85 3.20 4.80 5 20 35 50 INPUT VOLTAGE (V) 4 65 80 4.90 0 200 400 600 ILOAD (mA) 800 1000 0 200 400 600 ILOAD (mA) _______________________________________________________________________________________ 800 1000 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter 60 VIN = 7.5V 50 VIN = 12V 40 VIN = 24V VIN = 12V 40 VIN = 24V 200 400 600 800 50 VIN = 48V 40 VIN = 76V 20 VIN = 76V 10 0 200 400 600 800 0 1000 200 400 600 1000 800 LOAD CURRENT (mA) OUTPUT CURRENT LIMIT vs. TEMPERATURE OUTPUT CURRENT LIMIT vs. INPUT VOLTAGE QUIESCENT SUPPLY CURRENT vs. TEMPERATURE MAX5035DUSA VOUT = 5V 5% DROP IN VOUT 1.4 1.1 0.8 0 MAX5035DUSA VOUT = 5V 5% DROP IN VOUT 0.5 25 75 50 100 20 35 50 65 INPUT VOLTAGE (V) QUIESCENT SUPPLY CURRENT vs. INPUT VOLTAGE SHUTDOWN CURRENT vs. TEMPERATURE 260 26 36 46 56 INPUT VOLTAGE (V) 66 76 0 50 25 100 75 20 MAX5035 toc14 16 12 8 16 12 8 4 0 200 230 SHUTDOWN CURRENT vs. INPUT VOLTAGE 4 230 260 80 SHUTDOWN CURRENT (µA) 290 290 TEMPERATURE (°C) 20 SHUTDOWN CURRENT (µA) MAX5035 toc13 320 320 200 5 TEMPERATURE (°C) 350 MAX5035 toc12 MAX5035 toc11 1.7 350 QUIESCENT SUPPLY CURRENT (µA) 0.5 2.0 OUTPUT CURRENT LIMIT (A) MAX5035 toc10 1.0 16 VIN = 24V LOAD CURRENT (mA) 1.5 6 VIN = 15V 60 LOAD CURRENT (mA) 2.0 0 70 30 VIN = 48V 0 1000 MAX5035 toc09 80 0 0 OUTPUT CURRENT LIMIT (A) 50 10 0 QUIESCENT SUPPLY CURRENT (µA) VIN = 7.5V 20 VIN = 76V 10 60 30 VIN = 48V 20 70 90 MAX5035 toc15 30 80 EFFICIENCY (%) 70 90 EFFICIENCY (%) 80 100 MAX5035 toc08 90 EFFICIENCY (%) 100 MAX5035 toc07 100 EFFICIENCY vs. LOAD CURRENT (MAX5035DUSA, VOUT = 12V) EFFICIENCY vs. LOAD CURRENT (MAX5035DUSA, VOUT = 5V) EFFICIENCY vs. LOAD CURRENT (MAX5035AUSA, VOUT = 3.3V) 0 0 25 50 TEMPERATURE (°C) 75 100 6 16 26 36 46 56 66 76 INPUT VOLTAGE (V) _______________________________________________________________________________________ 5 MAX5035 Typical Operating Characteristics (continued) (VIN = 12V, VON/OFF = 12V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Application Circuit, if applicable.) Typical Operating Characteristics (continued) (VIN = 12V, VON/OFF = 12V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Application Circuit, if applicable.) MAX5035DUSA LOAD-TRANSIENT RESPONSE OUTPUT VOLTAGE vs. INPUT VOLTAGE MAX5035DUSA LOAD-TRANSIENT RESPONSE MAX5035 toc17 MAX5035 toc16 15 MAX5035DUSA VOUT = 12V VON/OFF = VIN 12 MAX5035 toc18 VOUT = 5V VOUT = 5V A A VOUT (V) MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter 9 6 IOUT = 1A 3 B B IOUT = 0.3A IOUT = 0 0 0 3 6 9 12 15 VIN (V) 400µs/div 400µs/div A: VOUT, 200mV/div, AC-COUPLED B: IOUT, 500mA/div, 0.1A TO 1A MAX5035DUSA LOAD-TRANSIENT RESPONSE A: VOUT, 200mV/div, AC-COUPLED B: VOUT, 500mA/div, 0.5A TO 1A MAX5035DUSA LX WAVEFORMS MAX5035DUSA LX WAVEFORMS MAX5035 toc20 MAX5035 toc19 MAX5035 toc21 VOUT = 5V A A A 0 0 B B B 0 0 400µs/div A: VOUT, 200mV/div, AC-COUPLED B: VOUT, 500mA/div, 0.1A TO 0.5A 6 4µs/div 4µs/div A: SWITCH VOLTAGE (LX PIN), 20V/div, (VIN = 48V) B: INDUCTOR CURRENT, 500mA/div (IOUT = 1A) A: SWITCH VOLTAGE (LX PIN), 20V/div, (VIN = 48V) B: INDUCTOR CURRENT, 200mA/div (IOUT = 100mA) _______________________________________________________________________________________ 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter MAX5035DUSA STARTUP WAVEFORM (IO = 0) MAX5035DUSA LX WAVEFORMS MAX5035 toc23 MAX5035 toc22 A A 0 0 B B 0 0 1ms/div 4µs/div A: VON/OFF, 2V/div B: VOUT, 2V/div A: SWITCH VOLTAGE (LX PIN), 20V/div, VIN = 48V B: INDUCTOR CURRENT, 200mA/div (IOUT = 0) MAX5035DUSA STARTUP WAVEFORM (IO = 1A) PEAK SWITCH CURRENT vs. INPUT VOLTAGE MAX5035 toc24 A 0 B MAX5035 toc25 PEAK SWITCH CURRENT (A) 3.0 2.5 2.0 1.5 1.0 MAX5035DUSA VOUT = 5V 5% DROP IN VOUT 0 0.5 1ms/div A: VON/OFF, 2V/div B: VOUT, 2V/div 6 16 26 36 46 56 66 76 INPUT VOLTAGE (V) _______________________________________________________________________________________ 7 MAX5035 Typical Operating Characteristics (continued) (VIN = 12V, VON/OFF = 12V, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Application Circuit, if applicable.) 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter MAX5035 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), 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. 4 FB 5 ON/OFF 6 GND 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 Shutdown Control Input. Pull ON/OFF low to put the device in shutdown mode. Drive ON/OFF high for normal operation. Ground Block Diagram VIN ON/OFF ENABLE REGULATOR (FOR ANALOG) 1.69V REGULATOR (FOR DRIVER) VD CPFM IREF-PFM HIGH-SIDE CURRENT SENSE CILIM OSC VREF RAMP IREF-LIM BST MAX5035 CLK FB RAMP CONTROL LOGIC Rh x1 Rl TYPE 3 COMPENSATION VREF THERMAL SHUTDOWN CPWM EAMP GND LX SGND 8 _______________________________________________________________________________________ 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter 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 feedforward 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 350µA, 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: R1 VUVLO(TH) = 1 + × 1.85V R2 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 V IN rise time, use the resistive-divider at ON/OFF. 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 100µH VIN LX 0.1µF ON/OFF R2 D1 50SQ100 BST COUT 68µF R3 41.2kΩ MAX5035D 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 VOUT 5V FB VD SGND GND 0.1µF R4 13.3kΩ Figure 1. Adjustable Output Voltage _______________________________________________________________________________________ 9 MAX5035 Detailed Description MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter 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 0.2 × IOUTMAX × fSW where: V D = OUT 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 twice the peak output current of the circuit. Use inductors with low DC resistance for higher efficiency. 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 = 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) 7.5 to 36 7.5 to 56 7.5 to 76 10 DIODE PART NUMBER MANUFACTURER 15MQ040N IR B240A Diodes, Inc. B240 Central Semiconductor MBRS240, MBRS1540 ON Semiconductor 30BQ060 IR B360A Diodes, Inc. CMSH3-60 Central Semiconductor MBRD360, MBR3060 ON Semiconductor 50SQ100, 50SQ80 IR MBRM5100 Diodes, Inc. CIN = where ∆IL = ∆VESR ∆IL IOUT + 2 IOUT × D (1− D) ∆VQ × fSW (VIN − VOUT ) × VOUT VIN × fSW × L , V D = OUT 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. ______________________________________________________________________________________ 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter ICRMS = capacitance and the ESR required for a specified ripple using the following equations: ESROUT = IPRMS2 − IAVGIN2 where COUT ≈ D IPRMS = IPK 2 + IDC2 + (IPK × IDC ) × 3 V ×I IAVGIN = OUT OUT VIN × η ∆I ∆I IPK = IOUT + L , IDC = IOUT − L 2 2 VOUT and D = 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 = 1 2 × π × 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 contribution from the ESR and capacitor discharge equal 80% and 20% respectively, calculate the output ∆VOESR ∆IL ∆IL 2.2 × ∆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 I ×t COUT = STEP RESPONSE ∆VOQ where I STEP is the load step and t RESPONSE 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” ______________________________________________________________________________________ 11 MAX5035 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: 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 heat sinking. Application Circuits VIN CIN VIN BST 0.1µF L1 VOUT LX D1 R1 MAX5035 COUT FB ON/OFF VD R2 SGND GND 0.1µF Figure 2. Fixed Output Voltages Table 2. Typical External Components Selection (Circuit of Figure 2) VIN (V) VOUT (V) IOUT (A) 7.5 to 76 3.3 0.5 7.5 to 76 3.3 1 7.5 to 76 5 0.5 7.5 to 76 5 1 15 to 76 12 12 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 CIN = 68µF, Panasonic, EEVFK2A680Q COUT = 15µF, Vishay Sprague, 594D156X0025C2T CBST = 0.1µF, 0805 R1 = 1MΩ ±1%, 0805 R2 = 139kΩ ±1%, 0805 D1 = 50SQ100, IR L1 = 220µH, Coilcraft Inc., DO5022P-224 ______________________________________________________________________________________ 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter MAX5035 Table 2. Typical External Components Selection (Circuit of Figure 2) (continued) VIN (V) VOUT (V) 3.3 IOUT (A) EXTERNAL COMPONENTS 1 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 1 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 1 CIN = 220µF, Panasonic, EEVFK1H221P COUT = 68µF, Vishay Sprague, 594D686X_010C2T CBST = 0.1µF, 0805 R1 = 1MΩ ±1%, 0805 R2 = 130kΩ ±1%, 0805 D1 = MBRS2040, ON Semiconductor L1 = 100µH, Coilcraft Inc., DO5022P-104 1 CIN = 220µF, Panasonic, EEVFK1H221P COUT = 68µF, Vishay Sprague, 594D686X_010C2T CBST = 0.1µF, 0805 R1 = 1MΩ ±1%, 0805 R2 = 130kΩ ±1%, 0805 D1 = MBRS2040, ON Semiconductor L1 = 100µH, Coilcraft Inc., DO5022P-104 1 CIN = 220µF, Panasonic, EEVFK1H221P COUT = 15µF, Vishay Sprague, 594D156X_0025C2T CBST = 0.1µF, 0805 R1 = 1MΩ ±1%, 0805 R2 = 130kΩ ±1%, 0805 D1 = MBRS2040, ON Semiconductor L1 = 220µH, Coilcraft Inc., DO5022P-224 9 to 14 5 3.3 18 to 36 5 12 ______________________________________________________________________________________ 13 MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter Table 3. Component Suppliers SUPPLIER AVX PHONE FAX 843-946-0238 843-626-3123 WEBSITE www.avxcorp.com Coilcraft 847-639-6400 847-639-1469 www.coilcraft.com Diodes Incorporated 805-446-4800 805-446-4850 www.diodes.com Panasonic 714-373-7366 714-737-7323 www.panasonic.com Sanyo 619-661-6835 619-661-1055 www.sanyo.com TDK 847-803-6100 847-390-4405 www.component.tdk.com Vishay 402-563-6866 402-563-6296 www.vishay.com MAX5035 PTC* ON/OFF VIN 12V VIN CIN 68µF Ct Rt FB BST 0.1µF L1 100µH VOUT 5V AT 1A LX VD SGND GND 0.1µF D1 B240 COUT 68µF *LOCATE PTC AS CLOSE TO HEAT-DISSIPATING COMPONENTS AS POSSIBLE. Figure 3. Load Temperature Monitoring with ON/OFF (Requires Accurate VIN) 14 ______________________________________________________________________________________ 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter VIN 7.5V TO 36V 0.1µF VIN CIN 68µF Ct FB BST ON/OFF L1 220µH VOUT 5V LX VD Rt MAX5035 MAX5035B R1 COUT 68µF D1 B240 SGND GND 0.1µF MAX5035A R1' ON/OFF VIN C'IN 68µF Ct' Rt' FB BST 0.1µF L1' 100µH V'OUT 3.3V LX VD SGND GND C'OUT 68µF D1' B240 0.1µF 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 ______________________________________________________________________________________ 15 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.) DIM A A1 B C e E H L N E H INCHES MILLIMETERS MAX MIN 0.069 0.053 0.010 0.004 0.014 0.019 0.007 0.010 0.050 BSC 0.150 0.157 0.228 0.244 0.016 0.050 MAX MIN 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 SOICN .EPS MAX5035 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter 1.27 VARIATIONS: 1 INCHES TOP VIEW DIM D D D MIN 0.189 0.337 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 D A B e C 0 -8 A1 L FRONT VIEW SIDE VIEW PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE, .150" SOIC APPROVAL DOCUMENT CONTROL NO. 21-0041 16 ______________________________________________________________________________________ REV. B 1 1 1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter 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. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17 © 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX5035 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.)