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19-2988; Rev 0; 9/03
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 350A 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. External shutdown is included, featuring 10A (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 (0C to +85C) temperature range. o Fixed (3.3V, 5V, 12V) and Adjustable (1.25V to 13.2V) Versions o 1A Output Current o Efficiency Up to 94% o Internal 0.4 High-Side DMOS FET o 350A Quiescent Current at No Load, 10A Shutdown Current o Internal Frequency Compensation o Fixed 125kHz Switching Frequency o Thermal Shutdown and Short-Circuit Current Limit o 8-Pin SO and PDIP Packages
Features
o Wide 7.5V to 76V Input Voltage Range
MAX5035
Ordering Information
PART MAX5035AUSA TEMP RANGE 0C to +85C 0C to +85C 0C to +85C 0C to +85C 0C to +85C 0C to +85C 0C to +85C 0C to +85C PINPACKAGE 8 SO 8 PDIP 8 SO 8 PDIP 8 SO 8 PDIP 8 SO 8 PDIP OUTPUT VOLTAGE (V) 3.3 5.0 12 ADJ
Applications
Consumer Electronics Industrial Distributed Power
MAX5035AUPA MAX5035BUSA MAX5035BUPA MAX5035CUSA MAX5035CUPA MAX5035DUSA MAX5035DUPA
Typical Operating Circuit
VIN 7.5V TO 76V 68F VIN BST 0.1F 100H LX ON/OFF ON R2 OFF SGND GND FB VD 0.1F D1 50SQ100
Pin Configuration
MAX5035
R1
VOUT 5V 68F
TOP VIEW
BST VD SGND FB 1 2 3 4 8 LX VIN GND ON/OFF 7 6 5
MAX5035
SO/PDIP
________________________________________________________________ Maxim Integrated Products
1
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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 = +70C) 8-Pin PDIP (derate 9.1mW/C above +70C)...............727mW 8-Pin SO (derate 5.9mW/C above +70C)..................471mW Operating Temperature Range MAX5035_U_ _ ...................................................0C to +85C Storage Temperature Range .............................-65C to +150C Junction Temperature ......................................................+150C Lead Temperature (soldering, 10s) .................................+300C
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 = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C. See the Typical Application Circuit.)
PARAMETER SYMBOL MAX5035A Input Voltage Range VIN MAX5035B MAX5035C MAX5035D Undervoltage Lockout UVLO MAX5035A Output Voltage VOUT MAX5035B MAX5035C Feedback Voltage VFB VIN = 7.5V to 76V, IOUT = 20mA to 1A VIN = 7.5V to 76V, IOUT = 20mA to 1A VIN = 15V to 76V, IOUT = 20mA to 1A 3.185 4.85 11.64 1.192 CONDITIONS MIN 7.5 7.5 15 7.5 5.2 3.3 5.0 12 1.221 86 90 94 90 350 350 350 350 460 460 460 460 A % 3.415 5.15 12.36 1.250 V V TYP MAX 76.0 76.0 76 76.0 V V UNITS
VIN = 7.5V to 76V, MAX5035D VIN = 12V, ILOAD = 0.5A, MAX5035A VIN = 12V, ILOAD = 0.5A, MAX5035B
Efficiency
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
Quiescent Supply Current
IQ
2
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1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter
ELECTRICAL CHARACTERISTICS (continued)
(VIN = +12V, VON/OFF = +12V, IOUT = 0, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C. See the Typical Application Circuit.)
PARAMETER 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 Oscillator Frequency Maximum Duty Cycle VOLTAGE REGULATOR Regulator Output Voltage Dropout Voltage Load Regulation Thermal Resistance (Junction to Ambient) THERMAL SHUTDOWN Thermal-Shutdown Junction Temperature Thermal-Shutdown Hysteresis TSH THYST +160 20 C C VD/IVD PACKAGE THERMAL CHARACTERISTICS JA SO package (JEDEC 51) DIP package (JEDEC 51) 170 110 C/W VD VIN = 8.5V to 76V, IL = 0mA 7.5V VIN 8.5V, IL = 1mA 0 to 5mA 6.9 7.8 2.0 150 8.8 V V mV/mA fOSC DMAX MAX5035D 109 125 95 135 kHz % VON/OFF VHYST ION/OFF VON/OFF = 0V to VIN Rising trip point 1.53 1.69 100 10 150 1.85 V mV nA SYMBOL ISHDN ILIM IOL RDS(ON) IPFM IB (Note 1) VIN = 76V, VON/OFF = 0V, VLX = 0V ISWITCH = 1A Minimum switch current in any cycle MAX5035D 55 -12 CONDITIONS VON/OFF = 0V, VIN = 7.5V to 76V MIN TYP 10 1.80 1 0.40 85 +0.01 0.80 110 +12 MAX 45 2.40 UNITS A A A mA nA
MAX5035
Note 1: Switch current at which current limit is activated.
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1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter MAX5035
Typical Operating Characteristics
(VIN = 12V, VON/OFF = 12V, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C. See the Typical Application Circuit, if applicable.)
OUTPUT VOLTAGE vs. TEMPERATURE (MAX5035AUSA, VOUT = 3.3V)
MAX5035 toc01
OUTPUT VOLTAGE vs. TEMPERATURE (MAX5035DUSA, VOUT = 5V)
MAX5035 toc02
LINE REGULATION (MAX5035AUSA, VOUT = 3.3V)
IOUT = 0.1A 3.36 OUTPUT VOLTAGE (V) IOUT = 1A 3.32
MAX5035 toc03
3.40 IOUT = 0.1A 3.36 IOUT = 1A VOUT (V)
5.20 5.15 5.10 VOUT (V) 5.05 5.00 4.95 4.90 4.85 IOUT = 1A IOUT = 0.1A
3.40
3.32
3.28
3.28
3.24
3.24
3.20 0 25 50 TEMPERATURE (C) 75 100
4.80 0 25 50 TEMPERATURE (C) 75 100
3.20 5 20 35 50 65 80 INPUT VOLTAGE (V)
LINE REGULATION (MAX5035DUSA, VOUT = 5V)
MAX5035 toc04
LOAD REGULATION (MAX5035AUSA, VOUT = 3.3V)
MAX5035 toc05
LOAD REGULATION (MAX5035DUSA, VOUT = 5V)
MAX5035 toc06
5.20 5.15 OUTPUT VOLTAGE (V) 5.10
3.40 VIN = 76V 3.36 VIN = 7.5V, 24V VOUT (V)
5.10
5.05 VIN = 24V VOUT (V) VIN = 7.5V 5.00 VIN = 76V
5.05 5.00 4.95 4.90 4.85 4.80 5
IOUT = 0.1A
3.32
IOUT = 1A
3.28 4.95
3.24
3.20 20 35 50 65 80 0 200 400 600 800 1000 INPUT VOLTAGE (V) ILOAD (mA)
4.90 0 200 400 600 800 1000 ILOAD (mA)
4
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1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter
Typical Operating Characteristics (continued)
(VIN = 12V, VON/OFF = 12V, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C. See the Typical Application Circuit, if applicable.)
EFFICIENCY vs. LOAD CURRENT (MAX5035AUSA, VOUT = 3.3V)
MAX5035 toc07
MAX5035
EFFICIENCY vs. LOAD CURRENT (MAX5035DUSA, VOUT = 5V)
MAX5035 toc08
EFFICIENCY vs. LOAD CURRENT (MAX5035DUSA, VOUT = 12V)
90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 VIN = 76V VIN = 15V VIN = 24V VIN = 48V
MAX5035 toc09
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 0 200 400 600 800 VIN = 7.5V VIN = 12V VIN = 24V VIN = 48V VIN = 76V
100 90 80 EFFICIENCY (%) 70 60 50 40 30 20 10 0 VIN = 7.5V VIN = 12V VIN = 24V VIN = 48V VIN = 76V
100
1000
0
200
400
600
800
1000
0
200
400
600
800
1000
LOAD CURRENT (mA)
LOAD CURRENT (mA)
LOAD CURRENT (mA)
OUTPUT CURRENT LIMIT vs. TEMPERATURE
MAX5035 toc10
OUTPUT CURRENT LIMIT vs. INPUT VOLTAGE
MAX5035 toc11
QUIESCENT SUPPLY CURRENT vs. TEMPERATURE
MAX5035 toc12
2.0
2.0
350 QUIESCENT SUPPLY CURRENT (A)
OUTPUT CURRENT LIMIT (A)
1.5
OUTPUT CURRENT LIMIT (A)
1.7
320
1.4
290
1.0
1.1
260
0.5
MAX5035DUSA VOUT = 5V 5% DROP IN VOUT 0 25 50 TEMPERATURE (C) 75 100
0.8
0
0.5 5 20 35
MAX5035DUSA VOUT = 5V 5% DROP IN VOUT 50 65 80
230
200 0 25 50 TEMPERATURE (C) 75 100 INPUT VOLTAGE (V)
QUIESCENT SUPPLY CURRENT vs. INPUT VOLTAGE
MAX5035 toc13
SHUTDOWN CURRENT vs. TEMPERATURE
MAX5035 toc14
SHUTDOWN CURRENT vs. INPUT VOLTAGE
MAX5035 toc15
350 QUIESCENT SUPPLY CURRENT (A)
20
20
SHUTDOWN CURRENT (A)
290
12
SHUTDOWN CURRENT (A) 0 25 50 TEMPERATURE (C) 75 100
320
16
16
12
260
8
8
230
4
4
200 6 16 26 36 46 56 66 76 INPUT VOLTAGE (V)
0
0 6 16 26 36 46 56 66 76 INPUT VOLTAGE (V)
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1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter MAX5035
Typical Operating Characteristics (continued)
(VIN = 12V, VON/OFF = 12V, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C. See the Typical Application Circuit, if applicable.)
OUTPUT VOLTAGE vs. INPUT VOLTAGE
MAX5035DUSA VOUT = 12V VON/OFF = VIN
MAX5035 toc16
MAX5035DUSA LOAD-TRANSIENT RESPONSE
MAX5035 toc17
MAX5035DUSA LOAD-TRANSIENT RESPONSE
MAX5035 toc18
15
VOUT = 5V A
VOUT = 5V A
12
VOUT (V)
9
6 IOUT = 1A 3 IOUT = 0.3A IOUT = 0 0 0 3 6 VIN (V) 9 12 15 400s/div A: VOUT, 200mV/div, AC-COUPLED B: IOUT, 500mA/div, 0.1A TO 1A 400s/div A: VOUT, 200mV/div, AC-COUPLED B: VOUT, 500mA/div, 0.5A TO 1A B B
MAX5035DUSA LOAD-TRANSIENT RESPONSE
MAX5035 toc19
MAX5035DUSA LX WAVEFORMS
MAX5035 toc20
MAX5035DUSA LX WAVEFORMS
MAX5035 toc21
VOUT = 5V A A 0 A 0 B B B 0 0 400s/div A: VOUT, 200mV/div, AC-COUPLED B: VOUT, 500mA/div, 0.1A TO 0.5A 4s/div A: SWITCH VOLTAGE (LX PIN), 20V/div, (VIN = 48V) B: INDUCTOR CURRENT, 500mA/div (IOUT = 1A) 4s/div A: SWITCH VOLTAGE (LX PIN), 20V/div, (VIN = 48V) B: INDUCTOR CURRENT, 200mA/div (IOUT = 100mA)
6
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1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter
Typical Operating Characteristics (continued)
(VIN = 12V, VON/OFF = 12V, TA = 0C to +85C, unless otherwise noted. Typical values are at TA = +25C. See the Typical Application Circuit, if applicable.)
MAX5035DUSA STARTUP WAVEFORM (IO = 0)
MAX5035
MAX5035DUSA LX WAVEFORMS
MAX5035 toc22
MAX5035 toc23
A A 0 B 0 0 0 B
4s/div A: SWITCH VOLTAGE (LX PIN), 20V/div, VIN = 48V B: INDUCTOR CURRENT, 200mA/div (IOUT = 0) A: VON/OFF, 2V/div B: VOUT, 2V/div
1ms/div
MAX5035DUSA STARTUP WAVEFORM (IO = 1A)
PEAK SWITCH CURRENT vs. INPUT VOLTAGE
MAX5035 toc25
MAX5035 toc24
3.0
A
PEAK SWITCH CURRENT (A)
2.5
2.0
0 B
1.5
1.0 0 0.5 1ms/div A: VON/OFF, 2V/div B: VOUT, 2V/div 6 16 26 36 46
MAX5035DUSA VOUT = 5V 5% DROP IN VOUT 56 66 76
INPUT VOLTAGE (V)
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1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter MAX5035
Pin Description
PIN 1 2 3 4 NAME BST VD SGND FB FUNCTION Boost Capacitor Connection. Connect a 0.1F ceramic capacitor from BST to LX. Internal Regulator Output. Bypass VD to GND with a 0.1F ceramic capacitor. 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. Shutdown Control Input. Pull ON/OFF low to put the device in shutdown mode. Drive ON/OFF high for normal operation. Ground Input Voltage. Bypass VIN to GND with a low ESR capacitor as close to the device as possible. Source Connection of Internal High-Side Switch
5 6 7 8
ON/OFF GND VIN LX
Block Diagram
ON/OFF VIN
ENABLE 1.69V REGULATOR (FOR DRIVER)
REGULATOR (FOR ANALOG)
CPFM
IREF-PFM HIGH-SIDE CURRENT SENSE IREF-LIM
VD
CILIM VREF OSC RAMP
BST
MAX5035
FB RAMP Rh x1 Rl GND TYPE 3 COMPENSATION VREF CPWM EAMP CLK CONTROL LOGIC
THERMAL SHUTDOWN
LX
SGND
8
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1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter
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 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 350A, and in shutdown mode, consumes only 10A. The MAX5035 also features undervoltage lockout, hiccup mode output shortcircuit protection, and thermal shutdown. 0.1F, 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.
MAX5035
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 +160C, 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 +140C, resulting in a pulsed output under continuous thermal overload conditions.
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 10A (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.
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 15k, then calculate R3 as follows: R3 = (VOUT - 1.22) x R4 1.22
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 + x 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 1M. 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.
VIN 7.5V TO 76V 68F R1 VIN ON/OFF R2 100H LX 0.1F BST D1 50SQ100 R3 41.2k FB VD SGND GND 0.1F R4 13.3k COUT 68F VOUT 5V
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
Figure 1. Adjustable Output Voltage _______________________________________________________________________________________ 9
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. drop (VFB) less than 0.45V at +25C 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.
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= 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. (VIN - VOUT ) x D 0.2 x IOUTMAX x fSW
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 IL IOUT + 2
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
CIN = where IL =
IOUT x D (1- D) VQ x fSW ,
(VIN - VOUT ) x VOUT VIN x fSW x L V D = OUT VIN
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.
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 80m and 51F, 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.
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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: ICRMS = where D IPRMS = IPK 2 + IDC2 + (IPK x IDC ) x 3 V xI IAVGIN = OUT OUT VIN x 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 is the converter efficiency. The ESR of aluminum electrolytic capacitors increases significantly at cold temperatures. Use a 1F or greater value ceramic capacitor in parallel with the aluminum electrolytic input capacitor, especially for input voltages below 8V. IPRMS2 - IAVGIN2 COUT capacitance and the ESR required for a specified ripple using the following equations: ESROUT = VOESR IL
MAX5035
IL 2.2 x VOQ x fSW
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 100m to 250m ESR are recommended to ensure the closedloop stability, while keeping the output ripple low. fZ = 1 2 x x COUT x ESROUT
The MAX5035 has an internal soft-start time (tSS) of 400s. 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 68F 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 xt 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.
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
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"
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1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter MAX5035
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 0.1F LX R1 D1 L1 VOUT COUT
MAX5035
ON/OFF FB VD SGND GND 0.1F
R2
Figure 2. Fixed Output Voltages
Table 2. Typical External Components Selection (Circuit of Figure 2)
VIN (V) 7.5 to 76 VOUT (V) 3.3 IOUT (A) 0.5 EXTERNAL COMPONENTS CIN = 68F, Panasonic, EEVFK2A680Q COUT = 68F, Vishay Sprague, 594D686X_010C2T CBST = 0.1F, 0805 R1 = 1M 1%, 0805 R2 = 384k 1%, 0805 D1 = 50SQ100, IR L1 = 100H, Coilcraft Inc., DO5022P-104 CIN = 68F, Panasonic, EEVFK2A680Q COUT = 68F, Vishay Sprague, 594D68X_010C2T CBST = 0.1F, 0805 R1 = 1M 1%, 0805 R2 = 384k 1%, 0805 D1 = 50SQ100, IR L1 = 100H, Coilcraft Inc., DO5022P-104 CIN = 68F, Panasonic, EEVFK2A680Q COUT = 15F, Vishay Sprague, 594D156X0025C2T CBST = 0.1F, 0805 R1 = 1M 1%, 0805 R2 = 139k 1%, 0805 D1 = 50SQ100, IR L1 = 220H, Coilcraft Inc., DO5022P-224
7.5 to 76
3.3
1
7.5 to 76
5
0.5
7.5 to 76
5
1
15 to 76
12
1
12
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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) IOUT (A) EXTERNAL COMPONENTS CIN = 220F, Panasonic, EEVFK1E221P COUT = 68F, Vishay Sprague, 594D686X_010C2T CBST = 0.1F, 0805 R1 = 1M 1%, 0805 R2 = 274k 1%, 0805 D1 = B220, Diodes Inc. L1 = 100H, Coilcraft Inc., DO5022P-104 CIN = 220F, Panasonic, EEVFK1E221P COUT = 68F, Vishay Sprague, 594D686X_010C2T CBST = 0.1F, 0805 R1 = 1M 1%, 0805 R2 = 274k 1%, 0805 D1 = B220, Diodes Inc. L1 = 100H, Coilcraft Inc., DO5022P-104 CIN = 220F, Panasonic, EEVFK1H221P COUT = 68F, Vishay Sprague, 594D686X_010C2T CBST = 0.1F, 0805 R1 = 1M 1%, 0805 R2 = 130k 1%, 0805 D1 = MBRS2040, ON Semiconductor L1 = 100H, Coilcraft Inc., DO5022P-104 CIN = 220F, Panasonic, EEVFK1H221P COUT = 68F, Vishay Sprague, 594D686X_010C2T CBST = 0.1F, 0805 R1 = 1M 1%, 0805 R2 = 130k 1%, 0805 D1 = MBRS2040, ON Semiconductor L1 = 100H, Coilcraft Inc., DO5022P-104 CIN = 220F, Panasonic, EEVFK1H221P COUT = 15F, Vishay Sprague, 594D156X_0025C2T CBST = 0.1F, 0805 R1 = 1M 1%, 0805 R2 = 130k 1%, 0805 D1 = MBRS2040, ON Semiconductor L1 = 220H, Coilcraft Inc., DO5022P-224
3.3
1
9 to 14
5
1
3.3
1
18 to 36
5
1
12
1
______________________________________________________________________________________
13
1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter MAX5035
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
MAX5035
PTC* VIN 12V CIN 68F Ct Rt ON/OFF VIN
FB BST 0.1F LX VD D1 B240 L1 100H
VOUT 5V AT 1A
SGND GND 0.1F
COUT 68F
*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 MAX5035
MAX5035B
R1 ON/OFF VIN 7.5V TO 36V CIN 68F Ct Rt VIN
FB BST 0.1F LX VD D1 B240 COUT 68F L1 220H
VOUT 5V
SGND GND 0.1F
MAX5035A
R1' ON/OFF VIN C'IN 68F Ct' Rt'
FB BST 0.1F LX VD D1' B240 C'OUT 68F L1' 100H
V'OUT 3.3V
SGND GND 0.1F
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
1A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converter MAX5035
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
INCHES DIM A A1 B C e E H L 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
MILLIMETERS 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 1.27
N
E
H
VARIATIONS:
1
INCHES
MILLIMETERS MIN 4.80 8.55 9.80 MAX 5.00 8.75 10.00 N MS012 8 AA 14 AB 16 AC
TOP VIEW
DIM D D D
MIN 0.189 0.337 0.386
MAX 0.197 0.344 0.394
D C
A e B A1
0 -8 L
FRONT VIEW
SIDE VIEW
PROPRIETARY INFORMATION TITLE:
PACKAGE OUTLINE, .150" SOIC
APPROVAL DOCUMENT CONTROL NO. REV.
21-0041
B
1 1
16
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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
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 (c) 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.
PDIPN.EPS

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