19-3872; Rev 0; 3/06 KIT ATION EVALU E L B AVAILA 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters The MAX5090A/B/C easy-to-use, high-efficiency, highvoltage step-down DC-DC converters operate from an input voltage up to 76V, and consume only 310µA quiescent current at no load. This pulse-width-modulated (PWM) converter operates at a fixed 127kHz switching frequency at heavy loads, and automatically switches to pulse-skipping mode to provide low quiescent current and high efficiency at light loads. The MAX5090 includes internal frequency compensation simplifying circuit implementation. The device can also be synchronized with external system clock frequency in a noise-sensitive application. The MAX5090 uses an internal low on-resistance and a 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 overtemperature shutdown. The MAX5090 delivers up to 2A output current. External shutdown is included, featuring 19µA (typ) shutdown current. The MAX5090A/MAX5090B versions have fixed output voltages of 3.3V and 5V, respectively, while the MAX5090C features an adjustable 1.265V to 11V output voltage. The MAX5090 is available in a space-saving 16-pin thin QFN package (5mm x 5mm) and operates over the automotive temperature range (-40°C to +125°C). Applications Automotive Industrial Features ♦ Wide Input Voltage Range: 6.5V to 76V ♦ Fixed (3.3V, 5V) and Adjustable (1.265V to 11V) Output-Voltage Versions ♦ 2A Output Current ♦ Efficiency Up to 92% ♦ Internal 0.26Ω High-Side DMOS FET ♦ 310µA Quiescent Current at No Load ♦ ♦ ♦ ♦ ♦ 19µA Shutdown Current Internal Frequency Compensation Fixed 127kHz Switching Frequency External Frequency Synchronization Thermal Shutdown and Short-Circuit Current Limit ♦ -40°C to +125°C Automotive Temperature Range ♦ 16-Pin (5mm x 5mm) Thin QFN Package ♦ Capable of Dissipating 2.67W at +70°C Ordering Information TEMP RANGE PART MAX5090AATE+ -40°C to +125°C 16 TQFN-EP** 3.3 MAX5090AATE -40°C to +125°C 16 TQFN-EP** 3.3 MAX5090BATE+ -40°C to +125°C 16 TQFN-EP** 5.0 MAX5090BATE 5.0 -40°C to +125°C 16 TQFN-EP** Ordering Information continued at end of data sheet. *The package code is T1655-3. **EP = Exposed pad. +Denotes lead-free package. Distributed Power Typical Operating Circuit RIN 10Ω DRAIN 13 CBYPASS 0.47µF 100µH DRAIN LX CBST 0.22µF ON/OFF MAX5090B D1 PDS5100H SGND ON/OFF 11 10 9 EP DRAIN 14 MA5090 N.C. 15 8 FB 7 SS 6 SYNC 5 VD BST N.C. 16 FB 3.3µF 1 2 3 4 VIN CSS 0.047µF VD BST PGND LX SS SYNC SGND COUT 100µF 12 LX VIN VOUT 5V/2A N.C. VIN 7.5V TO 76V PGND Pin Configuration TOP VIEW CIN 68µF OUTPUT VOLTAGE (V) PINPACKAGE* TQFN ________________________________________________________________ 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 MAX5090A/B/C General Description MAX5090A/B/C 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters ABSOLUTE MAXIMUM RATINGS (Voltages referenced to PGND, unless otherwise specified.) VIN, DRAIN .............................................................-0.3V to +80V SGND, PGND.………………………………………-0.3V to +0.3V LX.................................................................-0.8V to (VIN + 0.3V) BST ...............................................................-0.3V to (VIN + 10V) BST to LX................................................................-0.3V to +10V ON/OFF........................................................-0.3V to (VIN + 0.3V) VD, SYNC ...............................................................-0.3V to +12V SS…………………………………………………………-0.3 to +4V FB MAX5090A/MAX5090B…………….……… ...….-0.3V to +15V MAX5090C ................1mA (internally clamped to +2V, -0.3V) VOUT Short-Circuit Duration………………………… ...Continuous VD Short-Circuit Duration………….............................Continuous Continuous Power Dissipation (TA = +70°C)* 16-Pin TQFN (derate 33.3mW/°C above +70°C) ........2.667W Operating Junction Temperature Range ...........-40°C to +125°C Storage Temperature Range .........................…-65°C to +150°C Junction Temperature……...……………………………….+150°C Lead Temperature (soldering, 10s) .................................+300°C *As per JEDEC 51 Standard Multilayer Board. Stresses beyond those listed under "Absolute Maximum Ratings" may cause 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, VSYNC = 0V, IOUT = 0, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Operating Circuit.) (Note 1) PARAMETER Input Voltage Range Undervoltage Lockout UVLO Hysteresis SYMBOL UVLO VOUT Output Voltage Range VOUT Efficiency Quiescent Supply Current (Note 2) Quiescent Supply Current (Note 2) Quiescent Supply Current (Note 2) Shutdown Current MIN VFB η IQ IQ IQ ISHDN TYP 6.5 VIN rising 5.70 UVLOHYS Output Voltage Feedback Voltage CONDITIONS VIN 6.17 MAX UNITS 76.0 V 6.45 V 0.5 V MAX5090A VIN = 6.5V to 76V, IOUT = 0 to 2A 3.20 3.3 3.39 MAX5090B VIN = 7.5V to 76V, IOUT = 0 to 2A 4.85 5.0 5.15 MAX5090B VIN = 7V to 76V, IOUT = 0 to 1A 4.85 5.0 MAX5090C only 1.265 MAX5090C, VIN = 6.5V to 76V 1.191 1.228 V 5.15 11.000 V 1.265 V MAX5090A VIN = 12V, IOUT = 1A 80 MAX5090B VIN = 12V, IOUT = 1A 88 MAX5090C VIN = 12V, VOUT = 5V, IOUT = 1A 88 MAX5090A VIN = 6.5V to 28V 310 550 MAX5090B VIN = 7V to 28V 310 550 MAX5090C VIN = 6.5V to 28V 310 550 MAX5090A VIN = 6.5V to 40V 310 570 MAX5090B VIN = 7V to 40V 310 570 MAX5090C VIN = 6.5V to 40V 310 570 MAX5090A VIN = 6.5V to 76V 310 650 MAX5090B VIN = 7V to 76V 310 650 MAX5090C VIN = 6.5V to 76V % 310 650 VON/OFF = 0V, VIN = 14V 19 45 CSS = 0 700 µA µA µA µA SOFT-START Default Internal Soft-Start Period Soft-Start Charge Current 2 ISS 4.5 10 _______________________________________________________________________________________ µs 16.0 µA 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters (VIN = +12V, VON/OFF = +12V, VSYNC = 0V, IOUT = 0, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Operating Circuit.) (Note 1) PARAMETER SYMBOL Soft-Start Reference Voltage VSS(REF) CONDITIONS MIN TYP MAX UNITS 1.23 1.46 1.65 V 3.3 INTERNAL SWITCH/CURRENT LIMIT Peak Switch Current Limit ILIM (Note 3) 2.4 Switch Leakage Current IOL VIN = 76V, VON/OFF = 0V, VLX = 0V -10 Switch On-Resistance PFM Threshold PFM Threshold FB Input Bias Current RDS(ON) ISWITCH = 1A IPFM Minimum switch current in any cycle 1 IPFM Minimum switch current in any cycle at TJ ≤ +25°C (Note 4) 14 IB 5.0 A +10 µA 0.26 0.4 Ω 60 300 mA 300 mA MAX5090C, VFB = 1.2V -150 +0.1 +150 nA Rising trip point 1.180 1.38 1.546 V 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 mV 10 100 nA 127 150 kHz 200 kHz OSCILLATOR/SYNCHRONIZATION Oscillator Frequency f0SC 106 Synchronization fSYNC 119 Maximum Duty Cycle DMAX VIN = 6.5V to 76V, VOUT ≤ 11V SYNC High-Level Voltage 80 95 % 2.0 V SYNC Low-Level Voltage 0.8 V SYNC Minimum Pulse Width 350 ns +1 µA 8.4 V SYNC Input Leakage -1 INTERNAL VOLTAGE REGULATOR Regulator Output Voltage VD Dropout Voltage ∆VD/∆IVD Load Regulation VIN = 9V to 76V, IOUT = 0 7.0 7.8 6.5V ≤ VIN ≤ 8.5V, IOUT = 15mA 0.5 V 0 to 15mA 10 Ω 30 °C/W +175 °C 20 °C PACKAGE THERMAL CHARACTERISTICS Thermal Resistance (Junction to Ambient) θJA TQFN package (JEDEC 51) TSH Temperature rising THERMAL SHUTDOWN Thermal-Shutdown Junction Temperature Thermal-Shutdown Hysteresis THYST Note 1: All limits at -40°C are guaranteed by design, not production tested. Note 2: For total current consumption during switching (at no load), also see the Typical Operating Characteristics. Note 3: Switch current at which the current-limit circuit is activated. Note 4: Limits are guaranteed by design. _______________________________________________________________________________________ 3 MAX5090A/B/C ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VIN = 12V, VON/OFF =12V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Operating Circuit, if applicable.) VOUT vs. TEMPERATURE (MAX5090BATE, VOUT = 5V) 3.38 3.36 5.10 3.30 3.36 IOUT = 0 VOUT (V) IOUT = 0 3.32 3.38 3.34 5.05 VOUT (V) 5.00 3.28 3.30 3.28 3.26 4.95 IOUT = 2A 3.24 IOUT = 2A 3.26 IOUT = 2A 3.24 4.90 3.22 3.22 4.85 3.20 -25 0 25 50 75 -25 0 25 50 75 100 125 150 AMBIENT TEMPERATURE (°C) AMBIENT TEMPERATURE (°C) LINE REGULATION (MAX5090BATE, VOUT = 5V) LOAD REGULATION (MAX5090AATE, VOUT = 3.3V) 3.40 MAX5090 toc04 5.15 5.10 6.5 3.38 3.36 VOUT (V) 5.00 36 3.30 VIN = 24V VIN = 6.5V 3.26 IOUT = 2A 66 76 VIN = 76V 5.00 4.95 3.24 4.90 56 5.10 3.28 4.95 46 5.15 5.05 VIN = 76V 3.32 26 LOAD REGULATION (MAX5090BATE, VOUT = 5V) 3.34 IOUT = 0 16 VIN (V) VOUT (V) 5.05 3.20 -50 100 125 150 MAX5090 toc05 -50 VOUT (V) IOUT = 0 3.32 MAX5090 toc06 VOUT (V) 3.34 3.40 MAX5090 toc02 5.15 MAX5090 toc01 3.40 LINE REGULATION (MAX5090AATE, VOUT = 3.3V) MAX5090 toc03 VOUT vs. TEMPERATURE (MAX5090AATE, VOUT = 3.3V) VIN = 24V VIN = 6.5V 4.90 3.22 3.20 16 26 36 46 56 66 0.1 76 1 EFFICIENCY vs. LOAD CURRENT (MAX5090AATE, VOUT = 3.3V) 80 VIN = 12V VIN = 24V VIN = 48V 30 80 VIN = 12V 60 VIN = 24V 50 VIN = 48V 40 20 10 10 VIN = 76V 800 1200 LOAD CURRENT (mA) 10 1600 2000 100 1000 10,000 4.0 3.5 VOUT = 3.3V 5% DROP IN VOUT PULSED OUTPUT LOAD 3.0 2.5 2.0 1.5 1.0 0 400 1 OUTPUT CURRENT LIMIT vs. TEMPERATURE (MAX5090AATE) VIN = 6.5V 70 20 0 4 90 30 VIN = 76V 0 0.1 ILOAD (mA) 100 EFFICIENCY (%) VIN = 6.5V 40 10,000 MAX5090 toc08 90 50 1000 EFFICIENCY vs. LOAD CURRENT (MAX5090BATE, VOUT = 5V) MAX5090 toc07 100 60 100 ILOAD (mA) VIN (V) 70 4.85 10 OUTPUT CURRENT LIMIT (A) 6.5 MAX5090 toc09 4.85 EFFICIENCY (%) MAX5090A/B/C 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters 0 400 800 1200 LOAD CURRENT (mA) 1600 2000 -50 -25 0 25 50 75 100 125 150 AMBIENT TEMPERATURE (°C) _______________________________________________________________________________________ 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters 2.5 2.0 1.5 5.0 4.0 3.0 -25 0 25 50 75 100 125 150 MAX5090 toc12 6.0 VOUT = 5V 5% DROP IN VOUT PULSED OUTPUT LOAD 5.0 4.0 3.0 2.0 1.0 1.0 -50 6.5 16 26 36 46 56 66 6.5 76 16 26 36 46 56 66 76 INPUT VOLTAGE (V) NO-LOAD SUPPLY CURRENT vs. TEMPERATURE (MAX5090AATE) NO-LOAD SUPPLY CURRENT vs. INPUT VOLTAGE (MAX5090AATE) SHUTDOWN CURRENT vs. TEMPERATURE (MAX5090AATE) 600 600 450 400 500 450 400 -25 0 25 50 75 100 125 150 6.5 16 26 36 46 56 66 76 MAX5090 toc15 22 18 -50 -25 0 25 50 100 125 150 175 AMBIENT TEMPERATURE (°C) INPUT VOLTAGE (V) AMBIENT TEMPERATURE (°C) SHUTDOWN CURRENT vs. INPUT VOLTAGE OUTPUT VOLTAGE vs. INPUT VOLTAGE LOAD-TRANSIENT RESPONSE (MAX5090AATE) VOUT = 3.3V 35 MAX5090 toc18 13 MAX5090 toc16 45 MAX5090 toc17 -50 26 10 300 300 VOUT = 3.3V 14 350 350 40 550 30 SHUTDOWN CURRENT (µA) 500 VOUT = 3.3V NO-LOAD SUPPLY CURRENT 550 MAX5090 toc14 INPUT VOLTAGE (V) MAX5090 toc13 AMBIENT TEMPERATURE (°C) VOUT = 3.3V NO-LOAD SUPPLY CURRENT (µA) 6.0 7.0 2.0 1.0 MAX5090CATE VOUT = 11V VON/OFF = VIN 11 VOUT = 3.3V A 30 VOUT (V) SHUTDOWN CURRENT (µA) VOUT = 3.3V 5% DROP IN VOUT PULSED OUTPUT LOAD OUTPUT CURRENT LIMIT (A) 3.0 7.0 MAX5090 toc11 3.5 VOUT = 5V 5% DROP IN VOUT PULSED OUTPUT LOAD OUTPUT CURRENT LIMIT vs. INPUT VOLTAGE (MAX5090BATE) OUTPUT CURRENT LIMIT vs. INPUT VOLTAGE (MAX5090AATE) OUTPUT CURRENT LIMIT (A) OUTPUT CURRENT LIMIT (A) 4.0 MAX5090 toc010 OUTPUT CURRENT LIMIT vs. TEMPERATURE (MAX5090BATE) 25 20 9 IOUT = 2A IOUT = 1A 6 IOUT = 0A 15 10 B 3 5 0 6.5 16 26 36 46 56 INPUT VOLTAGE (V) 66 76 0 5 6 7 8 9 10 11 11.5 12 12.5 13 VIN (V) 400µs/div A: VOUT, 200mV/div, AC-COUPLED B: IOUT, 1A/div, 1A TO 2A _______________________________________________________________________________________ 5 MAX5090A/B/C Typical Operating Characteristics (continued) (VIN = 12V, VON/OFF =12V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Operating Circuit, if applicable.) MAX5090A/B/C 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters Typical Operating Characteristics (continued) (VIN = 12V, VON/OFF =12V, TA = TJ = -40°C to +125°C, unless otherwise noted. Typical values are at TA = +25°C. See the Typical Operating Circuit, if applicable.) LOAD-TRANSIENT RESPONSE (MAX5090AATE) LX WAVEFORMS (MAX5090AATE) LX WAVEFORMS (MAX5090AATE) MAX5090 toc20 MAX5090 toc19 MAX5090 toc21 VOUT = 3.3V A A A VOUT = 3.3V VOUT = 3.3V B B B 0 400µs/div 4µs/div A: VOUT, 200mV/div, AC-COUPLED B: IOUT, 500mA/div, 0.1A TO 1A 4µs/div A: SWITCH VOLTAGE (LX PIN), 20mV/div (VIN = 48V) B: INDUCTOR CURRENT, 2A/div (I0 = 2A) LX WAVEFORM (MAX5090AATE) STARTUP WAVEFORM (IOUT = 0) MAX5090 toc22 A: SWITCH VOLTAGE, 20V/div (VIN = 48V) B: INDUCTOR CURRENT, 200mA/div (I0 = 75mA) STARTUP WAVEFORM (IOUT = 2A) MAX5090 toc23 MAX5090 toc24 VOUT = 3.3V A A A B B B CSS = 0.047µF 4µs/div 4ms/div A: SWITCH VOLTAGE, 20V/div (VIN = 48V) B: INDUCTOR CURRENT, 200mA/div (IOUT = 0) 4ms/div A: VON/OFF, 2V/div B: VOUT, 1V/div PEAK SWITCH CURRENT vs. INPUT VOLTAGE A: VON/OFF, 2V/div B: VOUT, 1V/div SYNCHRONIZATION SYNCHRONIZATION MAX5090 toc26 MAX5090 toc25 7.0 PEAK SWITCH CURRENT (A) CSS = 0.047µF MAX5090AATE VOUT = 3.3V 5% DROP IN VOUT PULSED OUTPUT LOAD 6.0 MAX5090 toc27 fSYNC = 119kHz 5.0 fSYNC = 200kHz SYNC 2V/div SYNC 2V/div LX 10V/div LX 10V/div 4.0 3.0 2.0 1.0 6.5 16 26 36 46 56 66 76 2µs/div 1µs/div INPUT VOLTAGE (V) 6 _______________________________________________________________________________________ 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters PIN NAME 1, 2 LX FUNCTION 3 BST 4 VIN Input Voltage. Bypass VIN to SGND with a low-ESR capacitor as close to the device as possible. 5 VD Internal Regulator Output. Bypass VD to PGND with a 3.3µF/10V or greater ceramic capacitor. 6 SYNC Synchronization Input. Connect SYNC to an external clock for synchronization. Connect to SGND to select the internal 127kHz switching frequency. 7 SS Soft-Start Capacitor Connection. Connect an external capacitor from SS to SGND to adjust the softstart time. 8 FB Output Sense Feedback Connection. For fixed output voltage (MAX5090A/MAX5090B), connect FB to VOUT. For adjustable output voltage (MAX5090C), use an external resistive voltage-divider to set VOUT. VFB regulating set point is 1.228V. 9 ON/OFF Shutdown Control Input. Pull ON/OFF low to put the device in shutdown mode. Drive ON/OFF high for normal operation. Connect ON/OFF to VIN with short leads for always-on operation. Source Connection of Internal High-Side Switch Boost Capacitor Connection. Connect a 0.22µF ceramic capacitor from BST to LX. 10 SGND 11, 15, 16 N.C. 12 PGND 13, 14 DRAIN — EP Signal Ground. SGND must be connected to PGND for proper operation. No Connection. Not internally connected. Power Ground Internal High-Side Switch Drain Connection Exposed Pad. Solder EP to SGND plane to aid in heat dissipation. Do not use as the only electrical ground connection. Detailed Description The MAX5090 step-down DC-DC converter operates from a 6.5V 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 127kHz switching frequency or can be synchronized with an external system clock frequency. The device also features automatic pulse-skipping mode to provide high efficiency at light loads. Under no load, the MAX5090 consumes only 310µA, and in shutdown mode, consumes only 20µA. The MAX5090 also features undervoltage-lockout, hiccup-mode output short-circuit protection and thermal shutdown. ON/OFF/Undervoltage Lockout (UVLO) Use the ON/OFF function to program the external UVLO threshold at the input. Connect a resistive voltagedivider from V IN to SGND 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 1.38 R2 Set the external VUVLO(TH) to greater than 6.45V. The maximum recommended value for R2 is less than 1MΩ. ON/OFF is a logic input and can be safely driven to the full VIN range. Connect ON/OFF to VIN for automatic startup. Drive ON/OFF to ground to shut down the MAX5090. Shutdown forces the internal power MOSFET off, turns off all internal circuitry, and reduces the V IN supply current to 20µA (typ). The ON/OFF rising threshold is 1.546V (max). Before any operation begins, the voltage at ON/OFF must exceed 1.546V. The ON/OFF input has 100mV hysteresis. If the external UVLO threshold setting divider is not used, an internal undervoltage-lockout feature monitors the supply voltage at VIN and allows the operation to start when VIN rises above 6.45V (max). The internal UVLO rising threshold is set at 6.17V with 0.5V hysteresis. The VIN and VON/OFF voltages must be above 6.5V and 1.546V, respectively, for proper operation. _______________________________________________________________________________________ 7 MAX5090A/B/C Pin Description MAX5090A/B/C 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters Simplified Functional Diagram ON/OFF DRAIN VIN REGULATOR (FOR ANALOG) ENABLE 1.38V IREF-PFM CPFM HIGH-SIDE CURRENT SENSE REGULATOR (FOR DRIVER) VD VREF OSC CILIM RAMP IREF-LIM CLKI RMP BST SRMP SYNC SRAMP MUX SCK SS CLK MIN N FB RAMP CONTROL LOGIC *RH x1 LX TYPE 3 COMPENSATION CPWM EAMP *RL THERMAL SHUTDOWN PGND MAX5090 *RH = 0Ω AND RL = ∞ FOR MAX5090C SGND 8 _______________________________________________________________________________________ 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters Soft-Start (SS) The MAX5090 provides the flexibility to externally program a suitable soft-start time for a given application. Connect an external capacitor from SS to SGND to use the external soft-start. Soft-start gradually ramps up the reference voltage seen by the error amplifier to control the output’s rate of rise and reduce the input surge current during startup. For soft-start time longer than 700µs, use the following equation to calculate the soft-start capacitor (CSS) required for the soft-start time (tSS): On startup, an internal low-side switch connects LX to ground and charges the BST capacitor to (VD - VDIODE). 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. Synchronization (SYNC) SYNC controls the oscillator frequency. Connect SYNC to SGND to select 127kHz operation. Use the SYNC input to synchronize to an external clock. SYNC has a guaranteed frequency range of 119kHz to 200kHz when using an external clock. When SYNC is connected to SGND, the internal clock is used to generate a ramp with the amplitude in proportion to V IN and the period corresponding to the internal clock frequency to modulate the duty cycle of the high-side switch. If an external clock (SYNC clock) is applied at SYNC for four cycles, the MAX5090 selects the SYNC clock. The MAX5090 generates a ramp (SYNC ramp) with the amplitude in proportion to VIN and the period corresponding to the SYNC clock frequency. The MAX5090 initially blanks the SYNC ramp for 375µs (typ) to allow the ramp to reach its target amplitude (proportion to the VIN supply). After the SYNC blanking time, the SYNC ramp and the SYNC clock switch to the PWM controller and replace the internal ramp and the internal clock, respectively. If the SYNC clock is removed for three internal clock cycles, the internal clock and the internal ramp switch back to the PWM controller. The minimum pulse-width requirement for the external clock is 350ns, and if the requirement is not met, the MAX5090 could ignore the clock as a noisy bounce. CSS = 10 × 10 −6 × t SS 1.46 where tSS > 700µs and CSS is in Farads. The MAX5090 also provides an internal soft-start (700µs, typ) with a current source to charge an internal capacitor to rise up to the bandgap reference voltage. The internal soft-start voltage will eventually be pulled up to 3.4V. The internal soft-start reference also feeds to the error amplifier. The error amplifier takes the lowest voltage among SS, the internal soft-start voltage, and the bandgap reference voltage as the input reference for VOUT. Soft-start occurs when power is first applied and when the device exits shutdown. The MAX5090 also goes through soft-start when coming out of thermal-overload protection. During a soft-start, if the voltage at SS (VSS) is charged up to 1.46V in less than 700µs, the MAX5090 takes its default internal soft-start (700µs) to ramp up as its reference. After the SS and the internal soft-start ramp up over the bandgap reference, the error amplifier takes the bandgap reference. Thermal-Overload Protection The MAX5090 features integrated thermal-overload protection. Thermal-overload protection limits power dissipation in the device, and protects the device from a thermal overstress. When the die temperature exceeds +175°C, an internal thermal sensor signals the shutdown logic, turning off the internal power MOSFET, resetting the internal soft-start 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 +155°C, resulting in a pulsed output under continuous thermal-overload conditions. _______________________________________________________________________________________ 9 MAX5090A/B/C 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 0.22µF, 16V ceramic capacitor located as close to the device as possible. MAX5090A/B/C 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters VIN 6.5V TO 76V CIN 68µF R1 RIN 10Ω CBYPASS 0.47µF VIN DRAIN 100µH VOUT 3.3V, 2A D1 PDS5100H COUT 100µF LX ON/OFF 0.22µF R2 BST MAX5090A SS SYNC SGND FB PGND 0.047µF VD 3.3µF Figure 1. Fixed Output-Voltage Configuration VIN 7.5V TO 76V CIN 68µF RIN 10Ω CBYPASS 0.47µF VIN VOUT 5.25V, 2A 100µH DRAIN LX ON/OFF 0.22µF D1 PDS5100H R3 COUT 100µF BST MAX5090C SS SYNC SGND FB 0.047µF PGND VD R4 3.3µF Figure 2. Adjustable Output-Voltage Configuration 10 ______________________________________________________________________________________ 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters Table 1. Diode Selection VIN (V) DIODE PART NUMBER 6.5 to 36 RB051L-40 Central Semiconductor MBRS340T3 ON Semiconductor B340LB Setting the Output Voltage The MAX5090A/MAX5090B have preset output voltages of 3.3V and 5.0V, respectively. Connect FB to VOUT for the preset output voltage (Figure 1). The MAX5090C offers an adjustable output voltage. Set the output voltage with a resistive divider connected from the circuit’s output to ground (Figure 2). Connect the center node of the divider to FB. Choose R4 less than 15kΩ, then calculate R3 as follows: R3 = (VOUT − 1.228) x R4 1.228 The MAX5090 features internal compensation for optimum closed-loop bandwidth and phase margin. Because of the internal compensation, the output must be sensed immediately after the primary LC. Inductor Selection The MAX5090 is a fixed-frequency converter with fixed internal frequency compensation. The internal fixed compensation assumes a 100µH inductor and 100µF output capacitor with 50mΩ ESR. It relies on the location of the double LC pole and the ESR zero frequency for proper closed-loop bandwidth and the phase margin at the closed-loop unity-gain frequency. See Table 2 for proper component values. Usually, 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. However, use the recommended inductors in Table 2 to ensure stable operation with optimum bandwidth. Use an inductor with a maximum saturation current rating greater than or equal to the maximum peak current limit (5A). Use inductors with low DC resistance for a higher efficiency converter. Selecting a Rectifier The MAX5090 requires an external Schottky rectifier as a freewheeling diode. Connect this rectifier close to the device using short leads and short PC board traces. The rectifier diode must fully conduct the inductor current when the power FET is off to have a full rectifier function. Choose a rectifier with a continuous current 6.5 to 56 Diodes Inc. MBRM560 Diodes Inc. RB095B-60 Central Semiconductor MBRD360T4 6.5 to 76 MANUFACTURER 50SQ80 PDS5100H ON Semiconductor IR Diodes Inc. 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 reversevoltage Schottky rectifiers that have higher forward-voltage drops. Use a Schottky rectifier with forward-voltage drop (V F) less than 0.55V and 0.45V at +25°C and +125°C, respectively, and at maximum load current to avoid forward biasing of the internal parasitic body diode (LX to ground). See Figure 3 for forward-voltage drop vs. temperature of the internal body diode of the MAX5090. Internal parasitic body-diode conduction may cause improper operation, 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 reflecting back to the source dictate the capacitance requirement. The MAX5090 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: ______________________________________________________________________________________ 11 MAX5090A/B/C Thermal-overload protection is intended to protect the MAX5090 in the event of a fault condition. For normal circuit operation, do not exceed the absolute maximum junction temperature rating of TJ = +150°C. ESRIN = ∆VESR ∆IL IOUT + 2 I × D(1 − D) CIN = OUT ∆VQ × fSW where: ∆IL = (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 (127kHz). 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 40mΩ and 100µF, 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 the temperature. The maximum capacitor RMS current occurs at approximately 50% duty cycle. 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 = IPRMS2 − IAVGin2 where: IPRMS = IAVGin = D (IPK 2 + IDC 2 + IPK xIDC ) x 3 VOUT x IOUT VIN x η ∆IL IPK = IOUT + 2 ∆IL IDC = IOUT − 2 VOUT D = VIN IPRMS is the input switch RMS current, I AVGin is the input average current, and η is the converter efficiency. The ESR of the aluminum electrolytic capacitor 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. 12 800 700 600 VF_D1 (mV) MAX5090A/B/C 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters 500 400 300 200 100 0 -40 25 100 125 150 TEMPERATURE (°C) Figure 3. Forward-Voltage Drop vs. Temperature of the Internal Body Diode of MAX5090 Output Filter Capacitor The output capacitor COUT forms double pole with the inductor and a zero with its ESR. The MAX5090’s internal fixed compensation is designed for a 100µF capacitor, and the ESR must be from 20mΩ to 100mΩ. The use of an aluminum or tantalum electrolytic capacitor is recommended. See Table 2 to choose an output capacitor for stable operation. 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. Use the following equations to calculate the contribution of output capacitance and its ESR on the peak-to-peak output ripple voltage: ∆VOESR = ∆IL x ESR ∆IL ∆VOQ ≈ 8 xCOUT x fSW The MAX5090 has a programmable soft-start time (tSS). The output rise time is directly proportional to the output capacitor, output voltage, and the load. The output rise time also depends on the inductor value and the current-limit threshold. It is important to keep the output rise time at startup the same as the soft-start time (tSS) to avoid output overshoot. Large output capacitors take longer than the programmed soft-start time (tSS) and cause error-amplifier saturation. This results in output overshoot. Use greater than 2ms soft-start time for a 100µF output capacitor. ______________________________________________________________________________________ 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters ∆VOESR = ISTEP x ESROUT ∆VOQ = ISTEP x tRESPONSE COUT 2) 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 the BST and VD bypass capacitors very close to the device. 3) Connect the exposed pad of the IC to the SGND plane. Do not make a direct connection between the exposed pad plane and SGND (pin 7) under the IC. Connect the exposed pad and pin 7 to the SGND plane separately. Connect the ground connection of the feedback resistive divider, ON/OFF threshold resistive divider, and the soft-start capacitor to the SGND plane. Connect the SGND plane and PGND plane at one point near the input bypass capacitor at VIN. 4) Use large SGND plane as a heatsink for the MAX5090. Use large PGND and LX planes as heatsinks for the rectifier diode and the inductor. 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. Board Layout Guidelines 1) 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 large PGND plane. ______________________________________________________________________________________ 13 MAX5090A/B/C 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. Use the following equations to calculate the deviation of output voltage due to the ESR and capacitance value of the output capacitor: 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters MAX5090A/B/C Application Circuit VIN RIN CIN CBYPASS R1 VIN L1 DRAIN VOUT LX ON/OFF CBST R2 D1 BST MAX5090B SS SYNC SGND FB PGND CSS VD 3.3µF Figure 4. Fixed Output Voltage Table 2. Typical External Components Selection (Circuit of Figure 4) VIN (V) 6.5 to 76 7.5 to 76 14 VOUT (V) 3.3 5 IOUT (A) EXTERNAL COMPONENTS 2 MAX5090AATE CIN = 2 x 68µF/100V EEVFK2A680Q, Panasonic CBYPASS = 0.47µF/100V, GRM21BR72A474KA, Murata COUT = 220µF/6.3V 6SVP220MX, Sanyo CBST = 0.22µF/16V, GRM188R71C224K, Murata R1 = 0Ω R2 = Open RIN = 10Ω, ±1% (0603) D1 = PDS5100H, Diodes Inc. L1 = 47µH, DO5022P-473 2 MAX5090BATE CIN = 2 x 68µF/100V EEVFK2A680Q, Panasonic CBYPASS = 0.47µF/100V, GRM21BR72A474KA, Murata COUT = 100µF/6.3V 6SVP100M, Sanyo CBST = 0.22µF/16V, GRM188R71C224K, Murata R1 = 0Ω R2 = Open RIN = 10Ω, ±1% (0603) D1 = PDS5100H, Diodes Inc. L1 = 47µH, DO5022P-473 ______________________________________________________________________________________ COUT 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters VIN (V) 6.5 to 40 VOUT (V) 3.3 7.5 to 40 15 to 40 5 11 IOUT (A) MAX5090A/B/C Table 2. Typical External Components Selection (Circuit of Figure 4) (continued) EXTERNAL COMPONENTS 2 MAX5090AATE CIN = 330µF/50V EEVFK1H331Q, Panasonic CBYPASS = 0.47µF/50V, GRM21BR71H474KA, Murata COUT = 100µF/6.3V 6SVP100M, Sanyo CBST = 0.22µF/16V, GRM188R71C224K, Murata R1 = 0Ω R2 = Open RIN = 10Ω, ±1% (0603) D1 = B360, Diodes Inc. L1 = 100µH, DO5022P-104 2 MAX5090BATE CIN = 330µF/50V EEVFK1H331Q, Panasonic CBYPASS = 0.47µF/50V, GRM21BR71H474KA, Murata COUT = 100µF/6.3V 6SVP100M, Sanyo CBST = 0.22µF/16V, GRM188R71C224K, Murata R1 = 0Ω R2 = Open RIN = 10Ω, ±1% (0603) D1 = B360, Diodes Inc. L1 = 100µH, DO5022P-104 2 MAX5090CATE (VOUT programmed to 11V) CIN = 330µF/50V EEVFK1H331Q, Panasonic CBYPASS = 0.47µF/50V, GRM21BR71H474KA, Murata COUT = 100µF/16V 16SVP100M, Sanyo CBST = 0.22µF/16V, GRM188R71C224K, Murata R1 = 910kΩ R2 = 100kΩ R3 = 88.2kΩ, ±1% (0603) R4 = 10kΩ, ±1% (0603) RIN = 10Ω, ±1% (0603) D1 = B360, Diodes Inc. L1 = 100µH, DO5022P-104 Table 3. Component Suppliers SUPPLIER WEBSITE AVX www.avxcorp.com Coilcraft www.coilcraft.com Diodes Incorporated www.diodes.com Panasonic www.panasonic.com Sanyo www.sanyo.com TDK www.component.tdk.com Vishay www.vishay.com ______________________________________________________________________________________ 15 MAX5090A/B/C 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters VIN 12V RIN CIN 68µF CBYPASS VIN VOUT 5V, 2A 100µH DRAIN LX ON/OFF CBST PTC Rt Ct D1 B360 COUT 100µF BST MAX5090B FB SS SYNC SGND CSS VD PGND 3.3µF *LOCATE PTC AS CLOSE TO HEAT-DISSIPATING COMPONENT AS POSSIBLE. Figure 5. Load-Temperature Monitoring with ON/OFF (Requires Accurate VIN) Chip Information PROCESS: BCD TRANSISTOR COUNT: 7893 Ordering Information (continued) PART TEMP RANGE PINPACKAGE* MAX5090CATE+ -40°C to +125°C 16 TQFN-EP** Adj MAX5090CATE Adj -40°C to +125°C 16 TQFN-EP** *The package code is T1655-3. **EP = Exposed pad. +Denotes lead-free package. 16 OUTPUT VOLTAGE (V) ______________________________________________________________________________________ 2A, 76V, High-Efficiency MAXPower Step-Down DC-DC Converters QFN THIN.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 © 2006 Maxim Integrated Products Heslington Printed USA is a registered trademark of Maxim Integrated Products, Inc. MAX5090A/B/C 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.)