Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal
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19-4815; 7/09
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches
MAX15041 low-cost, synchronous DC-DC converter with internal switches delivers output current MAX15041 operates from input voltage 4.5V provides adjustable output voltage from 0.6V VIN, with external resistors. MAX15041 ideal distributed power systems, preregulation, set-top boxes, television, other consumer applications. MAX15041 features peak-current-mode controller with internally fixed 350kHz switching frequency maximum duty cycle. current-mode control architecture simplifies compensation design, ensures cycle-by-cycle current limit fast response line load transients. high-gain transconductance error amplifier allows flexibility setting external compensation using type compensation scheme, thereby allowing ceramic capacitors. This synchronous buck regulator features internal MOSFETs that provide better efficiency than asynchronous solutions, while simplifying design relative discrete controller solutions. addition simplifying design, integrated MOSFETs minimize EMI, reduce board space, provide higher reliability minimizing number external components. MAX15041 also features thermal shutdown overcurrent protection (high-side sourcing low-side sinking), internal with undervoltage lockout. addition, this device ensures safe startup when powering into prebiased output. Other features include externally adjustable soft-start that gradually ramps output voltage reduces inrush current. Independent enable control powergood signals allow flexible power sequencing. MAX15041 available space-saving, highpower, 3mm, 16-pin TQFN-EP package fully specified from -40°C +85°C.
Features
Continuous Output Current Output Accuracy Over Temperature 4.5V Input Voltage Range Adjustable Output Voltage Range from 0.606V Internal 170m RDS-ON High-Side 105m RDS-ON Low-Side Power Switches Fixed 350kHz Switching Frequency Efficiency Cycle-By-Cycle Overcurrent Protection Programmable Soft-Start Stable with Low-ESR Ceramic Output Capacitors Safe Startup into Prebiased Output Enable Input Power-Good Output Fully Protected Against Overcurrent Overtemperature Undervoltage Lockout Space-Saving, Thermally Enhanced, Package
MAX15041
Ordering Information
PART MAX15041ETE+ TEMP RANGE PINPACKAGE MARK
-40°C +85°C TQFN-EP*
+Denotes lead(Pb)-free/RoHS-compliant package. Exposed pad.
Typical Operating Circuit
INPUT MAX15041 PGND PGOOD PGOOD SGND COMP OUTPUT 1.8V
Applications
Distributed Power Systems Wall Adapters Preregulators Set-Top Boxes Televisions xDSL Modems Consumer Products
Configuration appears data sheet.
Maxim Integrated Products
pricing, delivery, ordering information, please contact Maxim Direct 1-888-629-4642, visit Maxim's website www.maxim-ic.com.
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches MAX15041
ABSOLUTE MAXIMUM RATINGS
SGND.-0.3V +30V SGND .-0.3V (VIN 0.3V) PGND .-0.3V (+30V, 0.3V) PGND .-1V (+30V, 0.3V) 50ns PGOOD SGND .-0.3V SGND.-0.3V COMP, SGND.-0.3V (+6V, 0.3V) .-0.3V SGND .-0.3V +36V SGND PGND .-0.3V +0.3V Current (Note .-5A Converter Output Short-Circuit Duration .Continuous Continuous Power Dissipation +70°C) 16-Pin TQFN-EP (derate 14.7mW/°C above +70°C) Multilayer Board .1666mW Package Thermal Resistance (Note .48°C/W .7°C/W Operating Temperature Range .-40°C +85°C Junction Temperature .+150°C Storage Temperature Range .-65°C +150°C Lead Temperature (soldering, 10s) .+300°C
Note internal clamp diodes PGND Applications that forward bias these diodes should take care exceed IC's package power dissipation. Note Package thermal resistances were obtained using method described JEDEC specification JESD51-7, using fourlayer board. detailed information package thermal considerations, refer
Stresses beyond those listed under "Absolute Maximum Ratings" cause permanent damage device. These stress ratings only, functional operation device these other conditions beyond those indicated operational sections specifications implied. Exposure absolute maximum rating conditions extended periods affect device reliability.
ELECTRICAL CHARACTERISTICS
(VIN 12V, CVDD 1µF, 22µF, -40°C +85°C, typical values +25°C, unless otherwise noted.) (Note
PARAMETER STEP-DOWN CONVERTER Input-Voltage Range Input Supply Current Shutdown Input Supply Current ENABLE INPUT Shutdown Threshold Voltage Shutdown Voltage Hysteresis Lockout Threshold Voltage Input Current POWER-GOOD OUTPUT PGOOD Threshold PGOOD Threshold Hysteresis PGOOD Output Voltage PGOOD Leakage Current ERROR AMPLIFIER Error Amplifier Transconductance Error Amplifier Voltage Gain Set-Point Accuracy Input Bias Current AVEA 0.5V 0.7V -100 -100 +100 +100 VPGOOD_TH VPGOOD_HYST VPGOOD_OL IPGOOD IPGOOD 5mA, 0.5V VPGOOD 0.7V rising VEN_SHDN VEN_HYST VEN_LOCK rising 2.9V VEN_LOCK_HYST falling rising 1.95 2.15 Switching regulated internal SYMBOL CONDITIONS UNITS
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches
ELECTRICAL CHARACTERISTICS (continued)
(VIN 12V, CVDD 1µF, 22µF, -40°C +85°C, typical values +25°C, unless otherwise noted.) (Note
PARAMETER Current Discharge Resistance Prebiased Mode Stop Voltage Current Sense COMP Transconductance COMP Clamp Compensation Ramp Valley CLOCK Switching Frequency Maximum Duty Cycle Minimum Controllable On-Time INTERNAL OUTPUT (VDD) Output Voltage Short-Circuit Current Dropout Voltage Undervoltage Lockout Threshold Undervoltage Lockout Hysteresis POWER SWITCH On-Resistance High-Side Switch Source Current-Limit Threshold Low-Side Switch Sink Current-Limit Threshold Leakage Current Leakage Current THERMAL SHUTDOWN Thermal-Shutdown Threshold Thermal-Shutdown Hysteresis HICCUP PROTECTION Blanking Time SoftStart Time Rising +155 VBST 33V, VBST 28V, VBST 33V, High-side switch, Low-side switch, VUVLO_TH VUVLO_HYST IVDD 25mA, 6.5V 6.5V IVDD 25mA, drops rising 4.75 4.25 GMOD 0.7V SYMBOL CONDITIONS 0.45V, sourcing 10mA, sinking, 1.6V 0.65 0.68 UNITS
MAX15041
Note Specifications 100% production tested +25°C. Limits over operating temperature range guaranteed design characterization.
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches MAX15041
Typical Operating Characteristics
(VIN 12V, VOUT 3.3V, CVDD 1µF, 22µF, +25°C, circuit Figure (see Table values), unless otherwise specified.)
EFFICIENCY LOAD CURRENT
MAX15041 toc01
EFFICIENCY LOAD CURRENT
MAX15041 toc02
OUTPUT-VOLTAGE REGULATION LOAD CURRENT
OUTPUT-VOLTAGE REGULATION
MAX15041 toc03
EFFICIENCY VOUT 5.0V VOUT 3.3V VOUT 2.5V VOUT 1.8V VOUT 1.2V
EFFICIENCY VOUT 3.3V VOUT 2.5V VOUT 1.8V VOUT 1.2V
-0.2 -0.4 -0.6 -0.8 -1.0 -1.2
LOAD CURRENT
LOAD CURRENT
LOAD CURRENT
LOAD-TRANSIENT WAVEFORMS
MAX15041 toc04
NORMALIZED OUTPUT VOLTAGE TEMPERATURE
MAX15041 toc05
NORMALIZED OUTPUT VOLTAGE TEMPERATURE
ILOAD NORMALIZED OUTPUT VOLTAGE 1.002 1.000 0.998 0.996 0.994 0.992
MAX15041 toc06
1.002 ILOAD NORMALIZED OUTPUT VOLTAGE 1.001 1.000 0.999 0.998 0.997 0.996 0.995
1.004
ILOAD 2A/div VOUT AC-COUPLED 200mV/div VPGOOD 5V/div 200µs/div
TEMPERATURE (NC)
TEMPERATURE (NC)
POINT vs.TEMPERATURE
MAX15041 toc07
SWITCHING FREQUENCY INPUT VOLTAGE
MAX15041 toc08
FREQUENCY (kHz) +85NC +25NC -40NC
POINT (mV)
TEMPERATURE (NC)
INPUT VOLTAGE
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches
Typical Operating Characteristics (continued)
(VIN 12V, VOUT 3.3V, CVDD 1µF, 22µF, +25°C, circuit Figure (see Table values), unless otherwise specified.)
MAX15041
INPUT SUPPLY CURRENT INPUT VOLTAGE
4.7FH ILOAD
MAX15041 toc09
SHUTDOWN CURRENT INPUT VOLTAGE
SHUTDOWN CURRENT (FA)
MAX15041 toc10
SHUTDOWN CURRENT TEMPERATURE
MAX15041 toc11
INPUT SUPPLY CURRENT (mA) INPUT VOLTAGE
INPUT VOLTAGE
SHUTDOWN CURRENT (FA)
TEMPERATURE (NC)
SHUTDOWN WAVEFORMS
MAX15041 toc12
OUTPUT SHORT-CIRCUIT WAVEFORMS
MAX15041 toc13
5V/div VOUT 2V/div 2A/div VPGOOD 5V/div
VOUT 2V/div 5A/div 5A/div 2V/div
100µs/div
10µs/div
SWITCHING WAVEFORMS
MAX15041 toc14
SOFT-START WAVEFORMS
MAX15041 toc15
10V/div
5V/div
VOUT 2V/div
2A/div
VOUT AC-COUPLED 50mV/div 1µs/div 400µs/div
2A/div VPGOOD 5V/div
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches MAX15041
Typical Operating Characteristics (continued)
(VIN 12V, VOUT 3.3V, CVDD 1µF, 22µF, +25°C, circuit Figure (see Table values), unless otherwise specified.)
SOFT-START TIME CAPACITANCE
MAX15041 toc16
STARTUP INTO PREBIASED OUTPUT
MAX15041 toc17
1000
5V/div
VOUT 2V/div
SOFT-START TIME (ms)
2A/div IOUT 2A/div (nF) 1000 400µs/div
STARTUP INTO PREBIASED OUTPUT
MAX15041 toc18
MAXIMUM LOAD CURRENT AMBIENT TEMPERATURE
5V/div
VOUT 2V/div
MAXIMUM LOAD CURRENT
+150NC
VOUT 3.3V VOUT 2.5V VOUT 1.8V
5A/div
IOUT 5A/div 400µs/div
VOUT 1.2V
AMBIENT TEMPERATURE (NC)
MAXIMUM LOAD CURRENT AMBIENT TEMPERATURE
MAX15041 toc20
MAXIMUM LOAD CURRENT AMBIENT TEMPERATURE
+150NC
MAX15041 toc21
MAXIMUM LOAD CURRENT
+150NC
MAXIMUM LOAD CURRENT
VOUT 3.3V AMBIENT TEMPERATURE (NC) VOUT 2.5V VOUT 1.8V VOUT 1.2V
VOUT 1.2V AMBIENT TEMPERATURE (NC) VOUT 3.3V VOUT 2.5V VOUT 1.8V
MAX15041 toc19
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches
Typical Operating Characteristics (continued)
(VIN 12V, VOUT 3.3V, CVDD 1µF, 22µF, +25°C, circuit Figure (see Table values), unless otherwise specified.)
DEVICE POWER DISSIPATION LOAD CURRENT
MAX15041 toc22
MAX15041
DEVICE POWER DISSIPATION LOAD CURRENT
POWER DISSIPATION VOUT 3.3V VOUT 2.5V VOUT 1.8V VOUT 1.2V
MAX15041 toc23
POWER DISSIPATION VOUT 3.3V VOUT 2.5V VOUT 1.8V VOUT 1.2V
LOAD CURRENT
LOAD CURRENT
Description
NAME PGOOD COMP SGND I.C. PGND FUNCTION Internal Output. Supply input internal analog core. Bypass with ceramic capacitor least SGND. Figure Power-Good Open-Drain Output. PGOOD goes below 545mV. Enable Input. digital input that turns regulator off. Drive high turn regulator. Connect always-on operations. Voltage Error-Amplifier Output. Connect necessary compensation network from COMP SGND. Feedback Input. Connect center external resistor-divider from output SGND output voltage from 0.606V VIN. Soft-Start Input. Connect capacitor from SGND soft-start time (see Setting SoftStart Time section). Analog Ground. Connect PGND plane point near input bypass capacitor return terminal. Internally Connected. Connect SGND. High-Side MOSFET Driver Supply. Bypass with 10nF capacitor. Connect external diode (see Diode Selection section) from BST. Inductor Connection. Connect switched side inductor. high impedance when shutdown mode, thermal shutdown mode, below UVLO threshold. Power Ground. Connect SGND copper plane point near input bypass capacitor return terminal. Input Power Supply. Input supply range from 4.5V 28V. Bypass with ceramic capacitor least 22µF PGND. Exposed Pad. Connect SGND externally. Solder exposed large contiguous copper plane maximize thermal performance.
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches MAX15041
Simplified Block Diagram
ENABLE CONTROL THERMAL SHUTDOWN
UVLO COMPARATOR
MAX15041
BIAS GENERATOR CURRENT-SENSE/CURRENT-LIMIT AMPLIFIER
VOLTAGE REFERENCE
0.65V
CONTROL LOGIC SINK LIMIT
0.606V STRONG PREBIAS COMPARATOR COMPARATOR
PGND
ERROR AMPLIFIER
OSCILLATOR PGOOD
COMP
SGND 0.560V RISING, 0.545V FALLING POWER-GOOD COMPARATOR
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches
Detailed Description
MAX15041 high-efficiency, peak-currentmode, step-down DC-DC converter with integrated high-side (170m, typ) low-side (105m, typ) power switches. output voltage from 0.606V using adjustable, external resistive divider deliver load current. 4.5V input voltage range makes device ideal distributed power systems, notebook computers, preregulation applications. MAX15041 features PWM, internally fixed 350kHz switching frequency with maximum duty cycle. current-mode control allows all-ceramic capacitor solution. MAX15041 comes with highgain transconductance error amplifier. currentmode control architecture simplifies compensation design ensures cycle-by-cycle current limit fast reaction line load transients. RDS-ON, on-chip, MOSFET switches ensure high efficiency heavy loads minimize critical inductances, reducing layout sensitivity. MAX15041 also features thermal shutdown overcurrent protection (high-side sourcing low-side sinking), internal with undervoltage lockout. externally adjustable voltage soft-start gradually ramps output voltage reduces inrush current. Independent enable control powergood signals allow flexible power sequencing. MAX15041 also provides ability start into prebiased output, below above point. high-side MOSFET current limit reached. maximum duty cycle reached. Then, low-side MOSFET turns low-side MOSFET turns when clock period ends.
MAX15041
Starting into Prebiased Output
MAX15041 capable safely soft-starting into prebiased output without discharging output capacitor. Starting into prebiased condition, both low-side high-side MOSFETs remain avoid discharging prebiased output. operation starts only when voltage crosses voltage. MAX15041 also capable soft-starting into output prebiased above nominal point. this case, forced operation starts when voltage reaches 0.65V (typ). case prebiased output, below above nominal point, low-side MOSFET sink current reaches sink current limit (-3A, typ), low-side MOSFET turns before clock period high-side MOSFET turns until following conditions happens: High-side MOSFET source current hits reduced high-side MOSFET current limit (0.75A, typ); this case, high-side MOSFET turned remaining clock period. clock period ends.
Enable Input Power-Good Output
MAX15041 features independent device enable control power-good signals that allow flexible power sequencing. enable input (EN) input with 1.95V (typ) threshold that controls regulator. Assert voltage exceeding threshold enable regulator, connect always-on operations. Power-good (PGOOD) open-drain output that deasserts (goes high impedance) when above 560mV (typ), asserts below 545mV (typ). When voltage higher than 1.4V (typ) lower than 1.95V (typ), most internal blocks disabled, only internal coarse preregulator, including accurate comparator, kept
Controller Function-PWM Logic
MAX15041 operates constant 350kHz switching frequency. When high, after brief settling time, operation starts when crosses voltage, beginning soft-start. first operation always high-side MOSFET turnon, beginning clock cycle. high-side MOSFET turned when: COMP voltage crosses internal current-mode ramp waveform, which compensation ramp current-mode ramp derived from inductor current waveform (current-sense block).
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches MAX15041
Programmable Soft-Start (SS)
MAX15041 utilizes soft-start feature slowly ramp regulated output voltage reduce input inrush current during startup. Connect capacitor from SGND startup time (see Setting SoftStart Time section capacitor selection details). capacitor, fixed period time 70ns, typ). overcurrent condition persists, pulled below 0.606V hiccup event triggered. During hiccup event, high-side low-side MOSFETs kept off, COMP pulled period equal times nominal soft-start time (blanking time). This obtained charging from 0.606V with (typ) current, then slowly discharging back with 333nA (typ) current. After blanking time elapsed, device attempts restart. overcurrent fault cleared, device resumes normal operation, otherwise hiccup event triggered (see Output Short-Circuit Waveforms Typical Operating Characteristics).
Internal (VDD) MAX15041 internal 5.1V (typ) LDO. externally compensated with minimum 1µF, low-ESR ceramic capacitor. voltage used supply low-side MOSFET driver, supply internal control logic. When input supply (IN) below 4.5V, 50mV (typ) lower than output current limit 80mA (typ) UVLO circuit inhibits switching when falls below 3.85V (typ). Error Amplifier
high-gain error amplifier provides accuracy voltage feedback loop regulation. Connect necessary compensation network between COMP SGND (see Compensation Design Guidelines section). erroramplifier transconductance 1.6mS (typ). COMP clamp 0.68V (typ), just below ramp compensation valley, helping COMP rapidly return correct point during load line transients.
Thermal-Shutdown Protection
MAX15041 contains internal thermal sensor that limits total power dissipation device protects event extended thermal fault condition. When temperature exceeds +155°C (typ), thermal sensor shuts down device, turning DC-DC converter regulator allow cool. After temperature falls 20°C (typ), device restarts, using soft-start sequence.
Applications Information
Setting Output Voltage
Connect resistive divider Figures from SGND DC-DC converter output voltage. Choose that errors input bias current affect output-voltage precision. With lower value resistors, error reduced, amount power consumed resistive divider increases. typical tradeoff value 10k, values between acceptable. Once chosen, calculate using: where feedback threshold voltage 0.606V (typ).
Comparator
comparator compares COMP voltage current-derived ramp waveform current COMP voltage transconductance value 9A/V, typ.). avoid instability subharmonic oscillations when duty cycle around higher, compensation ramp added current-derived ramp waveform. compensation ramp slope (0.45V 350kHz) equivalent half inductor current down slope worst case (load current ripple maximum duty cycle operation 90%). Compensation ramp valley 0.83V (typ).
Overcurrent Protection Hiccup Mode
When converter output shorted device overloaded, high-side MOSFET current-limit event (6A, typ) turns high-side MOSFET turns low-side MOSFET. addition, discharges
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches
Inductor Selection
larger inductor value results reduced inductor ripple current, leading reduced output ripple voltage. However, larger inductor value results either larger physical size higher series resistance (DCR) lower saturation current rating. Typically, inductor value chosen have current ripple equal load current. Choose inductor with following formula: VOUT where internally fixed 350kHz switching frequency, estimated inductor ripple current (typically LOAD addition, peak inductor current, IL_PK, must always below both minimum high-side MOSFET current-limit value, IHSCL_MIN (5A, typ), inductor saturation current rating, IL_SAT. Ensure that following relationship satisfied: ILOAD min(IHSCL ceramic capacitors, contribution negligible: RESR COUT COUT
MAX15041
tantalum electrolytic capacitors, contribution dominant: RESR COUT COUT
Compensation Design Guidelines
MAX15041 uses fixed-frequency, peak-currentmode control scheme provide easy compensation fast transient response. inductor peak current monitored cycle-by-cycle basis compared COMP voltage (output voltage error amplifier). regulator's duty-cycle modulated based inductor's peak current value. This cycle-by-cycle control inductor current emulates controlled current source. result, inductor's pole frequency shifted beyond gain-bandwidth regulator. System stability provided with addition simple series capacitor-resistor from COMP SGND. This pole-zero combination serves tailor desired response closed-loop system. basic regulator loop consists power modulator (comprising regulator's pulse-width modulator, compensation ramp, control circuitry, MOSFETs, inductor), capacitive output filter load, output feedback divider, voltage-loop error amplifier with associated compensation circuitry. Figure graphical representation. average current through inductor expressed GMOD VCOMP where average inductor current GMOD power modulator's transconductance. buck converter: LOAD where LOAD equivalent load resistor value. Combining previous equations, power modulator's transfer function terms VOUT with respect VCOMP VOUT LOAD RLOAD GMOD VCOMP
Diode Selection
MAX15041 requires external bootstrap steering diode. Connect diode between BST. diode should have reverse voltage rating, higher than converter input voltage 200mA minimum current rating. Typically, fast switching Schottky diode used this application, simple low-cost diode (1N4007) suffices.
Input Capacitor Selection
step-down converter, input capacitor helps keep input voltage steady, spite discontinuous input current. Low-ESR capacitors preferred minimize voltage ripple ESR. Size using following formula: ILOAD RIPPLE
Output-Capacitor Selection
Low-ESR capacitors recommended minimize voltage ripple ESR. Total output-voltage peak-topeak ripple estimated following formula:
VOUT VOUT RESR COUT COUT
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches MAX15041
FEEDBACK DIVIDER VOUT ERROR AMPLIFIER POWER MODULATOR OUTPUT FILTER LOAD
COMPENSATION RAMP
COMP
ROUT *CCC COMPARATOR CONTROL LOGIC
VOUT
RLOAD
COUT VCOMP GMOD VOUT ROUT AVEA/gMV *CCC OPTIONAL. NOTE: GMOD STAGE SHOWN ABOVE MODELS AVERAGE CURRENT INDUCTOR INJECTED INTO OUTPUT LOAD. THIS REPRESENTS SIMPLIFICATION POWER MODULATOR STAGE DRAWN ABOVE.
Figure Peak Current-Mode Regulator Transfer Model
Having defined power modulator's transfer function gain, total system loop gain written follows (see Figure
ROUT )(RC ROUT GMOD ROUT sCCRC
dominate poles zeros transfer loop gain shown below:
AVEA COUT (ESR RLOAD
(sCOUTESR RLOAD sCOUT (ESR RLOAD
CCCRC COUTESR
CCRC
Gain ROUT
order pole-zero occurrence Note under heavy load, fP2, approach fZ1. graphical representation asymptotic system closed-loop response, including dominant pole zero locations shown Figure
where ROUT quotient error amplifier's gain, AVEA, divided error amplifier's transconductance, gMV; ROUT much larger than much larger than CCC. Rewriting:
Gain
(sCCRC VOUT sCCCRC (sCOUTESR sCOUT (ESR RLOAD
GMODRLOAD
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches MAX15041
GAIN ASYMPTOTE VOUT 10AVEA[dB]/20 GMOD RLOAD ASYMPTOTE VOUT (CC)-1 GMOD RLOAD
ASYMPTOTE VOUT (CC)-1 GMOD RLOAD COUT(ESR RLOAD))-1
ASYMPTOTE VOUT GMOD RLOAD (COUT(ESR RLOAD))-1 POLE (CCCRC)-1 ZERO (COUTESR)-1 UNITY POLE (10AVEA[dB]/20 CC)-1 ZERO (CCRC)-1 POLE (COUT(ESR RLOAD))-1 RAD/S
ASYMPTOTE VOUT GMOD (ESR RLOAD) ASYMPTOTE VOUT CCC)-1 GMOD (ESR RLOAD)
Figure Asymptotic Loop Response Peak Current-Mode Regulator
COUT large, exhibits lossy equivalent series resistance (large ESR), circuit's second zero come into play around crossover frequency (fCO CO/2). this case, third pole induced second (optional) small compensation capacitor (CCC), connected from COMP SGND. loop response's fourth asymptote bold, Figure interest establishing desired crossover frequency (and determining compensation component values). lower crossover frequency provides stable closed-loop operation expense slower load line transient response. Increasing crossover frequency improves transient response (potential) cost system instability. standard rule thumb sets crossover frequency 1/10 switching frequency (for MAX15041, this approximately 35kHz 350kHz fixed switching frequency). First, select passive active power components that meet application's requirements. Then, choose small-signal compensation components achieve
desired closed-loop frequency response phase margin outlined Closing Loop: Designing Compensation Circuitry section.
Closing Loop: Designing Compensation Circuitry Select desired crossover frequency. Choose equal 1/10th fSW, 35kHz. Select using transfer-loop's fourth asymptote gain (assuming fP1, fP2, setting overall loop gain unity) follows:
therefore: COUT (ESR RLOAD GMOD RLOAD
GMOD RLOAD VOUT
COUT (ESR RLOAD
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches MAX15041
RLOAD much greater than ESR, equation further simplified follows: COUT GMOD where equal 0.606V. Select determined selecting desired first system zero, fZ1, based desired phase margin. Typically, setting below 1/5th provides sufficient phase margin. therefore: CCRC this third-pole placement well beyond desired crossover frequency, minimizing interaction with system loop response crossover. smaller than 10pF, neglected these calculations.
Setting Soft-Start Time
soft-start feature ramps output voltage slowly, reducing input inrush current during startup. Size capacitor achieve desired soft-start time using: ISS, soft-start current, (typ) VFB, output feedback voltage threshold, 0.606V (typ). When using large COUT capacitance values, high-side current limit trigger during soft-start period. ensure correct soft-start time, tSS, choose large enough satisfy: COUT VOUT (IHSCL IOUT
output zero located less than one-half switching frequency (optional) secondary compensation capacitor, CCC, cancel follows: CCCRC COUTESR therefore: COUT
IHSCL_MIN minimum high-side switch, currentlimit value.
Power Dissipation
MAX15041 available thermally enhanced TQFN package dissipate 1.666W +70°C. exposed should connected SGND externally, preferably soldered large ground plane maximize thermal performance. When temperature exceeds +155°C, thermal-shutdown protection activated (see Thermal-Shutdown Protection section).
zero exceeds switching frequency, following equation: therefore: CCCRC
Layout Procedure
Careful layout critical achieve clean stable operation. highly recommended duplicate MAX15041 evaluation layout optimum performance. deviation necessary, follow these guidelines good layout: Connect input output capacitors power ground plane; connect other capacitors signal ground plane.
downside that detracts from overall system phase margin. Care should taken guarantee
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches
Place capacitors VDD, close possible corresponding using direct traces. Keep power ground plane (connected PGND) signal ground plane (connected SGND) separate. PGND SGND connect only common point near input bypass capacitor return terminal. Keep high-current paths short wide possible. Keep path switching current short minimize loop area formed output capacitors, input capacitors. Connect PGND separately large copper area help cool further improve efficiency. Ensure feedback connections short direct. Place feedback resistors compensation components close possible Route high-speed switching nodes (such BST) away from sensitive analog areas (such COMP).
MAX15041
INPUT 4.5V
RBST 47µF CVDD PGND PGOOD I.C. 0.01µF SGND COMP 100pF 1.8k 12nF 10.0k
MAX15041
CBST
4.7µH OUTPUT 3.3V COUT 22µF
45.3k
PGOOD
Figure Typical Operating Circuit (4.5V Input Buck Converter)
Table Typical Component Values Common Output-Voltage Settings
VOUT (µH) (nF) 2.70 1.80 1.50 1.00 0.68 Select that: Calculate using equation Setting Output Voltage section.
Low-Cost, 4.5V Input, 350kHz, Step-Down DC-DC Regulator with Internal Switches MAX15041
Configuration
PROCESS: BiCMOS
Chip Information
VIEW
PGND PGND
I.C. SGND
Package Information
latest package outline information land patterns, www.maxim-ic.com/packages. PACKAGE TYPE PACKAGE CODE T1633+4 DOCUMENT 21-0136
MAX15041
PGOOD
TQFN
COMP
TQFN
*EXPOSED PAD, CONNECT SGND.
Maxim cannot assume responsibility circuitry other than circuitry entirely embodied Maxim product. circuit patent licenses implied. Maxim reserves right change circuitry specifications without notice time.
_Maxim Integrated Products, Gabriel Drive, Sunnyvale, 94086 408-737-7600 2009 Maxim Integrated Products Maxim registered trademark Maxim Integrated Products, Inc.
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