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MAXIM MAX748A/MAX763A 3.3V Step-Down Current-Mode PWM DC-DC Converters Manual

1. Figure 9 DIP PC Layout Drill Guide 1X Scale V 9 XVIW V8TtZXVIA MAX748A MAX 763A 3 3V Step Down Current Mode PWM DC DC Converters TOP VIEW MAXIM MAX748A MAX763A MAXIM MAX748A Pin Configurations continued _Ordering Information continued PART TEMP RANGE PIN PACKAGE MAX763ACPA 0 C to 70 C 8 Plastic DIP MAX763ACSA 0 C to 70 C 8 SO MAX763AC D 0 C to 70 C Dice MAX763AEPA 40 C to 85 C 8 Plastic DIP MAX763AESA 40 C to 85 C 8 SO MAX763AMJA 55 C to 125 C 8 CERDIP Contact factory for dice specifications 12 Chip Topographies 0 131 3 327mm SS REF cc OUT GND GND LX LX LX MAX748A TRANSISTOR COUNT 298 SUBSTRATE CONNECTION V MAX763A TRANSISTOR COUNT 281 SUBSTRATE CONNECTION V MAKIM
2. PWM 85 to 90 Efficiencies 1 7mA Quiescent Current MAX748A 1 4mA Quiescent Current MAX763A 0 2uA Shutdown Supply Current 22uH Preselected Inductor Value No Component Design Required Overcurrent Soft Start and Undervoltage Lockout Protection Cycle by Cycle Current Limiting 8 Pin DIP SO Packages MAX763A Ordering Information PART TEMP RANGE PIN PACKAGE MAX748ACPA 0 C to 70 C 8 Plastic DIP MAX748ACWE 0 C to 70 C 16 Wide SO MAX748AC D 0 C to 70 C Dice MAX748AEPA 40 C to 85 C 8 Plastic DIP MAX748AEWE 40 C to 85 C 16 Wide SO MAX748AMJA 55 C to 125 C 8 CERDIP Ordering Information continued on last page Contact factory for dice specifications TOP VIEW Pin Configurations MAX748A MAX763A Pin Configurations continued on last page Maxim Integrated Products 1 Call toll free 1 800 998 8800 for free samples or literature VE9LXVW V8VLXVIN MAX 748A MAX 763A 3 3V Step Down Current Mode PWM DC DC Converters ABSOLUTE MAXIMUM RATINGS Pin Voltages V MAX7484A 17V 0 3V V MAX7634A 12V 0 3V LX MAX748A V 21V to V 0 3V LX MAX763A V 12V to V 0 3V eU m 25V SS CC SHDN 0 3V to V 0 3V 2 0A 5mA Peak Switch Current l X Reference Current IREF Continuous Power Dissipation TA 70 C 8 Pin Plastic D
3. capacitor is low effective series resistance ESR The product of the inductor current variation and the output capacitors ESR determines the amplitude of the saw tooth ripple seen on the output voltage Minimize the output filter capacitor s ESR to maintain AC stability VE9LXVW V8VLXVIN MAX748A MAX 763A 3 3V Step Down Current Mode PWM DC DC Converters INPUT MAX748A 3 3VT016 0V y MAX763A 3 3V TO 11 0V SHDN MAX748A MAX763A MAXUM oT OUTPUT 3 3V Lt ct 220uF 10V C6 1000pF OS OON Series very low ESR Figure 4 Standard 3 3V Step Down Application Circuit Using Through Hole Components all temperature ranges The capacitor s ESR should be less than 0 25Q to keep the output ripple less than 50mVp p over the entire cur rent range using a 22uH inductor Capacitor ESR usually rises at low temperatures but OS CON capaci tors provide very low ESR below 0 C Table 3 lists capacitor suppliers Other Components The catch diode should be a Schottky or high speed silicon rectifier with a peak current rating of at least 1 0A for full load 500mA operation The 1N5817 is a good choice The 330pF outer loop compensation capacitor provides the widest input voltage range and best transient characteristics Printed Circuit Layouts A good layout is essential for stable low noise opera tion The layouts and component placement diagrams 10 INPUT MAX748A 3 3V TO
4. 16 0V V MAX763A 3 3V TO 11 0V IN SHDN MAXUM MAX748A MAX763A po 0 047uF Sprague 293D or 595D Series 16V See Table 3 for alternative suppliers Figure 5 Standard 3 3V Step Down Application Circuit Using Surface Mount Components Commercial and Extended Industrial Temperature Ranges in Figures 6 9 have been tested successfully over a wide range of operating conditions The 1pF input bypass capacitor must be positioned as close to the V and GND pins as possible Also place the output capacitor as close to the OUT and GND pins as possible The traces connecting ground to the input and output filter capacitors and to the catch diode must be short to reduce inductance Use an uninter rupted ground plane if possible Output Ripple Filtering A simple lowpass pi filter Figure 3 can be added to the output to reduce output ripple to about 5mVP P The cutoff frequency shown is 21kHz Since the filter inductor is in series with the circuit output minimize the filter inductor s resistance so the voltage drop across it is not excessive AVLAZCLAWI 3 3V Step Down Current Mode PWM DC DC Converters Bx Fee zit Ha uete re O VOUT GHD am 9 Figure 6 DIP PC Layout Through Hole Component Placement Diagram 1X Scale Figure 7 DIP PC Layout Component Side 1X Scale Figure 8 DIP PC Layout Solder Side 1X Scale MAXIM
5. 7500 7500 Q Note 1 The standby current typically settles to 10A over temperature within 2 seconds however to decrease test time the part is guaranteed at a 100UA maximum value Typical Operating Characteristics Circuit of Figure 3 TA 25 C Vout 3 3V unless otherwise noted MAXIMUM OUTPUT CURRENT vs SUPPLY VOLTAGE MAX763A EFFICIENCY vs OUTPUT CURRENT MAX748A EFFICIENCY vs OUTPUT CURRENT 1000 MAX748A 95 Vin 7 0V Vy 5 0V 800 J 5 90 MAX763A 600 85 i Vy 11 0V o IN o s 400 E z E 200 e fe NOTE 2 NOTE 2 is 0 60 0 2 4 6 8 10 12 14 16 0 100 200 300 400 500 600 700 800 0 100 200 300 400 500 600 700 800 900 SUPPLY VOLTAGE V MAKIM OUTPI UT CURRENT mA OU PUT CURRENT mA V 9 XVIW V8TtZXVIA MAX748A MAX 763A 3 3V Step Down Current Mode PWM DC DC Converters Typical Operating Characteristics continued Circuit of Figure 3 TA 25 C Vout 3 3V unless otherwise noted MAX763A QUIESCENT SUPPLY CURRENT vs SUPPLY VOLTAGE 0 1 23456789 101 12 SUPPLY VOLTAGE V OSCILLATOR FREQUENCY vs SUPPLY VOLTAGE MAX748A MAX763A 0 2 4 6 8 10 12 14 16 SUPPLY VOLTAGE V MAX748A QUI
6. feedback loop Connect to OUT with a 330pF capacitor Output Voltage Sense Input provides regulation feedback sensing 5 9 OUT Connect to 3 3V output 10 11 GND Ground 12 13 14 LX Drain of internal P channel power MOSFET Supply Voltage Input Bypass to GND with 1uF ceramic and large value 8 1 15 16 V electrolytic capacitor in parallel The 1uF capacitor must be as close to the GND and V pins as possible 4 5 6 N C No Connect no internal connections to these pins 16 pin wide SO package All pins sharing the same name must be connected together externally Detailed Description The MAX748A MAX763A switch mode regulators use a current mode pulse width modulation PWM control system in a step down buck regulator topography They convert an unregulated DC input voltage from 4V to 11V MAX763A or from 4V to 16V MAX748A to a regulated 3 3V output at 300mA For loads less than 300mA V may be less than 4 0V see the Output Voltage vs Supply Voltage graph in the Typical Operating Characteristics The current mode PWM architecture provides cycle by cycle current limit ing improved load transient response and simpler outerloop design The controller consists of two feedback loops an inner current loop that monitors the switch current via the current sense resistor and amplifier and an outer volt age loop that monitors the output voltage through the error amplifier Figure 1 The inner loop performs cycle b
7. voltage required for regulation depends on load conditions see the Output Voltage vs Supply Voltage graph in the Typical Operating Characteristics Shutdown Mode The MAX748A MAX763A are held in shutdown mode by keeping SHDN at ground In shutdown mode the output drops to OV and the output power FET is held in an off state The internal reference also turns off which causes the SS capacitor to discharge Typical supply current in shutdown mode is 0 2uA The actual design limit for shutdown current is much less than the 100A specified in the Electrical Characteristics However testing to tighter limits is prohibitive because the cur rent takes several seconds to settle to a final value For normal operation connect SHDN to V Coming out of shutdown mode initiates an SS cycle Continuous Disc ontinuous Conduction Modes The input voltage output voltage load current and inductor value determine whether the IC operates in continuous or discontinuous mode As the inductor value or load current decreases or the input voltage increases the MAX748A MAX763A tend to operate in discontinuous conduction mode DCM In DCM the inductor current slope is steep enough so it decays to zero before the end of the transistor off time In contin uous conduction mode CCM the inductor current never decays to zero which is typically more efficient than DCM CCM allows the MAX748A MAX763A to deliver maximum load current and is also slightly les
8. 19 0190 Rev 0 9 93 MAALMNVI 3 3V Step Down Current Mode PWM DC DC Converters General Description The MAX748A MAX763A are 3 3V output CMOS step down switching regulators The MAX748A accepts inputs from 3 3V to 16V and delivers up to 500mA The MAX763A accepts inputs between 3 3V and 11V and delivers up to 500mA Typical efficiencies are 85 to 90 Quiescent supply current is 1 4mA MAX763A and only 0 2uA in shutdown Pulse width modulation PWM current mode control pro vides precise output regulation and excellent transient responses Output voltage accuracy is guaranteed to be 5 over line load and temperature variations Fixed frequency switching allows easy filtering of output ripple and noise as well as the use of small external components A 22uH inductor works in most applica tions so no magnetics design is necessary The MAX 48A MAX763A also feature cycle by cycle cur rent limiting overcurrent limiting undervoltage lockout and programmable soft start protection The MAX748A is available in 8 pin DIP and 16 pin wide SO packages the MAX763A comes in 8 pin DIP and SO packages Applications 5V to 3 3V Converters Cellular Phones Portable Instruments Hand Held Computers Computer Peripherals Typical Operating Circuit INPUT 3 3V TO 16V OUTPUT V AA 3 3V LX MAAN MAX748A SHDN MAXIM Features Up to 500mA Load Currents Guaranteed 159kHz to 219 5kHz Current Mode
9. ESCENT SUPPLY CURRENT vs SUPPLY VOLTAGE 5 0 our OmA E 40 TA 55 C 3 30 E A 125 C B 20 d TA 25 C d 10 0 2 4 6 8 10 12 14 16 SUPPLY VOLTAGE V SHUTDOWN CURRENT vs TEMPERATURE 0 60 40 20 0 20 40 60 80 100 120 140 TEMPERATURE C PEAK INDUCTOR CURFENT mA PEAK INDUCTOR CURRENT vs OUTPUT CURRENT 0 0 50 100 150 200 250 300 350 400 450 500 550 OUTPUT CURRENT mA OUTPUT VOLTAGE vs SUPPLY VOLTAGE ILoap 50mA ILoap 300mA 20 25 30 35 40 45 50 SUPPLY VOLTAGE V OSCILLATOR FREQUENCY vs TEMPERATURE OUTPUT VOLTAGE vs OUTPUT CURRENT 40 V 2 40V 85 80 z lo 2 5 t V 2 35V 20 s V 2 30V 10 05 0 0 50 100 150 200 250 300 350 400 450 500 OUTPUT CURRENT mA 60 40 20 0 20 40 60 80 100 120 140 TEMPERATURE C AVLAZCLAM 3 3V Step Down Current Mode PWM DC DC Converters Typical Operating Characteristics continued Circuit of Figure 3 TA 25 C Vout 3 3V unless otherwise noted SWITCHING WAVEFORMS SWITCHING WAVEFORMS CONTINUOUS CONDUCTION DISCONTINUOUS CONDUCTION 2us div 2us div A SWITCH VOLTAGE LX PIN 5V div OV TO 46V A SWITCH VOLTAGE LX PI
10. ILoaD lt 400mA 3 135 3 3 3 465 C E temp ranges V 4 0V to 11V OmA lt ILoaD 300mA 3 135 3 8 3 465 M temp range V 4 0V to 11V OmA lt LOAD lt 250mA 3 135 3 3 3 465 C E temp ranges V 4 75V to 11V OMA lt ILoap lt 500mA 3 135 3 3 3 465 M temp range V 4 75V to 11V OmA lt ILoaD 400mA 3 135 3 8 3 465 Line Regulation 0 13 0 13 SIN Load Regulation li oAp OMA to 500mA 0 001 0 001 9e mA MAXIM 3 3V Step Down Current Mode PWM DC DC Converters ELECTRICAL CHARACTERISTICS continued Circuit of Figure 3 V 5V ILoap OMA Ta Tmn to Tmax unless otherwise noted MAX748A MAX763A PARAMETER CONDITIONS MIN TYP MAX MIN TYP MAX UNITS l A 88 Efficiency V 5y Loap 300m a ILoaD 100mA 90 90 Supply Current Includes switch current 1 7 3 0 1 4 2 5 mA Shutdown Current SHDN OV Note 1 0 2 100 0 0 2 100 0 pA Shutdown Input Vin 2 0 2 0 V Threshold Vib 0 25 0 25 Shutdown Input Leakage Current 1 0 1 0 pA Short Circuit Current 12 1 2 A Undervoltage Lockout V falling 2 7 3 0 2 7 3 0 V LX On Resistance lx 500mA 1 0 1 0 Q LX Leakage Current V 12V LX 0 10 10 nA Reference Voltage Ta 25 C 1 15 1 22 1 30 1 15 1 22 1 30 V Reference Drift Ta Tmn to Tmax 50 50 ppm C Oscillator Frequency 159 180 212 5 159 200 212 5 kHz Compensation Pin Impedance
11. IP derate 6 90mW C above 70 C 552mW 8 Pin SO derate 5 88mW C above 70 C AT71mW 16 Pin Wide SO derate 9 52mW C above 70 C 762mW 8 Pin CERDIP derate 8 00mW C above 70 C 640mW Operating Temperature Ranges MAX7 AC 0 C to 70 C MAX7__AE 40 C to 85 C MAX7 AMJA 55 C to 125 C Junction Temperatures MAXZ ACIE caer senda e ioter ier ratati MAXT7 AM Storage Temperature Range Lead Temperature soldering 10sec 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 Circuit of Figure 3 V 5V ILoap OMA Ta Tmn to Tmax unless otherwise noted PARAMETER CONDITIONS MAX748A MAX763A MIN TYP MAX MN TYP max UNITS Input Voltage Range 3 3 16 0 3 3 11 0 V C E temp ranges V 4 0V to 16V OmA li oAD 300mA 3 135 3 8 3 465 M temp range V 4 0V to 16V OMA lt li gAp lt 250mA 3 135 3 8 3 465 C E temp ranges V 4 75V to 16V OmA lt ILoaD lt 500mA 3 135 3 3 3 465 M temp range V 4 75V to 16V Output Voltage OmA lt
12. N 5V div OV TO 6V B INDUCTOR CURRENT 200mA div B INDUCTOR CURRENT 100mA div C OUTPUT VOLTAGE RIPPLE 50mV div C OUTPUT VOLTAGE RIPPLE 50mV div V 6V lour 250mA V 6V lg 75mA LINE TRANSIENT RESPONSE LOAD TRANSIENT RESPONSE 500mA OmA 5ms div 5ms div A Vout 50mV div A Vout 50mV div B V 5V div 7 0V TO 10 0V B lout 200mA div OmA TO 500mA lout 350mA V 6V Note 2 Operation beyond the specifications listed in the Electrical Characteristics may exceed the power dissipation ratings of the device Note 3 Wide temperature range circuit of Figure 5 using Sprague surface mount capacitors Note 4 Standby current includes all external component leakage currents Capacitor leakage currents dominate at TA 85 C MAKI LL LL Lu S VE9LXVW V8VLXVIN MAX 748A MAX 763A 3 3V Step Down Current Mode PWM DC DC Converters Pin Description PIN 16 PIN WIDE SO NAME FUNCTION 8 PIN DIP SO MAX748A 1 2 SHDN Shutdown active low Connect to ground to power down chip tie to V for normal operation Output voltage falls to OV when SHDN is low 2 3 REF Reference Voltage Output 1 23V supplies up to 100A for external loads Bypass to GND with a 0 047uF capacitor 3 7 ss Soft Start Capacitor between SS and GND provides soft start and short circuit protection 4 8 cc Compensation Capacitor Input externally compensates the outer voltage
13. cial temperature range applications Figures 4 5 and Table 2 suggest external component values for both SO and through hole wide temperature range applications These circuits are use ful in systems that require high current and high efficien cy and are powered by an unregulated supply such as a battery or wall plug AC DC adapter The MAX748A delivers a guaranteed 300mA for input voltages of 4V to 16V and a guaranteed 500mA for MAKIM input voltages of 4 75V to 16V with 800mA typical out put currents The MAX763A delivers a guaranteed 300mA for input voltages of 4V to 11V a guaranteed 500mA for input voltages of 4 75V to 11V and has 700mA typical output currents The MAX748A MAX763A operate from an input down to 3V the upper limit of undervoltage lockout but with some reduction in output voltage and maximum output current Inductor Selection The MAX748A MAX763A require no inductor design because they are tested in circuit and are guaranteed to deliver the power specified in the Electrical Characteristics with high efficiency using a single 22uH inductor The 22H inductor s incremental satu ration current rating should be greater than 1A for 500mA load operation Table 3 lists inductor types and suppliers for various applications The surface mount inductors have nearly equivalent efficiencies to the larger through hole inductors Output Filter Capacitor Selection The primary criterion for selecting the output filter
14. ed Note that the SS capacitor must be greater than 0 01uF for overcurrent protection to function prop erly A typical value is 0 047uF AVLAZCLAWI 3 3V Step Down Current Mode PWM DC DC Converters MAX748A 3 3V to 16 0V C2 C3 MAX763A 3 3V to 11 0V ViN 1 0uF 1504F OVERCURRENT COMPARATOR SLOPE COMPENSATION 3 SA GEN ERROR AMP CURRENT e SENSE AMP PWM S ann COMPARATOR UNDERVOLTAGE LOCKOUT a d j tie MAXIM Osc MAX748A L MAX763A SS CLAMP e Figure 1 Detailed Block Diagram with External Components Table 1 Typical Soft Start Times FROM SHDN Circuit of Figure 3 C4 150uF Circuit Cond Soft Start Time ms vs C1 pF V V I mA C1 0 01 C1 0 047 C1 0 1 C1 0 47 SS CLAMP V lour mA 8 0 1 4 7 12 S 12 0 1 2 3 6 Ss 8 200 10 33 50 200 12 200 7 17 20 80 1M zu 8 300 13 44 65 325 Civ 12 300 8 25 35 140 YN 123v E MAX748A only MAXIM MAX748A 25 E MAX763A Figure 2 Soft Start Circuitry Block Diagram MAKI LLL Le LI VE9LXVW V8VLXVIN MAX748A MAX 763A 3 3V Step Down Current Mode PWM DC DC Converters Table 3 External Component Suppliers Production Method Inductors Capacitors Sumida Matsuo CD105 series 267 series Surface Mount Coiltronics Sprague CTX series 595D 293D se
15. ries Coilcraft DT series High Performance Sumida Sanyo Miniature Through Hole RCH895 series OS CON series very low ESR Renco Nichicon Shroud Hole RL1284 series PL series low ESR Phone and FAX Numbers Coilcraft USA 708 639 6400 FAX 708 639 1469 Renco USA 516 586 5566 FAX 516 586 5562 Coiltronics USA 305 781 8900 FAX 305 782 4163 Sanyo USA 0720 70 1005 FAX 0720 70 1174 Matsuo USA 714 969 2491 FAX 714 960 6492 Sprague Elec Co USA 603 224 1961 FAX 603 224 1430 Japan 06 332 0871 Sumida USA 708 956 0666 FAX 708 956 0702 Nichicon USA 708 843 7500 FAX 708 843 2798 Japan 03 3607 5111 FAX 03 3607 5428 Undervoltage Lockout The undervoltage lockout feature monitors the supply voltage at V and allows operation to start when V rises above 2 95V When V falls operation continues until the supply voltage falls below 2 7V typ When an undervoltage condition is detected control logic turns off the output power FET and discharges the SS capac itor to ground This prevents partial turn on of the power MOSFET and avoids excessive power dissipation The control logic holds the output power FET off until the supply voltage rises above approximately 2 95V at which time an SS cycle begins When the input voltage exceeds the undervoltage lockout threshold switching action will occur but the output will not be regulated until the input voltage exceeds 3 3V no load The exact input
16. s noisy than DCM because it doesn t exhibit the ringing that occurs when the inductor current reaches zero Internal Reference The 1 23V bandgap reference supplies up to 100HA at REF A 1000pF bypass capacitor from REF to GND is required Oscillator The MAX748A MAX763A s internal oscillator is guaran teed to operate in the 159kHz to 212 5 kHz range over temperature for V 5V Temperature stability over the military temperature range is about 0 04 C AVLAZCLAWI 3 3V Step Down Current Mode PWM DC DC Converters INPUT MAX748A 3 3V TO 16 0V y MAX763A 3 3V TO 11 0V SHDN MAXIM MAX748A MAX763A OUT J 1000pF T OPTIONAL 21kHz LOWPASS OUTPUT FILTER 22uH L2 FILTER 25uH Y YN QUTPUT c A 22uF T OUTPUT 3 3V OUTPUT Figure 3 Standard 3 3V Step Down Application Circuit Using Through Hole Components commercial temperture range Table 2 Component Table for Wide Temperature Applications C1 uF C2 F C3 uF C4 uF C5 pF C6 pF L1 uH Through Hole 0 047 1 0 150 220 330 1000 22 SO 0 047 1 0 68 100 330 1000 22 Sanyo OS CON Series very low ESR 16V or greater maximum voltage rating 6 3V or greater maximum voltage rating Applications Information Fixed 3 3V Step Down Converter Application Figure 3 shows the standard 3 3V step down circuit with components shown for commer
17. y cycle current limiting truncating the power transistor on time when the switch current reaches a predetermined threshold This threshold is determined by the outer loop For example a sagging output volt age produces an error signal that raises the threshold allowing the circuit to store and transfer more energy during each cycle 6 Programmable Soft Start Figure 2 shows a capacitor connected to the soft start SS pin to ensure orderly power up A typical value is 0 047pgF SS controls both the SS timing and the maxi mum output current that can be delivered while main taining regulation The charging capacitor slowly raises the clamp on the error amplifier output voltage limiting surge currents at power up by slowly increasing the cycle by cycle current limit threshold Table 1 lists timing characteris tics for selected capacitor values and circuit conditions The overcurrent comparator trips when the load exceeds approximately 1 2A When either an undervoltage or over current fault condition is detected an SS cycle is actively initiated which triggers an internal transistor to discharge the SS capacitor to ground An SS cycle is also enabled at power up and when coming out of shutdown mode Overcurrent Limiting The overcurrent comparator triggers when the load current exceeds approximately 1 2A On each clock cycle the output FET turns on and attempts to deliver current until cycle by cycle or overcurrent limits are exceed

MAXIM MAX748A/MAX763A 3.3V Step-Down Current-Mode PWM DC-DC Converters Manual

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