19-0165; Alev 2; 1/96 General Description The MAX730A/MAX?38A/MAX744A are 5V-output CMOS, step-down switching regulators. The MAX/38A/ MAX744A accept inputs from 6V to 16V and deliver 750mA. The MAX744A guarantees S0OmA load capa- bility for inputs above 6V and has tighter oscillator fre- quency limits for low-noise (radio} applications. The MAX730A accepts inputs between 5.2V and 11V and delivers 450mA for inputs above 6V. Typical efficien- cies are 85% to 96%. Quiescent supply current is 1.7mA and only 6UA in shutdown. Pulse-width modulation (PWM) current-mode control provides precise output regulation and excellent tran- sient responses. Output voltage accuracy is guaran- teed to be +5% over line, load, and temperature varia- tions. Fixed-frequency switching allows easy filtering of output ripple and noise, as well as the use of small external components. These regulators require only a single inductor value to work in most applications, so no inductor design is necessary. The MAX730A/MAX738A/MAX744A also feature cycle- by-cycle current limiting, overcurrent limiting, undervolt- age lockout, and programmable soft-start protection. Applications Portable Instruments Cellular Phones and Radios Personal Communicators Distributed Power Systems Computer Peripherals Typical Operating Circuit MAXIM 5V, Step-Down, Current-Mode PWM DC-DC Converters Features 750mA Load Currents (MAX738A/MAX744A) @ High-Frequency, Current-Mode PWM # 159kHz to 212.5kHz Guaranteed Oscillator Frequency Limits (MAX744A) 85% to 96% Efficiencies 1.7mA Quiescent Current 6A Shutdown Supply Current Single Preselected Inductor Value, No Component Design Required # Overcurrent, Soft-Start, and Undervoltage Lockout Protection # Cycle-by-Cycle Current Limiting 8-Pin DIP/SO Packages (MAX730A) Ordering Information PART TEMP. RANGE PIN-PACKAGE MAX730ACPA 0T to +70T 8 Plastic DIP MAX730ACSA 0T to+70T 850 MAX730AC/D OT to+70T Dice* MAX730AEPA -40'T to +85C 8 Plastic DIP MAX730AESA -40'T ta +85'C 880 MAX730AMJA -55T to +125 8 CERDIP Ordering information continued at end of daia sheet. *Contact factory for dice specifications. Pin Configurations OUTPUT 5 tT 33H Ve LL BaF T LX = | MAXIM MAX738A _ ____ MAX744A ON CFF B] SHDN CUT REF cc | ss GD {OOF L C4 TOP VIEW SHON [11 | sf e Nee 8] V+ 2| AAAXLAA = | LX WAXTIOA FT a 4 MAX744A 5] cur DIP Pin Configurations continued on last page. MAAXLAA Maxim integrated Producis 1 For free samples & the latest Ifterature: htip:/(www.maxim-ic.com, or phone 1-800-998-8800 VPVLXVW/V8EZXVW/VOELXVWNMAX /730A/MAX738A/MAX 744A 5V, Step-Down, Current-Mode PWM DC-DC Converters ABSOLUTE MAXIMUM RATINGS Pin Voltages Operating Temperature Ranges: Ve (MAX7B0A) ooo. cce ete ceeee ee caeeeeeeeeae +12V, 0.3V MAXF AC ccc cece ceeeeeeeeeeenetteeeeeeees 0T to+70T V4 (MAX73BA/MAXT44A) oo cette +18V, 0.3V MAX?7__AE -40 C to +85 C LX (MAX730A) oo. e cee renee (V+ - 12V) to (V+ + 0.3) MAX7__AMJA -55C to +125 TC LX (MAX738A/MAX744A) ooo. (V+ - 21V) to (V+ + 0.3) Junction Temperatures: UT once ccc eee eee eee ee tec eeee eee eceeeseesesetneeseetneaneaeeeeees +25V MAX7 AC FAB ccc ceeteeeeteeteecteeteees +150C SS, CC, SHDN 0.0... cece cee ete -0.3V to (V+ + 0.3V) MAX? AMJA Lecce ccc ccee sete eteteeeeteeeeseneeeaees 4175 Peak Switch Current (Ip) ....eccceceec eee cr ceeeeeeeeereneeeeentees 2A Storage Temperature Range ............ cee -65C to +160C Reference Current (lace) occ ceccceccerecseesceeeereneeeenenenires 2.5mA Lead Temperature (soldering, 10S@C)..........ecceeeees +300C Continuous Power Dissipation (T, = +70C) 8-Pin Plastic DIP (derate 9. 09mW/C above +70)...727mW 8-Pin SO (derate 5.88mMW/C above +70) ow. 471mw 16-Pin Wide SO (derate 9.52mW/ above +70C}.....762mW 8-Pin CERDIP (derate 8.00mW/C above +70%)....... 640mW Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. These are siress 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+ = 9V for the MAX730A, V+ = 12V for the MAX738A/MAX744<A, lLoab = OMA, Ta = TIN to TMAX, unless otherwise noted.) MAX7304 MAX738A MAX744A PARAMETER CONDITIONS MIN TYP MAX] MIN TYP MAX | MIN TYP MAX UNITS OmA < ILoap < 450mA, MAX730AC V+ =6.0V | OmA< lLoaD < 450mA, to 11.0V MAX730AE OmA < ILoap < 300mA, MAX730AM OmA < ILoap < 450mA, MAX738AC/AE OmA < ILoap < 350mA, Vo ae 475 500 525 | 4.75 500 5.25 Output Voltage to 16.0V omA < ILoap < 5OOmA, . . . . . . V MAX744AC/AE OmA < ILoap < 375mA, MAX744AM V+ = 10.2V to 16.0V, OmA < lLoaD < 750mA 475 500 5.25 475 5.00 5.25 OmA < ILoap < 750mA, MAX744,AC/AE we ae 475 5.00 5.25 O18. OmA < ILoap < 600mA, MAX744.AM Input Voltage 5.2 14.0 | 6.0 16.0 | 6.0 160] V Range V4 = 5.2V to 11.0V 0.15 Line Regulation %/V V+ = 6.0V to 16.0V 0.15 0.15 2 MA AXLAAunless otherwise noted.) 5V, Step-Down, Current-Mode PWM DC-DC Converters ELECTRICAL CHARACTERISTICS (continued) (Circuit of Figure 3, V+ = 9V for the MAX730A, V+ = 12V for the MAX738A/MAX744A, ILoaD = OMA, Ta = TMIN to TMAXx, MAX7304 MAX738A MAX744A PARAMETER CONDITIONS MIN TYP MAX| MIN TYP MAX| MIN TYP. Max | UNITS | = OmA to 300mA 0.0005 Load Regulation LOAD %/mMA ILOAD = OmA to 750mMA 0.0005 0.0005 a V+ = 9.0V, ILoap = 300mA g2 90 90 Efficiency % V+ = 12V) lLoap = 750mA &7 87 1.7 3.0 17 3.0 1.7% 3.0 Va = 6.0V MAX744AC/AE 12 25 to 9.0V MAX744.AM 3.0 Supply Current Ve=9.0. | MAX744AC/AE 3.0 (includes switch to 12.0 mA current) . MAX744AM 3.5 MAX744AC 40 V+ = 12.0V to 16.0V MAX744.AE 43 MAX744AM 45 Standby Current SHDN = OV (Note 1) 6.0 100.0 6.0 100.0 6.0 100.0 pA Shutdown Input VIH 2.0 2.0 2.0 Vv Threshold VIL 0.25 0.25 0.25 Shutdown Input Leakage Current 1.0 1.0 1.0 HA Short-Circuit Current 1.5 1.5 1.5 A Undervoltage Vo rising 47 5.2 5.7 6.0 5.7 6.0 Vv Lockout V+ falling 5.0 5.7 LX On Resistance ILx = 500mA 0.5 0.5 0.5 Q LX Leakage Current V+ = 12V, LX = OV 1.0 1.0 1.0 pA Reference Voltage V+ = 12V, Ta = +25 1.15 1.23 1.30 1.15 1.23 1.30 1.15 1.23 1.30 Vv Reference Drift 50 50 50 ppm/ 130 #170 210 130 160 190 Oscillator Frequency | y= 6.0V MAX744AC/AE 159.0 185.0 212.5 | kHz to 16.0V MAX744.AM 159.0 216.5 Campensation Pin 7500 7500 7500 oO Impedance Note 1: The standby current typically settles to 25uA (over temperature) within 2 seconds; however, to decrease test time, the part is guaranteed at a 100A maximum value. MA AXLIA VPPLXVW/V8SEZXVW/VOELXVWNMAX /730A/MAX738A/MAX 744A 5V, Step-Down, Current-Mode PWM DC-DC Converters (Circuit of Figure 3, Ta = +250, unless otherwise noted.) MAX730A EFFICIENCY vs. OUTPUT CURRENT (NOTES 3, 6) 90 EFFICIENCY (%} a oa 70 0 200 400i OUTPUT CUPRENT (ma) MAXIMUM OUTPUT CURRENT vs. 1000 SUPPLY VOLTAGE 1400 (NOTES 3, 6) =z B s200 Sr MAXT38A J 3 va 5 MAX?4d A E // MAX720A = 1000 2 / 2 = 800 4 6 8 0 2 14 16 SUPPLY VOLTAGE () MAX738A/MAX7448 QUIESCENT SUPPLY CURRENT vs. SUPPLY VOLTAGE 25 = / 20 or fi Lae A = 4s +" Oo 5 3 10 fe _ UNDERVOLTAGE | te , { LOCKOUT HYSTERESIS | R 05 UNDERVCLTAGE a LOCKOUT ENABLED os 0 2 4 6 8 1 12 14 16 4 MAX738A EFFICIENCY vs. QUTPUT CURRENT (NOTES 3, 6) 90 EFFICIENCY (%} a oa 70 60 0 200 400 600 800 1000 OUTPUT GURRENT (ma) MAXIMUM OUTPUT CURRENT vs. SUPPLY VOLTAGE, NO Ri 1400 T T (NOTES 3, 6) = 1200 | 5 L, f 1000 Fa 3 KL E 800 MATL eh MAX738A I ae) i = 60 z Ly = 409 | MAX730A 200 4 6 8 10 12 14 16 SUPPLY VOLTAGE (V) MAX738A/MAX744A PEAK INDUCTOR CURRENT vs. OUTPUT CURRENT 1000 = a 2 A 0 7 3 |] re Gaon V4. = 6.6 py V+=8.0V To 16.0V Z L b awoly Li =100uH C4=150F o | 1 O 100 200 300 400 500 60 700 800 EFFICIENCY (%} QUIESCENT SUPPLY CURRENT (mA) STANDBY SUPPLY CURRENT (1A) Typical Operating Characteristics MAX744A EFFICIENCY vs. QUTPUT CURRENT 100 (NOTE 3) 90 Vee 80 V+=9,0V V+=12.0V 70 V+=16.0 60 0 200 400 600 800 OUTPUT CURRENT (mA) QUIESCENT SUPPLY CURRENT vs. TEMPERATURE 10K MAX7304, V+ =9.0V MAX738A, V+ = 12.0 MAX744A, V+ = 12.0 (NOTES 4, 5) -60 -40 20 0 20 40 &D 80 100 120 140 160 TEMPERATUFE (C) STANDBY SUPPLY CURRENT vs. TEM PERATURE (NOTES 4, 5) V+ =16V MAX738A/MAX7444, ONLY V+=12V MAX738A/MAX744A, ONLY V+= -60-40 -20 0 20 40 60 80 100 120140 160 MA AXLMM5V, Step-Down, Current-Mode PWM DC-DC Converters Typical Operating Characteristics (continued) (Circuit of Figure 3, Ta = +250, unless otherwise noted.) MAX730A OSCILLATOR FREQUENCY vs. OSCILLATOR FREQUENCY SUPPLY VOLTAGE vs. TEMPERATURE (NOTE3) 2H e MAXT304 a 220 5 = 200 & a o 5 E 8 g 140 0 4 6 8 10 12 14 16 -60 -40 -20 O 20 40 60 80 100 120 140 160 SUPPLY VOLTAGE (V) TEMPERATURE (C) MAX738A MAX744A CSCILLATOR FREQUENCY OSCILLATOR FREQUENCY vs. TEMPERATURE vs. TEMPERATURE 200 210 TT (NOTE 4) (NOTE4) i190 | | = 120 = 20 SY a Py = 608 B 170 8 IN \ | id 4 MAL v= 16.0 a} an 1 2 160 cr 190 ~ | pone EF 150 S | a 4 Pe, | Vt 8.0V 140 S 180 Pe| 8 mM | 430 | 120 170 -60 -40 -20 0 20 40 60 80100 120 140 160 -60 -40 -20 0 20 40 60 80 100120 140 160 TEMPERATURE (C) TEM PERATURE (C) Note 3: Commercial temperature range external component values in Table 3. Note 4: Wide temperature range external component values in Table 3. Note 5: Standby and shutdown current includes all external component leakage currents. Capacitor leakage currents dominate at Ta > +85 T, Sanyo OS-CON capacitors were used. Note 6: Operation beyond the specifications listed in the electrical characteristics may exceed the power dissipation ratings of the device. MA AXLIA > VPVLXVW/V8EZXVW/VOELXVWNMAX /730A/MAX738A/MAX 744A 5V, Step-Down, Current-Mode PWM DC-DC Converters Typical Operating Characteristics (continued) (Circuit of Figure 3, Ta = +250, unless otherwise noted.) MAX738A/MAX7444 MAX738A/MAX744A SWITCHING WAVEFORMS, SWITCHING WAVEFORMS, CONTINUOUS CONDITION DISCONTINUOUS CONDITION 12V | 12V | \ omA 5 omA j ere t C ] C a a 5 a 5 2usidiv 2usidiv Ac SWITCH VOLTAGE (LX PIN), 5V/div, OV TO+12V A: SWITCH VOLTAGE (LX PIN), 5V/div, OV TO+12 B: INDUCTCR CURRENT, 200mA/div B. INDUCTOR CURRENT, 200mVdiv C: QUTPUT VOLTAGE RIPPLE 50mVidiv, AC-COUPLED C: CUTPUT VOLTAGE RIPPLE S0mVaiv, AC-CCUPLED Cour = 390uF, Cour = 390uLF, V+= 12V, leg = 1504, V+=12Y, leypy = 150LA MAX730A LINE-TRANSIENT RESPGNSE MAX738A/M AX7444 LINE-TRANSIENT RESPONSE A ive | ~B av | ov 100ms/div 100ms/div A: Vou 50mWaliv, DC-COUPLED A: Vy: SomVidiv, DC-COUPLED B: V4, 5Vidiv, 6.0V TO 11.0V B: V+, 5Wadiv, 10.2V TO16.0V lou = SOMA lout = 750mA 6 MA AXLMM5V, Step-Down, Current-Mode PWM DC-DC Converters Typical Operating Characteristics (continued) (Circuit of Figure 3, Ta = +25C, unless otherwise noted.) MAX730A MAX? 38A/MAX?744.A LOAD-TRANSIENT RESPONSE LOAD-TRANSIENT RESPONSE 50ms/aiv A Vou, 5omvidiv, DC-CCUPLED B: Igurp: 200mAciv, 207A TO 300mA 50ms/div As Vey 5omvidiv, DC-COUPLED B. Igyp SOOT Adiv, SOMA TO 750m A VY+=9V V+=12V Pin Description PIN 8-PIN 46-PIN NAME FUNCTION DIPSO | WIDE SO 1 2 SHDN Shutdownactive low. Ground to power-down chip, tie to V+ for normal operation. Output voltage falls ta OV when SHDN is low. 2 4 REF Reference-Voltage Output (+1.23V) supplies up to 100A for extended loads. Bypass to GND with a capacitor that does not exceed 0.047uF. 3 7 es Soft-Start. Capacitor between SS and GND provides soft-start and short-circuit protection. 510k resistor from SS to SHDN provides current boost. 4 8 ce Compensation Capacitor Input externally compensates the cuter feedback loap. Connect to OUT with a 330pF capacitor. 5 9 OUT Output Voltage Sense Input provides regulation feedback sensing. Connect to +5V output. 10, 11 GND Ground pins are internally connected. Connect both pins to ground. 7 12,13, 14 LX Drain of internal P-channel power MOSFET. 8 1.15.46 Vv Supply-Voltage Input. Bypass to GND with 1pF ceramic and large-value electrolytic capaci- o_o * tors in parallel. The 1p.F capacitor must be as close to V+ and GND pins as possible. 45,6 N.C. No Connectno internal connections to these pins. MA AXLIA VPPLXVW/V8SEZXVW/VOELXVWNMAX /730A/MAX738A/MAX 744A 5V, Step-Down, Current-Mode PWM DC-DC Converters Detailed Description The MAX730A/MAX738A/MAX744A switch-mode regu- lators use a current-mode pulse-width-modulation (PWM) control system coupled with a simple step-down (buck) regulator topography. They convert an unregu- lated DC voltage from 5.2 to 11V for the MAX730A, and from 6V to 16 for the MAX738A/MAX744A. The current-mode PWM architecture provides cycle-by- cycle current limiting, improved load-transient response characteristics, and simpler outer-loop design. The controller consists of two feedback loops: an inner (current) loop that monitors the switch current via the cur- rent-sense resistor and amplifier, and an outer (voltage) loop that monitors the output voltage through the error amplifier (Figure 1). The inner loop performs cycle-by- 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 voltage produces an error signal that raises the threshold, allowing the circuit to store and transfer more energy during each cycle. Programmable Soft-Start Figures 1 and 2 show a capacitor and a resistor con- nected to the soft-start (SS) pin to ensure an orderly power-up. Typical values are 0.1uF and 610k. SS con- trols both the SS timing and the maximum output current that can be delivered while maintaining 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 cur- rent-limit threshold. The 610k& resistor sets the SS clamp at a value high enough to maintain regulation, even at currents exceeding 1A. This resistor is not nec- essary for lower-current loads. Refer to the Maximum Output Current vs. Supply Voltage graph in the Typica/ Operating Characteristics. Table 1 lists timing charac- teristics tor selected capacitor values and circuit condi- tions. The overcurrent comparator trips when the load exceeds approximately 1.5A. An SS cycle begins when either an undervoltage or overcurrent fault condition triggers an internal transistor to momentarily discharge the SS capacitor to ground. An SS cycle also begins at power-up and when coming out of shutdown mode. Overcurrent Limiting The overcurrent comparator triggers when the load cur- rent exceeds approximately 1.5A. On each clock cycle, the output FET turns on and attempts to deliver current until cycle-by-cycle or overcurrent limits are exceeded. Note that the SS capacitor must be greater than 0.01LF for overcurrent protection to function properly. A typical value is 0.1UF. Undervoitage Lockout The MAX738A/MAX744As undervoltage-lockout fea- ture monitors the supply voltage at V+, and allows operation to start when V+ rises above 5.7V (6V guar- anteed). When V+ falls, operation continues until the supply voltage falls below 5.45V (see the MAX738A/MAX744A Quiescent Supply Current vs. Supply Voltage graph in the Typica! Operating Characteristics). The MAX730A is similar, starting oper- ation at V+ > 4.7V and continuing to operate down to 4.45V. When an undervoltage condition is detected, control logic turns off the output power FET and dis- charges the SS capacitor to ground. This prevents par- tial 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 4.7V (MAX730A) or 5.7V (MAX738A/ MAX744A), at which time an SS cycle begins. Shutdown Mode The MAX730A/MAX738A/MAX744A are shut down 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 standby current in shutdown mode is 6A. The actual design limit for stand- by current is much less than the 100UA specified in the Electrical Characteristics (see Standby Current vs. Temperature in the Typical Operating Characteristics). However, testing to tighter limits is prohibitive because the current takes several seconds to settle to a final value. For normal operation, connect SHDN to V+. Note that coming out of shutdown mode initiates an SS cycle. Continuous-~/Discontinuous- Conduction Modes The input voltage, output voltage, load current, and induc- tor value determine whether the IC operates in continuous or discontinuous mode. As the inductor value or load cur- rent decreases, or the input voltage increases, the MAX730A/MAX738A/MAX744A tend to operate in discon- tinuous-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 continuous-conduc- tion mode (CCM), the inductor current never decays to zero, which is typically more efficient than DCM. CCM allows the MAX730A/ MAX/38A/MAX744A to deliver maxi- mum load current, and is also slightly less noisy than DCM, because the peak-to-average inductor current ratio is reduced. MA AXLAN5V, Step-Down, Current-Mode PWM DC-DC Converters Table 1. Typical Soft-Start Times MAX730A CIRCUIT CONDITIONS SOFT-START TIME (ms) vs. C1 (uF) R1 (ko) V+ () lour (mA) CA (uF) C1 = 0.01 C1 = 0.047 C1=0.1 C1 =0.47 510 6 0 100 2 6 11 28 510 9 0 100 1 4 6 15 510 11 0 100 1 2 4 11 510 9 150 100 1 4 8 24 510 9 300 100 1 5 9 27 510 9 150 390 3 6 9 23 510 9 150 680 4 6 9 24 None 6 0 100 16 34 54 125 None 9 0 100 10 22 34 82 None 14 0 100 8 18 28 66 None 9 150 100 34 134 270 1263 None 9 150 390 39 147 280 1275 None 9 150 680 40 152 285 1280 MAX738A/MAX744A CIRCUIT CONDITIONS SOFT-START TIME (ms) vs. C1 (uF) RI (kQ) V+ () lour (mA) CA (uF) C1 = 0.01 C1 = 0.047 Ci=0.1 C1 =0.47 510 7 0 100 1 4 6 18 510 12 0 100 1 2 3 8 510 16 0 100 1 1 2 6 510 12 300 100 1 3 5 3 510 12 750 100 1 5 8 21 None 7 0 100 12 27 40 100 None 12 0 100 7 16 25 54 None 16 0 100 6 13 20 68 None 12 300 100 27 112 215 1114 Internal Reference The +1.23V bandgap reference supplies up to 100UA at REF. Connect a 0.01uF bypass capacitor from REF to GND. Oscillator The internal oscillator of the MAX730A typically oper- ates at 170kHz (160kHz for the MAX738A and 185kHz for the MAX744A). The MAX744A is guaranteed to operate at a minimum of 159kHz and a maximum of 212.5kHz over the operating voltage and temperature range, making it ideal for use in portable communica- tions systems. The Typical Operating Characteristics graphs indicate oscillator frequency stability over tem- perature and supply voltage. MA AXLIA Applications Information Figure 3 shows the standard 5V step-down application circuits. Table 3 lists the components for the desired operating temperature range. These circuits are useful in systems that require high current at high efficiency and are powered by an unregulated supply, such as a battery or wall-plug AC-DC transformer. These circuits operate over the entire line, load, and temperature ranges using the single set of component values shown in Figure 3 and listed in Table 3. Inductor Selection The MAX730A/MAX738A/MAX744A 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 9 VPPLXVW/V8SEZXVW/VOELXVWNMAX /730A/MAX738A/MAX 744A 5V, Step-Down, Current-Mode PWM DC-DC Converters Vin = +6.0V TO+16.0V SHON we lt 1 CNERCURRENT COMPARATOR LL uF Tv SLOPE COMPENSATION BIAS RAMP OUT a | 330pF P ee LX uy VouT= MAXIM MAX730A = = MAX738A MAX7S4A UNDERVOLTAGE LOCKOUT L 0.1mF - | C ( I YUVLO ap SEE TABLE 2 FOR COMPONENT VALUES AND SUPPLIERS Figure 1. Detailed Block Diagram with External Components single 100WH (MAX7__AC} or 33H (MAX?7_ AE/AM) inductor. The inductors incremental saturation current rating should be greater than 1A, and its DC resistance should be less than 0.88. Table 2 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 capacitor is low equivalent series resistance (ESR). The product of the inductor current variation and the output capacitors ESR determines the amplitude of the sawtooth ripple seen on the output voltage. Also, mini- mize the output filter capacitors ESR to maintain AC stability. The capacitors ESR should be less than 0.25 to keep the output ripple less than 50mVp-p over the entire current range (using a 100UH inductor). 10 Capacitor ESR rises as the temperature falls, and excessive ESR is the most likely cause of trouble at temperatures below 0C. Sanyo OS-CON series through-hole and surface-mount tantalum capacitors exhibit low ESR at temperatures below 0C. Refer to Table 2 for recommended capacitor values and sug- gested capacitor suppliers. Other Components The catch diode should be a Schottky or high-speed silicon rectifier with a peak current rating of at least 1.5A for full-load (750mA)} operation. The 1N5817 is a good choice. The 330pF outer-loop compensation capacitor provides the widest input voltage range and best transient characteristics. For low-current applica- tions, the 510k resistor may be omitted (see the Maximum Output Current vs. Supply Voltage graph (R41 removed) in the Typical Operating Characteristics). MA AXLAN5V, Step-Down, Current-Mode PWM DC-DC Converters Table 2. Component Values and Suppliers . MAX730 AC/MAX738AC/MAX7444C MAX730AE/M, MAX738AE/M, MAX744AE/M Production Commercial Temp. Range Wide Temp. Range Method Inductors Capacitors Inductors Capacitors L1 = 33uH to 100HH C3 = 68yIF, 16V Lt = 33yH C3 = 68yF, 16V Sumida (708) 956-0666 C4 = 100HF, 6.3V Sumida (708) 956-0866 C4 = 100HF, 6.3V Surface CD54-101KC (MAX730AC) Matsuo (714) 969-2491 CD54-330N (MAX730AC) Matsuo (714) 969-2491 Mount CD105-101KC 267 series CD105-330N 267 series (MAX738AC/MAX744AC) (MAX738AEM, MAX744AE/M) . . Sprague (603) 224-1961 yo: Sprague (603) 224-1961 Coiltronics (407) 241-7876 . Coiltronics (407) 241-7876 : CTX4100 series 595D/293D series CTX50 series 595D/293D series C3 = 150uF, 16V C4 = 220uF, 10V _ Sanya (619) 661-6322 L1 = 33uH to 1004H C3 = 150pF, 16V Li = 33pH OS-CON series C4 = 150uF, 16V or Miniature 390)F, 6.3V Low-ESA Through. Sumida (708) 956-0666 Wr 8 Sumida (708) 956-0666 organic semiconductor Hole g RCH654-101K (MAX730A) Nichicon (708) 843-7500 RGH654-330M (MAX730A) (Rated from -55'C to +105 C) RCH895-1 01K PL series RCH895-330M (MAX738A/MAX744A) . (MAX738A/MAX744A) Mallory (317) 273-0090 Low-ESR electrolytics : THF series C3 = 100uF, 20V C4 = 220uF 10V (Rated fram -55 TC to +125 C) C3 = 150uF, 16V L1 = 100yH C4 = 390uF, 6.3V Low-Cost Maxim Maxim Th h MAXLO01 MAXCO001 Hole . 1 00pH iron-power toroid 150uF, low-ESR electrolytic Renco (516) 586-5566 RL1284-100 United Chemicon (708) 843-7500 Printed Circuit Layouts A good layout is essential for clean, stable operation. The layouts and component placement diagrams given in Figures 4, 5, 6, and 7 have been successfully tested over a wide range of operating conditions. Note that the 1pF bypass capacitor (C2) must be positioned as close to the V+ and GND pins as possible. Also, place the out- put capacitor as close to the OUT and GND pins as pos- sible. The traces connecting the input and output filter capacitors and the catch diode must be short to mini- mize inductance and capacitance. For this reason, avoid using sockets, and solder the IC directly to the PC board. Use an uninterrupted ground plane if possible. MA AXLIA Output-Ripple Filtering A simple lowpass pi-filter (Figure 3) can be added to the output to reduce output ripple to about S5mVp-p. The cutoff frequency shown is 21kHz. Since the filter inductor is in series with the circuit output, its resis- tance should be minimized so the voltage drop across it is not excessive. 11 VPPLXVW/V8SEZXVW/VOELXVWNMAX /730A/MAX738A/MAX 744A 5V, Step-Down, Current-Mode PWM DC-DC Converters FROM SHDN a Ri | 510k + $$ CLAMP 8S iM +35% a1 = MAAL/VI 1.23 MAX730A MAX738A MAX744A Figure 2. Block Diagram of Soft-Start Circuitry MAX730A +5.2V TO +11.0V MAX738A/MAX/444 +6.0V TO +16.0V son ox SUN AXILM MAX730A MAX738A cut MAX744A SEE TABLE 2 FOR COMPCNENT VALUES AND SUPPLIERS. OPTIONAL LOWPASS OUTPUT FILTER l2 FILTER 25)H OUTPUT OUTPUT 7 + 22uF T PART |INPUT SUPPLY RANGE () | GUARANTEED OUTPUT CURRENT AT 5 (mA} MAX730A, 6.010 11.0 450 6.0 to 16.0 450 MAX738A, 10.2 to 16.0 750 6.0 109.0 500 MAX744A, 9.0 to 16.0 750 NOTE: PIN NUMBERS REFER TO 8-PIN PACKAGES. Figure 3. Standard +5V Step-Down Application Circuit 12 MA AXLAN5V, Step-Down, Current-Mode PWM DC-DC Converters REV 8 avai eq SAXKIWVIg MAX730 EVALUATION KIT Rig} # i Rae C5 os @ ij weo re Lia @ +e 2 wae w te use = VOUTS = GHD Figure 4. DIP PC Layout, Through-Hole Component Placement Figure 5. DIP PC Layout, Component Side (1x scale) Diagram (1x scaie) VPPLXVW/V8SEZXVW/VOELXVWN Se be wi x MM OM x BKK RO yg RXR Fe Ry GC Swe % be x x XR pg Oe we. Figure 6. DIP PC Layout, Soider Side {1x scale) Figure 7. DIP PC Layout, Drill Guide (1x scale) MA AXLIA 13MAX /730A/MAX738A/MAX 744A 5V, Step-Down, Current-Mode PWM DC-DC Converters Pin Configurations (continued) __ Ordering Information (continued) TOP VIEW PART TEMP. RANGE PIN-PACKAGE . MAX738ACPA 0 to +70T 8 Plastic DIP SHON [1] rg | V+ MAX738ACWE 0T to+70TC 16 Wide SO PEF [2] MMAXIAA 7] LX MAX738AC/D OC to +70T Dice ss [31 MAX730A rs] cn MAX738AEPA -40'C to +85T 8 Plastic DIP oc [a 5] our MAX738AEWE -40 to +85 16 Wide SO 2 MAX738AMJA -55 C to +125 8 GERDIP sO MAX744ACPA 0 to +70T & Plastic DIP MAX744ACWE 0 to +70T 16 Wide SO * : at Vi fi 6] Vs MAX744AC/D 0 to +70T Dice SCN a is] y MAX744AEPA -40C to +85C & Plastic DIP * MAX744AEWE -40C to +85 C 16 Wide SO FFL] ~naxiaa [4] x MAX744AMJA -55C to 4+125T 8 CERDIP ne.[4] max7aea fig] Lx *Contact factory for dice specifications. MAX744A ne. [5 | 2] Lx nec. [6 | ht] oxo ss[7 Ho] exo cc [3 a] OUT Wide SO Chip Topographies MAX730A MAX738A/MAX744A SHDN vs SHON V+ $s GUT 0.072" (1.828mm) TRANSISTOR COUNT: 274 (MAX730A) 286 (MAX738A/MAX744 A): SUBSTRATE CONNECTED TO V+. 14 REF ss 0.116" (2.946mm) 0.131" (3.327mm) MA AXLAN5V, Step-Down, Current-Mode PWM DC-DC Converters Package Information ne a O127mm L c INGHES MILLIMETERS | [D1 DIM ain | max | MIN | MAX ol A 0.200 - 5.08 At | 0.015 Z 0.38 4 A2 10.125 | o175 | 348 | 4.45 ( A3 | 0.055 | 0.080 | 140 | 203 ~ B | oo16 | 0022 | o41 | 056 B1 | 0.050 | 0.085 | 1.27 | 1.65 eres es c |oo08 | 0012 | o20 | 020 E D | os48 | o3s90 | sa4 | ast D1 [o.005 | 0035 | 0.13 | 089 D { Lt 4 ] E | 0300 | 0325 | 752 | 826 . . E1 | 0.240 | o280 | 610 | 7.11 A A A3 | | e 0.100 BSC 2.54 BSC a AR A 0.300 BSC 7.62 BSC TU 4 en | 0.400 - 10.16 | ! L [o115 | 0.150 | 292 | 3.81 | | i 1 a 0 15 0 15 L F i 21-324A Al a. Fy Y Lee i 1 8-PIN PLASTIC 3 Bt C- DUAL-IN-LINE B . fA , PACKAGE eg m DIM INCHES MILLIMETERS min | max | mIN | Max A | 0053 | 0089 | 135 | 1.75 Atl | 0.004 [| oo10 | o10 | 0.25 _ B | 0.014 | oo19 | 035 | 049 4 c |ooo7 | oo10 [ o19 | 0.25 dD [o.189 | 0197 | 480 | 500 EF oH E | 0.150 | 01457 | 380 | 4.00 | 2 0.050 BSC 1.27 BSC H | 0.228 | 0244 | 5.80 | 620 h | 0.010 | 0020 | 025 | o50 Lt [oote | 0050 | 040 | 1.27 a | oO 3 O a 21-325A 8-PIN PLASTIC SMALL-OUTLINE PACKAGE MA AXLIA 15 VPPLXVW/V8SEZXVW/VOELXVWNMAX /730A/MAX738A/MAX 744A 5V, Step-Down, Current-Mode PWM DC-DC Converters Package Information (continued) DIN INCHES MILLIMETERS MIN | MAX | MIN | MAX A - 0.200 - 5.08 | {set [* s1 s B | 0.014 | 0.023 | o36 | 0.58 Co Od Bi | cosa | oss | o97 | 1.65 B2 | 0.023 | 0.045 | 058 | 1.14 C c [0.008 | 0.015 | 020 | 0.38 D - 0.405 - 10.29 E | 0.220 [| 0.310 | 559 | 7.87 Ta as E1 | o.290 | 0.320 | 7.37 | 38.13 D E11 8 0.100 BSC 2.54 BSC . , L_ [0.125 | 0.200 | 318 | 5.08 A | [= B2 <_E} ti |o150 | - | 3at - ] r] a | 0015 | oos0 | o38 | 152 | s - 0.055 - 1.40 L S1 | 0.005 - 0.13 - \ _| i ' s a O 15 O 15 A 4 | i 21 -a26D il 1 y Y i: f tw! e lM Cf 8-PIN CERAMIC B Bt DUAL-IN-LINE PACKAGE DIM INCHES MILLIMETERS MIN | MAX | MIN | MAX A | 0.093 | 0.104 | 235 | 265 HHHHHHEA At | 0.004 | 0.012 | 0.10 | 0.30 B | 0.014 | 0.019 | 0.35 | 0.49 c [0.009 | 0013 | 023 | 0.32 D | 0.398 | 0.413 | 10.10 | 10.50 E | 0201 | o299 | 7.40 | 7.60 a 0.050 BSC 1.27 BSG H | 0.394 | o419 | 10.00 | 10.65 AAAHAAE A h_| oo10 | 0.030 | 025 | 0.75 L_|oois | 0050 | 040 | 127 a | 0 8 0 8" 21-5898 i \ i n Fan Okita F 16-PIN PLASTIC Looo4in_| te @ ele SMALL-OUTLINE B . Lo (WIDE) PACKAGE Maxim cannot assume responsibility for use of any circuliry other than circuitry entirely embodied in a Maxim product. No circuil patent licenses are implied. Maxim reserves the right to change the circuitry and specilications without notice at any time. 16 Maxim Integrated Producis, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 1996 Maxim Integrated Products Printed USA MAAXIAA js a registered trademark of Maxim Integrated Products.