19-0165; Rev 2; 1/96 5V, Step-Down, Current-Mode PWM DC-DC Converters ________________________________Features The MAX730A/MAX738A/MAX744A are 5V-output CMOS, step-down switching regulators. The MAX738A/ MAX744A accept inputs from 6V to 16V and deliver 750mA. The MAX744A guarantees 500mA load capability for inputs above 6V and has tighter oscillator frequency limits for low-noise (radio) applications. The MAX730A accepts inputs between 5.2V and 11V and delivers 450mA for inputs above 6V. Typical efficiencies are 85% to 96%. Quiescent supply current is 1.7mA and only 6µA in shutdown. Pulse-width modulation (PWM) current-mode control provides 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. These regulators require only a single inductor value to work in most applications, so no inductor design is necessary. ♦ 750mA Load Currents (MAX738A/MAX744A) The MAX730A/MAX738A/MAX744A also feature cycleby-cycle current limiting, overcurrent limiting, undervoltage lockout, and programmable soft-start protection. ___________________________Applications Portable Instruments Cellular Phones and Radios Personal Communicators ♦ High-Frequency, Current-Mode PWM ♦ 159kHz to 212.5kHz Guaranteed Oscillator Frequency Limits (MAX744A) ♦ 85% to 96% Efficiencies ♦ 1.7mA Quiescent Current ♦ 6µA 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 MAX730ACPA 0°C to +70°C 8 Plastic DIP MAX730ACSA MAX730AC/D MAX730AEPA MAX730AESA MAX730AMJA 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C -55°C to +125°C 8 SO Dice* 8 Plastic DIP 8 SO 8 CERDIP Ordering Information continued at end of data sheet. *Contact factory for dice specifications. Distributed Power Systems Computer Peripherals __________Typical Operating Circuit INPUT 6V TO 16V _________________Pin Configurations TOP VIEW 33µH V+ 68µF LX OUTPUT 5V SHDN 1 MAX738A MAX744A ON/OFF PIN-PACKAGE SHDN 100µF OUT REF 2 SS 3 CC 4 REF CC SS GND MAX730A MAX738A MAX744A 8 V+ 7 LX 6 GND 5 OUT DIP Pin Configurations continued on last page. ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800 MAX730A/MAX738A/MAX744A __________________General Description MAX730A/MAX738A/MAX744A 5V, Step-Down, Current-Mode PWM DC-DC Converters ABSOLUTE MAXIMUM RATINGS Pin Voltages V+ (MAX730A) ......................................................+12V, -0.3V V+ (MAX738A/MAX744A) .....................................+18V, -0.3V LX (MAX730A) .................................(V+ - 12V) to (V+ + 0.3V) LX (MAX738A/MAX744A) ................(V+ - 21V) to (V+ + 0.3V) OUT .................................................................................±25V SS, CC, SHDN .........................................-0.3V to (V+ + 0.3V) Peak Switch Current (ILX) ........................................................2A Reference Current (IREF) ...................................................2.5mA Continuous Power Dissipation (TA = +70°C) 8-Pin Plastic DIP (derate 9.09mW/°C above +70°C)...727mW 8-Pin SO (derate 5.88mW/°C above +70°C) ...............471mW 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: MAX7_ _AC_ _/AE_ _...................................................+150°C MAX7_ _AMJA.............................................................+175°C Storage Temperature Range ............................-65°C to +160°C Lead Temperature (soldering, 10sec).............................+300°C 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+ = 9V for the MAX730A, V+ = 12V for the MAX738A/MAX744A, ILOAD = 0mA, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER CONDITIONS MAX730A MIN TYP MAX MAX738A MIN TYP MAX MAX744A MIN TYP MAX 4.75 5.00 5.25 4.75 5.00 5.25 4.75 5.00 5.25 4.75 5.00 5.25 6.0 16.0 UNITS 0mA < ILOAD < 450mA, MAX730AC V+ = 6.0V to 11.0V 0mA < ILOAD < 450mA, MAX730AE 4.75 5.00 5.25 0mA < ILOAD < 300mA, MAX730AM 0mA < ILOAD < 450mA, MAX738AC/AE Output Voltage V+ = 6.0V to 16.0V 0mA < ILOAD < 350mA, MAX738AM 0mA < ILOAD < 500mA, MAX744AC/AE V 0mA < ILOAD < 375mA, MAX744AM V+ = 10.2V to 16.0V, 0mA < ILOAD < 750mA V+ = 9.0V to 16.0V 0mA < ILOAD < 750mA, MAX744AC/AE 0mA < ILOAD < 600mA, MAX744AM Input Voltage Range Line Regulation 2 5.2 V+ = 5.2V to 11.0V V+ = 6.0V to 16.0V 11.0 6.0 16.0 0.15 0.15 0.15 _______________________________________________________________________________________ V %/V 5V, Step-Down, Current-Mode PWM DC-DC Converters (Circuit of Figure 3, V+ = 9V for the MAX730A, V+ = 12V for the MAX738A/MAX744A, ILOAD = 0mA, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER CONDITIONS MAX730A MIN TYP MAX ILOAD = 0mA to 300mA Load Regulation MAX738A MIN TYP MAX MAX744A MIN TYP MAX 0.0005 0.0005 90 90 87 87 0.0005 ILOAD = 0mA to 750mA V+ = 9.0V, ILOAD = 300mA Efficiency 92 V+ = 12V, ILOAD = 750mA 1.7 Supply Current (includes switch current) 3.0 1.7 3.0 1.7 %/mA % 3.0 V+ = 6.0V to 9.0V MAX744AC/AE MAX744AM 3.0 V+ = 9.0V to 12.0V MAX744AC/AE 3.0 MAX744AM 3.5 MAX744AC 4.0 MAX744AE 4.3 V+ = 12.0V to 16.0V 1.2 MAX744AM Standby Current SHDN = 0V (Note 1) Shutdown Input Threshold VIH UNITS 2.5 mA 4.5 6.0 100.0 2.0 100.0 2.0 VIL Shutdown Input Leakage Current Short-Circuit Current 6.0 100.0 2.0 0.25 0.25 0.25 1.0 1.0 1.0 1.5 4.7 6.0 1.5 5.7 1.5 6.0 µA A Undervoltage Lockout LX On Resistance ILX = 500mA 0.5 0.5 0.5 Ω LX Leakage Current V+ = 12V, LX = 0V 1.0 1.0 1.0 µA Reference Voltage V+ = 12V, TA = +25°C V+ falling 5.0 1.15 1.23 Reference Drift 1.30 1.15 1.23 50 130 Oscillator Frequency V+ = 6.0V to 16.0V 5.7 V V+ rising Compensation Pin Impedance 5.2 µA 170 1.30 210 130 160 5.7 1.15 1.23 50 6.0 1.30 50 190 159.0 185.0 212.5 MAX744AM 159.0 7500 V ppm/°C MAX744AC/AE 7500 V kHz 216.5 7500 Ω Note 1: The standby current typically settles to 25µA (over temperature) within 2 seconds; however, to decrease test time, the part is guaranteed at a 100µA maximum value. _______________________________________________________________________________________ 3 MAX730A/MAX738A/MAX744A ELECTRICAL CHARACTERISTICS (continued) __________________________________________Typical Operating Characteristics (Circuit of Figure 3, TA = +25°C, unless otherwise noted.) MAX730A EFFICIENCY vs. OUTPUT CURRENT 100 100 (NOTES 3, 6) (NOTES 3, 6) (NOTE 3) 90 V+ = 5.5V 80 V+ = 7V V+ = 9V 70 V+ = 6V 80 V+ = 8V V+ = 12V 60 200 400 600 800 OUTPUT CURRENT (mA) V+ = 12.0V 0 MAXIMUM OUTPUT CURRENT vs. SUPPLY VOLTAGE 200 400 600 800 OUTPUT CURRENT (mA) 0 1000 MAX730A 1000 QUIESCENT SUPPLY CURRENT (mA) MAXIMUM OUTPUT CURRENT (mA) (NOTES 3, 6) MAX738A 400 600 800 OUTPUT CURRENT (mA) 1000 3.0 1400 MAX744A 200 QUIESCENT SUPPLY CURRENT vs. TEMPERATURE MAXIMUM OUTPUT CURRENT vs. SUPPLY VOLTAGE, NO R1 (NOTES 3, 6) 1200 V+ = 16.0V 60 1000 1400 V+ = 9.0V V+ = 16V 60 0 V+ = 6.0V 80 70 70 V+ = 11V EFFICIENCY (%) 90 EFFICIENCY (%) EFFICIENCY (%) 90 MAXIMUM OUTPUT CURRENT (mA) MAX744A EFFICIENCY vs. OUTPUT CURRENT MAX738A EFFICIENCY vs. OUTPUT CURRENT 100 1200 1000 800 MAX738A MAX744A 600 MAX730A 400 2.5 MAX730A, V+ = 9.0V MAX738A, V+ = 12.0V MAX744A, V+ = 12.0V 2.0 1.5 1.0 0.5 (NOTES 4, 5) 800 4 8 6 10 12 14 0 -60 -40 -20 0 200 16 4 6 8 SUPPLY VOLTAGE (V) 10 12 14 16 SUPPLY VOLTAGE (V) MAX738A/MAX744A QUIESCENT SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX738A/MAX744A PEAK INDUCTOR CURRENT vs. OUTPUT CURRENT 2.5 20 40 60 80 100 120 140 160 TEMPERATURE (°C) STANDBY SUPPLY CURRENT vs. TEMPERATURE 20 1000 PEAK INDUCTOR CURRENT (mA) 2.0 1.5 UNDERVOLTAGE LOCKOUT HYSTERESIS 1.0 UNDERVOLTAGE LOCKOUT ENABLED 0.5 4 2 4 6 8 600 400 V+ = 6.6V V+ = 8.0V TO 16.0V 200 L1 = 100µH C4 = 150µF 0 0 800 10 12 14 16 STANDBY SUPPLY CURRENT (µA) (NOTES 4, 5) QUIESCENT SUPPLY CURRENT (mA) MAX730A/MAX738A/MAX744A 5V, Step-Down, Current-Mode PWM DC-DC Converters 18 16 V+ = 16V MAX738A/MAX744A ONLY 14 12 10 V+ = 12V MAX738A/MAX744A ONLY 8 6 V+ = 9V 4 2 V+ = 6V 0 0 0 100 200 300 400 500 600 700 800 -60 -40 -20 0 20 40 60 80 100 120 140 160 _______________________________________________________________________________________ 5V, Step-Down, Current-Mode PWM DC-DC Converters MAX730A OSCILLATOR FREQUENCY vs. TEMPERATURE OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE 220 240 (NOTE 3) MAX730A OSCILLATOR FREQUENCY (kHz) OSCILLATOR FREQUENCY (kHz) 210 200 190 MAX744A 180 170 160 220 200 V+ = 11.0V V+ = 5.5V 180 160 140 V+ = 7.0V V+ = 9.0V MAX738A 150 4 6 8 10 12 SUPPLY VOLTAGE (V) 14 0 -60 -40 -20 0 16 20 40 60 80 100 120 140 160 TEMPERATURE (°C) MAX744A OSCILLATOR FREQUENCY vs. TEMPERATURE MAX738A OSCILLATOR FREQUENCY vs. TEMPERATURE 210 200 (NOTE 4) V+ = 6.0V 180 V+ = 16.0V 170 160 150 V+ = 12.0V 140 V+ = 9.0V (NOTE 4) OSCILLATOR FREQUENCY (kHz) 190 SUPPLY CURRENT (mA) (NOTE 4) 200 V+ = 6.0V V+ = 16.0V 190 V+ = 9.0V 180 V+ = 12.0V 130 120 -60 -40 -20 0 20 40 60 80 100 120 140 160 TEMPERATURE (°C) 170 -60 -40 -20 0 20 40 60 80 100 120 140 160 TEMPERATURE (°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°C, 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. _______________________________________________________________________________________ 5 MAX730A/MAX738A/MAX744A ____________________________Typical Operating Characteristics (continued) (Circuit of Figure 3, TA = +25°C, unless otherwise noted.) MAX730A/MAX738A/MAX744A 5V, Step-Down, Current-Mode PWM DC-DC Converters ____________________________Typical Operating Characteristics (continued) (Circuit of Figure 3, TA = +25°C, unless otherwise noted.) MAX738A/MAX744A SWITCHING WAVEFORMS, DISCONTINUOUS CONDITION MAX738A/MAX744A SWITCHING WAVEFORMS, CONTINUOUS CONDITION 12V 12V A A 0V 0V 200mA 200mA B 0mA 0mA C B C 2µs/div 2µs/div A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +12V B: INDUCTOR CURRENT, 200mA/div C: OUTPUT VOLTAGE RIPPLE, 50mV/div, AC-COUPLED A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +12V B: INDUCTOR CURRENT, 200mA/div C: OUTPUT VOLTAGE RIPPLE, 50mV/div, AC-COUPLED COUT = 390µF, V+ = 12V, IOUT = 150µA, COUT = 390µF, V+ = 12V, IOUT = 150µA MAX738A/MAX744A LINE-TRANSIENT RESPONSE MAX730A LINE-TRANSIENT RESPONSE A A 16V B 11V 10.2V B 6V 0V 0V 100ms/div 100ms/div A: VOUT, 50mV/div, DC-COUPLED B: V+, 5V/div, 6.0V TO 11.0V A: VOUT, 50mV/div, DC-COUPLED B: V+, 5V/div, 10.2V TO 16.0V IOUT = 300mA IOUT = 750mA 6 _______________________________________________________________________________________ 5V, Step-Down, Current-Mode PWM DC-DC Converters MAX730A LOAD-TRANSIENT RESPONSE MAX738A/MAX744A LOAD-TRANSIENT RESPONSE A A 750mA 300mA B B 50mA 20mA 50ms/div 50ms/div A: VOUT, 50mV/div, DC-COUPLED B: IOUT, 200mA/div, 20mA TO 300mA A: VOUT, 50mV/div, DC-COUPLED B: IOUT, 500mA/div, 50mA TO 750mA V+ = 9V V+ = 12V ______________________________________________________________Pin Description PIN 8-PIN DIP/SO 16-PIN WIDE SO NAME FUNCTION 1 2 SHDN 2 3 REF 3 7 SS Soft-Start. Capacitor between SS and GND provides soft-start and short-circuit protection. 510kΩ resistor from SS to SHDN provides current boost. 4 8 CC Compensation Capacitor Input externally compensates the outer feedback loop. Connect to OUT with a 330pF capacitor. Shutdown—active low. Ground to power-down chip, tie to V+ for normal operation. Output voltage falls to 0V when SHDN is low. Reference-Voltage Output (+1.23V) supplies up to 100µA for extended loads. Bypass to GND with a capacitor that does not exceed 0.047µF. 5 9 OUT Output Voltage Sense Input provides regulation feedback sensing. Connect to +5V output. 6 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, 16 V+ Supply-Voltage Input. Bypass to GND with 1µF ceramic and large-value electrolytic capacitors in parallel. The 1µF capacitor must be as close to V+ and GND pins as possible. 4, 5, 6 N.C. No Connect—no internal connections to these pins. _______________________________________________________________________________________ 7 MAX730A/MAX738A/MAX744A ____________________________Typical Operating Characteristics (continued) (Circuit of Figure 3, TA = +25°C, unless otherwise noted.) MAX730A/MAX738A/MAX744A 5V, Step-Down, Current-Mode PWM DC-DC Converters _________________Detailed Description The MAX730A/MAX738A/MAX744A switch-mode regulators use a current-mode pulse-width-modulation (PWM) control system coupled with a simple step-down (buck) regulator topography. They convert an unregulated DC voltage from 5.2V to 11V for the MAX730A, and from 6V to 16V for the MAX738A/MAX744A. The current-mode PWM architecture provides cycle-bycycle 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 current-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-bycycle current limiting, truncating the power transistor ontime 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 connected to the soft-start (SS) pin to ensure an orderly power-up. Typical values are 0.1µF and 510kΩ. SS controls 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 current-limit threshold. The 510kΩ resistor sets the SS clamp at a value high enough to maintain regulation, even at currents exceeding 1A. This resistor is not necessary for lower-current loads. Refer to the Maximum Output Current vs. Supply Voltage graph in the Typical Operating Characteristics. Table 1 lists timing characteristics for selected capacitor values and circuit conditions. 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 current 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 0.01µF 8 for overcurrent protection to function properly. A typical value is 0.1µF. Undervoltage Lockout The MAX738A/MAX744A’s undervoltage-lockout feature monitors the supply voltage at V+, and allows operation to start when V+ rises above 5.7V (6V guaranteed). 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 Typical Operating Characteristics). The MAX730A is similar, starting operation 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 discharges the SS capacitor 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 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 0V 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 6µA. The actual design limit for standby current is much less than the 100µA 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-/DiscontinuousConduction 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 MAX730A/MAX738A/MAX744A 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 continuous-conduction mode (CCM), the inductor current never decays to zero, which is typically more efficient than DCM. CCM allows the MAX730A/ MAX738A/MAX744A to deliver maximum load current, and is also slightly less noisy than DCM, because the peak-to-average inductor current ratio is reduced. _______________________________________________________________________________________ 5V, Step-Down, Current-Mode PWM DC-DC Converters MAX730A/MAX738A/MAX744A Table 1. Typical Soft-Start Times MAX730A CIRCUIT CONDITIONS SOFT-START TIME (ms) vs. C1 (µF) R1 (kΩ) V+ (V) IOUT (mA) C4 (µF) 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 21 510 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 51 125 None 9 0 100 10 22 34 82 None None 11 9 0 150 100 100 8 34 18 134 28 270 66 1263 None 9 150 390 39 147 280 1275 None 9 150 680 40 152 285 1280 MAX738A/MAX744A CIRCUIT CONDITIONS R1 (kΩ) V+ (V) SOFT-START TIME (ms) vs. C1 (µF) IOUT (mA) C4 (µF) C1 = 0.01 C1 = 0.047 C1 = 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 100µA at REF. Connect a 0.01µF bypass capacitor from REF to GND. Oscillator The internal oscillator of the MAX730A typically operates 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 communications systems. The Typical Operating Characteristics graphs indicate oscillator frequency stability over temperature and supply voltage. ____________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 MAX730A/MAX738A/MAX744A 5V, Step-Down, Current-Mode PWM DC-DC Converters VIN = +6.0V TO +16.0V SHDN C2 C3* 1µF V+ OVERCURRENT COMPARATOR SLOPE COMPENSATION BIAS GEN Σ OUT C5 330pF RAMP GEN RSENSE ERROR AMP F/F CC R Q S 1.23V BANDGAP R1 510k CURRENT SENSE AMP PWM COMPARATOR D1 1N5817 REF OSC C6 0.01µF 1M ±35% L1 LX SS CLAMP SS VOUT = +5V C4* MAX730A MAX738A MAX744A UNDERVOLTAGE LOCKOUT C1 0.1µF VUVLO GND *SEE TABLE 2 FOR COMPONENT VALUES AND SUPPLIERS Figure 1. Detailed Block Diagram with External Components single 100µH (MAX7__AC) or 33µH (MAX7__AE/AM) inductor. The inductor’s incremental saturation current rating should be greater than 1A, and its DC resistance should be less than 0.8Ω. Table 2 lists inductor types and suppliers for various applications. The surfacemount inductors have nearly equivalent efficiencies to the larger through-hole inductors. Capacitor ESR rises as the temperature falls, and excessive ESR is the most likely cause of trouble at temperatures below 0°C. Sanyo OS-CON series through-hole and surface-mount tantalum capacitors exhibit low ESR at temperatures below 0°C. Refer to Table 2 for recommended capacitor values and suggested capacitor suppliers. Output Filter Capacitor Selection Other Components 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 capacitor’s ESR determines the amplitude of the sawtooth ripple seen on the output voltage. Also, minimize the output filter capacitor’s ESR to maintain AC stability. The capacitor’s ESR should be less than 0.25Ω to keep the output ripple less than 50mVp-p over the entire current range (using a 100µH inductor). 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 applications, the 510kΩ resistor may be omitted (see the Maximum Output Current vs. Supply Voltage graph (R1 removed) in the Typical Operating Characteristics). 10 ______________________________________________________________________________________ 5V, Step-Down, Current-Mode PWM DC-DC Converters Production Method MAX730AC/MAX738AC/MAX744AC Commercial Temp. Range Inductors L1 = 33µH to 100µH Surface Mount Sumida (708) 956-0666 CD54-101KC (MAX730AC) CD105-101KC (MAX738AC/MAX744AC) Coiltronics (407) 241-7876 CTX100 series MAX730AE/M, MAX738AE/M, MAX744AE/M Wide Temp. Range Capacitors Inductors Capacitors L1 = 33µH C3 = 68µF, 16V C4 = 100µF, 6.3V Sumida (708) 956-0666 CD54-330N (MAX730AC) CD105-330N (MAX738AE/M, MAX744AE/M) Matsuo (714) 969-2491 267 series Sprague (603) 224-1961 595D/293D series C3 = 68µF, 16V C4 = 100µF, 6.3V Matsuo (714) 969-2491 267 series Sprague (603) 224-1961 595D/293D series Coiltronics (407) 241-7876 CTX50 series C3 = 150µF, 16V C4 = 220µF, 10V L1 = 33µH to 100µH Miniature ThroughHole Sumida (708) 956-0666 RCH654-101K (MAX730A) RCH895-101K (MAX738A/MAX744A) L1 = 33µH Nichicon (708) 843-7500 PL series Low-ESR electrolytics Sumida (708) 956-0666 RCH654-330M (MAX730A) RCH895-330M (MAX738A/MAX744A) Sanyo (619) 661-6322 OS-CON series Low-ESR organic semiconductor (Rated from -55°C to +105°C) Mallory (317) 273-0090 THF series C3 = 100µF, 20V C4 = 220µF, 10V (Rated from -55°C to +125°C) C3 = 150µF, 16V C4 = 390µF, 6.3V L1 = 100µH Low-Cost ThroughHole C3 = 150µF, 16V C4 = 150µF, 16V or 390µF, 6.3V Maxim MAXL001 100µH iron-power toroid Renco (516) 586-5566 RL1284-100 Maxim MAXC001 150µF, low-ESR electrolytic United Chemicon (708) 843-7500 Printed Circuit Layouts Output-Ripple Filtering 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 1µF bypass capacitor (C2) 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 the input and output filter capacitors and the catch diode must be short to minimize 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. 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, its resistance should be minimized so the voltage drop across it is not excessive. ______________________________________________________________________________________ 11 MAX730A/MAX738A/MAX744A Table 2. Component Values and Suppliers MAX730A/MAX738A/MAX744A 5V, Step-Down, Current-Mode PWM DC-DC Converters FROM SHDN R1 510k SS CLAMP SS 1M ±35% C1 1.23V MAX730A MAX738A MAX744A Figure 2. Block Diagram of Soft-Start Circuitry MAX730A +5.2V TO +11.0V MAX738A/MAX744A +6.0V TO +16.0V OPTIONAL LOWPASS OUTPUT FILTER C2 1µF L2 25µH C3* 8 1 SHDN OUTPUT V+ LX 7 D1 1N5817 MAX730A MAX738A OUT 5 MAX744A R1 510k 3 C1 0.1µF SS GND 6 CC 4 FILTER OUTPUT C7 2.2µF L1* OUTPUT +5V C5 330pF C4* REF 2 PART INPUT SUPPLY RANGE (V) GUARANTEED OUTPUT CURRENT AT 5V (mA) MAX730A 6.0 to 11.0 450 6.0 to 16.0 450 10.2 to 16.0 750 6.0 to 9.0 500 9.0 to 16.0 750 MAX738A C6 0.01µF MAX744A *SEE TABLE 2 FOR COMPONENT VALUES AND SUPPLIERS. NOTE: PIN NUMBERS REFER TO 8-PIN PACKAGES. Figure 3. Standard +5V Step-Down Application Circuit 12 ______________________________________________________________________________________ 5V, Step-Down, Current-Mode PWM DC-DC Converters MAX730A/MAX738A/MAX744A MAX730 EVALUATION KIT Figure 4. DIP PC Layout, Through-Hole Component Placement Diagram (1x scale) Figure 5. DIP PC Layout, Component Side (1x scale) Figure 6. DIP PC Layout, Solder Side (1x scale) Figure 7. DIP PC Layout, Drill Guide (1x scale) ______________________________________________________________________________________ 13 MAX730A/MAX738A/MAX744A 5V, Step-Down, Current-Mode PWM DC-DC Converters ____Pin Configurations (continued) __Ordering Information (continued) TOP VIEW SHDN 1 REF 2 MAX730A SS 3 CC 4 8 V+ 7 LX 6 GND 5 OUT SO V+ 1 16 V+ SHDN 2 15 V+ REF 3 14 LX MAX738A MAX744A N.C. 4 N.C. 5 PART TEMP. RANGE PIN-PACKAGE MAX738ACPA 0°C to +70°C 8 Plastic DIP MAX738ACWE MAX738AC/D MAX738AEPA MAX738AEWE MAX738AMJA MAX744ACPA 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C -55°C to +125°C 0°C to +70°C 16 Wide SO Dice* 8 Plastic DIP 16 Wide SO 8 CERDIP 8 Plastic DIP MAX744ACWE 0°C to +70°C MAX744AC/D 0°C to +70°C MAX744AEPA -40°C to +85°C MAX744AEWE -40°C to +85°C MAX744AMJA -55°C to +125°C *Contact factory for dice specifications. 13 LX 16 Wide SO Dice* 8 Plastic DIP 16 Wide SO 8 CERDIP 12 LX N.C. 6 11 GND SS 7 10 GND 9 CC 8 OUT Wide SO __________________________________________________________Chip Topographies MAX738A/MAX744A MAX730A SHDN SHDN V+ V+ REF REF LX LX 0.116" (2.946mm) 0.131" (3.327mm) SS GND GND SS CC 0.072" (1.828mm) OUT TRANSISTOR COUNT: 274 (MAX730A) 286 (MAX738A/MAX744A); SUBSTRATE CONNECTED TO V+. 14 OUT CC 0.116" (2.946mm) ______________________________________________________________________________________ 5V, Step-Down, Current-Mode PWM DC-DC Converters DIM D1 A A1 A2 A3 B B1 C D D1 E E1 e eA eB L α E E1 D A3 A A2 L A1 INCHES MAX MIN 0.200 – – 0.015 0.175 0.125 0.080 0.055 0.022 0.016 0.065 0.050 0.012 0.008 0.390 0.348 0.035 0.005 0.325 0.300 0.280 0.240 0.100 BSC 0.300 BSC 0.400 – 0.150 0.115 15˚ 0˚ MILLIMETERS MIN MAX – 5.08 0.38 – 3.18 4.45 1.40 2.03 0.41 0.56 1.27 1.65 0.20 0.30 8.84 9.91 0.13 0.89 7.62 8.26 6.10 7.11 2.54 BSC 7.62 BSC – 10.16 2.92 3.81 0˚ 15˚ 21-324A α 8-PIN PLASTIC DUAL-IN-LINE PACKAGE C e B1 eA B eB DIM E A A1 B C D E e H h L α H INCHES MAX MIN 0.069 0.053 0.010 0.004 0.019 0.014 0.010 0.007 0.197 0.189 0.157 0.150 0.050 BSC 0.244 0.228 0.020 0.010 0.050 0.016 8˚ 0˚ MILLIMETERS MIN MAX 1.35 1.75 0.10 0.25 0.35 0.49 0.19 0.25 4.80 5.00 3.80 4.00 1.27 BSC 5.80 6.20 0.25 0.50 0.40 1.27 0˚ 8˚ 21-325A h x 45˚ D α A 0.127mm 0.004in. e A1 C L 8-PIN PLASTIC SMALL-OUTLINE PACKAGE B ______________________________________________________________________________________ 15 MAX730A/MAX738A/MAX744A ________________________________________________________Package Information MAX730A/MAX738A/MAX744A 5V, Step-Down, Current-Mode PWM DC-DC Converters ___________________________________________Package Information (continued) DIM E1 D E B2 A A B B1 B2 C D E E1 e L L1 Q S S1 α S S1 INCHES MAX MIN 0.200 – 0.023 0.014 0.065 0.038 0.045 0.023 0.015 0.008 0.405 – 0.310 0.220 0.320 0.290 0.100 BSC 0.200 0.125 – 0.150 0.060 0.015 0.055 – – 0.005 15˚ 0˚ MILLIMETERS MIN MAX – 5.08 0.36 0.58 0.97 1.65 0.58 1.14 0.20 0.38 – 10.29 5.59 7.87 7.37 8.13 2.54 BSC 3.18 5.08 3.81 – 0.38 1.52 – 1.40 0.13 – 0˚ 15˚ 21-326D α Q L L1 e 8-PIN CERAMIC DUAL-IN-LINE PACKAGE C B1 B DIM E A A1 B C D E e H h L α H INCHES MAX MIN 0.104 0.093 0.012 0.004 0.019 0.014 0.013 0.009 0.413 0.398 0.299 0.291 0.050 BSC 0.419 0.394 0.030 0.010 0.050 0.016 8˚ 0˚ MILLIMETERS MIN MAX 2.35 2.65 0.10 0.30 0.35 0.49 0.23 0.32 10.10 10.50 7.40 7.60 1.27 BSC 10.00 10.65 0.25 0.75 0.40 1.27 0˚ 8˚ 21-589B h x 45˚ D α A 0.127mm 0.004in. e B A1 C L 16-PIN PLASTIC SMALL-OUTLINE (WIDE) PACKAGE 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. 16 __________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 (408) 737-7600 © 1996 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.