19-0195; Rev 0; 10/93 Adjustable, Step-Down, Current-Mode PWM Regulators ________________________Applications Cellular Phones & Radios Portable Communications Equipment Portable Instruments ____________________________Features ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ ♦ Up to 750mA Load Currents 160kHz High-Frequency, Current-Mode PWM 85% to 96% Efficiencies 33µH or 100µH Pre-Selected Inductor Value, No Component Design Required 1.7mA Quiescent Supply Current 6µA Shutdown Supply Current Adjustable Output Voltage Overcurrent, Soft-Start, and Undervoltage Lockout Protection Cycle-by-Cycle Current Limiting 8-Pin DIP/SO Packages (MAX750A) ______________Ordering Information PART TEMP. RANGE MAX750ACPA 0°C to +70°C 8 Plastic DIP PIN-PACKAGE MAX750ACSA MAX750AC/D MAX750AEPA MAX750AESA 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C 8 SO Dice* 8 Plastic DIP 8 SO MAX750AMJA -55°C to +125°C 8 CERDIP** Ordering Information continued on last page. * Contact factory for dice specifications. **Contact factory for availability and processing to MIL-STD-883. Computer Peripherals _________________Pin Configurations __________Typical Operating Circuit INPUT 4V TO 16V TOP VIEW SHDN 1 8 V+ REF 2 7 LX 6 GND 5 I.C. SS 3 MAX750A MAX758A CC 4 V+ LX MAX750A MAX758A DIP ON/OFF SHDN 1 REF 2 SS 3 MAX750A CC 4 33µH OUTPUT ADJ. FROM VREF TO V+ 8 V+ 7 LX 6 GND 5 I.C. SHDN CC REF SS GND SO Pin Configurations continued on last page. ________________________________________________________________ Maxim Integrated Products Call toll free 1-800-998-8800 for free samples or literature. 1 MAX750A/MAX758A _______________General Description The MAX750A/MAX758A are adjustable-output, CMOS, step-down, DC-DC switching regulators. The MAX758A accepts inputs from 4V to 16V and delivers 750mA, while the MAX750A accepts inputs from 4V to 11V and delivers 450mA. Typical efficiencies are 85% to 90%. Typical quiescent current is 1.7mA, or only 6µA in shutdown mode. The output does not exhibit any ripple at subharmonics of the switching frequency over its specified range. Pulse-width-modulation (PWM) current-mode control provides precise output regulation and excellent transient responses. Output voltage accuracy is guaranteed to be ±4.5% plus feedback-resistor tolerance over line, load, and temperature variations. Fixed-frequency switching and absence of subharmonic ripple 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. MAX750A/MAX758A Adjustable, Step-Down, Current-Mode PWM Regulators ABSOLUTE MAXIMUM RATINGS Pin Voltages V+ (MAX750A).........................................................+12V, -0.3V V+ (MAX758A).........................................................+18V, -0.3V LX (MAX750A) ....................................(V+ - 12V) to (V+ + 0.3V) LX (MAX758A) ....................................(V+ - 21V) to (V+ + 0.3V) SS, CC, SHDN.............................................-0.3V to (V+ + 0.3V) Peak Switch Current (ILX).........................................................2A Reference Current (IREF) ...................................................2.5mA 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: MAX75_AC_ _ .......................................................0°C to +70°C MAX75_AE_ _ ....................................................-40°C to +85°C MAX75_AMJA ..................................................-55°C to +125°C Junction Temperatures: MAX75_AC_ _/AE_ _ ......................................................+150°C MAX75_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 MAX750A, V+ = 12V for the MAX758A, VOUT = 5V, R2 = 40.20kΩ, R3 = 13.0kΩ, ILOAD = 0mA, TA = TMIN to TMAX, unless otherwise noted.) MIN MAX758A TYP MAX V+ = 6.0V to 16.0V; 0mA < ILOAD < 450mA for MAX758AC/AE, 0mA < ILOAD < 350mA for MAX758AM 4.75 5.00 5.25 V+ = 10.2V to 16.0V, 0mA < ILOAD < 750mA 4.75 5.00 5.25 PARAMETER CONDITIONS V+ = 6.0V to 11.0V; 0mA < ILOAD < 450mA for MAX750AC, 0mA < ILOAD < 450mA for MAX750AE, 0mA < ILOAD < 300mA for MAX750AM Output Voltage (Note 1) Input Voltage Range Line Regulation Load Regulation Efficiency MIN MAX750A TYP MAX 4.75 5.00 5.25 4.0 V+ = 4.0V to 11.0V Shutdown Input Threshold ILOAD = 0mA to 450mA 92 2 90 V+ = 12V, ILOAD = 750mA % 87 SHDN = 0V 1.7 3.0 6.0 100.0 2.0 1.7 3.0 mA 6.0 100.0 µA 2.0 VIL 0.25 0.25 1.0 1.5 V %/mA 0.0005 V+ = 9.0V, ILOAD = 300mA V %/V 0.0005 ILOAD = 0mA to 750mA VIH 16.0 0.15 Shutdown Input Leakage Current Short-Circuit Current 4.0 V+ = 4.0V to 16.0V Supply Current Shutdown Supply Current (Note 2) 11.0 0.15 UNITS 1.0 1.5 _______________________________________________________________________________________ V µA A Adjustable, Step-Down, Current-Mode PWM Regulators (Circuit of Figure 3, V+ = 9V for the MAX750A, V+ = 12V for the MAX758A, VOUT = 5V, R2 = 40.20kΩ, R3 = 13.0kΩ, ILOAD = 0mA, TA = TMIN to TMAX, unless otherwise noted.) CONDITIONS PARAMETER MIN MAX750A TYP MAX 4.00 MIN MAX758A TYP MAX 3.75 4.00 UNITS Undervoltage Lockout V+ rising 3.75 V+ falling 3.5 3.5 LX On Resistance ILX = 500mA 0.5 0.5 Ω 1.0 1.0 µA LX Leakage Current Reference Voltage TA = +25°C 1.15 1.22 Reference Drift 1.30 1.15 50 Oscillator Frequency 130 Compensation Pin Impedance 1.22 1.30 50 170 210 130 7500 V V ppm/°C 160 190 kHz Ω 7500 Note 1: Output voltage tolerance over temperature is ±4.5% plus the tolerances of R3 and R4 in Figure 3. Note 2: 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. __________________________________________Typical Operating Characteristics (Circuit of Figure 3, VOUT = 5V, TA = +25°C, unless otherwise noted.) (NOTES 3, 6) 100 MAX750A/58A-1 100 MAX758A EFFICIENCY vs. OUTPUT CURRENT (NOTES 3, 6) 90 EFFICIENCY (%) EFFICIENCY (%) 90 MAX750A/58A-2 MAX750A EFFICIENCY vs. OUTPUT CURRENT V+ = 5.5V 80 V+ = 7V V+ = 9V 70 80 V+ = 6V V+ = 8V V+ = 12V 70 V+ = 11V V+ = 16V 60 60 0 200 400 600 800 OUTPUT CURRENT (mA) 1000 0 200 400 600 800 1000 OUTPUT CURRENT (mA) _______________________________________________________________________________________ 3 MAX750A/MAX758A ELECTRICAL CHARACTERISTICS (continued) _____________________________Typical Operating Characteristics (continued) (Circuit of Figure 3, VOUT = 5V, TA = +25°C, unless otherwise noted.) MAX758A PEAK INDUCTOR CURRENT vs. OUTPUT CURRENT 600 V+ 8.0V TO 16.0V 400 V+ = 6.6V 200 600 500 400 300 V+ = 10.2V V+ = 8.0V V+ = 6.6V V+ = 6.0V 200 100 220 (NOTE 3) 0 100 200 300 400 500 600 700 800 2.5 UNDERVOLTAGE LOCKOUT V+ FALLING (OPERATION ENDS) 1.0 UNDERVOLTAGE LOCKOUT V+ RISING (OPERATION BEGINS) 2 4 6 8 12 10 150 200 250 14 16 2.5 2.0 1.5 1.0 0.5 10 12 20 18 (NOTES 4, 5) 16 14 12 10 MAX758A ONLY, V+ = 16V MAX758A ONLY, V+ = 12V V+ = 9V V+ = 6V 8 6 4 2 MAX758A OSCILLATOR FREQUENCY vs. TEMPERATURE 200 (NOTE 4) 160 V+ = 7.0V V+ = 9.0V (NOTE 4) 190 V+ = 6.0V 180 V+ = 16.0V 170 160 150 V+ = 12.0V 140 V+ = 9.0V 130 0 20 40 60 80 100 120 140 TEMPERATURE (°C) 4 16 TEMPERATURE (°C) V+ = 5.5V 0 -60 -40 -20 14 TEMPERATURE (°C) OSCILLATOR FREQUENCY (kHz) OSCILLATOR FREQUENCY (kHz) 8 0 -60 -40 -20 0 20 40 60 80 100 120 140 180 140 6 0 -60 -40 -20 0 20 40 60 80 100 120 140 240 200 4 300 MAX750A, V+ = 9.0V MAX758A, V+ = 12.0V MAX750A OSCILLATOR FREQUENCY vs. TEMPERATURE 220 MAX758A 160 SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE (NOTES 4, 5) SUPPLY VOLTAGE (V) V+ = 11.0V 170 SUPPLY VOLTAGE (V) 2.0 0 0 MAX750A 180 SHUTDOWN SUPPLY CURRENT (µA) (NOTES 3, 5) NO-LOAD SUPPLY CURRENT (mA) MAX1750A/58A-7 3.0 0.5 190 NO-LOAD SUPPLY CURRENT vs. TEMPERATURE MAX758A NO-LOAD SUPPLY CURRENT vs. SUPPLY VOLTAGE 1.5 200 OUTPUT CURRENT (mA) OUTPUT CURRENT (mA) 2.0 100 50 MAX750A/58A-8 0 210 150 0 0 MAX1750A/58A-6 L1 = 18µH C4 = 1000µF MAX750A/58A-9 800 700 MAX1750A/58A-5 L1 = 100µH C4 = 300µF PEAK INDUCTOR CURRENT (mA) MAX1750A/58A-4 PEAK INDUCTOR CURRENT (mA) 1000 OSCILLATOR FREQUENCY vs. SUPPLY VOLTAGE OSCILLATOR FREQUENCY (kHz) MAX758A PEAK INDUCTOR CURRENT vs. OUTPUT CURRENT NO-LOAD SUPPLY CURRENT (mA) MAX750A/MAX758A Adjustable, Step-Down, Current-Mode PWM Regulators 120 -60 -40 -20 0 20 40 60 80 100 120 140 TEMPERATURE (°C) _______________________________________________________________________________________ Adjustable, Step-Down, Current-Mode PWM Regulators MAXIMUM OUTPUT CURRENT vs. SUPPLY VOLTAGE, R1 OMITTED MAXIMUM OUTPUT CURRENT vs. SUPPLY VOLTAGE MAX758A 1200 MAX750A 1000 MAX750A/58A-11 MAX750A/58A-10 MAXIMUM OUTPUT CURRENT (mA) (NOTES 3, 6) MAXIMUM OUTPUT CURRENT (mA) 1400 1400 (NOTES 3, 6) 1200 MAX758A 1000 800 600 MAX750A 400 200 800 4 6 8 10 12 14 16 4 6 8 10 12 14 16 SUPPLY VOLTAGE (V) SUPPLY VOLTAGE (V) MAX758A SWITCHING WAVEFORMS DISCONTINUOUS CONDUCTION MAX758A SWITCHING WAVEFORMS CONTINUOUS CONDUCTION 12V 12V A A 0V 0V 200mA 100mA B 0mA 0mA 5V 2µs/div 5V C B C 2µs/div A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +12V B: INDUCTOR CURRENT, 200mA/div C: OUTPUT VOLTAGE RIPPLE, 50mV/div A: SWITCH VOLTAGE (LX PIN), 5V/div, 0V TO +12V B: INDUCTOR CURRENT, 100mA/div C: OUTPUT VOLTAGE RIPPLE, 50mV/div COUT = 390µF, V+ = 12V, IOUT = 150mA COUT = 390µF, V+ = 12V, IOUT = 20mA _______________________________________________________________________________________ 5 MAX750A/MAX758A _____________________________Typical Operating Characteristics (continued) (Circuit of Figure 3, VOUT = 5V, TA = +25°C, unless otherwise noted.) MAX750A/MAX758A Adjustable, Step-Down, Current-Mode PWM Regulators _____________________________Typical Operating Characteristics (continued) (Circuit of Figure 3, VOUT = 5V, TA = +25°C, unless otherwise noted.) MAX750A LINE-TRANSIENT RESPONSE MAX758A LINE-TRANSIENT RESPONSE A A 16V 10.2V 11V 6V B 0V B 0V 100ms/div 100ms/div A: VOUT, 50mV/div, AC-COUPLED B: V+, 5V/div, 6.0V TO 11.0V A: VOUT, 50mV/div, AC-COUPLED B: V+, 5V/div, 10.2V TO 16.0V IOUT = 300mA IOUT = 750mA MAX750A LOAD-TRANSIENT RESPONSE MAX758A LOAD-TRANSIENT RESPONSE A A 750mA 300mA B B 50mA 20mA 50ms/div 50ms/div A: VOUT, 50mV/div, AC-COUPLED B: IOUT, 200mA/div, 20mA TO 300mA A: VOUT, 50mV/div, AC-COUPLED B: IOUT, 500mA/div, 50mA TO 750mA V+ = 9V V+ = 12V Note 3: Commercial temperature range external component values in Table 2. Note 4: Wide temperature range external component values in Table 2. Note 5: Supply current includes all external component leakage currents. External capacitor leakage currents dominate at TA > +85°C. C3 and C4 = Sanyo Oscon through-hole capacitors. Note 6: Operation beyond the specifications listed in the Electrical Characteristics may exceed the power dissipation ratings of the device. 6 _______________________________________________________________________________________ Adjustable, Step-Down, Current-Mode PWM Regulators PIN 8-PIN DIP/SO 16-PIN WIDE SO NAME 1 2 SHDN 2 3 REF Reference Voltage Output (+1.22V) supplies up to 100µA for external loads. Bypass to GND with a capacitor that does not exceed 0.047µF. 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 External voltage divider feedback point. When an external voltage divider is connected from the output voltage to CC and GND, this pin becomes the feedback input for adjusting the output voltage. Connect a 330pF compensation capacitor between the output and CC. Internal Connection. Make no external connection to this pin. FUNCTION Shutdown—active low. Ground to power-down chip, tie to V+ for normal operation. Output voltage falls to 0V when SHDN is low. 5 9 I.C. 6 10, 11 GND 7 12, 13, 14 LX Drain of internal P-channel power MOSFET* 8 1, 15, 16 V+ Supply Voltage Input. Bypass to GND with 1.0µF ceramic and large-value electrolytic capacitors in parallel. The 1µF capacitor must be as close to the V+ and GND pins are possible.* – 4, 5, 6 N.C. Ground* No Connect—not internally connected. *16-Pin Wide SO: All pins with the same name must be connected together externally. _______________Detailed Description The MAX750A/MAX758A switch-mode regulators use a current-mode pulse-width-modulation (PWM) control system coupled with a simple step-down (buck) regulator topography. Input voltages range from 4V to 11V for the MAX750A, and from 4V to 16V for the MAX758A. 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-by-cycle current limiting, truncating the powertransistor 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 connected to the soft-start (SS) pin to ensure an orderly powerup. Typical values are 0.1µF and 510kΩ. SS controls both the soft-start 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 currentlimit threshold. The 510kΩ resistor sets the soft-start 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, No. R1 graph in the Typical Operating Characteristics. Table 1 lists timing characteristics for selected capacitor values and circuit conditions. The overcurrent comparator trips if the load exceeds approximately 1.5A. A soft-start cycle begins when either an undervoltage or overcurrent fault condition triggers an internal transistor to discharge the softstart capacitor to ground. A soft-start cycle also begins at power-up and when coming out of the shutdown mode. _______________________________________________________________________________________ 7 MAX750A/MAX758A ______________________________________________________________Pin Description MAX750A/MAX758A Adjustable, Step-Down, Current-Mode PWM Regulators V IN V+ SHDN C2 1µF C3* OVERCURRENT COMPARATOR BIAS GEN SLOPE COMPENSATION Σ MAX750A MAX758A C5 330pF RAMP GEN RSENSE CURRENT SENSE AMP R2 ERROR AMP CC R1 510K R3 F/F R PWM COMPARATOR 1.23V BANDGAP REF C6 0.01µF LX L1 D1 1N5817 OSC VOUT C4* 1M ±35% SS C1 0.1µF Q S UNDERVOLTAGE LOCKOUT SS CLAMP VUVLO GND * SEE TABLE 3 FOR COMPONENT VALUES AND SUPPLIERS. Figure 1. Detailed Block Diagram with External Components 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 soft-start capacitor must be greater than 0.01µF for overcurrent protection to function properly. A typical value is 0.1µF. A soft-start cycle is initiated when the overcurrent comparator is triggered. Undervoltage Lockout The undervoltage lockout feature monitors the supply voltage at V+ and allows operation to start when V+ rises above 3.75V. When V+ falls, operation continues until the supply voltage falls below 3.50V. When an 8 undervoltage condition is detected, control logic turns off the output power FET and discharges the soft-start 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 3.75V, at which time a soft-start cycle begins. Shutdown Mode The MAX750A/MAX758A are shut down by keeping SHDN at ground. In shutdown mode, the output power FET is held off and the output drops to 0V. The internal reference also turns off, which causes the soft-start capacitor to discharge. The 6µA typical standby current includes external-component leakage currents. As temperature increases past +85°C, the external capaci- _______________________________________________________________________________________ Adjustable, Step-Down, Current-Mode PWM Regulators FROM SHDN MAX750A MAX758A R1 510k SS CLAMP SS 1M ±35% C1 1.23V __________Applications Information Figure 3 shows the MAX750A/MAX758A configured for a standard 5V step-down application. Table 2 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. They will operate over the entire line, load, and temperature ranges using the single set of component values shown in Figure 3 and listed in Table 2. Inductor Selection Figure 2. Block Diagram of Soft-Start Circuitry tors’ leakage currents rises sharply. The actual design limit for standby current is much less than the 100µA specified in the Electrical Characteristics (see the Standby Current vs. Temperature graph 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+. Coming out of shutdown mode initiates a soft-start 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 MAX750A/MAX758A 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 MAX750A/MAX758A to deliver maximum load current, and is also slightly less noisy than DCM because the ripple current in the output capacitor is smaller. Internal Reference The +1.23V bandgap reference supplies up to 100µA at REF. Connect a 0.01µF bypass capacitor from REF to GND. The MAX750A/MAX758A 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 100µH (MAX75_AC) or 33µH (MAX75_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 and the larger-size through-hole inductors have nearly equivalent efficiencies. Adjusting the Output Voltage The MAX750A/MAX758A have outputs adjustable from 1.25V to the input voltage. To set the output voltage, connect a voltage divider to the feedback input pin (CC) as shown in Figure 3. The output voltage is set by R2 and R3 as follows: Let R3 be any resistance in the 10kΩ to 20kΩ range (typically 10kΩ), then R2 = R3 [((VOUT/1.22V) - 1)] Output tolerance over temperature is ±4.5% plus external resistor tolerances. 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 ESR of the output capacitor determines the amplitude of the sawtooth ripple seen on the output voltage. In addition, the ESR of the output filter capacitor should be minimized to maintain AC stability. The ESR of the capacitor should be less than 0.25Ω to keep the output ripple less than 50mVp-p over the entire current range (using a 100µH inductor). Capacitor ESR ususally rises _______________________________________________________________________________________ 9 MAX750A/MAX758A Oscillator The internal oscillator of the MAX750A typically operates at 170kHz (160kHz for the MAX758A). The Typical Operating Characteristics indicate stability of the oscillator frequency over temperature and supply voltage. MAX750A/MAX758A Adjustable, Step-Down, Current-Mode PWM Regulators Table 1. Typical Soft-Start Times MAX750A 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 11 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 MAX750A 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 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 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. 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, R1 Removed graph in the Typical Operating Characteristics). Other Components A good layout is essential for clean, stable operation. The layouts and component placement diagrams given in Figures 4-7 have been successfully tested over a wide range of operating conditions. The 1µF bypass capacitor (C2) must be positioned as close to the V+ The catch diode should be a Schottky or high-speed silicon rectifier with a peak current rating of about 1A for full-load (750mA) operation. The 1N5817 is a good choice. The 330pF outer-loop compensation capacitor 10 Printed Circuit Layouts ______________________________________________________________________________________ Adjustable, Step-Down, Current-Mode PWM Regulators MAX750A/MAX758A MAX750A: 4.0V TO 11.0V MAX758A: 4.0V TO 16.0V C2 1µF C3* OPTIONAL LOWPASS OUTPUT FILTER 8 1 V+ SHDN LX 7 OUTPUT D1 IN5817 L1* MAX750A MAX758A R1 510k 3 C1 0.1µF I.C. 5 CC GND REF 6 2 FILTER OUTPUT C7 2.2µF OUTPUT 5V C5 330pF SS L2 25µF R2 40.2k C4* 4 R3 13.0k C6 0.01µF PART INPUT SUPPLY RANGE (V) GUARANTEED OUTPUT CURRENT AT 5V OUTPUT (mA) MAX750A 6.0 to 11.0 450 6.0 to 16.0 450 10.2 to 16.0 750 MAX758A NOTE: PIN NUMBERS REFER TO 8-PIN PACKAGES. * SEE TABLE 2 FOR EXTERNAL COMPONENT SUPPLIERS. Figure 3. Standard Step-Down Circuit and GND pins as possible. Also, place the output capacitor as close to the inductor and the GND pin 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; otherwise, use a star ground connection. 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 with the values shown is 21kHz. Since the filter inductor is in series with the circuit output, its resistance should be kept to a minimum so the voltage drop across it is not excessive. ______________________________________________________________________________________ 11 MAX750A/MAX758A Adjustable, Step-Down, Current-Mode PWM Regulators Table 2. Component Values and Suppliers ASSEMBLY METHOD MAX750AC/MAX758AC COMMERCIAL TEMPERATURE RANGE INDUCTORS L1 = 33µH to 100µH Surface Mount Sumida (708) 956-0666 CD54-101KC (MAX750AC) CD105-101KC (MAX758AC) Coiltronics (305) 781-8900 CTX100 series CAPACITORS C3 = 68µF, 16V C4 = 100µF, 6.3V Matsuo (714) 969-2491 267 series Sprague (603) 224-1961 595D/293D series MAX750AE/M, MAX758AE/M WIDE TEMPERATURE RANGE INDUCTORS L1 = 33µH Sumida (708) 956-0666 CD54-33ON (MAX750AC) CD105-33ON (MAX758AE/M) Coiltronics (305) 781-8900 CTX50 series CAPACITORS C3 = 68µF, 16V C4 = 100µF, 6.3V Matsuo (714) 969-2491 267 series Sprague (603) 224-1961 595D/295D series C3 = 150µF, 16V C4 = 220µF, 10V L1 = 33µH to 100µH Miniature ThroughHole Sumida (708) 956-0666 RCH654-101K (MAX750A) RCH895-101K (MAX758A) L1 = 100µH Low-Cost ThroughHole Maxim MAXL001 100µH iron-powder toroid Renco (516) 586-5566 RL1284-100 12 C3 = 150µF, 16V C4 = 150µF, 16V or 390µF, 6.3V Nichicon (708) 843-7500 PL series Low-ESR electrolytics L1 = 33µH Sumida (708) 956-0666 RCH654-330M (MAX750A) RCH895-330M (MAX758A) 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 Maxim MAXC001 150µF, low-ESR electrolytic United Chemicon (708) 843-7500 ______________________________________________________________________________________ Adjustable, Step-Down, Current-Mode PWM Regulators 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) ______________________________________________________________________________________ MAX750A/MAX758A Figure 4. DIP PC Layout, Through-Hole Component Placement Diagram (1x Scale) 13 MAX750A/MAX758A Adjustable, Step-Down, Current-Mode PWM Regulators ____Pin Configurations (continued) __Ordering Information (continued) TOP VIEW V+ 1 16 V+ SHDN 2 15 V+ REF 3 N.C. 4 14 LX MAX758A 13 LX N.C. 5 12 LX N.C. 6 11 GND SS 7 10 GND CC 8 9 PART TEMP. RANGE MAX758ACPA 0°C to +70°C 8 Plastic DIP PIN-PACKAGE MAX758ACWE MAX758AC/D MAX758AEPA MAX758AEWE 0°C to +70°C 0°C to +70°C -40°C to +85°C -40°C to +85°C 16 Wide SO Dice* 8 Plastic DIP 16 Wide SO MAX758AMJA -55°C to +125°C 8 CERDIP** * Contact factory for dice specifications. **Contact factory for availability and processing to MIL-STD-883. I.C. Wide SO ___________________________________________________________Chip Topographies MAX758A MAX750A 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) CC 0.116" (2.946mm) TRANSISTOR COUNT: 274 (MAX750A) 286 (MAX758A); SUBSTRATE CONNECTED TO V+. 14 ______________________________________________________________________________________ Adjustable, Step-Down, Current-Mode PWM Regulators 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 MAX750A/MAX758A ________________________________________________________Package Information MAX750A/MAX758A Adjustable, Step-Down, Current-Mode PWM Regulators ___________________________________________Package Information (continued) 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 © 1993 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.