EVALUATION KIT AVAILABLE MAX756/MAX757 LE AVAILAB 3.3V/5V/Adjustable-Output, Step-Up DC-DC Converters _______________General Description The MAX756/MAX757 are CMOS step-up DC-DC switching regulators for small, low input voltage or battery-powered systems. The MAX756 accepts a positive input voltage down to 0.7V and converts it to a higher pinselectable output voltage of 3.3V or 5V. The MAX757 is an adjustable version that accepts an input voltage down to 0.7V and generates a higher adjustable output voltage in the range from 2.7V to 5.5V. Typical full-load efficiencies for the MAX756/MAX757 are greater than 87%. The MAX756/MAX757 provide three improvements over previous devices. Physical size is reduced--the high switching frequencies (up to 0.5MHz) made possible by MOSFET power transistors allow for tiny (<5mm diameter) surface-mount magnetics. Efficiency is improved to 87% (10% better than with low-voltage regulators fabricated in bipolar technology). Supply current is reduced to 60A by CMOS construction and a unique constant-off-time pulse-frequency modulation control scheme. ________________________Applications 3.3V to 5V Step-Up Conversion Palmtop Computers Portable Data-Collection Equipment Personal Data Communicators/Computers Medical Instrumentation 2-Cell & 3-Cell Battery-Operated Equipment Glucose Meters Functional Diagrams __________Typical Operating Circuit INPUT 2V to VOUT 150F 5 1 LBI SHDN LX 8 ____________________________Features Operates Down to 0.7V Input Supply Voltage 87% Efficiency at 200mA 60A Quiescent Current 20A Shutdown Mode with Active Reference and LBI Detector 500kHz Maximum Switching Frequency 1.5% Reference Tolerance Over Temperature Low-Battery Detector (LBI/LBO) 8-Pin DIP and SO Packages ______________Ordering Information PART TEMP. RANGE 0C to +70C 8 Plastic DIP MAX756CSA MAX756C/D MAX756EPA MAX756ESA MAX757CPA 0C to +70C 0C to +70C -40C to +85C -40C to +85C 0C to +70C 8 SO Dice* 8 Plastic DIP 8 SO 8 Plastic DIP MAX757CSA MAX757C/D MAX757EPA MAX757ESA 0C to +70C 0C to +70C -40C to +85C -40C to +85C 8 SO Dice* 8 Plastic DIP 8 SO * Dice are tested at TA = +25C only. _________________Pin Configurations TOP VIEW OUTPUT 22H 5V at 200mA or 1N5817 3.3V at 300mA SHDN 1 8 LX 3/5 2 7 GND 6 OUT 5 LBI REF 3 3 MAX756 3/5 REF OUT DIP/SO LBO 6 4 LOW-BATTERY DETECTOR OUTPUT GNDat end of data sheet. 0.1F Pin Configurations appear 7 Functional Diagrams continued at end of data sheet. UCSP is a trademark of Maxim Integrated Products, Inc. MAX756 LBO 4 100F 2 PIN-PACKAGE MAX756CPA SHDN 1 8 LX FB 2 7 GND 6 OUT 5 LBI REF 3 MAX757 LBO 4 DIP/SO For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim's website at www.maximintegrated.com. 19-0113; Rev. 2; 1/95 MAX756/MAX757 3.3V/5V/Adjustable-Output, Step-Up DC-DC Converters ABSOLUTE MAXIMUM RATINGS Supply Voltage (OUT to GND) ....................................-0.3V, +7V Switch Voltage (LX to GND) ........................................-0.3V, +7V Auxiliary Pin Voltages (SHDN, LBI, LBO, REF, 3/5, FB to GND) ........................................-0.3V, (VOUT + 0.3V) Reference Current (IREF) ....................................................2.5mA Continuous Power Dissipation (TA = +70C) Plastic DIP (derate 9.09mW/C above +70C) .............727mW SO (derate 5.88mW/C above +70C) ..........................471mW Operating Temperature Ranges: MAX75_C_ _ ........................................................0C to +70C MAX75_E_ _......................................................-40C to +85C Junction Temperature ......................................................+150C Storage Temperature Range............................... -65to +160C Lead Temperature (soldering, 10sec) ........................... +300C 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 (Circuits of Figure 1 and Typical Operating Circuit, VIN = 2.5V, ILOAD = 0mA, TA = TMIN to TMAX, unless otherwise noted.) PARAMETER CONDITIONS MAX756, 3/5 = 0V, 0mA < ILOAD < 200mA MIN 4.8 TYP 5.0 MAX 5.2 UNITS 2V < VIN < 3V MAX756, 3/5 = 3V, 0mA < ILOAD < 300mA 3.17 3.30 3.43 V MAX757, VOUT = 5V, 0mA < ILOAD < 200mA 4.8 5.0 5.2 Minimum Start-Up Supply Voltage ILOAD = 10mA 1.1 1.8 Minimum Operating Supply Voltage (once started) ILOAD = 20mA 0.7 Quiescent Supply Current in 3.3V Mode (Note 1) ILOAD = 0mA, 3/5 = 3V, LBI = 1.25V, VOUT = 3.47V, FB = 1.3V (MAX757 only) Battery Quiescent Current Measured at VIN in Figure 1 Output set for 3.3V 60 Shutdown Quiescent Current (Note 1) SHDN = 0V, LBI = 1.25V, 3/5 = 3V, VOUT = 3.47V, FB = 1.3V (MAX757 only) 20 40 1.25 1.27 V 0.8 2.0 % 1.25 1.28 V Output Voltage Reference Voltage No REF load, CREF = 0.1F 3/5 = 3V, -20A < REF load < 250A, CREF = 0.22F 1.23 LBI Input Threshold With falling edge 1.22 LBI Input Hysteresis ISINK = 2mA LBO Output Leakage Current LBO = 5V SHDN, 3/5 Input Voltage Low SHDN, 3/5 Input Voltage High FB Voltage Output Voltage Range mV V 1 A 0.4 V V LBI = 1.25V, FB = 1.25V, SHDN = 0V or 3V, 3/5 = 0V or 3V 1.22 2.7 A 0.4 1.6 MAX757 MAX757, ILOAD = 0mA (Note 2) A A 25 LBO Output Voltage Low SHDN, 3/5, FB, LBI Input Current V 60 Reference-Voltage Regulation V 1.25 100 nA 1.28 V 5.5 V Note 1: Supply current from the 3.3V output is measured with an ammeter between the 3.3V output and OUT pin. This current correlates directly with actual battery supply current, but is reduced in value according to the step-up ratio and efficiency. Note 2: Minimum value is production tested. Maximum value is guaranteed by design and is not production tested. 2 Maxim Integrated MAX756/MAX757 3.3V/5V/Adjustable-Output, Step-Up DC-DC Converters __________________________________________Typical Operating Characteristics (Circuit of Figure 1, TA = +25C, unless otherwise noted.) 80 80 VIN = 2.5V EFFICIENCY (%) VIN = 1.2V EFFICIENCY (%) 800 70 60 VIN = 1.25V 70 60 50 50 MAX756-3 VIN = 3.3V MAXIMUM OUTPUT CURRENT (mA) VIN = 2.0V MAX756-2 90 MAX756-1 90 MAXIMUM OUTPUT CURRENT vs. INPUT VOLTAGE EFFICIENCY vs. LOAD CURRENT 5V OUTPUT MODE EFFICIENCY vs. LOAD CURRENT 3.3V OUTPUT MODE 700 600 500 5V MODE 3.3V MODE 400 300 200 100 40 40 0.1 10 1 10 1 0 1000 100 4 3 LOAD CURRENT (mA) INPUT VOLTAGE (V) SWITCHING FREQUENCY vs. LOAD CURRENT QUIESCENT CURRENT vs. INPUT VOLTAGE SHUTDOWN QUIESCENT CURRENT vs. INPUT VOLTAGE 300 VOUT = 5V 200 100 100 VIN = 2.5V VOUT = 3.3V 100 10m 1m 100m 1 1 2 4 3 30 20 10 1 5 2 5 REFERENCE VOLTAGE LOAD REGULATION MINIMUM START-UP INPUT VOLTAGE vs. LOAD CURRENT VREF LOAD REGULATION (mV) 1.6 1.4 1.2 1.0 MAX756-8 10 MAX756-7 1.8 4 3 INPUT VOLTAGE (V) INPUT VOLTAGE (V) LOAD CURRENT (A) START-UP INPUT VOLTAGE (V) CURRENT MEASURED AT VIN 40 0 0 10 MAX756-6 SHUTDOWN QUIESCENT CURRENT (A) 3.3V MODE 1k CURRENT MEASURED AT VIN 400 QUIESCENT CURRENT (A) 10k 5 50 MAX756-5 500 MAX756-4 5V MODE 100k 10 2 1 LOAD CURRENT (mA) 1M SWITCHING FREQUENCY (Hz) 0 0.1 1000 100 8 6 4 VOUT = 3.3V 2 3.3V MODE 0.8 0 1 10 100 LOAD CURRENT (mA) Maxim Integrated 1000 0 50 100 150 200 250 LOAD CURRENT (A) 3 MAX756/MAX757 3.3V/5V/Adjustable-Output, Step-Up DC-DC Converters _____________________________Typical Operating Characteristics (continued) (Circuit of Figure 1, TA = +25C, unless otherwise noted.) LOAD-TRANSIENT RESPONSE START-UP DELAY 3V OUTPUT VOLTAGE 50mV/div VSHDN 2V/div 0V 5V OUTPUT CURRENT 0mA to 200mA VOUT 2V/div 0V VIN = 2.5V HORIZONTAL = 5ms/div 5V Mode VIN = 2.5V HORIZONTAL = 50s/div 5V Mode ______________________________________________________________Pin Description PIN MAX756 MAX757 4 NAME FUNCTION Shutdown Input disables SMPS when low, but the voltage reference and low-battery comparator remain active. 1 1 SHDN 2 - 3/5 Selects the main output voltage setting; 5V when low, 3.3V when high. - 2 FB Feedback Input for adjustable output operation. Connect to an external voltage divider between OUT and GND. 3 3 REF 1.25V Reference Voltage Output. Bypass with 0.22F to GND (0.1F if there is no external reference load). Maximum load capability is 250A source, 20A sink. 4 4 LBO Low-Battery Output. An open-drain N-channel MOSFET sinks current when the voltage at LBI drops below +1.25V. 5 5 LBI Low-Battery Input. When the voltage on LBI drops below +1.25V, LBO sinks current. Connect to VIN if not used. 6 6 OUT Connect OUT to the regulator output. It provides bootstrapped power to both devices, and also senses the output voltage for the MAX756. 7 7 GND Power Ground. Must be low impedance; solder directly to ground plane. 8 8 LX 1A, 0.5 N-Channel Power MOSFET Drain Maxim Integrated MAX756/MAX757 3.3V/5V/Adjustable-Output, Step-Up DC-DC Converters _______________Detailed Description Operating Principle The MAX756/MAX757 combine a switch-mode regulator with an N-channel MOSFET, precision voltage reference, and power-fail detector in a single monolithic device. The MOSFET is a "sense-FET" type for best efficiency, and has a very low gate threshold voltage to ensure start-up under low-battery voltage conditions (1.1V typ). Pulse-Frequency Modulation Control Scheme A unique minimum off time, current-limited, pulse-frequency modulation (PFM) control scheme is a key feature of the MAX756/MAX757. This PFM scheme combines the advantages of pulse-width modulation (PWM) (high output power and efficiency) with those of a traditional PFM pulse-skipper (ultra-low quiescent currents). There is no oscillator; at heavy loads, switching is accomplished through a constant peak-current limit in the switch, which allows the inductor current to self-oscillate between this peak limit and some lesser value. At light loads, switching frequency is governed by a pair of one-shots, which set a minimum off-time (1s) and a maximum on-time (4s). The switching frequency depends on the load and the input voltage, and can range as high as 500kHz. The peak switch current of the internal MOSFET power switch is fixed at 1A 0.2A. The switch's on resistance is typically 0.5, resulting in a switch voltage drop (VSW) of about 500mV under high output loads. The value of VSW decreases with light current loads. Conventional PWM converters generate constant-frequency switching noise, whereas this architecture produces variable-frequency switching noise. However, the noise does not exceed the switch current limit times the filter-capacitor equivalent series resistance (ESR), unlike conventional pulse-skippers. Voltage Reference The precision voltage reference is suitable for driving external loads such as an analog-to-digital converter. It has guaranteed 250A source-current and 20A sink-current capability. The reference is kept alive even in shutdown mode. If the reference drives an external load, bypass it with 0.22F to GND. If the reference is unloaded, bypass it with at least 0.1F. Control-Logic Inputs The control inputs (3/5, SHDN) are high-impedance MOS gates protected against ESD damage by normally reverse-biased clamp diodes. If these inputs are driven from signal sources that exceed the main supply Maxim Integrated voltage, the diode current should be limited by a series resistor (1M suggested). The logic input threshold level is the same (approximately 1V) in both 3.3V and 5V modes. Do not leave the control inputs floating. __________________Design Procedure Output Voltage Selection The MAX756 output voltage can be selected to 3.3V or 5V under logic control, or it can be left in one mode or the other by tying 3/5 to GND or OUT. Efficiency varies depending upon the battery and the load, and is typically better than 80% over a 2mA to 200mA load range. The device is internally bootstrapped, with power derived from the output voltage (via OUT). When the output is set at 5V instead of 3.3V, the higher internal supply voltage results in lower switch-transistor on resistance and slightly greater output power. Bootstrapping allows the battery voltage to sag to less than 1V once the system is started. Therefore, the battery voltage range is from VOUT + VD to less than 1V (where VD is the forward drop of the Schottky rectifier). If the battery voltage exceeds the programmed output voltage, the output will follow the battery voltage. In many systems this is acceptable; however, the output voltage must not be forced above 7V. The output voltage of the MAX757 is set by two resistors, R1 and R2 (Figure 1), which form a voltage divider between the output and the FB pin. The output voltage is set by the equation: VOUT = (VREF) [(R2 + R1) / R2] where VREF = 1.25V. To simplify resistor selection: R1 = (R2) [(VOUT / VREF) - 1] Since the input bias current at FB has a maximum value of 100nA, large values (10k to 200k) can be used for R1 and R2 with no significant loss of accuracy. For 1% error, the current through R1 should be at least 100 times FB's bias current. Low-Battery Detection The MAX756/MAX757 contain on-chip circuitry for lowbattery detection. If the voltage at LBI falls below the regulator's internal reference voltage (1.25V), LBO (an opendrain output) sinks current to GND. The low-battery monitor's threshold is set by two resistors, R3 and R4 (Figure 1), which forms a voltage divider between the input voltage and the LBI pin. The threshold voltage is set by R3 and R4 using the following equation: R3 = [(VIN / VREF) - 1] (R4) 5 MAX756/MAX757 3.3V/5V/Adjustable-Output, Step-Up DC-DC Converters The inductor's DC resistance significantly affects efficiency. For highest efficiency, limit L1's DC resistance to 0.03 or less. See Table 1 for a list of suggested inductor suppliers. VIN C1 150F L1 22H R3 5 3 C3 0.1F D1 1N5817 MAX757 OUT 6 R1 LBI R4 1 8 LX SHDN FB REF LBO VOUT C2 100F Table 1. Component Suppliers PRODUCTION METHOD INDUCTORS Surface-Mount Sumida CD54-220 (22H) CoilCraft DT3316-223 Coiltronics CTX20-1 AVX TPS series Miniature Through-Hole Sumida RCH654-220 Sanyo OS-CON OS-CON series low-ESR organic semiconductor Low-Cost Through-Hole CoilCraft PCH-27-223 Nichicon PL series low-ESR electrolyic 2 4 R2 GND 7 Figure 1. Standard Application Circuit where VIN is the desired threshold of the low-battery detector, R3 and R4 are the input divider resistors at LBI, and VREF is the internal 1.25V reference. Since the LBI current is less than 100nA, large resistor values (typically 10k to 200k) can be used for R3 and R4 to minimize loading of the input supply. When the voltage at LBI is below the internal threshold, LBO sinks current to GND. A pull-up resistor of 10k or more connected from LBO to V OUT can be used when driving CMOS circuits. Any pull-up resistor connected to LBO should not be returned to a voltage source greater than V OUT . When LBI is above the threshold, the LBO output is off. The low-battery comparator and reference voltage remain active when the MAX756/MAX757 is in shutdown mode. If the low-battery comparator is not used, connect LBI to VIN and leave LBO open. Inductor Selection The inductors should have a saturation (incremental) current rating equal to or greater than the peak switchcurrent limit, which is 1.2A worst-case. However, it's generally acceptable to bias the inductor into saturation by 20%, although this will reduce the efficiency. The 22H inductor shown in the typical applications circuit is sufficient for most MAX756/MAX757 application circuits. Higher input voltages increase the energy transferred with each cycle, due to the reduced input/output differential. Minimize excess ripple due to increased energy transfer by reducing the inductor value (10H suggested). 6 CAPACITORS Sprague 595D series United Chemi-Con LXF series AVX USA: CoilCraft Coiltronics Collmer Semiconductor Motorola Nichicon USA: USA: (207) 282-5111, FAX (207) 283-1941 (800) 282-9975 (708) 639-6400, FAX (708) 639-1969 (407) 241-7876, FAX (407) 241-9339 USA: (214) 233-1589 USA: (602) 244-3576, FAX (602) 244-4015 USA: (708) 843-7500, FAX (708) 843-2798 Japan: +81-7-5231-8461, FAX (+81-) 7-5256-4158 Nihon USA: (805) 867-2555, FAX (805) 867-2556 Japan: +81-3-3494-7411, FAX (+81-) 3-3494-7414 Sanyo OS-CON USA: (619) 661-6835 Japan: +81-720-70-1005, FAX (+81-720-) 70-1174 Sprague USA: (603) 224-1961, FAX (603) 224-1430 Sumida USA: (708) 956-0666 Japan: +81-3-3607-5111, FAX (+81-3-) 3607-5428 United Chemi-Con USA: (708) 696-2000, FAX (708) 640-6311 Capacitor Selection A 100F, 10V surface-mount (SMT) tantalum capacitor typically provides 50mV output ripple when stepping up from 2V to 5V at 200mA. Smaller capacitors, down to 10F, are acceptable for light loads or in applications that can tolerate higher output ripple. Maxim Integrated MAX756/MAX757 3.3V/5V/Adjustable-Output, Step-Up DC-DC Converters Rectifier Diode The ESR of both bypass and filter capacitors affects efficiency. Best performance is obtained by using specialized low-ESR capacitors, or connecting two or more filter capacitors in parallel. The smallest low-ESR SMT tantalum capacitors currently available are Sprague 595D series, which are about half the size of competing products. Sanyo OS-CON organic semiconductor through-hole capacitors also exhibit very low ESR, and are especially useful for operation at cold temperatures. Table 1 lists suggested capacitor suppliers. For optimum performance, a switching Schottky diode, such as the 1N5817, is recommended. 1N5817 equivalent diodes are also available in surface-mount packages from Collmer Semiconductor in Dallas, TX, phone (214) 233-1589. The part numbers are SE014 or SE024. For low output power applications, a pn junction switching diode, such as the 1N4148, will also work well, although efficiency will suffer due to the greater forward voltage drop of the pn junction diode. VIN MINIMUM OFF-TIME ONE-SHOT SHDN Q TRIG ONE-SHOT LX F/F S VOUT N Q R 3/5 GND MAXIMUM ON-TIME ONE-SHOT TRIG Q ONE-SHOT OUT MAX756 LBO REF N LBI REFERENCE Figure 2. MAX756 Block Diagram Maxim Integrated 7 MAX756/MAX757 3.3V/5V/Adjustable-Output, 3.3V/5V/Adjustable-Output Step-Up DC-DC Converters ___________________Chip Topography PC Layout and Grounding The MAX756/MAX757 high peak currents and high-frequency operation make PC layout important for minimizing ground bounce and noise. The distance between the MAX756/MAX757's GND pin and the ground leads of C1 and C2 in Figure 1 must be kept to less than 0.2" (5mm). All connections to the FB and LX pins should also be kept as short as possible. To obtain maximum output power and efficiency and minimum output ripple voltage, use a ground plane and solder the MAX756/MAX757 GND (pin 7) directly to the ground plane. SHDN LX 3/5 (MAX756) FB (MAX757) GND 0.122" (3.10mm) GND REF OUT LBI LBO 0.080" (2.03mm) TRANSISTOR COUNT: 758 SUBSTRATE CONNECTED TO OUT ________________________________________________________Package Information DIM E A A1 B C D E e H h L 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 A 0.127mm 0.004in. e A1 C L 8-PIN PLASTIC SMALL-OUTLINE PACKAGE B 8 Maxim Integrated MAX756/MAX757 3.3V/5V/Adjustable-Output, Step-Up DC-DC Converters 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. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000 (c) Maxim Integrated 9 The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.