MAX1734EUK18+TGA8

19-1586; Rev 0; 7/00 Low-Voltage, Step-Down DC-DC Converters in SOT23 Features ♦ 250mA Guaranteed Output Current ♦ Synchronous Rectifier for Over 90% Efficiency ♦ Tiny 5-Pin SOT23 Package ♦ 40µA Quiescent Supply Current ♦ 0.01µA Logic-Controlled Shutdown ♦ Up to 1.2MHz Switching Frequency ♦ Fixed 1.8V or 1.5V Outputs (MAX1734) ♦ Adjustable Output Voltage (MAX1733) ♦ ±1.5% Initial Accuracy ♦ 2.7V to 5.5V Input Range ♦ Soft-Start Limits Startup Current Ordering Information PART Applications Cellular, PCS, and Cordless Telephones TEMP. RANGE MAX1733EUK-T -40°C to +85°C 5 SOT23-5 MAX1734EUK_ _-T -40°C to +85°C 5 SOT23-5 Note: The MAX1734 offers two output voltages. See the Selector Guide, then insert the proper designator into the blanks above to complete the part number. Selector Guide PDAs, Palmtops, and Handy-Terminals Battery-Powered Equipment PART VOUT (V) MAX1733EUK 10µH IN VOUT AT 250mA Adjustable ADKY 1.8 ADKW MAX1734EUK15 1.5 ADKX Pin Configuration TOP VIEW LX IN 2.2µF TOP MARK MAX1734EUK18 Typical Operating Circuit INPUT +2.7V TO +5.5V PIN-PACKAGE SHDN GND 1 5 LX 4 OUT (FB) 22µF MAX1734 OUT GND 2 MAX1733 MAX1734 SHDN 3 SOT23-5 ( ) ARE FOR MAX1733 ONLY. ________________________________________________________________ Maxim Integrated Products 1 For free samples and the latest literature, visit www.maxim-ic.com or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. MAX1733/MAX1734 General Description The MAX1733/MAX1734 step-down DC-DC converters deliver over 250mA to outputs as low as 1.25V. These converters use a unique proprietary current-limited control scheme that achieves over 90% efficiency. These devices maintain extremely low quiescent supply current (40µA), and their high 1.2MHz (max) operating frequency permits small, low-cost external components. This combination of features makes the MAX1733/ MAX1734 excellent high-efficiency alternatives to linear regulators in space-constrained applications. Internal synchronous rectification greatly improves efficiency and eliminates the external Schottky diode required in conventional step-down converters. Both devices also include internal digital soft-start to limit input current upon startup and reduce input capacitor requirements. The MAX1733 provides an adjustable output voltage (1.25V to 2.0V). The MAX1734 provides factory-preset output voltages (see Selector Guide). Both are available in space-saving 5-pin SOT23 packages. MAX1733/MAX1734 Low-Voltage, Step-Down DC-DC Converters in SOT23 ABSOLUTE MAXIMUM RATINGS IN, SHDN to GND .....................................................-0.3V to +6V OUT, FB, LX to GND ....................................-0.3V to (VIN + 0.3V) OUT Short Circuit to GND ..........................................Continuous Continuous Power Dissipation (TA = +70°C) 5-Pin SOT23 (derate 7.1mW/°C above +70°C)............571mW Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+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 (VIN = +2.7V to +5.5V, SHDN = IN, TA = 0°C to +85°C. Typical values are at TA = +25°C, unless otherwise noted.) PARAMETER Input Voltage Range SYMBOL CONDITIONS VIN Startup Voltage VSTART UVLO Threshold VUVLO MIN TYP 2.7 VIN rising VIN falling 1.85 1.55 UVLO Hysteresis MAX V 2.0 V 1.95 1.65 200 Quiescent Supply Current IIN Shutdown Supply Current ISHDN Output Voltage Range (MAX1733) VOUT No switching, no load (FB/OUT above trip point) µA 0.01 4 µA 1.25 2.0 V -1.5 +1.5 -3 +3 IOUT = 0 to 250mA Load Regulation IOUT = 0 to 250mA 0 Line Regulation VIN = 2.7V to 5.5V 0 OUT Sense Current (MAX1734) VOUT = VREG, VIN = V SHDN= 5V 4 TA = +25°C, VIN = 3.6V 1.231 VIN = 3.6V 1.220 VFB FB Leakage Current (MAX1733) IFB VFB = 1.5V SHDN Input High Voltage VIH 2.7V < VIN < 5.5V SHDN Input Low Voltage VIL 2.7V < VIN < 5.5V SHDN Leakage Current ISHDN High-Side Current Limit ILIMP Low-Side Current Limit ILIMN mV 70 Output Voltage Accuracy (MAX1734) FB Feedback Threshold (MAX1733) V 40 SHDN = GND IOUT = 0, TA = +25°C UNITS 5.5 1.250 %/mA %/V 8 1.269 1.280 0.001 % 0.2 1.6 µA V µA V 0.4 V 0.001 1 µA 300 425 535 mA 200 mA SHDN = GND or IN 325 430 ILX = -50mA, VIN = 3.0V 0.7 1.4 ILX = -50mA, VIN = 5.5V 0.5 1.1 ILX = -50mA, VIN = 3.0V 1.0 2 ILX = -50mA, VIN = 5.5V 0.8 1.6 Ω High-Side On-Resistance RONP Rectifier On-Resistance RONN Rectifier Off-Current Threshold ILXOFF LX Leakage Current ILXLEAK VIN = 5.5V, VLX = 0 to VIN 0.1 5 µA LX Reverse Leakage Current ILXLK,R IN unconnected, VLX = 5.5V, SHDN = GND 0.1 5 µA 40 Ω mA Minimum On-Time tON(MIN) VIN = 3.6V 0.28 0.4 0.5 µs Minimum Off-Time tOFF(MIN) VIN = 3.6V 0.28 0.4 0.5 µs 2 _______________________________________________________________________________________ Low-Voltage, Step-Down DC-DC Converters in SOT23 (VIN = +2.7V to +5.5V, SHDN = IN, TA = -40°C to +85°C, unless otherwise noted.) (Note 1) PARAMETER Input Voltage Range SYMBOL CONDITIONS VIN Startup Voltage VSTART UVLO Threshold VUVLO Quiescent Supply Current IIN Shutdown Supply Current ISHDN Output Voltage Range (MAX1733) VOUT Output Voltage Accuracy (MAX1734) MIN 2.7 VIN rising, 200mV typical hysteresis VIN falling MAX UNITS 5.5 V 2.0 V 1.95 1.55 V No switching (FB/OUT above trip point) 70 µA SHDN = GND 4 µA 1.25 2.0 V -3 +3 % 8 µA 1.280 V 0.2 µA IOUT = 0 to 250mA OUT Sense Current (MAX1734) IOUT VOUT = VREG, VIN = V SHDN = 5V FB Feedback Threshold (MAX1733) VFB VIN = 3.6V FB Leakage Current (MAX1733) IFB VFB = 1.5V SHDN Input High Voltage VIH 2.7V < VIN < 5.5V SHDN Input Low Voltage VIL 2.7V < VIN < 5.5V SHDN Leakage Current ISHDN 1 µA High-Side Current Limit ILIMP 300 565 mA Low-Side Current Limit ILIMN 200 430 mA High-Side On-Resistance RONP Rectifier On-Resistance RONN 1.210 1.6 V 0.4 SHDN = GND or IN ILX = -50mA, VIN = 3.0V 1.4 ILX = -50mA, VIN = 5.5V 1.1 ILX = -50mA, VIN = 3.0V 2 ILX = -50mA, VIN = 5.5V 1.6 V Ω Ω LX Leakage Current ILXLEAK VIN = 5.5V, VLX = 0 to VIN 5 µA LX Reverse Leakage Current ILXLK,R IN unconnected, VLX = 5.5V, SHDN = GND 5 µA Minimum On-Time tON(MIN) 0.25 0.55 µs Minimum Off-Time tOFF(MIN) 0.25 0.55 µs Note 1: All devices are 100% production tested at TA = +25°C. Limits over the operating temperature range are guaranteed by design. _______________________________________________________________________________________ 3 MAX1733/MAX1734 ELECTRICAL CHARACTERISTICS Typical Operating Characteristics (CIN = 2.2µF ceramic, COUT = 22µF tantalum, L = 10µH, unless otherwise noted.) EFFICIENCY vs. LOAD CURRENT (VOUT = 1.5V) 90 90 EFFICIENCY (%) VIN = 5.0V 70 VIN = 3.6V 60 VIN = 5.0V 70 VIN = 3.6V 60 58 54 52 40 40 48 30 30 46 0.1 1000 -1.0 VIN = 5.0V, TA = +25°C 1.0 0 -1.0 VIN = 2.7V, TA = +25°C -2.0 VIN = 5.0V, TA = +25°C -3.0 10 100 3.5 4.0 4.5 5.0 5.5 1.50 ILOAD = 50mA TO 250mA 1.25 1.00 VOUT = 1.8V VOUT = 1.5V 0.75 VIN = 3.6V, TA = -40°C VIN = 3.6V, TA = -40°C -3.0 1 3.0 SWITCHING FREQUENCY vs. SUPPLY VOLTAGE SWITCHING FREQUENCY (MHz) VIN = 2.7V, TA = +25°C 0.1 VOUT = 1.5V, TA = -40°C SUPPLY VOLTAGE (V) VIN = 3.6V, TA = +85°C 2.0 OUTPUT ACCURACY (%) VIN = 3.6V, TA = +85°C 0 -2.0 VOUT = 1.5V, TA = +25°C 2.5 1000 3.0 MAX1733/4-04 3.0 1.0 10 100 LOAD CURRENT (mA) 50 OUTPUT ACCURACY vs. LOAD CURRENT (VOUT = 1.5V) OUTPUT ACCURACY vs. LOAD CURRENT (VOUT = 1.8V) 2.0 1 MAX1733/4-05 10 100 LOAD CURRENT (mA) VOUT = 1.8V, TA = +25°C 56 50 1 VOUT = 1.8V, TA = +85°C 60 50 0.1 1000 0.50 0.1 1 10 100 1000 2.7 3.0 LOAD CURRENT (mA) LOAD CURRENT (mA) LIGHT-LOAD SWITCHING WAVEFORMS 3.6 MAX1733/4-08 VIN = 3.6V, VOUT = 1.8V, ILOAD = 20mA 400ns/div 3.3 SUPPLY VOLTAGE (V) HEAVY-LOAD SWITCHING WAVEFORMS MAX1733/4-07 4 62 SUPPLY CURRENT (µA) 80 80 EFFICIENCY (%) VIN = 2.7V MAX1733/4-03 VIN = 2.7V MAX1733/4-02 100 MAX1733/4-01 100 NO-LOAD SUPPLY CURRENT vs. SUPPLY VOLTAGE MAX1733/4-06 EFFICIENCY vs. LOAD CURRENT (VOUT = 1.8V) OUTPUT ACCURACY (%) MAX1733/MAX1734 Low-Voltage, Step-Down DC-DC Converters in SOT23 VIN = 3.6V, VOUT = 1.8V, ILOAD = 200mA VOUT AC-COUPLED 20mV/div VOUT AC-COUPLED 20mV/div VLX 2V/div VLX 2V/div 400ns/div _______________________________________________________________________________________ 3.9 4.2 Low-Voltage, Step-Down DC-DC Converters in SOT23 LOAD-TRANSIENT RESPONSE SOFT-START AND SHUTDOWN RESPONSE MAX1733/4-12 MAX1733/4-09 VIN = 3.6V, VOUT = 1.8V, ILOAD = 20mA TO 200mA VIN = 3.6V, VOUT = 1.8V, RLOAD = 7Ω VOUT 1V/div VOUT AC-COUPLED 50mV/div IIN 100mA/div ILOAD 100mA/div VSHDN 5V/div 4µs/div 200µs/div HEAVY-LOAD LINE-TRANSIENT RESPONSE LIGHT-LOAD LINE-TRANSIENT RESPONSE MAX1733/4-11 MAX1733/4-10 VIN = 3.4V TO 3.8V, VOUT = 1.8V, ILOAD = 200mA VIN = 3.4V TO 3.8V, VOUT = 1.8V, ILOAD = 20mA VOUT AC-COUPLED 50mV/div VOUT AC-COUPLED 50mV/div VIN AC-COUPLED 200mV/div VIN AC-COUPLED 200mV/div 4µs/div 4µs/div Pin Description PIN NAME 1 IN 2 GND Ground 3 SHDN Active-Low Shutdown Input. Connect SHDN to IN for normal operation. In shutdown, LX becomes high impedance and quiescent current drops to 0.01µA. FB 4 OUT 5 LX FUNCTION Supply Voltage Input. Input range from +2.7V to +5.5V. Bypass with a 2.2µF ceramic capacitor to GND. MAX1733 Voltage Feedback Input. FB regulates to 1.25V nominal. Connect FB to an external voltage-divider between the output voltage and GND. MAX1734 Voltage Sense Input. OUT is connected to an internal voltage-divider. Inductor Connection _______________________________________________________________________________________ 5 MAX1733/MAX1734 Typical Operating Characteristics (continued) (CIN = 2.2µF ceramic, COUT = 22µF tantalum, L = 10µH, unless otherwise noted.) MAX1733/MAX1734 Low-Voltage, Step-Down DC-DC Converters in SOT23 L1 10µH INPUT +2.7V TO +5.5V IN C1 2.2µF VOUT IN LX MAX1733 SHDN R1 C2 22µF MAX1733 MAX1734 CURRENT LIMIT FB R2 DIGITAL SOFT-START GND P CONTROL LOGIC LX N Figure 1. MAX1733 Typical Application Circuit SHDN SHUTDOWN CONTROL OUT (FB) Detailed Description The MAX1733/MAX1734 step-down DC-DC converters deliver over 250mA to outputs as low as 1.25V. They use a unique proprietary current-limited control scheme that maintains extremely low quiescent supply current (40µA), and their high 1.2MHz (max) operating frequency permits small, low-cost external components. Figure 2 is a simplified functional diagram. VREF ( ) ARE FOR MAX1733 ONLY. GND Figure 2. Simplified Functional Diagram Control Scheme The MAX1733/MAX1734 use a proprietary, current-limited control scheme to ensure high-efficiency, fast transient response, and physically small external components. This control scheme is simple: when the output voltage is out of regulation, the error comparator begins a switching cycle by turning on the high-side switch. This switch remains on until the minimum ontime of 400ns expires and the output voltage regulates or the current-limit threshold is exceeded. Once off, the high-side switch remains off until the minimum off-time of 400ns expires and the output voltage falls out of regulation. During this period, the low-side synchronous rectifier turns on and remains on until either the highside switch turns on again or the inductor current approaches zero. The internal synchronous rectifier eliminates the need for an external Schottky diode. This control scheme allows the MAX1733/MAX1734 to provide excellent performance throughout the entire load-current range. When delivering light loads, the high-side switch turns off after the minimum on-time to reduce peak inductor current, resulting in increased efficiency and reduced output voltage ripple. When delivering medium and higher output currents, the MAX1733/MAX1734 extend either the on-time or the offtime, as necessary to maintain regulation, resulting in 6 nearly constant frequency operation with high efficiency and low output voltage ripple. Shutdown Mode Connecting SHDN to GND places the MAX1733/ MAX1734 in shutdown mode and reduces supply current to 0.01µA. In shutdown, the control circuitry, internal switching MOSFET, and synchronous rectifier turn off and LX goes high impedance. Connect SHDN to IN for normal operation. Soft-Start The MAX1733/MAX1734 have internal soft-start circuitry that limits current draw at startup, reducing transients on the input source. Soft-start is particularly useful for higher impedance input sources, such as Li+ and alkaline cells. Soft-start is implemented by starting with the current limit at 25% of its full current value and gradually increasing it in 25% steps until the full current limit is reached. See Soft-Start and Shutdown Response in the Typical Operating Characteristics section. Design Information Setting the Output Voltage (MAX1733) Select an output voltage for the MAX1733 by connecting FB to a resistive divider between the output and _______________________________________________________________________________________ Low-Voltage, Step-Down DC-DC Converters in SOT23 INDUCTOR VALUE (µH) MANUFACTURER 10 Sumida 10 Coilcraft Table 3. Component Suppliers PHONE FAX AVX 843-946-0238 843-626-3123 CR43-100 Coilcraft 847-639-6400 847-639-1469 CDRH4D18-100 Kemet 408-986-0424 408-986-1442 DT1608C-103 Murata 814-237-1431 814-238-0490 847-956-0666 847-956-0702 81-3-3607-5111 81-3-3607-5144 408-573-4150 408-573-4159 PART NUMBER COMPANY Sumida Table 2. Suggested Capacitors CAPACITOR TYPE USA Japan Taiyo Yuden MANUFACTURER PART NUMBER Tantalum (22µF) Taiyo Yuden LMK212BJ225MG Ceramic (2.2µF) AVX ( ) IOUT  VOUT VIN − OUT  1 / 2   IRMS = VIN TAJA226M006R Tables 2 and 3 list some suggested capacitors and suppliers. GND (Figure 1). Choose R2 to be less than 50kΩ: V  R1 = R2 ×  OUT − 1  VREF  where VREF = 1.25V. Inductor Selection The MAX1733/MAX1734 are optimized to use a 10µH inductor over the entire operating range. A 300mA rated inductor is enough to prevent saturation for output currents up to 250mA. Saturation occurs when the inductor’s magnetic flux density reaches the maximum level the core can support and inductance falls. Choose a low DC-resistance inductor to improve efficiency. Tables 1 and 3 list some suggested inductors and suppliers. Using Ceramic COUT with MAX1733 The circuit of Figure 3 is designed to allow the use of ceramic output capacitors with the MAX1733. Feedback is derived from the LX pin instead of the output to remove the effects of phase lag in the feedback loop. Compared to the standard applications circuit, there are three benefits: 1) availability of ceramic vs. tantalum; 2) size of 2.2µF 0805 vs. 22µF A-case; 3) output ripple less than 10mVp-p vs. greater than 30mVp-p. Increase the output capacitance to 4.7µF to further reduce the output ripple. Note that this circuit exhibits load regulation equal to the series resistance of the inductor multiplied by the load current. This small amount of load regulation is helpful in reducing overshoot of the output voltage during load transients. 10µH IN Capacitor Selection The MAX1733/MAX1734 require output voltage ripple (approximately 30mVp-p) for stable switching behavior. Use a 10µF to 47µF tantalum output capacitor with about 200mΩ to 300mΩ ESR to provide stable switching while minimizing output ripple. Choose input and output capacitors to filter inductor currents for acceptable voltage ripple. The input capacitor reduces peak currents and noise at the voltage source. Input capacitors must meet the input ripple requirements and voltage rating. Use the following equation to calculate the maximum RMS input current: Li+ 2.7V TO 4.2V 2.2µF X7R OUTPUT 1.8V at 250mA LX MAX1733 30k 2.2µF X7R GND 1000pF ON OFF SHDN FB 68k Figure 3. Using a Ceramic Output Capacitor with the MAX1733 _______________________________________________________________________________________ 7 MAX1733/MAX1734 Table 1. Suggested Inductors MAX1733/MAX1734 Low-Voltage, Step-Down DC-DC Converters in SOT23 Layout Considerations High switching frequencies make PC board layout a very important part of design. Good design minimizes excessive EMI on the feedback paths and voltage gradients in the ground plane, both of which can result in instability or regulation errors. Connect the inductor, input filter capacitor, and output filter capacitor as close to the device as possible, and keep their traces short, direct, and wide. Connect their ground pins at a single common node in a star ground configuration. The external voltage-feedback network should be very close to the FB pin, within 0.2 inches (5mm). Keep noisy traces, such as the LX trace, away from the volt- age-feedback network; also keep them separate, using grounded copper. The MAX1733/MAX1734 evaluation kit data sheet includes a proper PC board layout and routing scheme. Chip Information TRANSISTOR COUNT: 1190 PROCESS: BiCMOS Package Information 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. 8 _____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2000 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.