MAX1831EEE+G002

19-2198; Rev 0; 10/01 KIT EVALUATION AVAILABLE 3A, 1MHz, Low-Voltage, Step-Down Regulators with Synchronous Rectification and Internal Switches Applications Features ♦ ±1.5% Output Accuracy ♦ 94% Efficiency ♦ Internal PMOS/NMOS Switches 45mΩ/55mΩ On-Resistance at VIN = +4.5V 50mΩ/55mΩ On-Resistance at VIN = +3V ♦ Output Voltages +3.3V, +2.5V, or +1.5V Pin Selectable (MAX1831) +2.5V, +1.8V, or +1.5V Pin Selectable (MAX1830) +1.1V to VIN Adjustable (Both Devices) ♦ +3V to +5.5V Input Voltage Range ♦ 750µA (max) Operating Supply Current ♦ 1% × L t OFF Stable operation requires the correct output-filter capacitor. When choosing the output capacitor, ensure that: t COUT ≥ OFF 79µFV / µs VOUT ______________________________________________________________________________________ 3A, 1MHz, Low-Voltage, Step-Down Regulators with Synchronous Rectification and Internal Switches MAX1830/MAX1831 MAX1830/MAX1831 MAXIMUM RECOMMENDED CONTINUOUS OUTPUT CURRENT vs. TEMPERATURE MAXIMUM RECOMMENDED BURST CURRENT vs. BURST CURRENT DUTY CYCLE 3.50 3.40 3.40 3.20 BURST CURRENT (A) OUTPUT CURRENT (A) 3.30 3.10 3.00 2.90 2.80 TA = +55°C 3.20 TA = +85°C 3.00 2.80 2.70 2.60 2.60 2.50 IOUT IS A 100Hz SQUARE WAVE FROM 1A TO THE BURST CURRENT 0.7IN2 OF 1-OZ COPPER 2.40 2.40 25 35 45 55 65 75 85 0 Figure 5. Maximum Recommended Continuous Output Current vs. Temperature High-Current Thermal Considerations High ambient temperatures can limit the maximum current or duty factor of the output current, depending on the total copper, are connected to the MAX1830/ MAX1831 and available airflow. Figure 5 shows the maximum recommended continuous output current vs. ambient temperature. Figure 6 shows the maximum recommended output current vs. the output current duty cycle at high temperatures. These figures are based on 0.7in2 of 1oz copper in free air. Figure 6 assumes that the output current is a square wave with a 100Hz frequency. The duty cycle is defined as the duration of the burst current divided by the period of the square wave. This figure shows the limitations for continuous bursts of output current. Note that if the thermal limitations of the MAX1830/ MAX1831 are exceeded, it enters thermal shutdown to prevent destructive failure. 40 60 80 100 Figure 6. Maximum Recommended Burst Current vs. Burst Current Duty Cycle Integrator Amplifier An internal transconductance amplifier fine tunes the output DC accuracy. A capacitor, CCOMP, from COMP to VCC compensates the transconductance amplifier. For stability, choose CCOMP = 470pF. A large capacitor value maintains a constant average output voltage but slows the loop response to changes in output voltage. A small capacitor value speeds up the loop response to changes in output voltage but decreases stability. 20 DUTY CYCLE (%) TEMPERATURE (°C) Frequency Variation with Output Current The operating frequency of the MAX1830/MAX1831 is determined primarily by tOFF (set by RTOFF), VIN, and VOUT as shown in the following formula: fPWM = (VIN − VOUT − VPMOS ) [tOFF (VIN − VPMOS + VNMOS )] However, as the output current increases, the voltage drop across the NMOS and PMOS switches increases and the voltage across the inductor decreases. This causes the frequency to drop. The change in frequency can be approximated with the following formula: ∆fPWM = -IOUT x RPMOS / (VIN x tOFF) where RPMOS is the resistance of the internal MOSFETs (50mΩ typ). Circuit Layout and Grounding Good layout is necessary to achieve the MAX1830/ MAX1831s’ intended output power level, high efficiency, and low noise. Good layout includes the use of a ground plane, careful component placement, and correct routing of traces using appropriate trace widths. ______________________________________________________________________________________ 11 MAX1830/MAX1831 3A, 1MHz, Low-Voltage, Step-Down Regulators with Synchronous Rectification and Internal Switches The following points are in order of decreasing importance: 1) Minimize switched-current and high-current ground loops. Connect the input capacitor’s ground, the output capacitor’s ground, and PGND. Connect the resulting island to GND at only one point. 2) Connect the input filter capacitor less than 5mm away from IN. The connecting copper trace carries large currents and must be at least 1mm wide, preferably 2.5mm. 3) Place the LX node components as close together and as near to the device as possible. This reduces resistive and switching losses as well as noise. 4) A ground plane is essential for optimum performance. In most applications, the circuit is located on a multilayer board, and full use of the four or more layers is recommended. Use the top and bottom layers for interconnections and the inner layers for an uninterrupted ground plane. Avoid large AC currents through the ground plane. Pin Configuration ___________________Chip Information TRANSISTOR COUNT: 3662 TOP VIEW LX 1 16 LX IN 2 15 PGND LX 3 14 LX IN 4 SHDN 5 MAX1830 MAX1831 COMP 6 13 PGND 12 VCC 11 FBSEL 10 REF TOFF 7 9 FB 8 GND QSOP 12 ______________________________________________________________________________________ 3A, 1MHz, Low-Voltage, Step-Down Regulators with Synchronous Rectification and Internal Switches QSOP.EPS 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. 13 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2001 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX1830/MAX1831 Package Information