MAX1623 19-1436 Rev 2 3/02 3A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches General Description Features The MAX1623 switch-mode buck regulator with syn- 1% Output Accuracy, Including Line and Load chronous rectification provides local CPU and bus-ter- Regulation mination power in notebook and desktop computers. 94% Efficiency An internal 55m (typ), 3A PMOS power switch and Internal Switches 60m (typ), 3A NMOS synchronous-rectifier switch 55m PMOS Power Switch deliver continuous load currents up to 3A from a 5V 60m NMOS Synchronous-Rectifier Switch supply with 95% typical efficiency. Output accuracy is 1%, including line and load regulation. Guaranteed 3A Load Capability The MAX1623 features constant-off-time, current-mode Minimal External Components pulse-width-modulation (PWM) control with switching Pin-Selectable Fixed 3.3V, 2.5V, or frequencies as high as 350kHz. An external resistor at Adjustable (1.1V to 3.8V) Output Voltage the TOFF pin sets the off-time, allowing optimum design 4.5V to 5.5V Input Voltage Range flexibility in terms of switching frequency, output switch- ing noise, and inductor size. This device is available in 400A (typ) Supply Current a space-saving 20-pin SSOP package. <1A Shutdown Supply Current Constant-Off-Time PWM Operation Switching Frequencies Up to 350kHz Applications Idle Mode Operation at Light Loads 5V to 3.3V Conversion Thermal Shutdown Protection Notebook Computer CPU I/O Supply Available in 20-Pin SSOP Desktop Computer Bus-Termination Supply CPU Daughter Card Supply Ordering Information DSP Supply PART TEMP RANGE PIN-PACKAGE MAX1623EAP -40C to +85C 20 SSOP Typical Operating Circuit Pin Configuration TOP VIEW 2.5V OUTPUT 5V IN LX INPUT LX 1 20 LX IN 2 19 PGND MAX1623 LX 3 18 LX V CC PGND IN 4 17 PGND FBSEL MAX1623 LX 5 16 LX FB IN 6 15 PGND SHDN SHDN 7 14 V CC TOFF GND FBSEL 8 13 COMP COMP REF TOFF 9 12 REF FB 10 11 GND SSOP Idle Mode is a trademark of Maxim Integrated Products. Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct at 1-888-629-4642, or visit Maxims website at www.maxim-ic.com. EVALUATION KIT MANUAL AVAILABLE3A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches ABSOLUTE MAXIMUM RATINGS IN to PGND .....................................................................0V to 6V REF Short to GND ......................................................Continuous V to GND ................................................................-0.3V to 6V Continuous Power Dissipation (T = +70C) (with part mounted CC A PGND to GND.....................................................................0.5V on 1 sq. inch of one ounce copper) IN to V .............................................................................0.5V 20-Pin SSOP (derate 22mW/C above +70C) ................1.3W CC LX Current (Note 1).............................................................5.5A Operating Temperature Range ...........................-40C to +85C SHDN to GND.............................................................-0.3V to 6V Storage Temperature Range .............................-65C to +150C REF, FBSEL, COMP, FB, TOFF to GND .....-0.3V to (V + 0.3V) Lead Temperature (soldering, 10s) .................................+300C CC Note 1: LX has internal clamp diodes to PGND and IN. Applications that forward bias these diodes should take care not to exceed the ICs package power dissipation limits. 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 (V = V = 5V, FBSEL unconnected, R = 110k , T = 0C to +85C, unless otherwise noted. Typical values are at IN CC TOFF A T = +25C.) A PARAMETER CONDITIONS MIN TYP MAX UNITS Input Voltage Range 4.5 5.5 V FBSEL = unconnected 3.296 3.330 3.366 V = 4.5V to 5.5V, IN Output Voltage FBSEL = V 2.49 2.525 2.550 V CC I = 0 to 3A LOAD FBSEL = GND or REF 1.089 1.100 1.110 Output Adjustment Range FBSEL = GND or REF (Note 2) V 3.80 V REF Reference Output Voltage I = 0 1.089 1.100 1.110 V REF Reference Load Regulation I = -1A to 10A 1 mV REF Current-Limit Threshold 3.65 4.65 A RMS LX Output Current 3.65 A PMOS Switch On-Resistance V = 4.5V 55 100 m IN NMOS Switch On-Resistance V = 4.5V 60 100 m IN Maximum Switching Frequency I 1.5A (Note 2) 350 kHz LOAD Idle Mode Threshold (Note 3) 1 1.25 1.5 A No-Load Supply Current Does not include switching losses 400 525 A Shutdown Supply Current SHDN = GND 0.5 10 A LX Leakage Current V = 5.5V, V = 5.5V or 0 20 A IN LX Thermal Shutdown Threshold 145 C Undervoltage Lockout Threshold V falling, 100mV hysteresis 4.1 4.2 4.3 V CC FB Input Bias Current FBSEL = GND, adjustable output mode, V = 1.2V -25 25 nA FB Error-Amplifier Gain Bandwidth (Note 2) 500 kHz Off-Time Adjustment Range 0.5 4 s Off-Time Default Period 0.85 1.00 1.15 s FBSEL = GND 1 AC Output Load Regulation % FBSEL = REF 2 SHDN Input Current SHDN = GND or V -1 0.03 1 A CC SHDN Input Low Voltage 0.8 V SHDN Input High Voltage 2 V 2 MAX1623