MAX1644 19-1457 Rev 3 8/05 2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches General Description Features The MAX1644 constant-off-time, PWM step-down DC- 1% Output Accuracy DC converter is ideal for use in applications such as PC 95% Efficiency cards, CPU daughter cards, and desktop computer bus-termination boards. The device features internal Internal PMOS and NMOS Switches synchronous rectification for high efficiency and 70m On-Resistance at V = +4.5V IN reduced component count. It requires no external 100m On-Resistance at V = +3V IN Schottky diode. The internal 0.10 PMOS power switch Output Voltage and 0.10 NMOS synchronous-rectifier switch easily deliver continuous load currents up to 2A. The +3.3V or +2.5V Pin-Selectable MAX1644 produces a preset +3.3V or +2.5V output +1.1V to V Adjustable IN voltage or an adjustable output from +1.1V to V . It IN +3V to +5.5V Input Voltage Range achieves efficiencies as high as 95%. 360A (max) Operating Supply Current The MAX1644 uses a unique current-mode, constant- off-time, PWM control scheme, which includes an Idle < 1A Shutdown Supply Current Mode to maintain high efficiency during light-load Programmable Constant-Off-Time Operation operation. The programmable constant-off-time archi- tecture sets switching frequencies up to 350kHz, allow- 350kHz (max) Switching Frequency ing the user to optimize performance trade-offs Idle Mode Operation at Light Loads between efficiency, output switching noise, component size, and cost. The device also features an adjustable Thermal Shutdown soft-start to limit surge currents during start-up, a 100% Adjustable Soft-Start Inrush Current Limiting duty cycle mode for low-dropout operation, and a low- power shutdown mode that disconnects the input from 100% Duty Cycle During Low-Dropout Operation the output and reduces supply current below 1A. The MAX1644 is available in a 16-pin SSOP package. Output Short-Circuit Protection 16-Pin SSOP Package Applications Ordering Information +5V to +3.3V/+2.5V Conversion CPU I/O Supply PART TEMP RANGE PIN-PACKAGE +3.3V PC Card and CardBus Applications MAX1644EAE 40C to +85C 16 SSOP Notebook and Subnotebook Computers MAX1644EAE+ 40C to +85C 16 SSOP Desktop Bus-Termination Boards +Denotes lead-free package. CPU Daughter Card Supply Pin Configuration Typical Operating Circuit TOP VIEW SHDN 1 16 LX INPUT OUTPUT IN LX +1.1V TO +3V TO IN 2 15 PGND +5.5V V IN FB MAX1644 LX 3 14 LX IN 4 MAX1644 13 PGND V PGND CC FBSEL SS 5 12 V CC GND SHDN COMP 6 11 FBSEL COMP REF TOFF 7 10 REF TOFF SS FB 8 9 GND R TOFF SSOP A SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES. Idle Mode is a trademark of Maxim Integrated Products, Inc. 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 AVAILABLE2A, Low-Voltage, Step-Down Regulator with Synchronous Rectification and Internal Switches ABSOLUTE MAXIMUM RATINGS V , IN to GND ........................................................-0.3V to +6V Continuous Power Dissipation (T = +70C) CC A IN to V .............................................................................0.3V SSOP (derate 16.7mW/C above +70C CC 2 GND to PGND.....................................................................0.3V part mounted on 1 in. of 1oz. copper)............................1.2W All Other Pins to GND.................................-0.3V to (V + 0.3V) Operating Temperature Range ...........................-40C to +85C CC LX Current (Note 1)...........................................................3.75A Storage Temperature Range .............................-65C to +150C REF Short Circuit to GND Duration ............................Continuous Lead Temperature (soldering, 10s) ................................ +300C ESD Protection.....................................................................2kV 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 = +3.3V, FBSEL = GND, T = 0C to +85C, unless otherwise noted. Typical values are at T = +25C.) IN CC A A PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Input Voltage V , V 3.0 5.5 V IN CC V = V = 4V to 5.5V, IN CC 3.300 3.333 3.366 FBSEL = unconnected I = 0 to LOAD V = V = 3V to 5.5V, IN CC Preset Output Voltage V 2A, 2.500 2.525 2.550 V OUT FBSEL = V CC V = V FB OUT V = V = 3V to 5.5V, IN CC 1.089 1.100 1.111 FBSEL = REF Adjustable Output Voltage V = V = 3V to 5.5V, IN CC V V V REF IN Range I = 0, FBSEL = GND or REF LOAD FBSEL = GND 1 AC Load Regulation Error % FBSEL = REF, V , or unconnected 2 CC FBSEL = GND 0.2 DC Load Regulation Error % FBSEL = REF, V , or unconnected 0.4 CC Dropout Voltage V V = V = 3V, I = 1A, FBSEL = V 200 mV DO IN CC LOAD CC Reference Voltage V 1.089 1.100 1.111 V REF Reference Load Regulation V I = -1A to +10A 0.5 1 mV REF REF V = 4.5V 70 150 IN PMOS Switch R I = 0.5A m ON, P LX On-Resistance V = 3V 100 200 IN V = 4.5V 70 150 IN NMOS Switch R I = 0.5A m ON, N LX On-Resistance V = 3V 100 200 IN Current-Limit Threshold I 2.5 2.9 3.3 A LIMIT RMS LX Output Current 2.5 A Idle Mode Current I 0.25 0.45 0.65 A IM Threshold Switching Frequency f (Note 2) 350 kHz No-Load Supply Current I + I V = 1.2V 240 360 A IN CC FB Shutdown Supply Current I SHDN = GND <1 3 A CC(SHDN) PMOS Switch Off-Leakage I SHDN = GND 15 A IN Current Thermal Shutdown T Hysteresis = 15C 150 C SHDN Threshold 2 MAX1644