MAX1843 9 2 4 13 12 11 10 MAX1843 8 3 19-1986 Rev 2 4/06 2.7A, 1MHz, Low-Voltage, Step-Down Regulator with Internal Synchronous Rectification in TQFN Package General Description Features The MAX1843 constant-off-time, pulse-width modulated 1% Output Accuracy (PWM) step-down DC-DC converter is ideal for use in 5V Up to 1MHz Switching Frequency and 3.3V to low-voltage conversion necessary in note- book and subnotebook computers. This device features 95% Efficiency an internal PMOS power switch and internal synchronous Internal pMOS/nMOS Switches rectification for high efficiency and reduced component 90m/70m On-Resistance at V = +4.5V count. An external Schottky diode is not required. The IN internal 90m power switch and 70m nMOS synchro- 110m/80m On-Resistance at V = +3V IN nous-rectifier switch easily deliver continuous load cur- Output Voltage rents up to 2.7A. The MAX1843 produces a preset +2.5V, +2.5V, +1.8V, or +1.5V Pin Selectable +1.8V, or +1.5V output voltage or an adjustable output +1.1V to V Adjustable IN from +1.1V to V . It achieves efficiencies as high as IN 95%. +3V to +5.5V Input Voltage Range The MAX1843 uses a unique current-mode, constant-off- 350A Operating Supply Current time, PWM control scheme, which includes Idle Mode < 1A Shutdown Supply Current to maintain high efficiency during light-load operation. The programmable constant-off-time architecture sets Programmable Constant-Off-Time Operation switching frequencies up to 1MHz, allowing the user to Idle Mode Operation at Light Loads optimize performance trade-offs between efficiency, out- put switching noise, component size, and cost. The Thermal Shutdown MAX1843 features an adjustable soft-start to limit surge Adjustable Soft-Start Inrush Current Limiting currents during startup, a 100% duty-cycle mode for low dropout operation, and a low-power shutdown mode that 100% Duty Cycle During Low-Dropout Operation disconnects the input from the output and reduces sup- Output Short-Circuit Protection ply current below 1A. The MAX1843 is available in a 28- pin TQFN package with an exposed backside pad. 28-Pin TQFN Package Applications Ordering Information 5V or 3.3V to Low-Voltage Conversion TEMP PIN- PKG PART CPU I/O Ring RANGE PACKAGE CODE Chipset Supplies 28 TQFN MAX1843ETI+ -40C to +85C T2855-6 Notebook and Subnotebook Computers +Denotes lead-free package. Pin Configuration Typical Configuration TOP VIEW OUTPUT INPUT 21 20 19 18 17 16 15 IN +1.1V TO LX +3V TO V IN +5.5V 14 N.C. REF 10 MAX1843 FB GND LX V PGND CC N.C. N.C. 2.2F 470pF GND SHDN LX N.C. FBSEL COMP N.C. N.C. TOFF REF 1F FB SHDN SS 0.01F N.C. TOFF 1 TQFN 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. 6 7 22 23 24 25 26 27 28 5 + N.C. PGND IN PGND LX LX IN LX N.C. PGND SS V CC COMP FBSEL2.7A, 1MHz, Low-Voltage, Step-Down Regulator with Synchronous Rectification in TQFN Package ABSOLUTE MAXIMUM RATINGS V , IN to GND ........................................................-0.3V to +6V Continuous Power Dissipation (T = +70C) CC A IN to V .............................................................................0.3V 28-Pin TQFN (derate 20mW/C above +70C, part mounted CC 2 GND to PGND.....................................................................0.3V on 1in of 1oz copper)......................................................1.6W All Other Pins to GND.................................-0.3V to (V + 0.3V) Operating Temperature Range ...........................-40C to +85C CC LX Current (Note 1).............................................................4.7A Storage Temperature Range .............................-65C to +150C REF Short Circuit to GND Duration ............................Continuous Junction Temperature......................................................+150C ESD Protection.....................................................................2kV Lead Temperature (soldering, 10s) ................................ +300C 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 T = +25C A 2.500 2.525 2.550 to +85C FBSEL = V CC T = 0C to A V = IN 2.487 2.525 2.563 +85C +3V to +5.5V T = +25C A 1.500 1.515 1.530 to +85C FBSEL = unconnected T = 0C to A 1.492 1.515 1.538 +85C Preset Output Voltage V V OUT I = LOAD T = +25C A 1.800 1.818 1.836 0 to 2.5A to +85C FBSEL = REF T = 0C to A 1.791 1.818 1.845 +85C V = FB T = +25C A 1.089 1.100 1.111 V OUT to +85C FBSEL = GND T = 0C to A 1.084 1.100 1.117 +85C Adjustable Output Voltage V = V = +3V to +5.5V, FBSEL = GND V V V IN CC REF IN Range AC-Load Regulation Error 2% DC-Load Regulation Error 0.4 % Dropout Voltage V V = V = +3V, I = 1A 250 mV DO IN CC LOAD T = +25C to +85C 1.089 1.100 1.111 A Reference Voltage V V REF T = 0C to +85C 1.084 1.100 1.117 A Reference Load Regulation V I = -1A to +10A 0.5 2 mV REF REF V = +4.5V 90 200 IN pMOS Switch On-Resistance R I = 0.5A m ON,P LX V = +3V 110 250 IN V = +4.5V 70 150 IN nMOS Switch On-Resistance R I = 0.5A m ON,N LX V = +3V 80 200 IN Current-Limit Threshold I 3.1 3.6 4.1 A LIMIT RMS LX Output Current 3.1 A 2 MAX1843