MAX1742/MAX1842 19-1760 Rev 2 9/05 1A/2.7A, 1MHz, Step-Down Regulators with Synchronous Rectification and Internal Switches General Description Features The MAX1742/MAX1842 constant-off-time, pulse-width- 1% Output Accuracy modulated (PWM) step-down DC-DC converters are ideal 95% Efficiency for use in 5V and 3.3V to low-voltage conversion neces- sary in notebook and subnotebook computers. These Internal PMOS and NMOS Switches devices feature internal synchronous rectification for high 90m On-Resistance at V = 4.5V IN efficiency and reduced component count. They require 110m On-Resistance at V = 3V IN no external Schottky diode. The internal 90m PMOS Output Voltage power switch and 70m NMOS synchronous-rectifier 2.5V, 1.8V, or 1.5V Pin Selectable switch easily deliver continuous load currents up to 1A. 1.1V to V Adjustable IN The MAX1742/MAX1842 produce a preset 2.5V, 1.8V, or 1.5V output voltage or an adjustable output from 1.1V to 3V to 5.5V Input Voltage Range V . They achieve efficiencies as high as 95%. IN 600A (max) Operating Supply Current The MAX1742/MAX1842 use a unique current-mode, <1A Shutdown Supply Current constant-off-time, PWM control scheme, which includes Idle Mode to maintain high efficiency during light-load Programmable Constant-Off-Time Operation operation. The programmable constant-off-time architec- 1MHz (max) Switching Frequency ture sets switching frequencies up to 1MHz, allowing the Idle-Mode Operation at Light Loads user to optimize performance trade-offs between effi- ciency, output switching noise, component size, and Thermal Shutdown cost. Both devices are designed for continuous output Adjustable Soft-Start Inrush Current Limiting currents up to 1A. The MAX1742 uses a peak current limit of 1.3A (min) and is suitable for applications requir- 100% Duty Cycle During Low-Dropout Operation ing small external component size and high efficiency. Output Short-Circuit Protection The MAX1842 has a higher current limit of 3.1A (min) 16-Pin QSOP Package and is intended for applications requiring an occasional burst of output current up to 2.7A. Both devices also fea- Ordering Information ture an adjustable soft-start to limit surge currents during startup, a 100% duty cycle mode for low-dropout opera- PART TEMP RANGE PIN-PACKAGE tion, and a low-power shutdown mode that disconnects MAX1742EEE -40C to +85C 16 QSOP the input from the output and reduces supply current MAX1742EEE+ -40C to +85C 16 QSOP below 1A. The MAX1742/MAX1842 are available in 16- pin QSOP packages. MAX1842EEE -40C to +85C 16 QSOP For similar devices that provide continuous output cur- MAX1842EEE+ -40C to +85C 16 QSOP rents up to 2A and 3A, refer to the MAX1644 and + Denotes lead-free package. MAX1623 data sheets. Applications Typical Configuration 5V or 3.3V to Low-Voltage Conversion CPU I/O Ring OUTPUT INPUT IN 1.1V TO LX 3V TO Chipset Supplies V IN 5.5V 10 FB MAX1742 Notebook and Subnotebook Computers MAX1842 V PGND CC 470pF 2.2F GND SHDN FBSEL COMP Pin Configuration appears at end of data sheet. REF TOFF 1F SS Idle Mode is a trademark of Maxim Integrated Products. 0.01F 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 AVAILABLE1A/2.7A, 1MHz, Step-Down Regulators 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)...............................1W 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 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 T = +25C A 2.500 2.525 2.550 to +85C FBSEL = V CC T = +0C A 2.487 2.525 2.563 to +85C T = +25C A V = 3V to IN 1.500 1.515 1.530 to +85C 5.5V, FBSEL = I = 0 LOAD unconnected T = +0C A 1.492 1.515 1.538 to 1A for to +85C Preset Output Voltage V MAX1742, V OUT T = +25C A I = 0 LOAD 1.800 1.818 1.836 to +85C to 2.5A for FBSEL = MAX1842, REF T = +0C A 1.791 1.818 1.845 V = V FB OUT to +85C T = +25C A 1.089 1.100 1.111 to +85C FBSEL = GND T = +0C A 1.084 1.100 1.117 to +85C Adjustable Output Voltage V = V = 3V to 5.5V, I = 0, IN CC LOAD V V V REF IN Range FBSEL = GND 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 PMOS Switch IN R I = 0.5A ON, P LX On-Resistance V = 3V 110 250 IN m V = 4.5V 70 150 NMOS Switch IN R I = 0.5A ON, N LX On-Resistance V = 3V 80 200 IN 2 MAX1742/MAX1842