MAX1845 19-1955 Rev 2 1/03 Dual, High-Efficiency, Step-Down Controller with Accurate Current Limit General Description Features The MAX1845 is a dual PWM controller configured for Ultra-High Efficiency step-down (buck) topologies that provides high efficien- Accurate Current-Limit Option cy, excellent transient response, and high DC output Quick-PWM with 100ns Load-Step Response accuracy necessary for stepping down high-voltage bat- teries to generate low-voltage chipset and RAM power 1% V Accuracy over Line and Load OUT supplies in notebook computers. The CS inputs can be Dual Mode Fixed 1.8V/1.5V/Adj or 2.5V/Adj Outputs used with low-side sense resistors to provide accurate current limits or can be connected to LX , using low-side Adjustable 1V to 5.5V Output Range MOSFETs as current-sense elements. 2V to 28V Battery Input Range The on-demand PWM controllers are free running, con- 200/300/420/540kHz Nominal Switching Frequency stant on-time with input feed-forward. This configuration Adjustable Overvoltage Protection provides ultra-fast transient response, wide input-output differential range, low supply current, and tight load-reg- 1.7ms Digital Soft-Start ulation characteristics. The MAX1845 is simple and easy Drives Large Synchronous-Rectifier FETs to compensate. Power-Good Window Comparator Single-stage buck conversion allows the MAX1845 to directly step down high-voltage batteries for the highest 2V 1% Reference Output possible efficiency. Alternatively, two-stage conversion (stepping down the 5V system supply instead of the bat- Ordering Information tery at a higher switching frequency) allows the minimum possible physical size. PART TEMP RANGE PIN-PACKAGE The MAX1845 is intended for generating chipset, DRAM, MAX1845EEI -40C to +85C 28 QSOP CPU I/O, or other low-voltage supplies down to 1V. For a single-output version, refer to the MAX1844 data sheet. 36 Thin QFN MAX1845ETX -40C to +85C The MAX1845 is available in 28-pin QSOP and 36-pin 6mm 6mm thin QFN packages. Applications Minimal Operating Circuit Notebook Computers 5V INPUT BATTERY CPU Core Supplies 4.5V TO 28V V V+ DD Chipset/RAM Supply as Low as 1V V UVP CC 1.8V and 2.5V I/O Supplies MAX1845EEI ILIM1 OVP ILIM2 ON1 ON2 BST1 BST2 OUTPUT1 OUTPUT2 DH1 DH2 1.8V 2.5V LX1 LX2 DL1 DL2 CS2 TON CS1 OUT1 PGOOD OUT2 REF SKIP FB2 FB1 GND Pin Configurations appear at end of data sheet. Quick-PWM and Dual Mode are trademarks 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 AVAILABLEDual, High-Efficiency, Step-Down Controller with Accurate Current Limit ABSOLUTE MAXIMUM RATINGS (Note 1) V+ to AGND..............................................................-0.3 to +30V LX to BST ..............................................................-6V to +0.3V V to AGND............................................................-0.3V to +6V DH2 to LX2 ..............................................-0.3V to (V + 0.3V) CC BST2 V to PGND............................................................-0.3V to +6V REF Short Circuit to GND...........................................Continuous DD AGND to PGND.....................................................-0.3V to +0.3V Continuous Power Dissipation (T = +70C) A PGOOD, OUT to AGND..........................................-0.3V to +6V 28-Pin QSOP (derate 10.8mW/C above +70C)........860mW OVP, UVP, ILIM , FB , REF, 36-Pin 6mm 6mm Thin QFN SKIP, TON, ON to AGND......................-0.3V to (V + 0.3V) (derate 26.3mW/C above +70C).............................2105mW CC DL to PGND..............................................-0.3V to (V + 0.3V) Operating Temperature Range ...........................-40C to +85C DD BST to AGND........................................................-0.3V to +36V Junction Temperature......................................................+150C CS to AGND.............................................................-6V to +30V Storage Temperature Range .............................-65C to +150C DH1 to LX1 ..............................................-0.3V to (V + 0.3V) Lead Temperature (soldering, 10s) .................................+300C BST1 Note 1: For the MAX1845EEI, AGND and PGND refer to a single pin designated GND. 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 (Circuit of Figure 1, V = V = 5V, SKIP = AGND, V+ = 15V, T = 0C to +85C, typical values are at +25C, unless otherwise DD CC A noted.) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS PWM CONTROLLERS V+ Battery voltage, V+ 2 28 Input Voltage Range V V /V V , V 4.5 5.5 CC DD CC DD FB1 to AGND 1.782 1.8 1.818 V+ = 2V to 28V, I LOAD = 0 to 8A, SKIP = V , FB1 to V 1.485 1.5 1.515 CC CC +25C to +85C FB1 to OUT1 0.99 1 1.01 DC Output Voltage OUT1 V V OUT1 (Note 2) FB1 to AGND 1.773 1.8 1.827 V+ = 2V to 28V, I LOAD = 0 to 8A, SKIP = V , FB1 to V 1.477 1.5 1.523 CC CC 0C to +85C FB1 to OUT1 0.985 1 1.015 V+ = 4.5V to 28V, FB2 to AGND 2.475 2.5 2.525 I = 0 to 4A, LOAD SKIP = V , CC FB2 to OUT2 0.99 1 1.01 +25C to +85C DC Output Voltage OUT2 V V OUT2 (Note 2) V+ = 4.5V to 28V, FB2 to AGND 2.463 2.5 2.537 I = 0 to 4A, LOAD SKIP = V , CC FB2 to OUT2 0.985 1 1.015 0C to +85C Output Voltage Adjust Range OUT1, OUT2 1 5.5 V Dual-Mode Threshold, Low OVP, FB 0.05 0.1 0.15 V V - V - CC CC OVP, ILIM 1.5 0.4 Dual-Mode Threshold, High V FB1 1.9 2.0 2.1 R V = 1.5V 75 OUT1 OUT1 OUT Input Resistance k R V = 2.5V 100 OUT2 OUT2 FB Input Bias Current I -0.1 0.1 A FB Soft-Start Ramp Time Zero to full ILIM 1700 s 2 MAX1845