MAX1844EEP

19-1993; Rev 3; 9/02 KIT ATION EVALU E L B A AVAIL High-Speed Step-Down Controller with Accurate Current Limit for Notebook Computers Features ♦ Ultra-High Efficiency Maxim’s proprietary Quick-PWM™ quick-response, constant-on-time PWM control scheme handles wide input/output voltage ratios with ease and provides 100ns “instant-on” response to load transients while maintaining a relatively constant switching frequency. Efficiency is enhanced by an ability to drive very large synchronous-rectifier MOSFETs. Accurate current sensing to ensure reliable overload protection is available using an external current-sense resistor in series with the synchronous rectifier. Alternatively, the synchronous rectifier itself can be used for less accurate current sensing at the lowest possible power dissipation. Single-stage buck conversion allows the MAX1844 to directly step down high-voltage batteries for the highest possible efficiency. Alternatively, two-stage conversion (stepping down the 5V system supply instead of the battery) at a higher switching frequency allows the minimum possible physical size. The MAX1844 is intended for CPU core, chipset, DRAM, or other low-voltage supplies as low as 1V. It is available in 20-pin QSOP, and QFN packages and includes both adjustable overvoltage and undervoltage protection. ♦ 1.8V/2.5V Fixed or 1V to 5.5V Adjustable Output Range For a dual step-down PWM controller with accurate current limit, refer to the MAX1845. The MAX1714/ MAX1715 single/dual PWM controllers are similar to the MAX1844/ MAX1845 but do not use current-sense resistors. Applications Notebook Computers ♦ Accurate Current-Limit Option ♦ Quick-PWM with 100ns Load-Step Response ♦ 1% VOUT Accuracy Over Line and Load ♦ 2V to 28V Battery Input Range ♦ 200/300/450/600kHz Switching Frequency ♦ Adjustable Overvoltage Protection ♦ Adjustable Undervoltage Protection ♦ 1.7ms Digital Soft-Start ♦ Drives Large Synchronous-Rectifier FETs ♦ 2V ±1% Reference Output ♦ Power-Good Window Comparator Ordering Information TEMP RANGE PIN-PACKAGE MAX1844EEP PART -40°C to +85°C 20 QSOP MAX1844EGP* -40°C to +85°C 20 QFN MAX1844ETP -40°C to +85°C 20 Thin QFN Minimal Operating Circuit BATTERY 4.5V TO 28V 5V INPUT VCC SHDN UVP BST ILIM CPU Core Supplies Chipset/RAM Supplies as Low as 1V VDD V+ DH MAX1844 LX REF 1.8V and 2.5V Supplies OUTPUT 2.5V DL PGOOD CS LATCH *Contact factory for availability. OUT OVP FB SKIP Quick-PWM is a trademark of Maxim Integrated Products. Pin Configuration appears at end of data sheet. GND ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX1844 General Description The MAX1844 pulse-width modulation (PWM) controller provides high efficiency, excellent transient response, and high DC output accuracy needed for stepping down high-voltage batteries to generate low-voltage CPU core or chipset/RAM supplies in notebook computers. MAX1844 High-Speed Step-Down Controller with Accurate Current Limit for Notebook Computers ABSOLUTE MAXIMUM RATINGS V+ to GND ..............................................................-0.3V to +28V VCC, VDD to GND .....................................................-0.3V to +6V OUT, PGOOD, SHDN to GND ..................................-0.3V to +6V FB, ILIM, LATCH, OVP, REF, SKIP, TON, UVP to GND ..................................-0.3V to (VCC + 0.3V) BST to GND ............................................................-0.3V to +34V CS to GND.................................................................-6V to +30V DL to GND ..................................................-0.3V to (VDD + 0.3V) DH to LX .....................................................-0.3V to (BST + 0.3V) LX to BST..................................................................-6V to +0.3V REF Short Circuit to GND ...........................................Continuous Continuous Power Dissipation (TA = +70°C) 20-Pin QSOP (derate 9.1mW/°C above +70°C)...........727mW 20-Pin 5mm ✕ 5mm QFN (derate 20.0mW/°C above +70°C).................................................................1.60W Operating Temperature Range ...........................-40°C to +85°C Junction Temperature ......................................................+150°C Storage Temperature Range .............................-65°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C 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+ = 15V, VCC = VDD = 5V, SKIP = GND, TA = 0°C to +85°C, unless otherwise noted. Typical values are at TA = +25°C.) PARAMETER Input Voltage Range CONDITIONS MIN Battery voltage, V+ VCC , VDD TYP MAX 2 28 4.5 5.5 FB = OUT 0.99 FB = GND 2.475 2.5 2.525 FB = VCC 1.782 1.8 1.818 UNITS V 1.01 Error Comparator Threshold (DC Output Voltage Accuracy) (Note 1) V+ = 4.5V to 28V, SKIP = VCC Load Regulation Error ILOAD = 0 to 3A, SKIP = VCC 9 mV Line Regulation Error VCC = 4.5V to 5.5V, V+ = 4.5V to 28V 5 mV FB Input Bias Current Output Adjustment Range OUT Input Resistance Soft-Start Ramp Time On-Time -0.1 +0.1 µA 1 5.5 V FB = GND 90 190 350 FB = VCC or adjustable feedback mode 70 145 270 TON = GND (600kHz) 140 160 180 TON = REF (450kHz) 175 200 225 TON = unconnected (300kHz) 260 290 320 TON = VCC (200kHz) 380 425 470 Rising edge of SHDN to full current limit V+ = 24V, VOUT = 2V (Note 2) V 1.7 kΩ ms ns Minimum Off-Time (Note 2) 400 500 ns Quiescent Supply Current (VCC) FB forced above the regulation point 550 800 µA Quiescent Supply Current (VDD) FB forced above the regulation point