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Part: MAX1844
Category:
Power Management
-> Regulators
-> Switching Regulators
Description: High-speed Step-down Controller With Accurate Current Limit For Notebook Computers
Company: Maxim Integrated Products
Datasheet: Download MAX1844 datasheet File size : 505 kB
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Datasheet text preview:
19-1993; Rev 3; 9/02
High-Speed Step-Down Controller with Accurate Current Limit for Notebook Computers MAX1844
General Description
The MAX1844 pulse-width modulation (PWM) controller provides high efficiency, excellent transient response, a n d high DC output accuracy needed for stepping down high-voltage batteries to generate low-voltage CPU core or chipset/RAM supplies in notebook computers. M a x i m ' s proprietary Quick-PWMTM quick-response, constant-on-time PWM control scheme handles wide i n p u t / o u t p u t 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. T h e MAX1844 is intended for CPU core, chipset, DRAM, or other low-voltage supplies as low as 1V. It is a v a i l a b l e in 20-pin QSOP, and QFN packages and includes both adjustable overvoltage and undervoltage protection. 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. o Ultra-High Efficiency o Accurate Current-Limit Option o Quick-PWM with 100ns Load-Step Response o 1% VOUT Accuracy Over Line and Load o 1.8V/2.5V Fixed or 1V to 5.5V Adjustable Output Range o 2V to 28V Battery Input Range o 200/300/450/600kHz Switching Frequency o Adjustable Overvoltage Protection o Adjustable Undervoltage Protection o 1.7ms Digital Soft-Start o Drives Large Synchronous-Rectifier FETs o 2V ±1% Reference Output o Power-Good Window Comparator
KIT ATION EVALU LABLE AVAI
Features
Ordering Information
PART MAX1844EEP MAX1844EGP* MAX1844ETP TEMP RANGE -40°C to +85°C -40°C to +85°C -40°C to +85°C PIN-PACKAGE 20 QSOP 20 QFN 20 Thin QFN
Minimal Operating Circuit
BATTERY 4.5V TO 28V 5V INPUT VCC SHDN UVP ILIM BST DH MAX1844 LX REF DL PGOOD LATCH CS OUT SKIP GND OUTPUT 2.5V VDD V+
Applications
Notebook Computers CPU Core Supplies Chipset/RAM Supplies as Low as 1V 1.8V and 2.5V Supplies
*Contact factory for availability. Quick-PWM is a trademark of Maxim Integrated Products. Pin Configuration appears at end of data sheet.
OVP FB
________________________________________________________________ Maxim Integrated Products
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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.
High-Speed Step-Down Controller with Accurate Current Limit for Notebook Computers MAX1844
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 Error Comparator Threshold (DC Output Voltage Accuracy) (Note 1) Load Regulation Error Line Regulation Error FB Input Bias Current Output Adjustment Range OUT Input Resistance Soft-Start Ramp Time FB = GND FB = VCC or adjustable feedback mode Rising edge of SHDN to full current limit TON = GND (600kHz) On-Time V+ = 24V, VOUT = 2V (Note 2) (Note 2) FB forced above the regulation point FB forced above the regulation point SHDN = GND SHDN = GND SHDN = GND, V+ = 28V, VCC = VDD = 0 or 5V VCC = 4.5V to 5.5V, no external REF load IREF = 0 to 50µA 1.98 TON = REF (450kHz) TON = unconnected (300kHz) TON = VCC (200kHz) Minimum Off-Time Quiescent Supply Current (VCC) Quiescent Supply Current (VDD) Quiescent Supply Current (V+) Shutdown Supply Current (VCC) Shutdown Supply Current (VDD) Shutdown Supply Current (V+) Reference Voltage Reference Load Regulation 140 175 260 380 Battery voltage, V+ VCC , VDD FB = OUT V+ = 4.5V to 28V, SKIP = VCC ILOAD = 0 to 3A, SKIP = VCC VCC = 4.5V to 5.5V, V+ = 4.5V to 28V -0.1 1 90 70 190 145 1.7 160 200 290 425 400 550 <1 25 <1 <1 <1 2.00 180 225 320 470 500 800 5 40 5 5 5 2.02 0.01 ns µA µA µA µA µA µA V V ns FB = GND FB = VCC CONDITIONS MIN 2 4.5 0.99 2.475 1.782 2.5 1.8 9 5 +0.1 5.5 350 270 TYP MAX 28 5.5 1.01 2.525 1.818 mV mV µA V k ms V UNITS V
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High-Speed Step-Down Controller with Accurate Current Limit for Notebook Computers
ELECTRICAL CHARACTERISTICS (continued)
(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 REF Sink Current REF Fault Lockout Voltage Overvoltage Trip Threshold (Fixed-Threshold Mode) REF in regulation Falling edge, hysteresis = 40mV With respect to error comparator threshold, no load OVP = GND, rising edge, hysteresis = 1% External feedback, measured at FB with respect to VOVP, 1V < VOVP < 1.8V, rising edge, hysteresis =1% Overvoltage Comparator Offset (Adjustable-Threshold Mode) Internal feedback, measured at OUT with respect to the nominal OUT regulation voltage, 1V < VOVP < 1.8V, rising edge, hysteresis = 1% 1V < VOVP < 1.8V FB forced 2% above trip threshold 12 -30 CONDITIONS MIN 10 1.6 14.5 17 +30 TYP MAX UNITS µA V % mV
MAX1844
-3.5 -100 0 1.5
+3.5 +100
% nA µs
OVP Input Leakage Current Overvoltage Fault Propagation Delay Output Undervoltage Protection Trip Threshold (Fixed-Threshold Mode) Output Undervoltage Protection Trip Threshold (AdjustableThreshold Mode) UVP Input Leakage Current Output Undervoltage Protection Blanking Time PGOOD Trip Threshold (Lower) PGOOD Trip Threshold (Upper) PGOOD Propagation Delay PGOOD Output Low Voltage PGOOD Leakage Current ILIM Adjustment Range Current-Limit Threshold (Fixed) Current-Limit Threshold (Adjustable) Current-Limit Threshold (Negative Direction) Current-Limit Threshold (Zero Crossing) Thermal Shutdown Threshold VCC Undervoltage Lockout Threshold
With respect to error comparator threshold, UVP = VCC External feedback, measured at FB with respect to VUVP, 0.4V < VUVP < 1V Internal feedback, measured at OUT with respect to the nominal OUT regulation voltage, 0.4V < VUVP < 1V 0.4V < VUVP < 1V From rising edge of SHDN With respect to error comparator threshold, no load With respect to error comparator threshold, no load FB forced 2% beyond PGOOD trip threshold, falling ISINK = 1mA High state, forced to 5.5V
65
70
75
%
-40 -5 -100 10 -12.5 8 -10 10 10 <1
+40 +5 +100 30 -8 12.5 0.4 1
mV % nA ms % % µs V µA V mV mV mV mV °C
0.25 GND - VCS, ILIM = VCC GND - VCS VILIM = 0.5V VILIM = 2V 90 40 170 -140 100 50 200 -117 3 150 4.1
3 110 60 230 -95
GND - VCS, SKIP = VCC, ILIM = VCC ,TA = +25°C GND - VCS, SKIP = GND Hysteresis = 10°C Rising edge, hysteresis = 20mV, PWM disabled below this level
4.4
V
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