MAX1954A 19-3154 Rev 1 5/05 Low-Cost, Current-Mode PWM Buck Controller with Foldback Current Limit General Description Features The MAX1954A synchronous current-mode, pulse- Current-Mode Controller width modulation (PWM) buck controller is pin compati- Fixed-Frequency PWM ble with the popular MAX1954 and is suitable for applications where cost and size are critical. Foldback Current Limit The MAX1954A operates from an input voltage range of Output Down to 0.8V with 1% FB Accuracy 3.0V to 13.2V, independent of the IC supply. The output voltage is adjustable down to 0.8V. The IC operates at 3.0V to 13.2V Input Voltage a fixed 300kHz switching frequency and provides up to 300kHz Switching Frequency 25A of output current with efficiency up to 95%. This controller has excellent transient response resulting in 25A Output-Current Capability smaller output capacitance. 93% Efficiency The MAX1954A features foldback current limiting that All-N-Channel-MOSFET Design for Low Cost greatly reduces input current and component power dissipation during output overload or short-circuit No Current-Sense Resistor Needed conditions. Internal Digital Soft-Start The compensation and shutdown control (COMP) input, in addition to providing compensation to the error Small 10-Pin MAX Package amplifier, can be pulled low to shut down the converter. An input undervoltage lockout is provided to ensure proper operation during power sags to prevent the external power MOSFETs from overheating. Internal digital soft-start is included to reduce inrush current and save an external capacitor. The MAX1954A is available in a tiny 10-pin MAX package to minimize PC board space. Applications Ordering Information Printers and Scanners PART TEMP RANGE PIN-PACKAGE Graphic Cards and Video Cards MAX1954AEUB -40C to +85C 10 MAX MAX1954AEUB+ -40C to +85C 10 MAX PCs and Servers +Denotes lead-free package. Microprocessor Cores Low-Voltage Distributed Power Telecom/Networks Pin Configuration TOP VIEW HSD 1 10 BST COMP 2 9 LX MAX1954A FB 3 8 DH GND 4 7 PGND IN 5 6 DL MAX MAX is a registered 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. EVALUATION KIT AVAILABLELow-Cost, Current-Mode PWM Buck Controller with Foldback Current Limit ABSOLUTE MAXIMUM RATINGS IN, FB to GND...........................................................-0.3V to +6V Continuous Power Dissipation (T = +70C) A LX to BST..................................................................-6V to +0.3V 10-Pin MAX (derate 5.6mW/C above +70C) ...........444mW BST to GND............................................................-0.3V to +20V Operating Temperature Range ...........................-40C to +85C DH to LX................................................... -0.3V to (V + 0.3V) Junction Temperature......................................................+150C BST DL, COMP to GND.......................................-0.3V to (V + 0.3V) Storage Temperature Range............................+65C to +150C IN HSD to GND..............................................................-0.3V to 14V Lead Temperature (soldering, 10s) .................................+300C PGND to GND .......................................................-0.3V to +0.3V 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 = 5V, V - V = 5V, T = 0C to +85C, unless otherwise noted.) IN BST LX A PARAMETER CONDITIONS MIN TYP MAX UNITS GENERAL Operating Input Voltage Range 3.0 5.5 V HSD Voltage Range (Note 1) 3.0 13.2 V Quiescent Supply Current V = 1.5V 1 2 mA FB V = V = 5.5V, V = 13.2V, LX = unconnected, IN BST HSD Standby Supply Current 2 mA COMP = GND Undervoltage-Lockout Trip Level Falling V , 50mV (typ) hysteresis 2.5 2.7 2.9 V IN DC-DC CONTROLLER Output-Voltage Adjust Range Maximum output voltage depends on external components 0.8 V (V ) and maximum duty cycle OUT ERROR AMPLIFIER FB Regulation Voltage -1.0 +0.8 +1.0 % Transconductance 70 110 160 S Voltage Gain 200 V/ V FB Input Leakage Current V = 0.9V 50 500 NA FB FB Input Common-Mode Range -0.1 +1.5 V COMP Output-Voltage Swing 0.80 2.36 V Current-Sense Amplifier 3.15 3.5 3.85 V / V Voltage Gain V = 0.8V 110 135 145 FB Current-Limit Threshold V - V mV PGND LX V = 0V 21 36 51 FB OSCILLATOR Switching Frequency MAX1954A 240 300 360 kHz Maximum Duty Cycle Measured at DH 89 91 93 % Minimum Duty Cycle V = 1.25V, LX = GND, V = V = 3.3V 2.5 3 % COMP BST IN 2 MAX1954A