MAX1927/MAX1928 19-2527 Rev 0 7/02 Low-Output-Voltage, 800mA, PWM Step-Down DC-DC Converters General Description Features The MAX1927/MAX1928 800mA step-down converters 800mA Output Current power low-voltage microprocessors in compact equip- Output Voltages from 0.75V to 5V ment requiring the highest possible efficiency. The MAX1927/MAX1928 are optimized for generating low 2.6V to 5.5V Input Voltage Range output voltages (down to 750mV) at high efficiency Power-OK Output using small external components. The supply voltage range is from 2.6V to 5.5V and the guaranteed minimum No Schottky Diode Required output current is 800mA. 1MHz pulse-width modulation Selectable Forced PWM Operation (PWM) switching allows for small external components. A unique control scheme minimizes ripple at light loads, 1MHz Fixed-Frequency PWM Operation while maintaining a low 140A quiescent current. 140A Quiescent Current The MAX1927/MAX1928 include a low on-resistance internal MOSFET switch and synchronous rectifier to Soft-Start maximize efficiency and minimize external component 10-Pin MAX Package count. No external diode is needed. 100% duty-cycle operation allows for a dropout voltage of only 340mV at 800mA. Other features include internal soft-start, power-OK (POK) output, and selectable forced PWM operation for lower noise at all load currents. The MAX1928 is available with several preset output Ordering Information voltages: 1.5V (MAX1928-15), 1.8V (MAX1928-18), and 2.5V (MAX1928-25). The MAX1927R has adjustable PRESET TEMP PIN- output range down to 0.75V. The MAX1927/MAX1928 PART OUTPUT RANGE PACKAGE are available in a tiny 10-pin MAX package. VOLTAGE MAX1927REUB Adj. to 0.75V -40C to +85C 10 MAX MAX1928EUB15 1.5V -40C to +85C 10 MAX Applications MAX1928EUB18 1.8V -40C to +85C 10 MAX WCDMA Handsets MAX1928EUB25 2.5V -40C to +85C 10 MAX PDAs and Palmtops DSP Core Power Battery-Powered Equipment Pin Configuration Typical Operating Circuit V IN 2.6V TO 5.5V PWM TOP VIEW BATT V OUT L1 C1 0.75V AT 800mA LX PWM 1 10 POK SHDN C2 FB GND 2 9 BATT R C MAX1927R MAX1927R COMP REF 3 8 LX MAX1928 POK C C C f FB 4 7 PGND COMP 5 6 SHDN PGND REF MAX GND 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.Low-Output-Voltage, 800mA, PWM Step-Down DC-DC Converters ABSOLUTE MAXIMUM RATINGS Operating Temperature Range ...........................-40C to +85C BATT, PWM, POK, COMP, SHDN to GND ...............-0.3V to +6V Junction Temperature......................................................+150C PGND to GND .......................................................-0.3V to +0.3V LX, REF, FB to GND ................................-0.3V to (V + 0.3V) Storage Temperature Range .............................-65C to +150C BATT Lead Temperature (soldering, 10s) .................................+300C Continuous Power Dissipation (T = +70C) A 10-Pin MAX (derate 5.6mW/C above +70C) ...........444mW 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 = 3.6V, SHDN = BATT, C = 0.1F, T = 0C to +85C, unless otherwise noted. Typical values are at T = +25C.) BATT REF A A PARAMETER CONDITIONS MIN TYP MAX UNITS BATT Input Voltage 2.6 5.5 V 2.55 Undervoltage Lockout Threshold V rising or falling (35mV hysteresis) 2.15 2.35 V BATT No load, pulse skipping, PWM = GND 140 240 A Quiescent Current 1MHz switching 2 mA Quiescent Current in Dropout 190 340 A Shutdown Supply Current SHDN = GND 0.1 10 A REFERENCE AND ERROR AMP MAX1927R 0.738 0.75 0.762 MAX1928-15 1.477 1.5 1.523 FB Voltage Accuracy V MAX1928-18 1.773 1.8 1.827 MAX1928-25 2.462 2.5 2.538 MAX1928 5 10 15 A FB Input Current MAX1927R 10 150 nA MAX1927R 250 MAX1928-15 210 S Transconductance (g ) m MAX1928-18 175 MAX1928-25 125 Reference Voltage Accuracy 1.231 1.25 1.269 V Reference Supply Rejection 2.6V < V < 5.5V 0.5 2 mV BATT PWM CONTROLLER V = 3.6V 0.25 0.4 BATT P-Channel On-Resistance V = 2.6V 0.3 0.5 BATT V = 3.6V 0.17 0.3 BATT N-Channel On-Resistance V = 2.6V 0.2 0.35 BATT Current-Sense Transresistance (R ) 0.48 V/A CS P-Channel Current-Limit Threshold 1.1 1.3 1.6 A P-Channel Pulse-Skipping Current Threshold 0.11 0.13 0.15 A N-Channel Negative Current-Limit Threshold -0.55 A 2 MAX1927/MAX1928