MAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 General Description Features The MAX1920/MAX1921 step-down converters deliver 400mA Guaranteed Output Current over 400mA to outputs as low as 1.25V. These converters Internal Synchronous Rectifier for > 90% Efficiency use a unique proprietary current-limited control scheme Tiny 6-Pin SOT23 Package that achieves over 90% efficiency. These devices maintain extremely low quiescent supply current (50A), and their Available in 6-Pin TDFN Package (MAX1920) high 1.2MHz (max) operating frequency permits small, Up to 1.2MHz Switching Frequency for Small low-cost external components. This combination makes External Components the MAX1920/MAX1921 excellent high-efficiency alterna- 50A Quiescent Supply Current tives to linear regulators in space-constrained applications. 0.1A Logic-Controlled Shutdown Internal synchronous rectification greatly improves effi- 2V to 5.5V Input Range ciency and eliminates the external Schottky diode required in conventional step-down converters. Both devices also Fixed 1.5V, 1.8V, 2.5V, 3V, and 3.3V Output include internal digital soft-start to limit input current upon Voltages (MAX1921) startup and reduce input capacitor requirements. Adjustable Output Voltage (MAX1920) The MAX1920 provides an adjustable output voltage 1.5% Initial Accuracy (1.25V to 4V). The MAX1921 provides factory-preset Soft-Start Limits Startup Current output voltages (see the Selector Guide). Both are available in space-saving 6-pin SOT23 packages. The Ordering Information MAX1920 is also available in a 6-pin TDFN package. PART TEMP RANGE PIN-PACKAGE MAX1920EUT-T -40C to +85C 6 SOT23-6 Applications MAX1920EUT+T -40C to +85C 6 SOT23-6 Next-Generation Wireless Handsets PDAs, Palmtops, and Handy-Terminals MAX1920ETT-T -40C to +85C 6 TDFN Battery-Powered Equipment MAX1920ETT+T -40C to +85C 6 TDFN CDMA Power Amplifier Supply MAX1921EUT -T -40C to +85C 6 SOT23-6 MAX1921EUT +T -40C to +85C 6 SOT23-6 Note: The MAX1921 offers five preset output voltage options. See the Selector Guide, and then insert the proper designator into the blanks above to complete the part number. +Denotes a lead-free package. Pin Configuration Typical Operating Circuit TOP VIEW INPUT OUTPUT 6 5 4 4.7H 2V TO 5.5V 1.5V UP TO 400mA IN 1 6 LX IN LX 4.75k C 4.7F IN MAX1920 MAX1921 MAX1920 AGND 2 5 PGND MAX1921 5600pF AGND PGND SHDN 3 4 OUT (FB) 1 2 3 ON SOT23-6 SHDN OUT OFF TDFN ( ) ARE FOR MAX1920 ONLY A SIGN WILL REPLACE THE FIRST PIN INDICATOR ON LEAD-FREE PACKAGES. 19-2296 Rev 3 8/05 AGND SHDN IN FB PGND LXMAX1920/MAX1921 Low-Voltage, 400mA Step-Down DC-DC Converters in SOT23 Absolute Maximum Ratings IN, FB, SHDN to AGND ........................................... -0.3V to +6V Operating Temperature Range ........................... -40C to +85C OUT to AGND, LX to PGND.........................-0.3V to (IN + 0.3V) Junction Temperature ......................................................+150C AGND to PGND ....................................................-0.3V to +0.3V Storage Temperature ........................................ -65C to +150C OUT Short Circuit to GND ..................................................... 10s Lead Temperature (soldering, 10s) .................................+300C Continuous Power Dissipation (T = +70C) A 6-Pin SOT23-6 (derate 8.7mW/C above +70C) .......695mW 6-Pin TDFN (derate 18.2mW/C above +70C) .....1454.5mW 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 = IN, T = 0C to +85C. Typical parameters are at T = +25C, unless otherwise noted.) (Note 1) IN A A PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS I(LX) < 400mA 2.5 5.5 Input Voltage Range V V IN I(LX) < 200mA 2.0 2.5 (MAX1921EUT15, MAX1921EUT18) Startup Voltage 2.0 V V rising 1.85 1.95 IN UVLO Threshold UVLO V V falling 1.50 1.65 IN UVLO Hysteresis 200 mV Quiescent Supply Current I No switching, no load 50 70 A IN Quiescent Supply Current Dropout I SHDN = IN, OUT/FB = 0 220 300 A IN Shutdown Supply Current I SHDN = GND 0.1 4.0 A SHDN I = 0, T = +25C -1.5 +1.5 OUT A Output Voltage Accuracy I = 0 to 400mA, T = -40C to +85C -3 +3 % OUT A (MAX1921) I = 0 to 200mA, T = -40C to +85C -3 +3 OUT A SHDN = 0 1 OUT BIAS Current I A OUT OUT at regulation voltage 8 16 Output Voltage Range Figure 4, IN = 4.5V 1.25 4.00 V (MAX1920) T = +25C 1.231 1.25 1.269 A FB Feedback Threshold V 1.220 1.25 1.280 V FB (MAX1920) T = -40C to +85C 1.210 1.280 A FB Feedback Hysteresis V 5 mV HYS (MAX1920) FB Bias Current (MAX1920) I FB = 1.5V 0.01 0.20 A FB Load Regulation I = 0 to 400mA 0.005 %/mA OUT Line Regulation V = 2.5V to 5.5V 0.2 %/V IN SHDN Input Voltage High V 1.6 V IH SHDN Input Voltage Low V 0.4 V IL SHDN Leakage Current I SHDN = GND or IN 0.001 1.000 A SHDN High-Side Current Limit I 525 730 950 mA LIMP Maxim Integrated 2 www.maximintegrated.com