LT1940/LT1940L Dual Monolithic 1.4A, 1.1MHz Step-Down Switching Regulator FEATURES DESCRIPTIO n Wide Input Voltage Range The LT 1940 is a dual current mode PWM step-down LT1940: 3.6V to 25V DC/DC converter with internal 2A power switches. Both con- LT1940L: 3.6V to 7V verters are synchronized to a single 1.1MHz oscillator and n Two 1.4A Output Switching Regulators with run with opposite phases, reducing input ripple current. The Internal Power Switches output voltages are set with external resistor dividers, and n Constant 1.1MHz Switching Frequency each regulator has independent shutdown and soft-start n Anti-Phase Switching Reduces Ripple circuits. Each regulator generates a power-good signal n Independent Shutdown/Soft-Start Pins when its output is in regulation, easing power supply se- n Independent Power Good Indicators Ease quencing and interfacing with microcontrollers and DSPs. Supply Sequencing The LT1940s 1.1MHz switching frequency allows the use n Uses Small Inductors and Ceramic Capacitors of tiny inductors and capacitors, resulting in a very small n Small 16-Lead Thermally Enhanced dual 1.4A output solution. Constant frequency and ceramic TSSOP Surface Mount Package capacitors combine to produce low, predictable output U ripple voltage. With its wide input range of 3.6V to 25V, the APPLICATIO S LT1940 regulates a wide variety of power sources, from n Disk Drives 4-cell batteries and 5V logic rails to unregulated wall trans- n DSP Power Supplies formers, lead acid batteries and distributed-power supplies. n Wall Transformer Regulation The LT1940L is intended to operate from regulated 5V n Distributed Power Regulation supplies. A current mode PWM architecture provides fast n DSL Modems transient response with simple compensation components n Cable Modems and cycle-by-cycle current limiting. Frequency foldback and thermal shutdown provide additional protection. , LTC and LT are registered trademarks of Linear Technology Corporation. TYPICAL APPLICATIO V IN 7V TO 25V 4.7F V CMDSH-3 CMDSH-3 IN Efficiency vs Load Current OUT2 5V BOOST1 BOOST2 100 1.4A V = 12V IN LT1940 0.1F 0.1F 3.3H 4.7H OUT1 90 3.3V SW1 SW2 1.4A V = 5V OUT UPS140 UPS140 16.5k 30.1k 80 FB1 FB2 V = 3.3V OUT V V C1 C2 70 10.0k 15k RUN/SS1 PG1 15k 10.0k 10F 330pF RUN/SS2 PG2 10F 60 330pF GND 100k 1nF 0 0.5 1.0 1.5 LOAD CURRENT (A) POWER 1940 F01b 1940 F01 GOOD Figure 1. 3.3V and 5V Dual Output Step-Down Converter with Output Sequencing (LT1940) 1940fa 1 EFFICIENCY (%) U ULT1940/LT1940L UUW ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) TOP VIEW ORDER PART V Voltage IN NUMBER 1 BOOST1 16 FB1 LT1940 .................................................... (0.3), 25V 2 SW1 15 V C1 LT1940L ................................................... (0.3), 7V LT1940EFE 3 V 14 PG1 IN BOOST Pin Voltage LT1940LEFE 4 V 13 RUN/SS1 IN 17 LT1940 ................................................................ 35V 5 V 12 RUN/SS2 IN LT1940L ............................................................. 16V 6 V 11 PG2 IN BOOST Pin Above SW Pin FE PART SW2 7 10 V C2 LT1940 ................................................................ 25V MARKING BOOST2 8 9 FB2 LT1940L ............................................................. 16V FE PACKAGE 1940EFE PG Pin Voltage 16-LEAD PLASTIC TSSOP EXPOSED PAD (PIN 17) IS GND 1940LEFE LT1940 ................................................................ 25V MUST BE SOLDERED TO PCB T = 125 C, q = 45 C/W, q = 10 C/W LT1940L ............................................................... 7V JMAX JA JC SW Voltage ................................................................V IN Consult LTC Marketing for parts specified with wider operating temperature ranges. RUN/SS, FB Pins ...................................................... 6V Maximum Junction Temperature .......................... 125 C Operating Temperature Range (Note 2) ...40 C to 85 C Storage Temperature Range ..................65 C to 150 C Lead Temperature (Soldering, 10 sec).................. 300 C ELECTRICAL CHARACTERISTICS The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25 C. V = 5V, V = 8V unless otherwise noted. (Note 2) A IN BOOST PARAMETER CONDITIONS MIN TYP MAX UNITS Minimum Operating Voltage l 3.4 3.6 V Quiescent Current Not Switching 3.8 4.8 mA Shutdown Current V = 0V 30 45 m A RUNSS Feedback Voltage 1.230 1.250 1.270 V 0 C to 70 C l 1.225 1.250 1.270 V 40 C to 85 C l 1.215 1.250 1.270 V FB Pin Bias Current V = 1.25V, V = 0.4V l 240 1200 nA FB C Reference Line Regulation LT1940: V 5V to 25V 0.005 %/V IN LT1940L: V 4V to 7V 0.005 %/V IN Error Amp GM 330 uMhos Error Amp Voltage Gain 180 V Source Current V = 1V 42 m A C FB V Sink Current V = 1.5V 60 m A C FB V Pin to Switch Current Gain 2.4 A/V C V Switching Threshold 0.75 V C V Clamp Voltage 1.8 V C Switching Frequency V = 1.1V 1 1.1 1.25 MHz FB l 0.95 1.1 1.35 MHz Switching Phase 150 180 210 Deg Maximum Duty Cycle l 78 88 % Frequency Shift Threshold on FB f = 1MHz 0.5 V SW 1940fa 2 U WWW