LT1941 Triple Monolithic Switching Regulator FEATURES DESCRIPTION n Wide Input Range: 3.5V to 25V The LT 1941 is a triple current mode DC/DC converter n Three Switching Regulators with Internal Power with internal power switches. Two of the regulators are Switches: 3A Step-Down, 2A Step-Down, step-down converters with 3A and 2A power switches. 1.5A Inverting/Boost The third regulator can be con gured as a boost, inverter n Antiphase Switching Reduces Ripple or SEPIC converter and has a 1.5A power switch. All n Independent Shutdown/Soft-Start Pins three converters are synchronized to a 1.1MHz oscillator. n Independent Power Good Indicators Ease Supply The two step-down converters run with opposite phase, Sequencing reducing input ripple current. The output voltages are n Input Voltage Power Good Indicators Monitor Input set with external resistor dividers and each regulator Supply has independent shutdown and soft-start circuits. Each n Uses Small Inductors and Ceramic Capacitors regulator generates a power good signal when its output n Constant 1.1MHz Switching Frequency is in regulation, easing power supply sequencing and n Thermally Enhanced 28-Lead TSSOP Package interfacing with microcontrollers and DSPs. The high switching frequency offers several advantages APPLICATIONS by permitting the use of small inductors and ceramic capacitors, leading to a very small triple output solution. n Cable Modems The constant switching frequency, combined with low n DSL Modems impedance ceramic capacitors, result in low, predictable n Distributed Power Regulation output ripple. With its wide input voltage range of 3.5V to n Wall Transformer Regulation 25V, the LT1941 regulates a broad array of power sources n Disk Drives from 4-cell batteries and 5V logic rails to unregulated wall n DSP Power transformers, lead acid batteries and distributed-power L, LT, LTC and LTM are registered trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. supplies. TYPICAL APPLICATION V V OUT1 OUT2 V IN 4.7V TO 14V 130k 100k 100k 100k 100k V IN PGOOD1 PGOOD1 Start-Up Waveforms 5GOOD 5GOOD PGOOD2 PGOOD2 with Sequencing 12GOOD 12GOOD PGOOD3 PGOOD3 BOOST1 BOOST2 0.22F 0.22F 3H LT1941 3.3H V RUN/SS OUT1 2V/DIV 1.8V SW1 SW2 V 13.7k 10.7k OUT2 2.4A V FB1 FB2 3.3V OUT1 3300pF 1000pF 1.4A 2V/DIV V V C1 C2 33F 22F V OUT2 10k 2.49k 7.32k 3.3k 5V/DIV 1.5nF 1.5nF RUNSS1 RUNSS2 V OUT3 SW3 BIAS1 10V/DIV 22H 22nF 1F NFB BIAS2 I V VIN(AVE) OUT3 13.7k V 1A/DIV 133k C3 12V 22H 350mA* PGOOD2 FB3 RUNSS3 1.5k 5V/DIV GND 1.5nF 1941 F01b 2ms/DIV 10F 10F 1941 F01 *240mA AT V = 5V, 550mA AT V = 12V IN IN Figure 1. Triple Output Power Supply: 3.3V, 1.8V, 12V 1941fb 1LT1941 ABSOLUTE MAXIMUM RATINGS PIN CONFIGURATION (Note 1) TOP VIEW V Pin ........................................................(0.3V), 25V IN V 1 28 BIAS2 IN BOOST Pin Voltage ...................................................35V V 2 27 SW3 IN BOOST Above SW Pin ...............................................25V SW1 3 26 PGND BIAS1, BIAS2 Pins ....................................................25V SW1 4 25 V IN PGOOD, 5GOOD, 12GOOD Pins .................................25V BOOST1 5 24 BOOST2 RUN/SS, V , FB, NFB Pins ..........................................3V C PGOOD1 6 23 SW2 SW1, SW2 Voltage .....................................................V IN V 7 22 V IN C1 29 SW3 Voltage .............................................................40V FB1 8 21 PGOOD3 Maximum Junction Temperature (Note 6) ............ 125C PGOOD2 9 20 FB3 V 10 19 NFB Operating Ambient Temperature Range C2 FB2 11 18 V C3 (Note 2) ....................................................40C to 85C RUN/SS1 12 17 5GOOD Storage Temperature Range .................. 65C to 150C RUN/SS2 13 16 12GOOD Lead Temperature (Soldering, 10 sec)...................300C RUN/SS3 14 15 BIAS1 FE PACKAGE 28-LEAD PLASTIC TSSOP T = 125C, = 25C/W JMAX JA EXPOSED PAD (PIN 29) IS GND, MUST BE SOLDERED TO PCB ORDER INFORMATION LEAD FREE FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT1941EFE PBF LT1941EFE TRPBF LT1941EFE 28-LEAD PLASTIC TSSOP 40C to 85C LEAD BASED FINISH TAPE AND REEL PART MARKING PACKAGE DESCRIPTION TEMPERATURE RANGE LT1941EFE LT1941EFE TR LT1941EFE 28-LEAD PLASTIC TSSOP 40C to 85C Consult LTC Marketing for parts speci ed with wider operating temperature ranges. For more information on lead free part marking, go to: