QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 621 1.25MHZ TRIPLE DC/DC CONVERTER LT1941 DESCRIPTION Demonstration circuit 621 is a 1.25MHz triple DC/DC switching converter using the LT1941. The LT1941 features fast switching speed, three internal power switches, and a wide input voltage range, making it a versatile and powerful IC that fits easily into spaceconstrained applications and removes the need for three separate DC/DC converters in triple output applications. The constant 1.1MHz switching frequency allows for the use of tiny, surface mount external components. The current-mode control topology yields fast transient response and good loop stability, requiring a minimum number of external compensation components and allowing the use of ceramic input and output capacitors. The anti-phase switching and single-IC solution reduces the input capacitance requirements from three separate capacitors to only two. The low resistance internal power switches maintain high efficiencies (typically 80% to 85%) over a wide range of input voltages and loads. Its 260µA shutdown current (activated by grounding all three of the RUN/SS pins) extends battery life. All three outputs have external adjustable soft-start capacitors to limit inrush current during turn-on. The wide VIN range of the LT1941 allows step-down, SEPIC, and boost configurations with up to 25V input. Power good terminals provide diagnostics for each output voltage (within 10% of final value) and the input voltage (within 10% of 5V and 12V). This board is designed for applications that require three outputs (two step-down supplies and a SEPIC or boost) with high load current in a small board space with low cost and low parts count as well as simple circuit design. The high current, on-board, triple monolithic switches eliminate the need for external switches. The use of ceramic capacitors in this circuit not only demonstrates small size and low cost, but the advantage of current-mode control in step-down, SEPIC, and boost applications with a simple compensation network for good stability and transient response. For optional adjustments in the output voltage, compensation, ripple, power good diagnostics, run/soft-start, and other aspects of LT1941 design, please consult the datasheet. With three outputs and internal power switches, this design can start to heat up under maximum load current and high ambient temperature conditions. Please consult the datasheet for thermal considerations, especially when altering the output voltage for much higher power DC/DC converters. Design files for this circuit board are available. Call the LTC factory. LT is a trademark of Linear Technology Corporation 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 621 1.25MHZ TRIPLE DC/DC CONVERTER Table 1. Typical Performance Summary (TA = 25°C) Parameter Conditions Value VIN 4.7V to 14V VOUT1 1.8V VOUT2 3.3V VOUT3 -12V VOUT1 Maximum Load Current 2.4A VOUT2 Maximum Load Current 1.4A VOUT3 Maximum Load Current VIN = 12V 550mA VIN = 5V 240mA VIN = 12V, IOUT1 = 1.2A, IOUT2 = 700mA, IOUT3 = 275mA 79% VIN = 5V, IOUT1 = 1.2A, IOUT2 = 700mA, IOUT3 = 120mA 82.5% VOUT1 ripple VIN = 12V, IOUT1 = 2.4A, IOUT2 = 0A, IOUT3 = 0A 25mV pk-pk VOUT2 ripple VIN = 12V, IOUT1 = 0A, IOUT2 = 1.4A, IOUT3 = 0A 10mV pk-pk VOUT3 ripple VIN = 12V, IOUT1 = 0A, IOUT2 = 0A, IOUT3 = 550mA 15mV pk-pk Zero-Load Quiescent Current IOUT1 = IOUT2 = IOUT3 = 0A, VIN = 12V 8mA Shutdown Quiescent Current RUN/SS1 = RUN/SS2 = RUN/SS3 = GND, VIN = 12V 260µA Efficiency 100 100 95 80 12V IN V O U T2 @ 700m A V O U T3 @ 275m A 75 70 5V IN V O U T1 @ 1200m A V O U T3 @ 120m A 90 E F F IC IE N C Y (%) 85 EFFICIENCY (%) 95 5V IN V O U T2 @ 700m A V O U T3 @ 120m A 90 65 85 80 75 65 60 60 55 55 50 12V IN V O U T1 @ 1200m A V O U T3 @ 275m A 70 50 0 500 1000 1500 2000 2500 VOUT1 LOAD CURRENT (mA) Figure 1. Typical Efficiency of Demo Circuit 621 LT1941 with varying load current on VOUT1 0 250 500 750 1000 1250 1500 V O U T 2 LO A D C U R R E N T (mA ) Figure 2. Typical Efficiency of Demo Circuit 621 LT1941 with varying load current on VOUT2 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 621 1.25MHZ TRIPLE DC/DC CONVERTER 100 95 E F F IC IE N C Y (%) 90 5V IN 85 80 12V IN 75 70 65 V O U T1 @ 1200m A V O U T2 @ 700m A 60 55 50 0 100 200 300 400 500 600 V O U T 3 LO A D C U R R E N T (mA ) Figure 4. Proper Measurement Equipment Setup OPTIONS Figure 3. Typical Efficiency of Demo Circuit 621 LT1941 with varying load current on VOUT3 QUICK START PROCEDURE Demonstration circuit 621 is easy to set up to evaluate the performance of the LT1941. Refer to Figure 5 for proper measurement equipment setup and follow the procedure below: 1. Connect the 4.7V–14V input power supply to the VIN and GND terminals. 2. After all connections are made, turn on input power and verify that the output voltages are 3.3V, 1.8V, and -12V. 3. The RUN/SS and Power Good functions are optional and their terminals can be left floating (disconnected) if their functions are not being used. Connecting a RUN/SS terminal to the GND terminal will disable the corresponding output. Connecting RUN/SS2 to the GND terminal will disable VOUT3 as well as VOUT2. POWER GOOD TERMINALS The power good terminals indicate the state of the three outputs and the input voltage. PGOOD1, PGOOD2, and PGOOD3 indicate when VOUT1, VOUT2, and VOUT3 are within 10% of their final values. PGOOD1 is pulled up to VIN and both PGOOD2 and PGOOD3 are pulled up to VOUT2. PGOOD3 is therefore dependent upon the state of VOUT2. 5GOOD and 12GOOD indicate when the input voltage is within 10% of 5V and 12V. Each has a pull-up resistor to VIN. The power good terminals are not valid if the input voltage is below 3.5V or if all three of the RUN/SS terminals are pulled low and the LT1941 is in shutdown. RUN / SOFT-START TERMINALS The run/soft-start terminals (RUN/SS1, RUN/SS2, RUN/SS3) are used to disable or enable the three outputs and to adjust soft-start for each output. C2, C4, 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 621 1.25MHZ TRIPLE DC/DC CONVERTER and C5 (1500pF) provide soft-start to all three outputs and can be easily adjusted. For normal operation (RUN), the terminals are left floating. In order to disable, or shutdown, an output stage, the RUN/SS terminal for that stage must be pulled to GND. If all three of the RUN/SS terminals are pulled to GND, the LT1941 enters micropower shutdown and the quiescent current drops to only 260µA at 12V input. Table 2. RUN/SS Terminal Logic Table RUN/SS1 RUN/SS2 RUN/SS3 VOUT1 VOUT2 VOUT3 n/c n/c n/c 1.8V 3.3V -12V GND n/c n/c 0V 3.3V -12V n/c GND n/c 1.8V 0V 0V n/c n/c GND 1.8V 3.3V 0V GND GND n/c 0V 0V 0V n/c GND GND 1.8V 0V 0V GND n/c GND 0V 3.3V 0V GND GND GND 0V 0V 0V R15 / R16 BIAS2 SOURCE The BIAS2 pin supplies the current to the driver of SW3. This pin is tied to the lowest available voltage source above 2.5V (VOUT2) for highest efficiency. R15 (0Ω) provides a direct connection from BIAS2 to VOUT2. BIAS2 can be tied directly to VIN if VOUT2 is not guaranteed to be available or if VOUT2 can be in shutdown when VOUT3 is required. By removing R15 and installing R16 (0Ω), BIAS2 is tied directly to VIN. R16 and R15 must never be installed simultaneously. Installing R16 will change the logic in Table 2 to reflect a direct correlation between RUN/SS3 and VOUT3; RUN/SS2 no longer affects VOUT3. 4 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 621 1.25MHZ TRIPLE DC/DC CONVERTER 5 5 4 3 2 ECO REV DESCRIPTION DATE PROTO 4 D APPROVED 02/23/04 D VIN TP3 TP4 PGOOD1 TP5 C13 0.1uF VOUT1 VOUT1 TP1 1.8V @2.4A GND 25 Pgood3 21 Pgood1 12Good 16 5 BOOST1 Pgood2 9 0.22uF R8 13.7k 1% 33uF 6.3V 5Good 6 BOOST2 D3 SW1 4 SW1 SW2 TP9 R6 2.2k C1 R7 7.32k 1% 3300pF 8 FB1 7 Vc1 12 TP14 C2 23 11 Vc2 10 RUN/SS2 13 L3 22uH B VOUT3 TP12 -12V 240mA@5VIN 550mA@12VIN L4 22uH C12 10uF 16V C11 1uF 35V R10 133k 1% D5 B130 27 SW3 19 NFb BIAS1 15 BIAS2 28 VC3 18 TP7 D2 R9 13.7k 1% RUN/SS3 20 GND TP11 D4 UPS120 0.22uF TP2 VOUT2 R14 10.7k 1% C10 R13 2.49k 1% C 3.3V @1.4A 22uF 6.3V GND TP10 RUN/SS2 1500pF TP15 R15 0 C3 22nF R11 1.5k VIN R16 B OPT RUN/SS3 14 TP16 C4 FB3 12GOOD PGOOD2 VOUT2 L1 3.3uH C6 1000pF R12 10k PGOOD3 1500pF 26 TP13 CMDSH-3 C14 15pF GND VIN RUN/SS1 1500pF R3 100k TP6 C5 RUN/SS1 R2 130k C7 FB2 B220A VOUT2 24 LT1941EFE 3 VIN R1 100k 17 C8 L2 3.0uH C9 U1 VIN3 5GOOD R4 100k 2 R5 100k CMDSH-3 VIN2 D1 VOUT2 22 VOUT1 VIN1 TP8 GND CIN2 4.7uF 16V 1 CIN1 10uF 16V 4.7V to 14V VIN0 VIN C 1 REVISION HISTORY This circuit is proprietary to Linear Technology and supplied for use with Linear Technology parts. Customer Notice:Linear Technology has made a best effort to design a circuit that meets customer-supplied specifications; however, it remains the customers responsibility to verify proper and reliable operation in the actual application, Component substitution and printed circuit board layout may significantly affect circuit performance or reliability. Contact Linear Applications Engineering for assistance. UNLESS OTHERWISE SPECIFIED DIMENSIONS ARE IN INCHES TOLERANCE ON ANGLE - - 2 PLACES - - - 3 PLACES - - INTERPRET DIM AND TOL PER ASME Y14.5M -1994 A THIRD ANGLE PROJECTION CONTRACT NO. APPROVALS DRAWN MEI DATE 10/24/02 CHECKED TECHNOLOGY TITLE DC/DC CONVERTER ENGINEER SIZE CAGE CODE Custom DO NOT SCALE DRAWING 5 4 3 Monday, April 19, 2004 A SCH, LT1941EFE 1.1MHz TRIPLE OUTPUT APPROVED DESIGNER 1630 McCarthy Blvd. Milpitas, CA 95035 Phone: (408)432-1900 Fax: (408)434-0507 SCALE:NONE 2 DWG NO REV 4 DC621A FILENAME: 621A-4.DSN SHEET 1 1 OF 1 Linear Technology Corporation LT1941EFE Item 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 Qty 1 1 1 3 1 1 2 1 1 1 1 1 1 2 1 1 1 1 1 2 4 1 1 1 2 1 1 1 1 1 1 0 16 1 Parts List Ref CIN1 CIN2 C1 C2,C4,C5 C3 C6 C8,C7 C9 C10 C11 C12 C13 C14 D2,D1 D3 D4 D5 L1 L2 L3,L4 R1,R3,R4,R5 R2 R6 R7 R9,R8 R10 R11 R12 R13 R14 R15 R16 TP1-TP16 U1 Desc CAP, X5R 10uF 16V 20% 1210 CAP, X5R 4.7uF 16V 10% 1206 CAP, X7R 3300pF 50V 10% 0402 CAP, X7R 1500pF 50V 5% 0402 CAP, X7R 22nF 25V 10% 0402 CAP, X7R 1000pF 10V 10% 0402 CAP, X5R 0.22uF 16V 20% 0603 CAP, X5R 33uF 6.3V 20% 1210 CAP, X5R 22uF 6.3V 20% 1206 CAP, X7R 1uF 35V 10% 1206 CAP, X7R 10uF 16V 20% 1206 CAP, X5R 0.1uF 10V 10% 0402 CAP, NPO 15pF 50V 5% 0402 DIODE,CMDSH-3 SOD323 DIODE, B220A SCHOTTKY RECTIFIER 2A DIODE, SCHOTTKY 20V 1A DIODE, B130 SCHOTTKY RECTIFIER 1.0A IND, 3.3uH IND, 3.0uH IND, 22uH RES, 100K OHMS 5% 1/16W 0402 RES, 130K OHMS 5% 1/16W 0402 RES, 2.2K OHMS 5% 1/16W 0402 RES, 7.32K OHMS 1% 1/16W 0402 RES, 13.7K OHMS 1% 1/16W 0402 RES, 133K OHMS 1% 1/16W 0402 RES, 1.5K OHMS 5% 1/16W 0402 RES, 10K OHMS 1% 1/16W 0402 RES, 2.49K OHMS 1% 1/16W 0402 RES, 10.7K OHMS 1% 1/16W 0402 RES, 0 OHM JUMPER 0402 OPTION TURRET IC, LT1941EFE 1 of 1 DC621A Rev 4 6/17/2005 Manufacturer / Part # TAIYO YUDEN EMK325BJ106MN-T TAIYO YUDEN EMK316BJ475KL AVX 04025C332KAT AVX 04025C152JAT TDK C1005X7R1E223K AVX 0402ZC102K AVX 0603YD224MAT TDK C3225X5R0J336ML TAIYO YUDEN JMK316BJ226KL TAIYO YUDEN GMK316BJ105KL TDK C3216X7R1C106M AVX 0402ZD104KAT AVX 04025A150JAT2A CENTRAL CMDSH-3-LTC DIODES INC. B220A MICROSEMI UPS120 DIODES INC. B130 SUMIDA CDRH5D28R-3R3 SUMIDA CDRH6D28-3R0 SUMIDA CDRH5D28-220 AAC CR05-104JM AAC CR05-134JM AAC CR05-222JM KOA RK73H1E7321F AAC CR05-1372FM AAC CR05-1333FM AAC CR05-152JM AAC CR05-1002FM AAC CR05-2491FM AAC CR05-1072FM AAC CJ05-000M OPTION MILL-MAX-2501-2 LINEAR TECH LT1941EFE