QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 448 DUAL OUTPUT ISOLATED POWER SUPPLY LT3710 DESCRIPTION Demonstration circuit 448 is a dual output high efficiency isolated DC/DC power supply with 36V to 72V input range. It has two outputs: 3.3V at 10A max and 1.8V or 2.5V at 10A max. LT3710, a secondary side synchronous post regulator controller, is used to generate a tightly regulated second output directly from the transformer secondary winding, thus minimizing the size of the output inductor and capacitor at the first output stage. Synchronous MOSFETs significantly improve efficiency, making it suitable for low output voltage applications. The complete design is mounted within a standard half brick PCB area with about half inch height. Design files for this circuit board are available. Call the LTC factory. Table 1. Performance Summary (TA = 25°C) PARAMETER CONDITION VALUE Minimum Input Voltage 36V Maximum Input Voltage 72V VOUT1 VIN = 36V to 72V, IOUT1 = 0A to 10A, 3.3V ±2% IOUT2 = 0A to 10A VIN = 36V to 72V, IOUT1 = 0A to 10A, 1.83V ±2% (JP1, JP2: 1.8V position) IOUT2 = 0A to 10A or 2.53V ±2% (JP1, JP2: 2.5V position) Typical Output Ripple VOUT1 VIN = 48V, IOUT1 = 10A (20MHz BW) 70mVP–P Typical Output Ripple VOUT2 VIN = 48V, IOUT2 = 10A (20MHz BW) 50mVP–P for 1.8Vo VOUT2 60mVP–P for 2.5Vo Output Regulation Line ±0.1% Load ±0.2% Nominal Switching Frequency Efficiency Output Voltage VOUT1 Trim On/Off Control Isolation Voltage 230kHz VIN = 48V, VOUT1 =3.3V, VOUT2 =1.8V, IOUT1 =IOUT2 =10A 86% Typical VIN = 48V, VOUT1 =3.3V, VOUT2 =2.5V, IOUT1 =IOUT2 =10A 87% Typical VO1 TRIM =3.3V 5% Typical VO1 TRIM =0V –5% Typical Logic Low Voltage-Off 0.6V Max Logic High Voltage-On 1V Min Basic Insulation 1500VDC 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 448 DUAL OUTPUT ISOLATED POWER SUPPLY OPERATING PRINCIPLES Demonstration circuit 448A features the LT3710, LT3781 and LTC1698 controllers. The basic power stage topology is a two-switch forward converter with synchronous rectification. The primary side controller uses the LT3781, a current mode two-switch forward controller with built-in MOSFET drivers. On the secondary side, an LTC1698 is used to provide the voltage feedback for the 3.3V output, as well as the gate drive for the synchronous MOSFETs in the 3.3V output stage. The error amplifier output of the 3.3V circuit is fed into the optocoupler and then relayed to LT3781 on the primary side to complete the 3.3V regulation. The second 1.8V/2.5V output is directly regulated by the LT3710 circuit. A planar transformer PA0191 built by Pulse Engineering is employed as the power transformer in this design. This transformer is constructed on a PQ20 core with nine turns of primary windings, two turns of secondary windings and seven turns of auxiliary windings for the LT3781 bias supply. A Vishay Si7892DP is used due to its low RDS(ON), 30V VDSS rating and its compact and thermally enhanced PowerPak SO-8 package. The switching frequency of the circuit is about 230KHz. 1500V input to output isolation is provided. Additional features of this demo board include primary side on/off control, ±5% secondary side trimming on the 3.3V output, input overvoltage protection, under voltage lockout, 3.3V output overvoltage protection, 1.8V/2.5V output current limit and board overtemperature shutdown. The demo board can deliver the full rated currents (10A at both outputs) at room temperature without airflow. The hottest spot on the demo board (T1 transformer) has a temperature rise of 50°C at 48V input and full loads (without airflow). QUICK START PROCEDURE Demonstration circuit DC448 is easy to set up to evaluate the performance of the LT3710, LT3781 and LTC1698. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: NOTE: When measuring the input or output voltage rip- ple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the input or output voltage ripple by touching the probe tip directly across the Vin or Vout and GND terminals. See Figure 2 for proper scope probe technique. Default jumper setting: both jumpers at 1.8V position 1. Select Vout2 1.8V (or 2.5V): Place both jumpers JP1 and JP2 at 1.8V (or 2.5V) position. 3. The on/off control pin should be left open for normal operation. (Connecting the on/off pin to the –Vin turns off the converter.) 4. For normal 3.3V output, Vo1 Trim pin should be left open. 5. Connect the 3.3V load (Load 1 in Figure 1) between +Vo1 and Vo RTN; connect the 1.8V/2.5V load (Load 2 in Figure 1) between +Vo2 and Vo RTN. 6. Connect the DVMs to the input and outputs. 7. Turn on the input power supply and check for the proper output voltages. Vo1 should be 3.3V ±2%. Vo2 should be 1.83V ±2% if 1.8Vo is selected (or Vo2 should be 2.53V ±2% if 2.5Vo is selected). 2. With power off, connect the input power supply to +Vin (36V–72V) and –Vin (input return). 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 448 DUAL OUTPUT ISOLATED POWER SUPPLY + + + + – – + LOAD 2 – – LOAD 1 + – + – – – + Figure 1. Proper Measurement Equipment Setup GND VIN Figure 2. Measuring Input or Output Ripple 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 448 DUAL OUTPUT ISOLATED POWER SUPPLY 90 VIN = 36V 85 EFFICIENCY (%) 80 VIN = 48V 75 70 VIN = 72V 65 VOUT1 = 3.3V VOUT2 = 1.8V LOAD CURRENT = IVOUT1 = IVOUT2 60 55 0 1 2 3 4 5 6 7 LOAD CURRENT (A) 8 9 10 Figure 3. Efficiency vs load current: Vout1=3.3V and Vout2=1.8V 90 VIN = 36V 85 EFFICIENCY (%) 80 VIN = 48V 75 VIN = 72V 70 65 VOUT1 = 3.3V VOUT2 = 2.5V LOAD CURRENT = IVOUT1 = IVOUT2 60 55 0 1 2 3 4 5 6 7 LOAD CURRENT (A) 8 9 10 Figure 4. Efficiency vs load current: Vout1=3.3V and Vout2=2.5V 4 5 4 3 2 1 REVISIONHISTORY N O T E S : UNLESS OTHERWISE SPECIFIED, L T C CONFIDENTIAL - For Customer Use Only ECO [1] DESCRIPTION DATE APPROVED OPTIONAL. 0 36V-72V REV 5 PROTO < ?? Vi L1 1.2uH P1 VIN +Vin DO1813P-122HC R1 1 5 6 7 8 2 Q1 Si7456DP 5 6 7 8 2 0 4 Q2 1 MMBT3906LT1 [1] 1 2 3 SEC T1 Pulse PA0191 1 2 3 1 3 D Q15 Si7456DP [1] 4 L3 CEP125-2R5 D Vout P8 7 Vout +Vo1 D2 D1 3.3V@10A B2100 1.5uF 1.5uF 100V B2100 5 6 7 8 R2 100V 1 2 5 6 7 8 Q3 Si7456DP 4 4 5 Q16 Si7456DP [1] 2 4 1 2 3 2 0 Q8 1 8 7 6 5 Q4 1 2 3 8 7 6 5 Q5 Si7892DP 4 Si7892DP 4 C9 1000pF 100V R3 10 1/4W R4 10 1/4W 8 7 6 5 C4 + 470uF 4V POSCAP C5 + 470uF 4V POSCAP C18 10uF 6.3V Q6 Si7892DP 4 3 R9 C8 1000pF 100V C7 + 470uF 4V [1] 2 C3 1 C2 3 2 1 MMBT3906LT1 [1] 3 2 1 3 2 1 P2 Vo RTN C10 R6 -Vin L2 1mH P7 3 0.020 1 % 1/2W Vout 3.3 2200pF D3 D18 C6 250VAC Vcc 1uF DO1608C-105 COILCRAFT Vi B0540W BAS21TA D6 D4 BAS21TA Q10 B0540W R16 2K 0.25W ZVN3310F 2 R25 20K 1 D7 R18 100 2 C VccS Q12 FZT690B Q7 FZT853 C13 C 0.22uF 1 0.25W 2 3 Vcc BAT54 D20 R17 R8 10 B0540W 1 3 Vcc D19 5241B 11V D12 2 10K D10 10V MMBZ5240B C15 4.7uF 16V 2 1 3 C14 330pF 1 BAT54S Vi 2 0.01uF LT3781EG 1 8 4 3 5Vref 1 2 5 6 CG VCOMP 2 16 11 FG R33 3.01K 1% B 8 MARGIN VAUX 4700pF 3 ICOMP 1 [1] R46 1K 13 R47 1.24K 1% R48 1.78K 1% C33 0.1uF 2 2 Vout Vo1 Trim 2 1 0 0.01uF C30 0.1uF 2 C32 82pF R40 2 C11 1 C31 1uF C29 8 3300pF PWRGGD C26 GND C22 7 10 6 5 R42 2.43K 1% 9 P5 OPTODRV PGND VC SGND SS R41 10 R45 1.24K 1% OVPIN 1K 1 1 2 ISNSGND 2 1 4 R37 52.3K 1 % R43 10K R34 2.43K 1% LTC1698EGN MOC207 14 100K C28 1000pF Vout U4 ISO1 9 R39 C25 4.7uF 16V SYNC VFB 7 1uF 15 2 470 R35 10 4 8 VFB 3K C27 1 VDD 14 11 15 SYNC FSET 5Vref RT1 3 5 SHDN 6 1 12 220pF THERM D17 MMBD4148 5VREF P9 ON OFF SG R31 1 0.022uF R32 470 OVLO 7 2 7 C17 PGND TG U3 SENSE VCC VBST 13 B 18 100V 19 0.1uF 20 BAS21TA 1000pF C19 T2 PULSE ENG. P2033 4 1 C20 BG D13 C16 C21 1uF 16V 1 C1 12 R26 73.2K 1% BSTREF R24 270K 0.25W ISNS Vcc A A CONTRACTNO. U N LESS OTHERWISE SPECIFIED D IMENSIONS ARE IN INCHES TOLERANCE ON ANGLE - - 2 PLACES - - 3 PLACES - - INTERPRET DIM AND TOL PER ASME Y14.5M -1994 APPROV ALS D R A W N MEI DATE 07/15/02 TECHNOLOGY TITLE CHECKED THIRD ANGLE PROJECTION APPROVED 1630 McCarthy Blvd. Milpitas, CA 95035 Phone: (408)432-1900 Fax: (408)434-0507 SCH, LT3710EFE/LT3781EG/LTC1698EGN DUAL OUTPUT ISOLATED POWER SUPPLY ENGINEER DESIGNER SIZE CAGE CODE C Friday, October 25, 2002 DO NOT SCALE DRAWING 5 4 3 2 SCALE:NONE DWG NO REV 5 DC448A FILENAME: 448A-5.DSN SHEET 1 1 OF 2 5 4 3 2 1 REVI SION HISTORY ECO REV > DESCRIPTION 5 DATE Proto APPROVED < ? D D C37 4 680pF 14 2 C35 1 1 2 6 SW CSET BGATE PGND BGS ILCOMP 10K CL+ 1 2 1 1 2 3 2 15 R7 9 L4 CEP125-1R8 R49 0.004 1% P10 D15 CMDSH-3 5 6 7 8 0 [1] 1 Q14 Si7892DP 4 2 11 D16 Q17 Si7892DP [1] 1 2 3 1 2 3 +Vo2 2512 C46 1000pF 5 6 7 8 4 12 C42 [1] B340A R64 10 [1] 1/4W R59 100 4700pF C12 + 680uF 4V [1] C40 C41 + 680uF + 680uF 4V 4V POSCAP POSCAP 1.8V/2.5V@10A C C23 10uF 6.3V R53 220 C43 8 CL- R56 10 16 3 5 6 7 8 4 2 TGATE 10 180pF 50V R57 2 Q13 Si7892DP 2 C C47 1uF GBIAS LT3710EFE VCC C44 0.1uF 16V 1 1 VccS SS D14 CMDSH-3 1 13 SYNC VFB 7 0.01uF BOOST C34 5 VAOUT 10K 1 2 C36 4.7uF 16V 1 2 2 U5 1 R58 1 SEC [NOT USED] R5 1 C45 10pF 2 2 Vout 0.01uF R50 1 C38 R51 3.01K 1% 2 3.30K .033uF C39 330pF JP2 R60 B 9.1K 1 2 . 5V 2 3 4 R61 R52 2.32K 1% 6.2K R54 3.40K 1% B 1 . 8V JP1 1 2 . 5V 2 Vo2 SELECT 3 4 1 . 8V 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 08-02-01 CHECKED TECHNOLOGY TITLE APPROVED 1630 McCarthy Blvd. Milpitas, CA 95035 Phone: (408)432-1900 Fax: (408)434-0507 A SCH, LT3710EFE/LT3781EG/LTC1698EGN DUAL OUTPUT ISOLATED POWER SUPPLY ENGINEER SIZE CAGE CODE DESIGNER B DO NOT SCALE DRAWING 5 4 3 Friday, October 25, 2002 SCALE:NONE 2 DWG NO REV 5 DC448A FILENAME: 448A-5.PCB SHEET 1 2 OF 2