QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894B-C 36V-72VIN, SYNCHRONOUS FLYBACK LT3825 DESCRIPTION Demonstration circuit 894B-C is a 36V-72Vin, synchronous flyback converter featuring the LT3825. This circuit was designed specifically to attain a high current, low ripple, synchronously rectified flyback to efficiently power 12V loads at up to 5A from a typical telecom input voltage range. This circuit features synchronous rectifier drive outputs, output voltage Table 1. regulation without the need of an optocoupler, self-starting architecture and input undervoltage lockout. Design files for this circuit board are available. Call the LTC factory. , LTC and LT are registered trademarks of Linear Technology Corporation. Performance Summary (TA = 25°C) PARAMETER CONDITION VALUE Minimum Input Voltage 36V Maximum Input Voltage 72V Output Voltage VOUT VIN = 36V to 72V, IOUT = 0A to 5A Maximum Output Current 12.0V 5A Typical Output Ripple VOUT VIN = 48V, IOUT = 5A < 120mVP–P Output Regulation Over All Input Voltages and Output Currents ±1% Peak Deviation with Load Step of 3.75A to 5A (10A/us) ±250mV (< ±2.5%) Load Transient Response Settling Time 100us Nominal Switching Frequency Efficiency 200kHz VIN = 48V, IOUT = 5A 91% Typical OPERATING PRINCIPLES The LT3825 controller exhibits a self-starting capability. When an input voltage is applied, a trickle charge resistor, R8, charges C10 (See Figure 9) to power Vcc. Then, the IC begins a controlled soft-start of the output voltage. As this voltage begins to rise, Vcc power is quickly taken over by T1, D2, and R7. When the softstart period is over, the LT3825 then regulates output voltage by observing the pulses across the auxiliary winding of T1 during the flyback time. The Primary Gate drive (PG) and Synchronous Gate (SG) drive is then Pulse Width Modulated (PWM) in order to keep the output voltage constant. The synchronous gate drive signal is transmitted to the secondary via the small signal transformer, T2. The output of T2 then drives a discreet gate drive buffer, R26, Q12, and Q13 in order to achieve fast gate transition times, hence a higher efficiency. The two-stage input filter, C25, L1, and C30 and output filter, C1, C2, L2, and C29 are the reasons that this flyback has exceptionally low conducted emissions. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894B-C 36V-72VIN, SYNCHRONOUS FLYBACK QUICK START PROCEDURE Demonstration circuit 894B-C is easy to set up to evaluate the performance of the LT3825. Refer to Figure 1 for proper measurement equipment setup and follow the procedure below: NOTE: When measuring the input or output volt- age ripple, care must be taken to avoid a long ground lead on the oscilloscope probe. Measure the output (or input) voltage ripple by touching the probe tip and probe ground directly across the +Vout and –Vout (or +Vin and –Vin) terminals. See Figure 2 for proper scope probe technique. 3. Turn on the power at the input. NOTE: Make sure that the input voltage never exceeds 72V. 4. Check for the proper output voltage of 12V 5. Turn off the power at the input. 6. Once the proper output voltages are estab- lished, connect a variable load capable of sinking 5A at 12V to the output terminals +Vout and –Vout. Set the current for 0A. a. If efficiency measurements are desired, an 36V to 72V at a current of at least 2.5A to a voltage of 36V. Then, turn off the supply. ammeter or a resistor current shunt that is capable of handling at least 5Adc can be put in series with the output load in order to measure the DC894B-C’s output current. 2. With power off, connect the supply to the in- b. A voltmeter with a capability of measuring 1. Set an input power supply that is capable of put terminals +Vin and –Vin. a. Input voltages lower than 36V can keep the converter from turning on due to the undervoltage lockout feature of the LT3825. b. If efficiency measurements are desired, an ammeter capable of measuring 2.5Adc can be put in series with the input supply in order to measure the DC894B-C’s input current. c. A voltmeter with a capability of measuring at least 72V can be placed across the input terminals in order to get an accurate input voltage measurement. at least 12V can be placed across the output terminals in order to get an accurate output voltage measurement. 7. Turn on the power at the input. NOTE: If there is no output, temporarily dis- connect the load to make sure that the load is not set too high. 8. Once the proper output voltage is estab- lished, adjust the load within the operating range and observe the output voltage regulation, ripple voltage, efficiency and other desired parameters. 2 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894B-C 36V-72VIN, SYNCHRONOUS FLYBACK Figure 1. Proper Measurement Equipment Setup GND VIN Figure 2. Measuring Input or Output Ripple 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894B-C 36V-72VIN, SYNCHRONOUS FLYBACK MEASURED DATA Figures 3 through 8 are measured data for a typical DC894B-C. Figures 9 through 11 are schematics and bill of materials. Efficiency vs. Load Current 94% 92% 90% Efficiency (%) 88% 86% 36Vin 84% 48Vin 82% 72Vin 80% 78% 76% 74% 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 Load Current (A) Figure 3. Efficiency Output Voltage vs. Load Current 12.25 Output Voltage (V) 12.15 12.05 36Vin 48Vin 72Vin 11.95 11.85 11.75 0 1 2 3 4 5 6 Load Current (A) Figure 4. Regulation 4 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894B-C 36V-72VIN, SYNCHRONOUS FLYBACK Figure 5. Output Voltage Ripple (48Vin 5A) Figure 6. Load Transient Response (10A/us) 5 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894B-C 36V-72VIN, SYNCHRONOUS FLYBACK Figure 7. Temp Data (48Vin, 5A, 100LFM airflow – front) Figure 8. Temp Data (48Vin, 8A, 100LFM airflow – back) 6 -VIN E2 36V- 72V +VIN E1 C30 22uF 100V + C25 2.2uF 100V 4.7uH L1 R5 412K 1% R14 15k 1% R3 30.9k 1% R20 12k 1% R15 3.01k 8 PGDLY UVLO FB R16 169k 1% 15 10 R7 68 0.125W D2 BAS21LT1 VCC 2 TON 3 C10 47uF 20V R8 47K 0.25W R18 1.5k 1% SYNC 5 + ROC MP 14 0.1uF C11 SG 1 U1 LT3825EFE SG 16 PG EN DLY R19 100k 4 C13 0.1uF VC SENN 47pF 160 0.25W R11 160 0.25W R6 7.5k R22 3.3n C23 9 11 12 Q1 Si7450DP SENP C4 100pF C17 OSCAP 7 SGND /PGN D 17 SFST 6 CC M P 13 330p C19 R9 0.012 0.5W SG 470p PA0184 T2 C8 0.1uF R4 330 R2 15 0.25W C3 T1 PA1736NL BAT54 2.2nF D5 C20 R26 15 FMMT718 Q12 R13 10K +VOUT C7 4.7nF 250V 1uF -VOUT C29 12V @ 5A SANYO 16CE150BS C21 +VOUT FMMT618 Q13 Si4470EY Q3 C3225X5R1C226M C1 C2 22uF 16V L2 IHLP2525CZER1R0M QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894B-C 36V-72VIN, SYNCHRONOUS FLYBACK Figure 9. Simplified Schematic 7 -VIN E2 36V- 72V +VIN E1 C30 22uF 100V + C12 OPT 4.7uH L1 R5 412K 1% C25 2.2uF 100V R14 15k 1% R3 30.9k 1% 1% R15 3.01k R10 OPT R20 12k 8 PGDLY UVLO FB R16 169k 1% 15 10 R7 68 0.125W D2 BAS21LT1 VC C C10 47uF 20V R8 47K 0.25W R18 1.5k 1% + 0.1uF C11 SG R1 0 1 16 U1 LT3825EFE SG 2 T ON 3 SYN C 5 R OC M P 14 PG EN D LY R19 100k 4 OPT C18 10nF C17 47pF OSC AP 7 SGN D /PGN D 17 SF ST 6 4 Q1 0.1uF C13 VC SENN SENP C23 1 2 3 R22 7.5k R9 0.012 0.5W 5 6 7 8 160 0.25W R11 160 0.25W R6 3.3nF 9 11 12 Si7450DP C4 100pF CCMP 13 330p C19 SG 1 8 T2 PA0184 C8 0.1uF 3 2 1 4 5 4 C1 22uF 16V D5 R26 15 4 R13 10K D7 R27 OPT OPT FMMT618 Q13 OPT C6 1uF C21 L2 IHLP2525CZER1R0M Q3 Si4470EY OPT C5 BAT54 2.2nF C20 FMMT718 Q12 3 2 1 8 7 6 5 C2 22uF 16V C1, C2: C3225X5R1C226M 8 7 6 5 Q4 OPT R4 330 470p C3 10 11 12 7 8 9 T1 PA1736NL R2 15 0.25W 3 4 6 2 1 5 R28 0 +VOUT C7 4.7nF 250V E4 -VOUT C29 12V @ 5A SANYO 16CE150BS E3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894B-C 36V-72VIN, SYNCHRONOUS FLYBACK Figure 10. Full Board Schematic 8 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894B-C 36V-72VIN, SYNCHRONOUS FLYBACK Item Qty Ref-Des Description Manufacturer's Part Number REQUIRED CIRCUIT COMPONENTS1 1 2 C1,C2 CAP, 1210 22uF 20% 16V X5R 2 1 C3 CAP, 1206 470pF 5% 100V COG 3 1 C4 CAP, 1206 100pF 10% 630V COG 4 1 C7 CAP, 4.7nF 10% 250V X7R 5 3 C8,C11,C13 CAP, 0603 0.1uF 10% 50V X7R 6 1 C10 CAP, 6032 47uF 20% 20V TANT 7 0 C12 CAP, 0603 470pF 10% 25V NPO 8 1 C17 CAP, 0603 47pF 10% 25V NPO 9 1 C19 CAP, 0603 330pF 5% 50V COG 10 1 C20 CAP, 0603 2.2nF 5% 50V X7R 11 1 C21 CAP, 1206 1uF 20% 25V X7R 12 1 C23 CAP, 0603 3.3nF 10% 25V X7R 13 1 C25 CAP, 1812 2.2uF 10% 100V X7R 14 1 C29 CAP, 150uF 20% 16V 15 1 D2 DIODE, BAS21-7 16 1 D5 DIODE, SCHOTTKY 17 1 L2 IND, 1.0uH 18 1 Q1 XSTR, MOSFET N-CHANNEL 19 1 Q3 XSTR, MOSFET N-CHANNEL 20 1 Q12 XSTR, PNP 21 1 Q13 XSTR, NPN 22 1 R2 RES, 1206 15 OHMS 5% 1/4W 23 1 R3 RES, 0603 30.9k OHMS 1% 1/10W 24 1 R4 RES, 0603 330 OHMS 5% 1/10W 25 1 R5 RES, 0603 412K OHMS 1% 1/8W 26 2 R6,R11 RES, 1206 160 OHMS 5% 1/4W 27 1 R7 RES, 0805 68 OHMS 5% 1/8W 28 1 R8 RES, 1206 47K OHMS 5% 1/4W 29 1 R9 RES, 1206 0.012 OHMS 1% 0.5W 30 1 R13 RES, 0603 10K OHMS 5% 1/10W 31 1 R14 RES, 0603 15K OHMS 1% 1/10W 32 1 R15 RES, 0603 3.01K OHMS 1% 1/10W 33 1 R16 RES, 0603 169K OHMS 1% 1/10W 34 1 R18 RES, 0603 1.5K OHMS 1% 1/10W 35 1 R19 RES, 0603 100K OHMS 5% 1/10W 36 1 R20 RES, 0603 12K OHMS 5% 1/10W 37 1 R22 RES, 0603 7.5K OHMS 5% 1/10W 38 1 R26 RES, 0603 15 OHMS 5% 1/10W 39 1 T1 XFMR, PA1736NL 40 1 T2 XFMR, 1.4mH MIN, 50KHz 41 1 U1 IC, LT3825EFE TDK C3225X5R1C226M AVX 12061A471JAT TDK C3216COG2J101K MURATA GA343DR7GD472KW01L TDK C1608X7R1H104K AVX TAJC476M020R AVX 06033A471KAT2A OPTION AVX 06033A470KAT2A AVX 06035A331JAT AVX 06035C222JAT AVX 12063C105MAT2A AVX 06033C332KAT TDK C4532X7R2A225K SANYO 16CE150BS DIODES INC. BAS21-7-F DIODES INC. BAT54-7 VISHAY IHLP2525CZER1R0M VISHAY SILICONIX Si7450DP VISHAY SILICONIX Si4470EY ZETEX FMMT718TA ZETEX FMMT618TA AAC CR18-150JM AAC CR16-1R50FM AAC CR16-331JM AAC CR16-4123FM AAC CR18-161JM AAC CR10-680JM AAC CR18-473JM IRC LRC-LRF1206-01-R012-F AAC CR16-103JM AAC CR16-1502FM AAC CR16-3011FM AAC CR16-1693FM AAC CR16-1501FM AAC CR16-104JM AAC CR16-123JM AAC CR16-752JM AAC CR16-150JM PULSE PA1736NL PULSE PA0184 LINEAR TECH LT3825EFE ADDITIONAL DEMO BOARD CIRCUIT COMPONENTS2 42 0 C5 CAP, 1210 OPTION 43 0 C6 CAP, 1210 47uF 20% 6.3V X5R OPTION 44 0 C18 CAP, 0603 10nF 10% 25V X7R OPTION 45 1 C30 CAP, 22uF 100V OPTION TDK C3225X5R0J476MT OPTION AVX 06033C103KAT OPTION SUN ELECTRIC 100ME22AX 9 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894B-C 36V-72VIN, SYNCHRONOUS FLYBACK 46 47 48 49 50 51 52 0 1 0 1 0 0 1 D7 L1 Q4 R1 R10 R27 R28 DIODE, OPTION IND, 4.7uH XSTR, MOSFET N-CHANNEL OPTION RES, 0603 0 OHM JUMPER RES, OPTION RES, OPTION RES, 0603 0 OHM JUMPER OPTION VISHAY IHPL2525CZER4R7M01 VISHAY SILICONIX Si7336ADP OPTION VISHAY CRCW0603000ZRT6 OPTION OPTION VISHAY CRCW0603000ZRT6 Notes: 1. Required Circuit Components are those parts that are required to implement the circuit function 2. Additional Demo Board Circuit Components are those parts that provide added functionality for the demo board but are or may not be required in the actual circuit. Figure 11. Bill of Materials 10