QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894A-A 36V-72VIN, FORWARD CONVERTER LT3825 DESCRIPTION Demonstration circuit 894A-A 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 3.3V loads at up to 12A from a typical telecom input voltage range. This circuit features synchronous rectifier drive outputs, output voltage regulation without the need of an optocoupler, selfstarting 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. Table 1. 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 12A Maximum Output Current 3.3V 12A Typical Output Ripple VOUT VIN = 48V, IOUT = 12A < 20mVP–P Output Regulation Over All Input Voltages and Output Currents ±1.25% Peak Deviation with Load Step of 9A to 12A (10A/us) ±140mV (< ±4.5%) Settling Time 100us Load Transient Response Nominal Switching Frequency Efficiency 200kHz VIN = 48V, IOUT = 12A 89% 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 12) 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 soft-start 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 drive (SG) 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, C5, L2, and C29 are the reasons that this flyback has exceptionally low conducted emissions. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894A-A 36V-72VIN, FORWARD CONVERTER QUICK START PROCEDURE Demonstration circuit 894A-A 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 voltage 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. 1. Set an input power supply that is capable of 36V to 72V at a current of at least 2A to a voltage of 36V. Then, turn off the supply. 2. With power off, connect the supply to the input 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 2Adc can be put in series with the input supply in order to measure the DC894A-A’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. 3. Turn on the power at the input. NOTE: Make sure that the input voltage never ex- ceeds 72V. 4. Check for the proper output voltage of 3.3V Turn off the power at the input. 5. Once the proper output voltages are established, connect a variable load capable of sinking 12A at 3.3V to the output terminals +Vout and –Vout. Set the current for 0A. 6. a. If efficiency measurements are desired, an ammeter or a resistor current shunt that is capable of handling at least 12Adc can be put in series with the output load in order to measure the DC894A-A’s output current. b. A voltmeter with a capability of measuring at least 3.3V can be placed across the output terminals in order to get an accurate output voltage measurement. Turn on the power at the input. NOTE: If there is no output, temporarily disconnect the load to make sure that the load is not set too high. 7. Once the proper output voltage is established, 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 894A-A 36V-72VIN, FORWARD CONVERTER Figure 1. Proper Measurement Equipment Setup GND VIN Figure 2. Measuring Input or Output Ripple 3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894A-A 36V-72VIN, FORWARD CONVERTER MEASURED DATA Figures 3 through 10 are measured data for a typical DC894A-A. Figures 11 through 13 are schematics and bill of materials. Efficiency vs. Load Current 92% 90% Efficiency (%) 88% 86% 36VIN 84% 48VIN 82% 72VIN 80% 78% 76% 2 4 6 8 10 12 Load Current (A) Figure 3. Efficiency (no airflow) Output Voltage vs. Load Current 3.45 Output Voltage (V) 3.40 3.35 36Vin 48Vin 72Vin 3.30 3.25 3.20 3.15 0 2 4 6 8 10 12 Load Current (A) Figure 4. Regulation (400LFM) 4 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894A-A 36V-72VIN, FORWARD CONVERTER Figure 5. Output Voltage Ripple (48Vin 12A) Figure 6. Load Transient Response (10A/us) 5 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894A-A 36V-72VIN, FORWARD CONVERTER Figure 7. Temp Data (48Vin, 12A, 100LFM airflow – front) Figure 8. Temp Data (48Vin, 12A, 100LFM airflow – back) 6 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894A-A 36V-72VIN, FORWARD CONVERTER Figure 9. Temp Data (48Vin, 12A, no airflow – front) Figure 10. Temp Data (48Vin, 12A, no airflow – back) 7 E1 -VIN E2 36V- 72V +VIN C30 22uF 100V + C25 2.2uF 100V 4.7uH L1 R5 412K 1% R14 15k 1% R3 28.7k 1% R20 12k 1% R15 3.01k 8 PGDLY UVLO FB R16 169k 1% 15 10 R7 20 D2 BAS21LT1 2 VCC TON 3 C10 47uF 20V R8 47K 0.25W R18 887 1% SYNC 5 + ROCMP 14 0.1uF C11 SG 1 U1 LT3825EFE SG 16 PG ENDLY R19 100k 4 0.1uF 47pF VC SENN C13 56 R6 20K R22 10nF C23 9 11 12 Q1 Si4490DY SENP C4 100pF C17 OSCAP 7 SGND/PGND 17 SFST 6 CCMP 13 2.2nF C19 R9 0.02 0.5W SG Q12 C20 2.2nF BAT54 D5 R26 15 R13 10K FMMT618 Q13 B0540W D7 C1 C2 C5 47uF 6.3V 1uF C21 R27 47 L2 FP2S-100-R Si7336ADP Q3 FMMT718 2.2nF PA0184 T2 C8 0.1uF R4 330 R2 4.7 C3 C3225X5R0J476M T1 PA1477NL +VOUT C7 4.7nF 250V -VOUT C29 3.3V @ 12A SANYO 6TPD470M QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894A-A 36V-72VIN, FORWARD CONVERTER Figure 11. Simplified Schematic 8 -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 28.7k 1% R20 12k 1% R15 3.01k 8 PGDLY UVLO FB R16 169k 1% 15 10 R7 20 D2 BAS21LT1 C10 47uF 20V R8 47K 0.25W + R18 887 1% 0.1uF C11 SG R1 0 1 16 U1 LT3825EFE SG 2 VCC TON 3 SYNC 5 ROCMP 14 PG ENDLY R19 100k 4 OPT C18 10nF C17 47pF OSCAP 7 SGND/PGND 17 SFST 6 CCMP 13 4 0.1uF C13 VC SENN SENP C23 1 2 3 20K R22 R9 0.02 0.5W 5 6 7 8 56 R6 10nF 9 11 12 Q1 Si4490DY C4 100pF 2.2nF C19 R2 4.7 3 4 6 2 1 SG 1 8 T2 PA0184 C8 0.1uF 3 2 1 4 5 4 C1 47uF 6.3V C20 2.2nF R26 15 D5 E 4 Q13 C R13 10K FMMT618 E D7 1uF C21 R27 47 L2 FP2S-100-R B0540W OPT C6 Q3 Si7336ADP C5 47uF 6.3V BAT54 FMMT718 C Q12 3 2 1 8 7 6 5 C2 47uF 6.3V C1, C2, C5: C3225X5R0J476M 8 7 6 5 Q4 OPT R4 330 2.2nF C3 10 11 12 7 8 9 B T1 PA1477NL B 5 R28 OPT +VOUT C7 4.7nF 250V E4 -VOUT C29 3.3V @ 12A SANYO 6TPD470M E3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894A-A 36V-72VIN, FORWARD CONVERTER Figure 12. Full Board Schematic 9 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894A-A 36V-72VIN, FORWARD CONVERTER Item Qty Ref-Des Description Manufacturer's Part Number 1 REQUIRED CIRCUIT COMPONENTS 1 1 C3 CAP, 1206 2.2nF 20% 100V X7R 2 1 C4 CAP, 1206 100pF 10% 630V COG 3 3 C5,C2,C1 CAP, 1210 47uF 20% 6.3V X5R 5 1 C7 CAP, 4.7nF 10% 250V X7R 6 3 C8,C11,C13 CAP, 0603 0.1uF 10% 50V X7R 7 1 C10 CAP, 6032 47uF 20% 20V TANT 9 1 C17 CAP, 0603 47pF 10% 25V NPO 11 2 C19,C20 CAP, 0603 2.2nF 5% 50V X7R 12 1 C21 CAP, 1206 1uF 20% 25V X7R 13 1 C23 CAP, 0603 10nF 10% 25V X7R 14 1 C25 CAP, 1812 2.2uF 10% 100V X7R 15 1 C29 CAP, 7343 470uF 20% 6.3V POSCAP 17 1 D2 DIODE, BAS21-7 18 1 D5 DIODE, SCHOTTKY 19 1 D7 DIODE, SCHOTTKY 22 1 L2 IND, 0.1uH 23 1 Q1 XSTR, MOSFET N-CHANNEL 24 1 Q3 XSTR, MOSFET N-CHANNEL 26 1 Q12 XSTR, PNP 27 1 Q13 XSTR, NPN 29 1 R2 RES, 1206 4.7 OHMS 5% 1/4W 30 1 R3 RES, 0603 28.7K OHMS 1% 1/10W 31 1 R4 RES, 0603 330 OHMS 5% 1/10W 32 1 R5 RES, 0603 412K OHMS 1% 1/8W 33 1 R6 RES, 1206 56 OHMS 5% 1/4W 34 1 R7 RES, 0805 20 OHMS 5% 1/8W 35 1 R8 RES, 1206 47K OHMS 5% 1/4W 36 1 R9 RES, 1206 0.02 OHMS 1% 0.5W 37 1 R13 RES, 0603 10K OHMS 5% 1/10W 38 1 R22 RES, 0603 20K OHMS 5% 1/10W 39 1 R14 RES, 0603 15K OHMS 1% 1/10W 40 1 R15 RES, 0603 3.01K OHMS 1% 1/10W 41 1 R16 RES, 0603 169K OHMS 1% 1/10W 42 1 R18 RES, 0603 909 OHMS 1% 1/10W 43 1 R19 RES, 0603 100K OHMS 5% 1/10W 44 1 R20 RES, 0603 12K OHMS 5% 1/10W 45 1 R26 RES, 0603 15 OHMS 5% 1/10W 46 1 R27 RES, 0805 47 OHMS 5% 1/8W 48 1 T1 XFMR, PA1477NL 49 1 T2 XFMR, 1.4mH MIN, 50KHz 50 1 U1 IC, LT3825EFE AVX 12061C222MAT TDK C3216COG2J101K TDK C3225X5R0J476MT MURATA GA343DR7GD472KW01L TDK C1608X7R1H104K AVX TAJC476M020R AVX 06033A470KAT2A AVX 06035C222JAT AVX 12063C105MAT2A AVX 06033C103KAT TDK C4532X7R2A225K SANYO 6TPD470M DIODES INC. BAS21-7-F DIODES INC. BAT54-7 DIODES INC. B0540W-7-F COILTRONICS FP2S-100-R VISHAY SILICONIX Si4490DY VISHAY SILICONIX Si7336ADP ZETEX FMMT718TA ZETEX FMMT618TA AAC CR18-4R7JM VISHAY CRCW06032872FRT6 AAC CR16-331JM AAC CR16-4123FM AAC CR18-560JM AAC CR10-200JM AAC CR18-473JM IRC LRC-LRF1206-01-R020-F AAC CR16-103JM AAC CR16-203JM AAC CR16-1502FM AAC CR16-3011FM AAC CR16-1693FM AAC CR16-9090FM AAC CR16-104JM AAC CR16-123JM AAC CR16-150JM VISHAY CRCW0805470JRT6 PULSE PA1477NL PULSE PA0184 LINEAR TECH LT3825EFE 2 ADDITIONAL DEMO BOARD CIRCUIT COMPONENTS 4 0 C6 CAP, 1210 47uF 20% 6.3V X5R OPTION 8 0 C12 CAP, 0603 470pF 10% 25V NPO OPTION 10 0 C18 CAP, 0603 10nF 10% 25V X7R OPTION 16 1 C30 CAP, 22uF 100V TDK C3225X5R0J476MT OPTION AVX 06033A471KAT2A OPTION AVX 06033C103KAT OPTION SANYO 100ME22AXTS 10 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894A-A 36V-72VIN, FORWARD CONVERTER 20 21 25 28 47 4 1 0 1 0 E1,E2,E3,E4 L1 Q4 R1 R28 TURRET IND, 4.7uH XSTR, MOSFET N-CHANNEL OPTION RES, 0603 0 OHM JUMPER RES, 0805 OPTION MILL-MAX 2501-2 VISHAY IHPL2525CZER4R7M01 VISHAY SILICONIX Si7336ADP OPTION VISHAY CRCW0603000ZRT6 OPTION 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 13. Bill of Materials 11