QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894C-B 36V-72VIN, SYNCHRONOUS FLYBACK LT3825 DESCRIPTION Demonstration circuit 894C-B 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 5.0V loads at up to 8A from a typical telecom input voltage range. This circuit features synchronous rectifier drive outputs, output voltage reg- Table 1. ulation 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 8A Maximum Output Current 5.0V 8A Output Ripple VOUT VIN = 48V, IOUT = 8A < 20mVP–P (typical) Output Regulation Over All Input Voltages and Output Currents ±1.0% (typical) Peak Deviation with Load Step of 6A to 8A (10A/us) ±100mV (< ± 2%) Settling Time 100us Load Transient Response Nominal Switching Frequency Efficiency 200kHz VIN = 48V, IOUT = 8A 92% (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, C5, L2, and C29 are the reasons that this flyback has exceptionally low conducted emissions. 1 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894C-B 36V-72VIN, SYNCHRONOUS FLYBACK QUICK START PROCEDURE Demonstration circuit 894C-B 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 5.0V 5. Turn off the power at the input. 6. Once the proper output voltages are estab- lished, connect a variable load capable of sinking 8A at 5.0V 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 2A to a voltage of 36V. Then, turn off the supply. ammeter or a resistor current shunt that is capable of handling at least 8Adc can be put in series with the output load in order to measure the DC894C-B’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 2Adc can be put in series with the input supply in order to measure the DC894C-B’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 5.0V 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 894C-B 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 894C-B 36V-72VIN, SYNCHRONOUS FLYBACK MEASURED DATA Figures 3 through 10 are measured data for a typical DC894C-B. 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 1 2 3 4 5 6 7 8 Load Current (A) Figure 3. Efficiency (no airflow) Output Voltage vs. Load Current Output Voltage (V) 5.10 5.05 36Vin 48Vin 72Vin 5.00 4.95 4.90 1 2 3 4 5 6 7 8 9 10 Load Current (A) Figure 4. Regulation (no airflow) 4 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894C-B 36V-72VIN, SYNCHRONOUS FLYBACK Figure 5. Output Voltage Ripple (48Vin 8A) Figure 6. Load Transient Response (10A/us) 5 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894C-B 36V-72VIN, SYNCHRONOUS FLYBACK Figure 7. Temp Data (48Vin, 8A, 100LFM airflow – front) Figure 8. Temp Data (48Vin, 8A, 100LFM airflow – back) 6 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894C-B 36V-72VIN, SYNCHRONOUS FLYBACK Figure 9. Temp Data (48Vin, 8A, no airflow – front) Figure 10. Temp Data (48Vin, 8A, 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 29.4k 1% R20 12k 1% R15 3.01k 8 PGDLY UVLO FB R16 169k 1% 15 10 R7 20 0.25W D2 BAS21LT1 VCC 2 TON 3 C10 47uF 20V R8 47K 0.25W R18 1.47k 1% SYNC 5 + ROCMP 14 0.1uF C11 SG 1 U1 LT3825EFE SG 16 PG ENDLY R19 100k 4 D8 BAT760 150 0.25W R11 150 0.25W R6 C13 0.1uF 47pF VC SENN SENP 2k R22 2.2n C23 9 11 12 Q1 BSC320N20NS C4 100pF C17 OSCAP 7 SGND/PGND 17 SFST 6 CCMP 13 220p C19 R9 0.018 0.5W SG C20 2.2nF C1 C2 C5 47uF 6.3V L2 FP2S-100-R Q12 BAT54 D5 R26 15 D7 R13 10K FMMT618 Q13 B0540W BSC011N03LSI Q3 C3225X5R0J476M FMMT718 2.2nF PA0184 T2 C8 0.1uF R4 330 R2 4.7 0.25W C3 T1 PA1735NL +VOUT 1uF C21 R27 47 0.125W C7 4.7nF 250V -VOUT C29 5.0V @ 8A SANYO 6TPE470M QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894C-B 36V-72VIN, SYNCHRONOUS FLYBACK Figure 11. Simplified Schematic 8 -VIN E2 C30 36V- 72V 22uF 100V +VIN E1 + C12 OPT 4.7uH L1 R5 412K 1% C25 2.2uF 100V R14 15k 1% R3 29.4k 1% 1% R15 3.01k R10 OPT R20 12k 8 PGDLY UVLO FB R16 169k 1% 15 10 R7 20 0.25W D2 BAS21LT1 2 VC C TON 3 C10 + 47uF 20V R8 47K 0.25W SYN C R18 1.47k 1% 5 0.1uF C11 SG R1 0 U1 LT3825EFE EN D LY R19 100k 4 D8 BAT760 C17 C18 OPT 47pF 10nF OSC AP 7 ROCM P 14 16 PG 1 SG SG N D /PG N D 17 SF ST 6 0.1uF C13 VC SENN SENP 4 9 R6 C23 1 2 3 R22 2K R9 0.018 0.5W 5 6 7 8 150 0.25W R11 150 0.25W 2.2n 11 12 BSC320N20NS Q1 C4 100pF CCMP 13 220p C19 SG 1 8 T2 PA0184 C8 0.1uF 3 2 1 4 5 4 C1 47uF 6.3V C20 2.2nF D5 R26 15 4 OPT C6 R13 10K FMMT618 Q13 B0540W 1uF C21 R27 47 0.125W L2 FP2S-100-R Q3 D7 BSC011N03LSI C5 47uF 6.3V BAT54 FMMT718 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 T1 PA1735NL R2 4.7 0.25W 3 4 6 2 1 5 +VOUT OPT R28 C7 4.7nF 250V E4 -VOUT C29 SANYO 5.0V @ 8A 6TPE470M E3 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894C-B 36V-72VIN, SYNCHRONOUS FLYBACK Figure 12. Full Board Schematic 9 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894C-B 36V-72VIN, SYNCHRONOUS FLYBACK Item Qty Ref-Des Description Manufacturer's Part Number REQUIRED CIRCUIT COMPONENTS1 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 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 220pF 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 2.2nF 5% 50V X7R 13 1 C25 CAP, 1812 2.2uF 10% 100V X7R 14 1 C29 CAP, 7343 470uF 20% 6.3V POSCAP 15 1 D2 DIODE, BAS21-7 16 1 D5 DIODE, SCHOTTKY 17 1 D7 DIODE, SCHOTTKY 18 1 D8 DIODE, SCHOTTKY 19 1 L2 IND, 0.1uH 20 1 Q1 MOSFET, N-CH 200V 36A TDSON-8 21 1 Q3 MOSFET, N-CH 30V 37A TDSON-8 22 1 Q12 XSTR, PNP 23 1 Q13 XSTR, NPN 24 1 R2 RES, 1206 4.7 OHMS 5% 1/4W 25 1 R3 RES, 0603 29.4K OHMS 1% 1/10W 26 1 R4 RES, 0603 330 OHMS 5% 1/10W 27 1 R5 RES, 0603 412K OHMS 1% 1/10W 28 2 R6,R11 RES, 1206 150 OHMS 5% 1/4W 29 1 R7 RES, 1206 20 OHMS 5% 1/4W 30 1 R8 RES, 1206 47K OHMS 5% 1/4W 31 1 R9 RES, 1206 0.018 OHMS 1% 0.5W 32 1 R13 RES, 0603 10K OHMS 5% 1/10W 33 1 R14 RES, 0603 15K OHMS 1% 1/10W 34 1 R15 RES, 0603 3.01K OHMS 1% 1/10W 35 1 R16 RES, 0603 169K OHMS 1% 1/10W 36 1 R18 RES, 0603 1.47K OHMS 1% 1/10W 37 1 R19 RES, 0603 100K OHMS 5% 1/10W 38 1 R20 RES, 0603 12K OHMS 5% 1/10W 39 1 R22 RES, 0603 2K OHMS 5% 1/10W 40 1 R26 RES, 0603 15 OHMS 5% 1/10W 41 1 R27 RES, 0805 47 OHMS 5% 1/8W 42 1 T1 XFMR, PA1735NL 43 1 T2 XFMR, 1.4mH MIN, 50KHz 44 1 U1 IC, LT3825EFE AVX 12061C222MAT TDK C3216COG2J101K TDK C3225X5R0J476MT MURATA GA343DR7GD472KW01L TDK C1608X7R1H104K AVX TAJC476M020R AVX 06033A471KAT2A OPTION AVX 06033A470KAT2A AVX 06035A221JAT AVX 06035C222JAT AVX 12063C105MAT2A AVX 06035C222JAT TDK C4532X7R2A225K SANYO 6TPE470M DIODES INC. BAS21-7-F DIODES INC. BAT54-7 DIODES INC. B0540W-7-F DIODES INC. BAT760-7 COILTRONICS FP2S-100-R INFINEON, BSC320N20NS3 G INFINEON, BSC011N03LSI ZETEX FMMT718TA ZETEX FMMT618TA VISHAY, CRCW12064K70JNEA VISHAY, CRCW060329K4FKEA VISHAY, CRCW0603330RJNEA VISHAY, CRCW0603412KFKEA VISHAY, CRCW1206150RJNEA VISHAY, CRCW120620R0JNEA VISHAY, CRCW120647K0JNEA SUSUMU, RL1632T-R018-G VISHAY, CRCW060310K0JNEA VISHAY, CRCW060315K0FKEA VISHAY, CRCW06033K01FKEA VISHAY, CRCW0603169KFKEA VISHAY, CRCW06031K47FKEA VISHAY, CRCW0603100KJNEA VISHAY, CRCW060312K0JNEA VISHAY, CRCW06032K00JNEA VISHAY, CRCW060315R0JNEA VISHAY, CRCW080547R0JNEA PULSE PA1735NL PULSE PA0184NL LINEAR TECH LT3825EFE ADDITIONAL DEMO BOARD CIRCUIT COMPONENTS2 45 0 C6 CAP, 1210 47uF 20% 6.3V X5R OPTION TDK C3225X5R0J476MT OPTION 10 QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 894C-B 36V-72VIN, SYNCHRONOUS FLYBACK 46 47 48 49 50 51 52 0 1 1 0 1 0 0 C18 C30 L1 Q4 R1 R10 R28 CAP, 0603 10nF 10% 25V X7R OPTION CAP, 22uF 100V IND, 4.7uH MOSFET N-CHANNEL OPTION RES, 0603 0 OHM JUMPER RES, 1206 OPTIONAL RES, 0805 OPTION AVX 06033C103KAT OPTION SUN ELECTRONIC 100ME22AX VISHAY IHPL2525CZER4R7M01 INFINEON, BSC011N03LSI OPTION VISHAY, CRCW06030000Z0EA OPTION 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