DC894C-B - Demo Manual

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
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