DC894B-C - Demo Manual

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
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