DC894A-A - Demo Manual

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
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