LT3825 AND LT3837
1
DESCRIPTION
Demonstration circuit 950A is a 30W multi-output syn-
chronous flyback converter in 1/8 brick format featuring
the LT3825 and LT3837. Output voltage sensing is im-
plemented without the use of opto-coupler, by sensing
the voltage across a primary side auxiliary winding. A
load compensation circuit is used to compensate for
voltage drops caused by load currents.
DC950A-A has input voltage range 36V-72V and features
the LT3825.
DC950A-B has input voltage range 9V-36V and features
the LT3837.
Demonstration circuit 950A uses a transformer design
with tapped secondary winding, to achieve higher effi-
ciency and better cross regulation than is possible with a
transformer that uses a separate winding for each out-
put.
Design files for this circuit board are available. Call
the LTC factory.
L, LTC, LTM, LT, Burst Mode, OPTI-LOOP, Over-The-Top and PolyPhase are registered
trademarks of Linear Technology Corporation. Adaptive Power, C-Load, DirectSense, Easy
Drive, FilterCAD, Hot Swap, LinearView, µModule, Micropower SwitcherCAD, Multimode
Dimming, No Latency ∆Σ, No Latency Delta-Sigma, No RSENSE, Operational Filter, PanelProtect,
PowerPath, PowerSOT, SmartStart, SoftSpan, Stage Shedding, SwitcherCAD, ThinSOT,
UltraFast and VLDO are trademarks of Linear Technology Corporation. Other product names
may be trademarks of the companies that manufacture the products.
PERFORMANCE SUMMARY
Specifications are at TA = 25°C
SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS
V
IN
Input Supply Range DC950A-A
DC950A-B
36
9
72
36
V
V
V
OUT
Output Voltage V
OUT1
V
OUT2
V
OUT3
4.85
3.20
2.42
5V
3.3V
2.5V
5.15
3.40
2.58
V
V
V
I
OUT
Output Current (Note: Total output power not to
exceed 30W)
I
OUT1
(5V output)
I
OUT2
(3.3V output)
I
OUT3
(2.5V output)
0
0
0
2
3
3
4
4
4
A
A
A
Efficiency
Efficiency DC950A-A,V
IN
=48V,I
OUT1
=2A,I
OUT1
=3A,I
OUT3
=3A
DC950A-B,V
IN
=24V,I
OUT1
=2A,I
OUT1
=3A,I
OUT3
=3A
90
89
%
%
EQUIPMENT
8 DMMs
1 DC Supply 0-72V 1A for DC950A-A test
1 DC Supply 0-36V 5A for DC950A-B test
3 Adjustable loads 0-3A
DEMO CIRCUI
T
950
A
QUICK START GUID
E
LT3825 and LT3837
Non-opto Synchronous Fly
-
back Controlle
r
LT3825 AND LT3837
2
GETTING STARTED
Demonstration circuit 950A is easy to set up to evaluate
the performance of the LT3825 and LT3837. Refer to
Figure 1 for proper measurement equipment setup and
follow the procedure below:
1.
With power off, connect the input power supply to Vin
and GND.
2.
With no loads, adjust input voltage to be within the
input voltage range (36V-72V for DC950A-A, 9V-36V
for DC950A-B) and turn on the power at the input.
3.
Check for the proper output voltages. Vout1 = 5V,
Vout2 = 3.3V, Vout3 = 2.5V.
4.
Adjust the loads and study the performance of the
circuit. Note that the load current should not exceed
4A, and the total load on the three outputs should not
exceed 30W continuous power.
Figure 1.
Proper Measurement Equipment Setup
LT3825 AND LT3837
3
LT3825 AND LT3837
4
DC950A-A BILL OF MATERIAL
Item Qty Reference Part Description Manufacture / Part #
REQUIRED CIRCUIT COMPONENTS1
1 1 C38 Capacitor, NP0, 33pF, 50V, 0603 AVX, 06035A330KAT2
2 1 C41 Capacitor, NPO, 330PF, 50V, 0603 AVX, 06035A331KAT
3 1 C1 Capacitor, NPO 330PF 100V 1206 AVX, 12061A331KAT
4 2 C34,C30 Capacitor, X7R, 2200pF, 50V, 0603 AVX, 06035C222JAT
5 3 C19,C31,C32 Capacitor, X5R, 0.1uF, 25V, 0603 AVX, 06033D104KAT2A
6 1 C40 Capacitor, X7R, 1000pF, 50V, 0603 AVX, 06035C102KAT2A
7 1 C36 Capacitor, X5R, 0.47uF, 16V, 0603 AVX, 0603YD474M
8 6 C3,C4,C13,C14,C26,C27 Capacitor, X5R, 47uF, 6.3V, 1210 TDK, 3225X 5R0J476M
9 0 C33,C39 Capacitor, 0603 OPT
10 1 C35 Capacitor, X7R, 3300PF, 50V, 0603 KEMET, C0603C332J5RAC
11 1 C37 Capacitor, NPO, 680PF, 50V, 0603 AVX, 06035A681JAT
12 1 C9 Capacitor, NPO, 150pF, 200V, 1206 AVX, 12062A151KAT2A
13 1 C18 Capacitor, X7R, 22uF, 16V, 1210 TDK, C3225RX7R1C226M
14 2 C20,C21 Capacitor, X7R, 2.2uF, 100V, 1812 TDK, C4532X7R2A225M
15 1 D2 BAS21 Diodes, Inc.,BAS21-7-F
16 2 D8,D6 BAT54 Diodes, Inc.,BAT54-7-F
17 1 D5 BAT54A Diodes, Inc.,BAT54A-7
18 1 D10 BAT54S Diodes, Inc.,BAT54S-7-F
19 1 D9 B0530W Diodes, Inc.,B0530W-7-F
20 0 D4 Zenerdiode, 12V, 5%, SOT23 OPT
21 1 L5 Inductor, 330uH Coilcraft, DO1608C-334MLB
22 1 L6 Inductor, 120uH Wurth Elektronik, 744 032 121
23 1 Q1 MOSFET, n-ch, SO8 Vishay, Si4850EY-T1-E3
24 1 Q3 MOSFET, n-ch, SO8 Vishay, Si4840DY-T1-E3
25 2 Q7,Q9 Transistor, npn, SOT23 Zetex, FMMT619TA
26 3 Q8,Q10,Q12 Transistor, pnp, SOT23 Zetex, FMMT718TA
27 0 Q4 Transistor, npn, SOT23 OPT
28 1 Q5 MOSFET, n-ch, SO8 Vishay, Si4840DY-T1-E3
29 1 Q6 MOSFET, n-ch, SO8 Vishay, Si4488DY-T1-E3
30 1 R11 Resistor, 0 OHMS 0603 VISHAY, CRCW06030000Z0EA
31 1 R2 Resistor, 18 OHMS 1206 VISHAY, CRCW120618R0JNEA
32 2 R21,R16 Resistor, 15 OHMS 0603 VISHAY, CRCW060315R0FKEA
33 1 R15 Resistor, 330 OHMS 0603 VISHAY, CRCW0603330RFKEA
34 2 R9,R29 Resistor, 1.00k, 0603 VISHAY, CRCW06031K0FKED
35 1 R14 Resistor, 1.00k, 0805 VISHAY, CRCW08051K0FKED
36 1 R22 Resistor, 3.01K, 0603 VISHAY, CRCW06033011FRT6
37 1 R30 Resistor, 4.64K, 0603 VISHAY, CRCW06034K64FKED
38 3 R19,R23,R28 Resistor, 10.0K, 0603 VISHAY, CRCW060310K0FKED
39 1 R12 Resistor, 28.7K, 0805 VISHAY, CRCW080528K7FKED
40 1 R25 Resistor, 100K, 0603 VISHAY, CRCW0603100KJNEA
41 1 R27 Resistor, 150K, 0603 VISHAY, CRCW0603150KJNEA
42 1 R5 Resistor, 22 OHM, 1206 VISHAY, CRCW120622ROJNEA
43 1 R17 Resistor, 0.025 OHM 1% 1206 IRC, LRF1206LF-01-R025-F
44 1 R26 Resistor, 1.00K, 0603 VISHAY, CRCW06031K00FKEA
45 1 R6 Resistor, 47K, 1206 VISHAY, CRCW120647K0JNEA
46 1 R13 Resistor, 402K, 0805 VISHAY, CRCW0805402KFKEA
47 0 R4,R18 Resistor, 1206 OPT
48 1 R8 Resistor, 91 OHMS 0805 VISHAY, CRCW080591R0FKEA
49 1 R20 Resistor, 14.7K, 0603 VISHAY, CRCW060314K7FKEA
50 1 R24 Resistor, 12.4K, 0603 VISHAY, CRCW060312K4FKEA
LT3825 AND LT3837
5
51 1 T2 Gatedrive transformer Pulse Engineering, PA0173
52 1 T1 EFD20 Flyback transformer Pulse Engineering, PA2046NL
53 1 U1 LT3825EFE#PBF Linear Technology,
LT3825EFE#PBF
ADDITIONAL DEMO BOARD CIRCUIT COMPO NENTS2
1 1 C8 Capacitor, electrolytic, 12UF, 100V Sanyo, 100ME12AX+TS
2 3 C7,C17,C23 Capacitor, TANT, 100uF, 6.3V, 3528 Kemet, T520B107M006ASE070
3 1 C43 Capacitor, X7R, 4700pF 250V, 1812 MURATA,
GA343DR7GD472KW01L
4 3 L1,L3,L4 Inductor, 0.2uH Cooper, FP2-S200
5 1 L2 Inductor, 4.7u H Cooper, HCP0703-4R7-R
HARDWARE-FOR DEMO BOARD ONLY:
1 4 (STAND-OFF), STAND-OFF, NYLON 0.50" KEYSTONE, 8833(SNAP ON)
2 6 E1-E6 Turret, 0.094" Mill-Max, 2501-200-80-00-00-07-0
Notes:
1. Required Circuit Component s are those parts that are required to implement the circuit function
2. Additional Demo Board Circuit Component s are those parts that provide added functionality for the demo
board but
are not required in the actual circuit.
DC950A-B BILL OF MATERIAL
Item Qty Reference Part Description Manufacture / Part #
REQUIRED CIRCUIT COMPONENTS1
1 1 C38 Capacitor, NP0, 33pF, 50V, 0603 AVX, 06035A330KAT2
2 1 C41 Capacitor, NPO, 330PF, 50V, 0603 AVX, 06035A331KAT
3 1 C1 Capacitor, NPO 330PF 100V 1206 AVX, 12061A331KAT
4 2 C34,C30 Capacitor, X7R, 2200pF, 50V, 0603 AVX, 06035C222JAT
5 3 C19,C31,C32 Capacitor, X5R, 0.1uF, 25V, 0603 AVX, 06033D104KAT2A
6 1 C40 Capacitor, X7R, 1000pF, 50V, 0603 AVX, 06035C102KAT2A
7 1 C36 Capacitor, X5R, 0.47uF, 16V, 0603 AVX, 0603YD474M
8 6 C3,C4,C13,C14,C26,C27 Capacitor, X5R, 47uF, 6.3V, 1210 TDK, 3225X5R0J476M
9 0 C33,C39 Capacitor, 0603 OPT
10 1 C35 Capacitor, X7R, 3300PF, 50V, 0603 KEMET, C0603C332J5RAC
11 1 C37 Capacitor, NPO, 680PF, 50V, 0603 AVX, 06035A681JAT
12 1 C9 Capacitor, NPO, 560pF, 100V, 1206 AVX, 12061A561KAT2A
13 0 C18 Capacitor, 1210 OPT
14 2 C20,C21 Capacitor, X7R, 4.7uF, 50V, 1812 TDK,C4532X7R1H475MT
15 1 D2 BAS21 Diodes, Inc.,BAS21-7-F
16 2 D8,D6 BAT54 Diodes, Inc.,BAT54-7-F
17 1 D5 BAT54A Diodes, Inc.,BAT54A-7
18 1 D10 BAT54S Diodes, Inc.,BAT54S-7-F
19 1 D9 B0530W Diodes, Inc.,B0530W-7-F
20 1 D4 Zenerdiode, 11V, 5%, SOT23 Vishay, BZX84C11-V
21 1 L5 Inductor, 330uH Coilcraft, DO1608C-334MLB
22 1 L6 Inductor, 120uH Wurth Elektronik, 744 032 121
23 1 Q1 MOSFET, n-ch, SO8 Vishay, Si4850EY-T1-E3
24 1 Q3 MOSFET, n-ch, SO8 Vishay, Si4840DY-T1-E3
25 2 Q7,Q9 Transistor, npn, SOT23 Zetex, FMMT619TA
26 3 Q8,Q10,Q12 Transistor, pnp, SOT23 Zetex, FMMT718TA
LT3825 AND LT3837
6
27 1 Q4 Transistor, npn, SOT23 MMBT3904L T
28 1 Q5 MOSFET, n-ch, SO8 Renesas, HAT2165H
29 1 Q6 MOSFET, n-ch, SO8 Vishay, Si7852DP-T1-E3
30 1 R11 Resistor, 0 OHMS 0603 VISHAY, CRCW06030000 Z0EA
31 1 R2 Resistor, 18 OHMS 1206 VISHAY, CRCW120618R0JNEA
32 2 R21,R16 Resistor, 15 OHMS 0603 VISHAY, CRCW060315R0FKEA
33 1 R15 Resistor, 330 OHMS 0603 VISHAY, CRCW0603330RFKEA
34 2 R9,R29 Resistor, 1.00k, 0603 VISHAY, CRCW06031K0FKED
35 1 R14 Resistor, 1.00k, 0805 VISHAY, CRCW08051K0FKED
36 1 R22 Resistor, 3.01K, 0603 VISHAY, CRCW06033011 FRT6
37 1 R30 Resistor, 4.64K, 0603 VISHAY, CRCW06034K64FKED
38 3 R19,R23,R28 Resistor, 10.0K, 0603 VISHAY, CRCW060310K0FKED
39 1 R12 Resistor, 28.7K, 0805 VISHAY, CRCW080528K7FKED
40 1 R25 Resistor, 100K, 0603 VISHAY, CRCW0603100 K JNEA
41 1 R27 Resistor, 150K, 0603 VISHAY, CRCW0603150 K JNEA
42 1 R5 Resistor, 22 OHM, 1206 VISHAY, CRCW120622ROJNEA
43 2 R17,R18 Resistor, 0.015 OHM 1% 1206 IRC, LRF12 06-01-R015-F
44 1 R26 Resistor, 750 OHMS, 0603 VISHAY, CRCW0603750RFKEA
45 1 R4 Resistor, 4.7k, 1206 VISHAY, CRCW12064K70FKEA
46 1 R13 Resistor, 121K, 0805 VISHAY, CRCW0805121KFKEA
47 0 R6 Resistor, 1206 OPT
48 1 R8 Resistor, 22.1 OHMS 080 5 VISHAY, CRCW080522R1FKEA
49 1 R20 Resistor, 22.1K, 0603 VISHAY, CRCW060322K1FKEA
50 1 R24 Resistor, 13.0K, 0603 VISHAY, CRCW060313K0FKEA
51 1 T2 Gatedrive transformer Pulse Engineering, PA0173
52 1 T1 EFD20 Flyback transformer Pulse Engineering, PA2047NL
53 1 U1 LT3837EFE#PBF Linear Technology,
LT3837EFE#PBF
ADDITIONAL DEMO BOARD CIRCUIT COMPO NENTS2
1 1 C8 Capacitor, electrolytic, 47UF, 50V Sanyo, 50ME47AX+TS
2 3 C7,C17,C23 Capacitor, TANT, 100uF, 6.3V, 3528 Kemet, T520B107M006ASE070
3 1 C43 Capacitor, X7R, 4700pF 250V, 1812 MURATA,
GA343DR7GD472KW01L
4 3 L1,L3,L4 Inductor, 0.2uH Cooper, FP2-S200
5 1 L2 Inductor, 4.7u H Cooper, HCP0703-4R7-R
HARDWARE-FOR DEMO BOARD ONLY:
1 4 (STAND-OFF), STAND-OFF, NYLON 0.50" KEYSTONE, 8833(SNAP ON)
2 6 E1-E6 Turret, 0.094" Mill-Max, 2501-200-80-00 -00-07-0
Notes:
1. Required Circuit Component s are those parts that are required to implement the circuit function
2. Additional Demo Board Circuit Component s are those parts that provide added functionality for the demo
board but
are not required in the actual circuit.
