DC1300A-B - Demo Manual

DEMO CIRCUIT 1300A-B
LTC3725
/ LTC3726
QUICK
START
GUIDE
LTC3725 / LTC3726
100W Isolated Forward Converter with Synchronous Rectification
DESCRIPTION
Demonstration circuit 1300A-B is a 100W Isolated
Forward Converter with Synchronous Rectification
featuring the LTC3725 / LTC3726.
This circuit was designed to demonstrate the high levels of performance, efficiency, and small solution
size attainable using this part in a Resonant-Reset
Forward Converter power supply. It operates at
200kHz and produces a regulated 12V, 8.4A output
from an input voltage range of 9 to 36V: suitable for
automotive, industrial, and other applications. It has a
quarter-brick footprint area. Synchronous rectification
helps to attain efficiency exceeding 90%. Secondaryside control eliminates complex optocoupler feedback,
providing fast transient response with minimum output capacitance. For other output requirements, see
DC1300A-A/C ([email protected] / [email protected]) or DC1174AA/B/C ([email protected] [email protected] / [email protected]). For telecom
input requirements, see DC1031A-A/B/C
([email protected]), or DC1032A-A ([email protected]), or
DC888A-A/B/C ([email protected] / [email protected] [email protected]).
Design files for this circuit board are available. Call
the LTC factory.
, 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 ΔΣ, 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
VIN
VOUT
IOUT
FSW
VOUT P-P
IREG
POUT/PIN
PARAMETER
Input Supply Range
Output Voltage
Output Current Range
Switching (Clock) Frequency
Output Ripple
Output Regulation
Efficiency (see Figure 3)
Isolation
Approximate Size
CONDITIONS
200LFM
VIN = 18V, IOUT = 8.4A (20MHz BW)
Line and Load (9-36V, 0-8.4A)
VIN =18V, IOUT = 8.4A
Basic
Component Area x Top Component Height
MIN
9*
TYP
MAX
36
UNITS
V
12.0
V
0
8.4
A
200
kHz
60
mVP–P
±0.06
%
90
%
1500
Vdc
2.3 x 1.45 x 0.47
Inches
*Typical minimum startup is 9.3V
1
LTC3725 / LTC3726
OPERATING PRINCIPLES
The LTC3725 Single-Switch Forward Controller is
used on the primary and provides start-up, gate drive,
and protection functions. Once start-up is accomplished, the LTC3726 Secondary-Side Synchronous
Forward Controller takes over, and provides the
LTC3725 with timing information and bias power
through a small pulse transformer.
When input voltage is applied, the LTC3725 commences soft-start of the output voltage. When the
secondary bias source reaches the undervoltage threshold, the LTC3726 comes alive and takes control by
sending encoded PWM gate pulses to the LTC3725
through T2. These pulses also provide primary bias
power efficiently over a wide input voltage range.
The transition from primary to secondary control occurs at a fraction of the nominal output voltage. From
then on, operation and design is simplified to that of a
simple buck converter. Secondary control eliminates
delays, tames large-signal overshoot, and reduces
output capacitance needed to meet transient response
requirements.
An optional LC filter stage on the input lowers rms input
current. The filter must have output impedance that is
less than the converter input impedance to assure stability. This may require a damping impedance. (See Linear
Technology Application Note AN19 for a discussion of
input filter stability.) A source with a 50mOhm or higher
ESR at the filter resonant frequency is one way of providing damping for the filter elements provided on the
DC1300A. For bench testing, adding an electrolytic capacitor such as a Sanyo 50ME470AX to the input terminals
will provide suitable damping and ripple current capability. The values selected have a filter resonant frequency
that is below the converter switching frequency, thus
avoiding high circulating currents in the filter.
QUICK START PROCEDURE
Demonstration circuit 1300 is easy to set up to evaluate the performance of the LTC3725 / LTC3726. Refer to Figure 1 for proper measurement equipment
setup and follow the procedure below:
NOTE. When measuring the output voltage ripple, care must be taken to
avoid a long ground lead on the oscilloscope probe. Measure the output
voltage ripple by touching the probe tip and ground ring directly across
the last output capacitor as shown in Figure 12.
shunt can be put in series with the input supply
in order to measure the DC1300A’s input current.
c. A voltmeter with a capability of measuring at
least 36V can be placed across the input terminals in order to get an accurate input voltage
measurement.
1. Set an input power supply that is capable of 9V to
36V to 18V. Then turn off the supply.
4. Turn on the power at the input.
2. Direct an airflow of 200lfm across the unit for sustained operation at full load.
5. Check for the proper output voltage of 12V. Turn
off the power at the input.
3. With power off, connect the supply to the input
terminals +Vin and –Vin.
6. Once the proper output voltages are established,
connect a variable load capable of sinking 8.4A at
12V to the output terminals +Vout and –Vout. Set
the current for 0A.
a. Input voltages lower than 9V can keep the con-
verter from turning on due to the undervoltage
lockout feature of the LTC3725 / LTC3726.
b. If efficiency measurements are desired, an am-
meter capable of measuring 7Adc or a resistor
NOTE. Make sure that the input voltage never exceeds 36V.
a. If efficiency measurements are desired, an am-
meter or a resistor shunt that is capable of handling 8.4Adc can be put in series with the out-
2
LTC3725 / LTC3726
put load in order to measure the DC1300A’s
output current.
NOTE. If there is no output, temporarily disconnect the load to make
b. A voltmeter with a capability of measuring at
8. Once the proper output voltage is again established, adjust the load within the operating range
and observe the output voltage regulation, ripple
voltage, efficiency and other desired parameters.
least 5V can be placed across the output terminals in order to get an accurate output voltage measurement.
sure that the load is not set too high.
7. Turn on the power at the input.
Figure 1. Proper Measurement Equipment Setup
3
LTC3725 / LTC3726
Figure 2. Proper Noise Measurement Setup
92.00
90.00
88.00
Efficiency (%)
86.00
9VIN
84.00
18VIN
82.00
36VIN
80.00
78.00
76.00
74.00
72.00
70.00
1.000
2.000
3.000
4.000
5.000
6.000
7.000
8.000
Curre nt in Am ps
Figure 3. Efficiency
4
LTC3725 / LTC3726
Figure 4. Output Ripple at 18Vin and 8.4Aout (25MHz) (50mV, 5us / div, 25MHz)
Figure 5. Transient Response Waveform at 18Vin and 4.2 – 8.4Aout (5A, 100mV, 100us / div)
5
LTC3725 / LTC3726
Ce lsius
153.0
90.0
85.0
80.0
75.0
70.0
65.0
60.0
55.0
50.0
45.0
-22.0
40.0
Th ermo teknix T V S-70 0 1:52:03 PM 2/26/2008 e : 0.95 Bg : 32.7°C
Figure 6. Thermal Map, Frontside at 18Vin and 8.4Aout (Ta = 25 degrees C)
Celsius
153.0 90.0
85.0
80.0
75.0
70.0
65.0
60.0
55.0
50.0
45.0
-22.0
40.0
Thermoteknix TVS-700 2:38:29 PM 2/26/2008 e : 0.95 Bg : 33.0°C
Figure 7. Thermal Map, Backside at 18Vin and 8.4Aout (Ta = 25 degrees C)
6
D3
22V
MMSZ5251BS
C55
4.7nF
1
2
Q28
FMMT38C
VIN
R18
147K
E2
-VOUTS
1
C81
10pF
2
1
8
2
C88
47pF
R49
FS/IN-
1
5
4
VSB
C9
0.22uF
VIN
VCC
R86
261K
R93
147
1%
0
5.1K
8
R92
C8
470pF
R91
10.0K
R90
7.50K
C1
1.5nF
100V
1206
47K
5
VSW
14
15
PT-
PT+
R84
0
Q14
Q15
Si7852DP
SS
VA
R79
3.3K
-VOUTS
2
Q36
MBT3946DW1T1
R50
0.005
1W
1
D25
(Opt.)
R55
100
1%
C70
3.9nF
R85
(Opt.)
C78
4.7nF
SS
R54
100
1%
-VOUTP1
-VOUTS -VOUTP
U2
LTC3726EGN
PT-
C71
1uF
C20
(Opt.)
200V
-VOUTP
C30
2.2nF
250V
5
6
4
3
R23
R24
(Opt.)
1/4W
T2
PA0297
2
3
4
1
5
6
-VOUTS
R7
47K
Q27C
R63
90.9K
R61
100
C73
470pF
1
C66
3.3nF
100V
T1
PA0910
C72
0.1uF
R58
7
8
9
10
11
D6
4.3V
MMSZ4687T1
C7
100pF
C6
100pF
R95
U1
LTC3725EMSE
FB/IN+
R13
0
1206
Q8 Q11 Q39
Si7370DP
C89
0.22uF
FMMT718
Q2
VCp
C27 2.2nF
R98
22
1
(Opt.)
Q37
MMBT2907A
1%
R94 147
R89
715
1
2.2K
T3
PA1005.100
Q1
FMMT619
1
SSFLT
ULVO
1
2
D7
BAS21
VCC
R87
0
10K
10K
3
7 46 5 8
R97
D29
PT1N4148WS
C29
33nF
C82
82pF
SG
Q34
2N7002
VSW
C24
4.7uF
Ra
R6
VCp
Rb
162K
1
R3
100
Q6
MMBFJ201
3
CUT
1.0
R11
R12
1
3
C2
6.8uF
50V
1812
3
2
1
2
C3
C4
C5
6.8uF
50V
1812
7
VIN
10
3
2 2
3
E1
D2
1N4148WS
R22
28.7K
D4
4.7V
MMSZ5230BS
1
2
10
-Vin
1
2
2
FG
12
SW
3
11
3
Q32
FMMT718
3
2
C69
220pF
200V
1206
1
R56
100
C79
2.2nF
R68
19.6K
SG
VSB
Q27C
VCC
10uH
PULSE,
PA2050.103NL
L2
25V
C67
4.7uF
R46
619
R9
(Opt.)
C10
(Opt.)
-Vout
+Vout
12V/8.4A
LTC CONFIDENTIAL - FOR CUSTOMER USE ONLY
-VOUTS
C77
22uF
1210
-VOUTP
C76
(Opt.)
R41
11.8K
E4
68uF
16V
C80
E3
+ C83
+VOUT
-VOUTP
VCC
C31
C33
22uF
16V
1210
+VOUT
LINEAR TECHNOLOGY CORPORATION
FB/PH
4
Q27
FCX491A
1
R76
470
1206
D28
MMSZ5236BS
7.5V
R4
10
1630 McCARTHY BLVD.
MILPITAS, CA. 95035
Linear Technology Has Made A Best Ef f ort To Design A
408-432-1900
Circuit That Meets Customer-Supplied Specif ications;
408-434-0507 FAX
Howev er, It Remains The Customer's Responsibility To
Verif y Proper And Reliable Operation In The Actual
Title
Application. Component Substitution And Printed
LTC3725EMSE, LTC3726EGN 9V-36Vin Forward Converter
Circuit Board Lay out May Signif icantly Af f ect Circuit
Perf ormance Or Reliability . Contact Linear Technology Size
Document Number
Rev
Applications Engineering For Assistance.
Demo Circuit 1300A-B
This Circuit Is Proprietary To Linear Technology And
Friday, June 05, 2009
2
3
Supplied For Use With Linear Technology Parts.
of
Date:
Sheet
Customer Notice
-VOUTS
C75
68pF
R69
0
R83
(Opt.)
VA
Q26
FMMT619
2
3
Q3
Q12
Q38
Si7450DP
D1
(Opt.)
R1
R2
R51
R52
75
R66
100K
IS+
3
NDRV
VSLMT
9
GND
8
GATE
PGND
6
PGND
13
ISRUN/SS
6
IS
11
SLP
7
1
FS/SYNC
9
1
SG
+Vin
9V - 36V
3
2
1
L1
0.47uH
4
3
GND
2
3
1
2
6
1
ITH
5
2
3
16
VCC
3
MODE
2
1
L3
(Opt.)
LTC3725 / LTC3726
7
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