DC1300A-A - Demo Manual

DEMO CIRCUIT 1300A-A
QUICK START GUIDE
LTC3725 /
LTC3725 / LTC3726
100W Isolated Forward
Converter with Synchronous
Rectification
DESCRIPTION
Demonstration circuit 1300A-A 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 5.0V, 20A 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-B/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
MIN
9*
200LFM
VIN = 18V, IOUT = 20A (20MHz BW)
Line and Load (9-36V, 0-20A)
VIN =18V, IOUT = 18A
Basic
Component Area x Top Component Height
TYP
MAX
36
UNITS
V
5.0
V
0
20
A
200
kHz
60
mVP–P
±0.2
%
90
%
1500
Vdc
2.3 x 1.45 x 0.40
Inches
*Typical minimum startup is 9.3V
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
1
LTC3725 /
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.
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
shunt can be put in series with the input supply
in order to measure the DC1300A’s input current.
1. Set an input power supply that is capable of 9V to
36V to 18V. Then turn off the supply.
c. A voltmeter with a capability of measuring at
2. Direct an airflow of 200lfm across the unit for sustained operation at full load.
least 36V can be placed across the input terminals in order to get an accurate input voltage
measurement.
3. With power off, connect the supply to the input
terminals +Vin and –Vin.
4. Turn on the power at the input.
NOTE. Make sure that the input voltage never exceeds 36V.
5. Check for the proper output voltage of 5V. Turn off
the power at the input.
6. Once the proper output voltages are established,
connect a variable load capable of sinking 20A at
5V to the output terminals +Vout and –Vout. Set
the current for 0A.
2
LTC3725 /
a. If efficiency measurements are desired, an am-
meter or a resistor shunt that is capable of handling 20Adc can be put in series with the output
load in order to measure the DC1300A’s output
current.
b. A voltmeter with a capability of measuring at
least 5V 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 disconnect the load to make
sure that the load is not set too high.
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.
Figure 1. Proper Measurement Equipment Setup
3
LTC3725 / LTC3726
Figure 2. Proper Noise Measurement Setup
Efficiency vs. Load Current
92%
90%
88%
Efficiency (%)
86%
84%
82%
9VIN
80%
18VIN
78%
36VIN
76%
74%
72%
70%
2
4
6
8
10
12
14
16
18
20
Load Curre nt (A)
Figure 3. Efficiency
4
LTC3725 / LTC3726
Figure 4. Output Ripple at 18Vin and 20Aout (25MHz) (20mV, 5us / div, 25MHz)
Figure 5. Transient Response Waveform at 18Vin and 10 - 20Aout (10A, 1000mV, 100us / div)
5
LTC3725 / LTC3726
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 8:20:51 AM 2/19/2008 e : 0.95 Bg : 28.8°C
Figure 6. Thermal Map, Frontside at 18Vin and 20Aout (Ta = 25 degrees C, 200 LFM)
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 9:00:28 AM 2/19/2008 e : 0.95 Bg : 29.6°C
Figure 7. Thermal Map, Backside at 18Vin and 20Aout (Ta = 25 degrees C, 200 LFM)
6
D3
12V
MMSZ5242BS
-VOUTS
CUT
1
C81
10pF
C82
75pF
SG
2
C88
47pF
2
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
3.3nF
100V
1206
47K
5
14
15
PT-
PT+
R84
0
Q14
HAT2169H
Q15
(Opt.)
VSW
SS
VA
R79
1.0K
-VOUTS
2
Q36
MBT3946DW1T1
R50
0.002
1W
1
D25
BAS21
R55
100
1%
C70
2.2nF
R85
(Opt.)
C78
4.7nF
SS
R54
100
1%
-VOUTP1
-VOUTS -VOUTP
U2
LTC3726EGN
PT-
C71
1uF
C20
1.5nF
200V
-VOUTP
C30
2.2nF
250V
5
6
4
3
R24
R23
16.2
1/4W
T2
PA0297
2
3
4
1
5
-VOUTS
R7
47K
Q27C
R63
90.9K
R61
100
C73
470pF
1
C66
5.6nF
100V
C72
0.1uF
R58
7
8
9
10
11
T1
PA0901.005
6
D6
4.3V
MMSZ4687T1
C7
100pF
C6
100pF
R95
U1
LTC3725EMSE
FB/IN+
R13
(Opt.)
1206
Q8 Q11Q39
Si7852DP
C89
0.22uF
FMMT718
Q2
VCp
C27 2.2nF
R98
22
1
(Opt.)
R49
Q37
MMBT2907A
1%
R94 147
R89
604
1
1
T3
PA1005.100
Q1
FMMT619
1
SSFLT
ULVO
R87
0
2
2.2K
D7
BAS21
D29
PT1N4148WS
C29
33nF
1
8
3
R97
VCC
10K
10K
R6
Ra
VCp
Rb
162K
1
R3
100
C3
C4
C5
6.8uF
50V
1812
1
Q6
MMBFJ201
3
R11
R12
1.0
Q34
2N7002
VSW
D2
1N4148WS
1
C24
4.7uF
2
Q28
FMMT38C
VIN
R18
147K
E2
C2
6.8uF
50V
1812
1
2
3
7 46 5 8
7
VIN
10
3
2 2
3
E1
3
2
C55
1nF
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
2.2nF
200V
1206
1
R56
100
C79
2.2nF
R68
6.81K
SG
VSB
Q27C
VCC
2.4uH
PA1494.242
L2
25V
C67
4.7uF
R46
619
E4
-Vout
+Vout
5V/20A
LTC CONFIDENTIAL - FOR CUSTOMER USE ONLY
R9
100
C10
1.0nF
220uF
6.3V
-VOUTS
C77
22uF
1210
-VOUTP
C76
(Opt.)
R41
4.53K
C80
E3
+ C83
+VOUT
-VOUTP
VCC
C31
C33
100uF
6.3V
1210
+VOUT
LINEAR TECHNOLOGY CORPORATION
FB/PH
4
Q27
FCX491A
1
R76
470
1206
D28
MMSZ5236BS
7.5V
R4
(Opt.)
1630 McCARTHY BLVD.
MILPITAS, CA. 95035
408-432-1900
Linear Technology Has Made A Best Ef f ort To Design A
408-434-0507 FAX
Circuit That Meets Customer-Supplied Specif ications;
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
Document Number
Rev
Perf ormance Or Reliability . Contact Linear Technology Size
Applications Engineering For Assistance.
Demo Circuit 1300A-A
This Circuit Is Proprietary To Linear Technology And
Friday, June 05, 2009
1
3
Date:
Sheet
Supplied For Use With Linear Technology Parts.
of
Customer Notice
-VOUTS
C75
68pF
R69
0
R83
(Opt.)
VA
Q26
FMMT619
2
3
Q3
Q12
Q38
Si7852DP
D1
BAS21
R1
R2
R51
R52
31.6
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
470uH
LTC3725 / LTC3726
7
Similar pages