DC1317A-E - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-E
ACTIVE RESET ISOLATED DC/DC POWER CONVERTER
LT1952
DESCRIPTION
Demonstration circuit 1317A-E is isolated input to
high current output 1/8th Brick footprint converter
featuring the LT®1952 switching controller with Active Reset circuit. The Active Reset circuit can improve the efficiency in wide input voltage applications. Also, the Active Reset allows the implementation of self-driven synchronous secondary rectifiers
in some applications.
The DC1317A-E converts isolated 36V to 72V input
to 5V output and provides over 12A of output current. The converter operates at 260kHz with the peak
efficiency greater than 94% at 8A load. The DC1317
can be easily modified to generate output voltages in
the range from 0.6V to 48V. The output currents are
limited by total output power of up to 150W.
The other available versions of DC1317A are:
DC1317A-F, 9-36Vin to 3.3V, 20A
DC1317A-G, 9-36Vin to 12V, 5A
DC1317A-H, 9-36Vin to 48V, 1.5A
The DC1317 circuit features soft-start which prevents output voltage overshoot on startup or when
recovering from overload condition.
The DC1317 has precise over-current protection circuit that allows for continuous operation under short
circuit conditions. The low power dissipation under
short circuit conditions insures high reliability even
during short circuits.
The LT1952 can be synchronized to an external
clock of up to 400kHz. Please refer to LT1952 data
sheet for design details and applications information.
DC1317A-A, 36-72Vin to 3.3V, 30A
DC1317A-B, 18-72Vin to 5V, 25A
DC1317A-C, 18-72Vin to 12V, 10A
Design files for this circuit board are available.
Call the LTC factory.
DC1317A-D, 18-72Vin to 24V, 5A
LT is a trademark of Linear Technology Corporation
Table 1.
Performance Summary
PARAMETER
CONDITION
VALUE
Minimum Input Voltage
IOUT = 0A to 12A
36V
Maximum Input Voltage
IOUT = 0A to 12A
72V
VOUT
VIN = 36V to 72V, IOUT = 0A to 12A
5V ±3%
Typical Output Ripple VOUT
VIN = 36V to 72V, IOUT = 0A to 12A
50mVP–P
Nominal Switching Frequency
260kHz
QUICK START PROCEDURE
Demonstration circuit 1317 is easy to set up to
evaluate the performance of LT1952 circuit. 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 input or
output voltage ripple by touching the probe tip di-
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-E
ACTIVE RESET ISOLATED DC/DC POWER CONVERTER
rectly across the Vin or Vout and GND terminals.
See Figure 2. for proper scope probe technique.
If there is no output, temporarily disconnect the
load to make sure that the load is not set too high.
1.
With power off, connect the input power supply to
Vin and GND. Make sure that the input power
supply has sufficient current rating at minimum
input voltage for the required output load.
4.
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 parameters.
2.
Turn on the power at the input.
5.
The DC1317 is equipped with an output capacitor
CSYS (470uF) that approximates typical system
rail capacitance. If system board already has capacitance of similar value CSYS can be removed.
NOTE: Make sure that the input voltage does not
exceed 72V.
3.
Check for the proper output voltage.
Vout = 5V.
Figure 1. Proper Measurement Equipment Setup
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-E
ACTIVE RESET ISOLATED DC/DC POWER CONVERTER
Figure 2. Scope Probe Placement for Measuring Input or Output Ripple
PRIMARY MOSFET DRIVER LTC4440
The DC1317 has an optional LTC4440 MOSFET
driver U2. The LTC4440 can be used if much bigger MOSFETs are used. Please contact LT factory
for assistance.
ACTIVE RESET CIRCUIT
The DC1317 is equipped with an active reset circuit that consists of Q13 and C25. The capacitor
C25 charges to the appropriate transformer reset
voltage. The MOSFET Q13 applies the C25 reset
voltage across the primary of transformer T1. The
C25 reset voltage varies with the duty cycle and
automatically adjusts to provide volt-second balance for transformer magnetizing current.
OUTPUT LOAD STEP RESPONSE
The load step response of DC1317A-E is very fast
even though relatively small amount of output capacitance is present (100uF ceramic and 470uF
electrolytic). This is thanks to fast error amplifier
of LT4430, optimal amount of current slope compensation of LT1952, fast opto coupler and fast
error amplifier of LT1952. If higher load steps
need to be handled more output capacitance can be
added in order to keep the voltage transients at the
desired level. The load step transients are shown in
Figure 4.
Efficiency
LT1952 Efficiency (DC1317A-E) Self Driven SR,
5V output
95%
94%
93%
92%
91%
90%
89%
88%
87%
86%
Figure 4. Fast transient response of DC1317A-E
is superior to many competing power modules
without the additional output capacitors.
0
2
4
6
8
10
12
14
Iout [A]
Figure 3. High efficiency of DC1317A-E allows
the board to be used in thermally demanding
applications
SOFT START FUNCTION
The DC1317 features LT4430 opto coupler driver
that has soft start function which produces monotonic startup ramp shown if Figure 5. The rise time
of output voltage is controlled by capacitor C19
that is connected to OC (overshoot control) pin of
LT4430.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-E
ACTIVE RESET ISOLATED DC/DC POWER CONVERTER
components that can be removed. Also, the PCB layout has a common schematic that is used just for the
layout. The actual circuit schematic shows component values. In some cases, a resistor is used inplace
holder for a capacitor as in case of C4. Please modify
the reference designators in your schematic to reflect
the actual component used. The following simple
PCB layout rules should be helpful.
Figure 5. The LT4430 opto coupler driver produces monotonic output voltage rise at startup
without output voltage overshoot.
DEBUGGING AND TESTING
The DC1317 can easily be tested and debugged by
powering the bias circuit separately from the main
power circuit. To place DC1317 into debug mode
remove the resistor R1 and connect 48V, 100mA
power source to +Vb node (right side of R1). By
doing this, the primary PWM controller LT1952
can be activated without the main primary power
being applied to +Vin.
To activate the secondary side feedback circuit
LT4430 diode OR a 10V, 100mA power source
into collector of Q9.
Once the primary and secondary controllers are
running the MOSFET gate timing can be checked.
If the MOSFET gate timing is correct the main
power input can be applied to +Vin. By slowly increasing the +Vin from 0V to 48V the output voltage and input current can be monitored. The input
current should not exceeded 100mA without the
output load. If one of the MOSFETs is damaged,
the input current will exceed 100mA.
If possible use solid ground planes on layers 2 and NThe ground planes will prevent the switching noise
from coupling into sensitive lines.
Place sensitive lines on the inner layers that will be
shielded by grounds on layers 2 and N-1.
Keep the loop formed by Q1, RCS1, Cin and T1
tight.
Keep the loop formed by Q2, Q3 and T1 tight.
Keep noise sensitive nodes like SD/VSEC, ROSC,
FB, COMP, ISENSE, BLANK and DELAY as small
as posible by placing the associated components
close to the LT1952 and LT4430 chips.
Use local vias for all components that connect to
ground planes.
Do not place any traces on the layers 2 and N-1 to
avoid ground planes from being compromised.
If the PCB layout has to be done on 2 or 4-layer PCB
use the same guidelines as outlined above. Also,
maximize the ground connections between components by placing the components tight together.
Please contact LT factory for additional assistance.
PCB LAYOUT
The pcb layout should be carefully planned to avoid
potential noise problems. The PCB layout for
DC1317A can be used as a guide. Since demo board
DC1317A has 8 versions the PCB layout has optional
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-E
ACTIVE RESET ISOLATED DC/DC POWER CONVERTER
+Vin
2.2R
R11
82k
Cin1
Cin3
2.2uF, 100V
C25
C33
0.1u
Q13
Si2325
R13
22K
BC856T
R14
33K
U1
LT1952-1
1
2
Q12
R15
115k 3
R42
C10
0.1u
0R 4
SS
5
6
R22
7
13.3k
R32
332k
8
R28
442k
+Vr2 +Vb
DC1317A-E schematic
9, 10
GND
2
4
Q1
Si7818
Comp
Sout
FB=1.23V
Vin
Rosc
Out
Sync
PGND
MaxDC
Delay
Vr=2.5V
OC
SD
Isense
GND
Blank
16
Vu1
15
14
T1
PA2720
Q2
Q3
FDMC8854
FDMC8854
R8
100R
13
C9
12
100p
11
10
R33
158k
R20
75k
9
R24
39K
U6
PS2801-1
Vfb
D11
BAS516
U4
LT4430
1
R26
220R
C23
1uF
R23 910
D6
BAS516
Rcs1
0.025R
Cu1
4.7u
5V, 12A
+
D14
BAS516
SS
R29
22K
5
+Vo1
+Vout
33n, 200V, 1206
BAS516
Vfb
6, 7
L1
3.1uH
R50
3.3R
+Vin
R45
10k
D17
1
D5
PDZ10B
-Vin
R53
200
D2
BAS516
D3
BAS516
+Vr2
36V to 72V
1.5mH
Csys
470uF, 6.3V
R1
L2
Q10
PBSS8110 Vu1
+Vb
Co1
100uF, X7R
+Vin
C16
.22u, 10V
2
3
R30
1.2k
R27
270R
Vcc
Opto
GND
Comp
SS
C19
0.33u
FB
6
5
4
C17
10n
R34
5.36k
R35
137k
R38
18.2K
C15
2.2nF, 2kV
NOTE:
C13
.47u
This schematic shows only the components required for operation of -E version of DC1317A demo board.
All optional components of DC1317A demo board have been removed.
Also, all zero-ohm resistors have been replaced with wires.
Please consult the full DC1317A-E schematic to decide if any of the optional components should be included in your design.
5
+Vo1
C24
47p
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-E
ACTIVE RESET ISOLATED DC/DC POWER CONVERTER
6
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-E
ACTIVE RESET ISOLATED DC/DC POWER CONVERTER
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