DC1317A-B - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-B
ACTIVE RESET ISOLATED 18-72V INPUT TO 5V @25A DC/DC POWER CONVERTER
LT1952
DESCRIPTION
Demonstration circuit 1317A-B 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.
DC1317A-D, 18-72Vin to 24V, 5A
The DC1317A-B converts isolated wide 18V to 72V
input to 5V output and provides over 30A of output
current depending on cooling. When determining the
cooling requirements the actual input voltage range
and continuous maximum output current must be
taken into account. The converter operates at 200kHz
with the peak efficiency greater than 94%. 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 DC1317 circuit features soft-start which prevents
output voltage overshoot on startup or when recovering from overload condition.
The available versions of DC1317A are:
DC1317A-E, 36-72Vin to 5V, 12A
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 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.
Design files for this circuit board are avai
available.
Call the LTC factory.
DC1317A-A, 34-75Vin to 3.3V, 35A
DC1317A-B, 18-72Vin to 5V, 25A
LT is a trademark of Linear Technology Corporation
DC1317A-C, 18-72Vin to 12V, 10A
Table 1. Performance
Summary
PARAMETER
CONDITION
VALUE
Minimum Input Voltage
IOUT = 0A to 25A
18V
Maximum Input Voltage
IOUT = 0A to 25A
72V
VOUT
VIN = 18V to 72V, IOUT = 0A to 25A
(30Amax)
5V ±3%
Typical Output Ripple VOUT
VIN = 18V to 72V, IOUT = 0A to 25A
50mVP–P
Nominal Switching Frequency
200kHz
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-B
ACTIVE RESET ISOLATED 18-72V INPUT TO 5V @25A DC/DC POWER CONVERTER
QUICK START PROCEDURE
PROCEDURE
Demonstration circuit 1317 is easy to set up to evaluate the performance of LT1952 circuit. Refer to FigFigure 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 directly
across the Vin or Vout and GND terminals. See Figure
2. for proper scope probe technique.
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.
2.
Turn on the power at the input.
3.
Check for the proper output voltage.
Vout = 5V.
If there is no output, temporarily disconnect the
load to make sure that the load is not set too high.
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.
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.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-B
ACTIVE RESET ISOLATED 18-72V INPUT TO 5V @25A DC/DC POWER CONVERTER
Figure 1. Proper Measurement Equipment Setup
Figure 2. Scope Probe Placement
Placement for Measuring Input or Output Rip
Rip ple
ACTIVE RESET CIRCUIT
The Active Reset circuit on DC1317A-B demo board
consists of a small P-Channel MOSFET Q13 and
reset capacitor C25. The MOSFET Q13 is used to
connect the reset capacitor across the transformer
T1 primary winding during the reset period when
Q1 MOSFET is off. The voltage across capacitor
C25 automatically adjusts with the duty cycle to
provide complete transformer reset under all operating conditions.
Also the active reset circuit shapes the reset voltage
into a square waveform that results in lower drain
voltages for Q1 and Q2 MOSFETs. The lower
MOSFET drain voltages allow lower voltage and
lower Rdson MOSFETs to be used. The MOSFETs
must be avalanche rated for the peak reset voltage.
If non-avalanche rated MOSFETs are used a proper
drain voltage derating should be used.
The main benefit of active reset circuit in the case of
DC1317A-B demo board is high efficiency (shown
in Figure 3), wide input range, high power density
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-B
ACTIVE RESET ISOLATED 18-72V INPUT TO 5V @25A DC/DC POWER CONVERTER
and small size. To achieve such high efficiency all of
the power components were carefully selected.
Please consult LT factory for assistance if any
changes to the circuit are required.
DC1317A-B (LT1952) 5V Output Efficiency
95%
93%
Figure 4. Fast transient response of DC1317 is
su perior to many competing power modules
without the additional output capaci
capacitors.
91%
89%
87%
24V input
85%
48V input
83%
0
10
20
30
Iout [A]
Figure 3. High efficiency of DC1317ADC1317A-B al
allows
the board to be used
u sed in thermally critical appliapplications
SOFT START FUNCTION
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. Also, the soft-start function will prevent
input current surges even with full load at the output.
OUTPUT LOAD STEP RESPONSE
RESPONSE
The load step response of DC1317A-B, shown in
Figure 4, is very fast even though relatively small
amount of output capacitance is present (300uF
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. Also, the loop response can be improved further by faster loop
compensation.
Figure 5. The LT4430 opto coupler driver proproduces monotonic output voltage rise at startup
without out
out put voltage overshoot.
DEBUGGING AND TESTING
TESTIN G
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
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-B
ACTIVE RESET ISOLATED 18-72V INPUT TO 5V @25A DC/DC POWER CONVERTER
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 control circuit
LT4430 diode OR a 10V, 100mA power source into
collector of Q9 bias transistor.
Once the primary and secondary controllers are
running the main power (+Vin) can be applied
slowly while observing the switching waveforms
and output voltage.
The input current supplying the power transformer
T1 should not exceeded 100mA without the output
load. If one of the MOSFETs is damaged, the input
current will exceed 100mA.
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 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.
The PCB layout schematic does not show the component values.
In some cases, a different component like a diode is
used in a place holder for a capacitor such as in the
case of C6. Please modify the reference designators in
your schematic to reflect the actual component used.
The following simple PCB layout rules should be helpful.
If possible use solid ground planes on layers 2 and
n-1. The 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
try to stay close to the guidelines outlined above. Also,
maximize the ground connections between components by placing the components tight together.
Please contact LT factory for additional assistance.
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QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-B
ACTIVE RESET ISOLATED 18-72V INPUT TO 5V @25A DC/DC POWER CONVERTER
+Vb
R1
Q10
PBSS8110 Vu1
PA1393.202
1
+Vin
18V to 72V
L2
1.5mH
R11
75k
2.2R
Cin3
3x2.2uF
+Vr2
6
+Vin
C1, C35
1n
2
Q3
HAT2165
HAT2169
CG
U2
LTC4440-5
T1
5
C4*
BAS516
G45R2-0502-005
Vu1
1
C3
1u
2
C21
470p
3
R3
301R
R14
33K
Vfb
2
R15
174k 3
4
C13
.47u
5
C10
0.1u
6
187k
8
R32
7
13.3k
R28
309k
R22
+Vb
+Vr2 R2
560k
Vcc
Boost
GND
TG
Inp
TS
D1
BAS516
6
Q1
5
R54
10R
4
Rcs1
0.006R
D17
BAS516
Comp
Sout
FB=1.23V
Vin
Rosc
Out
Sync
PGND
MaxDC
Delay
Vr=2.5V
SD
GND
OC
Isense
Blank
R29*
PMEG3002
Vu1
14
D10*
100p
C8
100p
Cu1
4.7u
13
12
11
10
C9
100p
R23 1k
9
D7
B0540W
C25
33n
C34
0.22u
C6*
BAS516
C5
0.22u
Q13
Si2325
16
15
Out
L3
220uH
HAT2173
U1
LT1952-1
1
Csys
470uF, 6.3V
+
GND
R5
10R
R13
22K
Co1
Co2
Co3
Q2
FG
Q12
BC856T
L1
10, 11
D5
PDZ10B
-Vin
+Vout
R4, R55
3.3R
D2
D3
BAS516
+Vo1
7, 8
100uF, X7R
+Vin
R53
200
R45
10k
C33
0.1u
CG
CS+
U6
PS2801-1
Vfb
R24
47k
R27
470R
D11
BAS516
CG
GND
Vcc
FG
1
2
3
R30
1.2k
8
L4
10uH
R17
560R
7
6
5
FG
R19
T2A
PE-68386
56k
C12
470p
R31
10R
C16
.22u
Sync
CS- Timer
3
4
C14
1u
U5
LTC3900
D9
PDZ7.5B
Vu1
NOTE:
This schematic shows only the components required for operation of
-B version of DC1317A demo board.
All optional components of DC1317A demo board have been removed.
C23
Also, all zero-ohm resistors have been replaced with wires.
1uF
Please consult the full DC1317A-B schematic to decide if any of the
optional components should be included in your design.
1
R21
10k
R10
1k
R20
100k
R16
33k
2
Q9
BCX55
D14
BAS516
R26
220R
R18
10k
C7
220p
R8*
1uF
C17
15n
U4
LT4430
Vcc
Opto
GND
Comp
SS
C19 1uF
FB
6
5
4
R38
R34
3.4k
R35
137k
+Vo1
C24
22p
18.2K
C15
2.2nF, 2kV
Demo Board DC1317A-B schematic
* Please change the reference designator to reflect the symbol.
6
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-B
ACTIVE RESET ISOLATED 18-72V INPUT TO 5V @25A DC/DC POWER CONVERTER
7
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-B
ACTIVE RESET ISOLATED 18-72V INPUT TO 5V @25A DC/DC POWER CONVERTER
8
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