DC1317A-C - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-C
ACTIVE RESET ISOLATED 18-72V INPUT TO 12V @8A DC/DC POWER CONVERTER
LT1952
DESCRIPTION
Demonstration circuit 1317A-C 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-C converts isolated 18V to 72V input to
12V output and provides over 12A 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 300kHz 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 other 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 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, 34-75Vin to 3.3V, 35A
Design files for this circuit board are avail
available.
Call the LTC factory.
DC1317A-B, 18-72Vin to 5V, 25A
LT is a trademark of Linear Technology Corporation
DC1317A-D, 18-72Vin to 24V, 5A
Table 1. Performance
Summary
PARAMETER
CONDITION
VALUE
Minimum Input Voltage
IOUT = 0A to 8A
18V
Maximum Input Voltage
IOUT = 0A to 8A
72V
VOUT
VIN = 34V to 75V, IOUT = 0A to 8A
(12Amax)
12V ±3%
Typical Output Ripple VOUT
VIN = 34V to 75V, IOUT = 0A to 8A
50mVP–P
Nominal Switching Frequency
300kHz
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-C
ACTIVE RESET ISOLATED 18-72V INPUT TO 12V @8A 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.
2.
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.
Turn on the power at the input.
NOTE: Make sure that the input voltage does not
exceed 72V.
3.
Check for the proper output voltage.
Vout = 12V.
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 (220uF) that approximates typical system
rail capacitance. If system board already has capacitance of similar value CSYS can be removed.
Figure 1. Proper Measurement Equipment Setup
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-C
ACTIVE RESET ISOLATED 18-72V INPUT TO 12V @8A DC/DC POWER CONVERTER
Output
utput Rip
Figure 2. Scope Probe Placement for Measuring Input or O
Rip ple
ACTIVE RESET CIRCUIT
The Active Reset circuit on DC1317A-C 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-C demo board is high efficiency (shown
in Figure 3), wide input range, high power density
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-C (LT1952) 12V Output Efficiency
96%
95%
94%
93%
92%
91%
90%
89%
88%
87%
86%
85%
84%
24V input
48V input
0
2
4
6
8
10
12
Iout [A]
Figure 3. High efficiency of DC1317ADC1317A-C al
allows
the board to be used in thermally critical appliapplications
OUTPUT LOAD STEP RESPONSE
RESPONSE
The load step response of DC1317A-C is very fast
even though relatively small amount of output capacitance is present (33uF ceramic and 220uF 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.
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-C
ACTIVE RESET ISOLATED 18-72V INPUT TO 12V @8A 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 5V, 100mA power source into
pin 1 of LT4430 controller.
Figure 4. Fast transient response of DC1317 is
su perior to many competing power modules
without the additional output capaci
capacitors.
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. Also, the soft-start function will prevent
input current surges even with full load at the output.
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.
Figure 5. The LT4430 opto coupler driver proproduces monotonic output voltage rise at startup
without out
out put voltage overshoot.
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.
DEBUGGING AND TESTING
TESTIN G
Place sensitive lines on the inner layers that will be
shielded by grounds on layers 2 and n-1.
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
Keep the loop formed by Q1, RCS1, Cin and T1 tight.
Keep the loop formed by Q2, Q3 and T1 tight.
4
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-C
ACTIVE RESET ISOLATED 18-72V INPUT TO 12V @8A DC/DC POWER CONVERTER
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.
5
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-C
ACTIVE RESET ISOLATED 18-72V INPUT TO 12V @8A DC/DC POWER CONVERTER
Vu1
HR-PQA2050-10 +Vo1
1
2.2R
Q10
PBSS8110
D3
R11
47k
-Vin
+Vout
D2
BAS516
L2
D5
PDZ10B 1.5mH
18V to 72V
Cin
3x2.2uF
7, 8
L1
6
9, 10, 11
Q2
HAT2266
Q3
HAT2173
+Vr2
2, 3
+Vin
FG
U2
LTC4440-5
T1
4, 5
G45R2-0405.005
Vu1
3
C21
220p
R3
Vfb
2
Q12
BC856T
R15
115k 3
4
C13
.47u
5
C10
0.1u
6
R22
7
13.3k
8
Comp
Vin
Rosc
Sync
MaxDC
Out
PGND
Delay
Vr=2.5V
SD
GND
R28
309k
R32
187k
+Vr2
TS
442
Q1
HAT2173
5
OC
Isense
Blank
R54
4.7R
Rcs1
4
C34
0.22u
C5
0.22u
Q13
Si2325
R53*
10uH
Vu1
Q9
BCX55
C33
0.1u
D14
BAS516
14
C8
100p
Cu1
4.7u
11
10
C9
100p
Demo Board DC1317A-C schematic
1
2
3
4
U5
LTC3900
CS+
U6
PS2801-1
7
CS- Timer
CG
GND
Vcc
FG
6
5
R17
560R
FG
C12
470p
C7
220p
L4
10uH
Out
C14
1u
D11
BAS516
R31
10R
C16
.22u, 10V
Vfb
This schematic shows only the components required for operation of -C 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-C schematic to decide if any of the optional
components should be included in your design.
8
Sync
47.5K
9
C23
1uF
T2A
PE-68386
R19
R26
220R
NOTE:
R2
560k
R18
10k
Vu1
R20
115k
R23 2k
R24
68k
R16
33k
CG
D9
PDZ10B
13
12
R8
2.2R
R10
1k
15
D10*
100p
C6*
BAS521
R21
10k
R45
10k
D17
D7
BAS521
L3
680uH
0.006R
16
R29*
PMEG3002
+Vb
TG
6
BAS516
Sout
FB=1.23V
Inp
D1
BAS516
U1
LT1952-1
1
GND
Boost
10n
2
Vcc
C25
1
C3
1u
R14
33K
+
CG
GND
R5
10R
R13
22K
Csys
220uF, 16V, APXE
+Vb
R1
Co1
33uF, X7R
+Vin
+Vin
U4
LT4430
1
2
3
R30
1.2k
R27
470R
Vcc
Opto
GND
Comp
SS
C19
1uF, X5R
FB
6
C17
15n
R34
12.1k
5
4
R38
18.2K
C15
2.2nF, 2kV
* Please change the ref designator to reflect the symbol.
6
R35
348k +Vo1
C24
22p
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-C
ACTIVE RESET ISOLATED 18-72V INPUT TO 12V @8A DC/DC POWER CONVERTER
7
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-C
ACTIVE RESET ISOLATED 18-72V INPUT TO 12V @8A DC/DC POWER CONVERTER
8
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