DC1317A-G - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G
ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER
LT1952-1
DESCRIPTION
Demonstration circuit 1317A-G 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-G (Figure 7) converts isolated 9V to
36V input to 12V output and provides over 8A 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 available versions of DC1317A are:
DC1317A-F, 9-36Vin to 3.3V, 22A
* DC1317A-F5, 9-36Vin to 5V, 20A
DC1317A-G, 9-36Vin to 12V, 8A
* DC1317A-G18, 9-36Vin to 18V, 5A
DC1317A-H, 9-36Vin to 48V, 1.5A
* The DC1317A-G18 is a slightly modified design featuring 18V @6A output. Please contact the LTC factory for details.
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
DC1317A-B, 18-72Vin to 5V, 25A
DC1317A-C, 18-72Vin to 12V, 8A-12A
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
DC1317A-E, 36-72Vin to 5V, 12A
Table 1. Performance Summary
PARAMETER
CONDITION
VALUE
Minimum Input Voltage
IOUT = 0A to 8A
9V
Maximum Input Voltage
IOUT = 0A to 8A
36V
VOUT
VIN = 9V to 36V, IOUT = 0A to 8A (27Amax) 12V ±3%
Typical Output Ripple VOUT
VIN = 9V to 36V, IOUT = 0A to 8A
Nominal Switching Frequency
50mVP–P
200kHz
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G
ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER
QUICK START PROCEDURE
Demonstration circuit 1317 is easy to set up to evaluate the performance of LT1952-1 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 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.
NOTE: Make sure that the input voltage does not
exceed 36V.
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-G
ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER
Figure 2. Scope Probe Placement for Measuring Input or Output Ripple
ACTIVE RESET CIRCUIT
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-G 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.
If PCB space is limited, a smaller 1825R2-3366.006
transformer from Champs engineering can be used.
However, the efficiency will be about 1% lower. For
more information please consult LT factory.
DC1317A-G 12V Output Efficiency
95%
94%
Efficiency
The Active Reset circuit on DC1317A-F 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.
93%
92%
12V input
91%
24V input
90%
89%
0
1
2
3
4
5
6
7
8
9
Iout [A]
Figure 3. High efficiency of DC1317A-G allows the
board to be used in thermally critical applications
18V OUTPUT CIRCUIT
The DC1317A-G demo board can easily be modified
for 18V output. Only few minor component changes
are required and are shown in the schematic in Figure
8.
The efficiency of 18V Output version of DC1317A-G is
shown in the Figure 4. The efficiency is slightly lower
than the efficiency of 12V version due to higher DC
resistance of transformer and output MOSFETs.
Also, the 18V output can be further increased to 19.5V
just by changing the voltage divider on the FB pin of
LT4430 circuit. The 19.5V version is suitable for supplying laptop computer power from 12V automotive
power source.
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G
ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER
DC1317A-G-18V 18V Output Efficiency,
95%
Efficiency
94%
93%
92%
12V input
91%
24V input
90%
89%
0
1
2
3
4
5
6
7
8
Iout [A]
Figure 4. The efficiency of modified DC1317A-G
demo board for 18V output.
OUTPUT LOAD STEP RESPONSE
The load step response of DC1317A-G is very fast
even though relatively small amount of output capacitance is present (200uF 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
5.
Figure 5. Fast transient response of DC1317A-F is
superior to many competing power modules without the additional output capacitors.
SOFT START FUNCTION
The DC1317 features LT4430 opto coupler driver
that has soft start function which produces monotonic startup ramp shown if Figure 6. 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.
Figure 6. 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
4
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G
ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER
remove the resistor R1 and connect 12V, 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.
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.
Once the primary and secondary controllers are
running the main power (+Vin) can be applied
slowly while observing the switching waveforms
and output voltage.
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.
The input current supplying the power transformer
T1 should not exceeded 200mA without the output
load. If one of the MOSFETs is damaged, the input
current will exceed 200mA.
Use local vias for all components that connect to
ground planes.
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. The schematic in figure 7
is showing the circuit without any optional components. Also, the circuit in figure 7 does not show any
zero-ohm resistors. Please consult the schematic on
page 7 to determine if any of the options should be
included in your PCB layout.
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.
Also, the PCB layout has a common schematic that is
used just for the layout. The PCB layout schematic is
not included in this quick start guide but it is included
with PCB design files.
Please note that the actual circuit schematic on page 7
shows the component values. The PCB layout schematic included with design files 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.
5
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G
ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER
1
2.2R
9-36V Input
Q10
PBSS8110
Cin
3x6.8uF
R11
10k
-Vin
D3
+Vr2
6
3
R3
665R
R14
33K
1
2
R15
178k 3
4
C13
.47u
5
C10
0.1u
6
R22
7
13.3k
8
Comp
R28
115k
R32
196k
+Vr2
TG
Inp
TS
FB=1.23V
Vin
Rosc
Out
Sync
MaxDC
PGND
Delay
Vr=2.5V
OC
SD
Isense
GND
Blank
R2
560k
6
Q1
HAT2266
5
4
D17
BAS516
16
C33
0.1u
Vu1
15
D10*
100p
14
C8
100p
R10
1k
D14
BAS516
11
10
R23 910R
R24
100k
1
CS+
2
R21
10k
4
D9
PDZ10B
Sync
CS- Timer
3
CG
U5
LTC3900
CG
GND
Vcc
FG
60.4k
U4
LT4430
U6
PS2801-1
R26
220R
1
Vu1
2
Vfb
R30
1.2k
C15
2.2nF, 2kV
C19
1uF
3
6
5
T2A
PE-68386
470p
R27
470R
Opto
GND
Comp
FB
C17
15n
6
5
4
R34
12.1k
R35
348k +Vo1
R38
18.2K
NOTE:
This schematic shows only the components required for operation of -G 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-G schematic to decide if any of the optional
components should be included in your design.
7
C12
Vcc
SS
8
L4
10uH
R17
560R
FG
R19
D11
BAS516
C23
1uF
9
R18
10k
C7
220p
C14
1u
Cu1
4.7u
R20
100k
R16
33k
Q9
BCX55
13
12
D7
BAS521
C5
0.22u
R45
10k
GND
Out
C6*
BAS521
C34
0.33u
+
CG
L3
680uH
Q13
Si7309
R53*
10uH
Q3
HAT2173
FG
R54
2.2R
Rcs1
0.005R
D1
BAS516
Sout
R29*
PMEG3002
+Vb
GND
U1
LT1952-1
Vfb
Q12
BC856T
Boost
Q2
HAT2266
2, 3
4, 5
33n
2
C21
220p
R13
22K
Vcc
10, 11
G45R2-0306.006
C25
1
C3
1u
L1
T1
U2
LTC4440-5
Vu1
+Vout
D2
BAS516
L2
D5
PDZ10B 1.5mH
+Vin
Figure 7. DC1317A-G
schematic.
HR-PQA2050-16 +Vo1
7, 8
220uF, APXE
Vu1
Csys
+Vb
R1
Co1
33uF, X7R
+Vin
+Vin
Demo Board DC1317A-G schematic
* Please change the ref designator to reflect the symbol.
6
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G
ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER
+Vb
R1
Vu1
1
2.2R
9-36V Input
Q10
PBSS8110
Cin
3x6.8uF
R11
10k
-Vin
3
R3
511R
1
Vfb
2
R15
178k 3
4
C13
.47u
5
6
C10
0.1u
R22
7
13.3k
8
Comp
R28
115k
R32
196k
+Vr2
GND
TG
Inp
TS
6
FB=1.23V
Vin
Rosc
Out
Sync
PGND
MaxDC
Delay
Vr=2.5V
OC
SD
Isense
GND
Blank
6
Q1
RJK0652
2, 3
5
4
BAS516
16
Vu1
15
C8
100p
D14
BAS516
Cu1
4.7u
R20
100k
11
10
R23 910R
NOTE:
R24
100k
1
4
D9
PDZ10B
Sync
CS- Timer
3
CG
CG
GND
Vcc
FG
60.4k
U4
LT4430
U6
PS2801-1
R26
220R
1
Vu1
2
Vfb
R30
1.2k
C15
2.2nF, 2kV
C19
1uF
3
7
6
5
T2A
PE-68386
C12
470p
R27
470R
Vcc
Opto
GND
Comp
SS
8
L4
10uH
R17
560R
FG
R19
FB
C17
15n
6
5
4
R34
12.1k
R35
348k +Vo1
R38
11K
This schematic shows the required modifications of DC1317A-G for 18V @6A output.
The component values and part numbers shown in RED are the only changes required for 18V output.
Please contact LT factory for assistance.
R2
560k
CS+
2
R21
10k
U5
LTC3900
D11
BAS516
C23
1uF
9
R18
10k
C7
220p
C14
1u
13
12
R16
33k
Q9
BCX55
R10
1k
GND
Out
C5
0.22u
R45
10k
Csys
150uF, 20V, APXE
+
D7
BAS521
C6*
BAS521
C34
0.33u
18V Output
CG
L3
1.5mH
Q13
Si7309
C33
0.1u
Q3
RJK2055
FG
R54
2.2R
R53*
10uH
D10*
100p
Q2
HAT2266
4, 5
D17
14
10, 11
G45R2-0207.005
Rcs1
0.005R
D1
BAS516
Sout
R29*
PMEG3002
+Vb
Boost
U1
LT1952-1
R14
33K
+Vr2
C25
2
C21
220p
Q12
BC856T
Vcc
L1
T1
33n
1
C3
1u
R13
22K
D3
U2
LTC4440-5
Vu1
+Vout
D2
BAS516
L2
D5
PDZ10B 1.5mH
+Vin
Figure 8. The 18V @6A
version of DC1317A-G.
HR-PQA2050-27 +Vo1
7, 8
Co1
33uF, X7R
+Vin
+Vin
Demo Board DC1317A-G18V schematic
* Please change the ref designator to reflect the symbol.
7
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G
ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER
8
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-G
ACTIVE RESET ISOLATED 9-36V INPUT TO 12V @8A DC/DC POWER CONVERTER
9
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