Linear Technology DC1317A-B User manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-B
ACTIVE RESET ISOLATED 18-72V INPUT TO 5V @25A DC/DC POWER CONVERTER
1
LT1 52
DESCRIPTION
DESCRIPTIONDESCRIPTION
DESCRIPTION
Demonstration circuit 1317A-B is isolated input to
high current output 1/8th Brick footprint
1/8th Brick footprint1/8th Brick footprint
1/8th Brick footprint converter
featuring the LT®1952 switching controller with Ac-
tive Reset circuit. The Active Reset circuit can im-
prove the efficiency in wide input voltage applica-
tions. Also, the Active Reset allows the implementa-
tion of self-driven synchronous secondary rectifiers
in some applications.
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 available versions of DC1317A are:
DC1317A-A, 34-75Vin to 3.3V, 35A
DC1317A-B, 18-72Vin to 5V, 25A
DC1317A-C, 18-72Vin to 12V, 10A
DC1317A-D, 18-72Vin to 24V, 5A
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 recover-
ing from overload condition.
The DC1317 has precise over-current protection cir-
cuit 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 ava
Design files for this circuit board are avaDesign files for this circuit board are ava
Design files for this circuit board are avai
ii
il
ll
lable.
able.able.
able.
Call the LTC factory.
Call the LTC factory.Call the LTC factory.
Call the LTC factory.
LT is a trademark of Linear Technology Corporation
Table 1.
Table 1.Table 1.
Table 1. Performance Summary
Performance SummaryPerformance Summary
Performance Summary
PARAMETER
PARAMETERPARAMETER
PARAMETER CONDITION
CONDITIONCONDITION
CONDITION VALUE
VALUEVALUE
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
2
QUICK START PROCEDUR
QUICK START PROCEDURQUICK START PROCEDUR
QUICK START PROCEDURE
EE
E
Demonstration circuit 1317 is easy to set up to evalu-
ate the performance of LT1952 circuit. Refer to Fi
Refer to FiRefer to Fi
Refer to Fig-
g-g-
g-
ure 1 for proper measurement equipment setup
ure 1 for proper measurement equipment setupure 1 for proper measurement equipment setup
ure 1 for proper measurement equipment setup
and follow the procedure below:
NOTE:
NOTE:NOTE:
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 out-
put 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.
1.1.
1. With power off, connect the input power supply to
Vin and GND. Make sure that the input power sup-
ply has sufficient current rating at minimum input
voltage for the required output load.
2.
2.2.
2. Turn on the power at the input.
NOTE:
NOTE:NOTE:
NOTE: Make sure that the input voltage does not
exceed 72V.
3.
3.3.
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.
4.4.
4. Once the proper output voltage is established, ad-
just the load within the operating range and ob-
serve the output voltage regulation, ripple voltage,
efficiency and other parameters.
5.
5.5.
5. The DC1317 is equipped with an output capacitor
CSYS (470uF) that approximates typical system
rail capacitance. If system board already has ca-
pacitance of similar value CSYS can be removed.
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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
3
Figure 1. Proper Measurement Equipment Setup
Figure 1. Proper Measurement Equipment SetupFigure 1. Proper Measurement Equipment Setup
Figure 1. Proper Measurement Equipment Setup
Figure 2. Scope Probe Plac
Figure 2. Scope Probe PlacFigure 2. Scope Probe Plac
Figure 2. Scope Probe Placement for Measuring Input or Output Ri
ement for Measuring Input or Output Riement for Measuring Input or Output Ri
ement for Measuring Input or Output Rip
pp
pple
pleple
ple
ACTIVE RESET CIRCUIT
ACTIVE RESET CIRCUITACTIVE RESET CIRCUIT
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 oper-
ating 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
4
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
83%
85%
87%
89%
91%
93%
95%
0 10 20 30
Iout [A]
24V input
48V input
Figure 3. High efficiency of DC1317A
Figure 3. High efficiency of DC1317AFigure 3. High efficiency of DC1317A
Figure 3. High efficiency of DC1317A-
--
-B a
B aB a
B al
ll
llows
lowslows
lows
the board to be u
the board to be uthe board to be u
the board to be used in thermally critical appl
sed in thermally critical applsed in thermally critical appl
sed in thermally critical appli-
i-i-
i-
cations
cationscations
cations
OUTPUT LOAD STEP RES
OUTPUT LOAD STEP RESOUTPUT LOAD STEP RES
OUTPUT LOAD STEP RESPONSE
PONSEPONSE
PONSE
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 capaci-
tance can be added in order to keep the voltage
transients at the desired level. Also, the loop re-
sponse can be improved further by faster loop
compensation.
Figure 4. Fast transient response of DC1317 is
Figure 4. Fast transient response of DC1317 isFigure 4. Fast transient response of DC1317 is
Figure 4. Fast transient response of DC1317 is
s
ss
su
uu
uperior to many competing power modules
perior to many competing power modulesperior to many competing power modules
perior to many competing power modules
without the additional output capac
without the additional output capacwithout the additional output capac
without the additional output capaci
ii
itors.
tors.tors.
tors.
SOFT START FUNCTI
SOFT START FUNCTISOFT START FUNCTI
SOFT START FUNCTION
ONON
ON
The DC1317 features LT4430 opto coupler driver
that has soft start function which produces mono-
tonic 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 out-
put.
Figure 5. The LT4430 opto coupler driver pr
Figure 5. The LT4430 opto coupler driver prFigure 5. The LT4430 opto coupler driver pr
Figure 5. The LT4430 opto coupler driver pro-
o-o-
o-
duces monotonic output voltage rise at startup
duces monotonic output voltage rise at startupduces monotonic output voltage rise at startup
duces monotonic output voltage rise at startup
without ou
without ouwithout ou
without out
tt
tput voltage overshoot.
put voltage overshoot.put voltage overshoot.
put voltage overshoot.
DEBUGGING AND TESTIN
DEBUGGING AND TESTINDEBUGGING AND TESTIN
DEBUGGING AND TESTING
GG
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
5
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
PCB LAYOUTPCB LAYOUT
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 compo-
nents 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 compo-
nent 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 help-
ful.
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 compo-
nents 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
6
Rcs1 0.006R
+Vin
Cu1 4.7u
R23 1k
R24 47k
Vu1
R15 174k
R20 100k
C10 0.1u
Vu1
Q1
D10* 100p
R3 301R
C15
2.2nF, 2kV
R28
309k
R22 13.3k
HAT2173
G45R2-0502-005
GND
8
SD
7
MaxDC
5
FB=1.23V
2
Comp
1
Rosc
3
Vr=2.5V
6
Blank 9
Delay 12
OC 11
Sync
4
Isense 10
PGND 13
Out 14 Vin 15
Sout 16
U1
LT1952-1
C13 .47u
R26 220R
R30 1.2k
R14 33K
C23 1uF
Vfb
Vfb
R13 22K
Co1
100uF, X7R
+Vo1
Co2
T2A
PE-68386
C14 1u
C12 470p
R19 56k
CS-
2
CS+
1
CG
3
Vcc
4FG 5
GND 6
Timer 7
Sync 8
U5
LTC3900
R21 10k
R27 470R
R38 18.2K
R35 137k
R34 3.4k
C19 1uF
C16 .22u
C17 15n
+Vo1
R31 10R
SS
3
Vcc
1
FB 4
Opto 6
GND
2Comp 5
U4
LT4430
R18 10k
Cin3 3x2.2uF
+Vin
D5 PDZ10B
Vu1
D2
BAS516
R11 75k
-Vin +Vin
18V to 72V
R1 2.2R
R32
187k
L1
PA1393.202
Q2 HAT2165
Q3 HAT2169
R16 33k
C5 0.22u
Q9 BCX55
R10 1k
D9 PDZ7.5B
R8* 1uF
FG
FG
CG
CG
C3 1u
R5 10R
Q12 BC856T
D3
Q10 PBSS8110
+Vb
+Vb
L2
1.5mH
U6
PS2801-1
T1
Inp
3
Vcc
1
TS 4
Boost 6
GND
2TG 5
U2
LTC4440-5
C21 470p
D1 BAS516
Vu1
D11
BAS516
GND
+Vout
C7 220p
Out
C8 100p
C6* BAS516
D7
B0540W
C4* BAS516
+
Csys 470uF, 6.3V
C24 22p
C9 100p
C25 33n
Q13 Si2325
D14
BAS516
R45 10k
+Vr2
+Vr2
Co3
D17 BAS516
R53 200
2 5
7, 8 10, 11
C33 0.1u
R29* PMEG3002
R2 560k
C34 0.22u
R54 10R
C1, C35
1n
R4, R55 3.3R
L4 10uH
L3 220uH
R17 560R
1 6
* Please change the reference designator to reflect the symbol. Demo Board DC1317A-B schematic
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.
Also, all zero-ohm resistors have been replaced with wires.
Please consult the full DC1317A-B schematic to decide if any of the
optional components should be included in your design.
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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
7
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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
8
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