DC1317A-A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-A
ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A DC/DC POWER CONVERTER
LT1952
DESCRIPTION
Demonstration circuit 1317A-A 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-A converts isolated 34V to 75V input to
3.3V output and provides over 30A of output current.
The converter operates at 300kHz with the peak efficiency greater than 93%. 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-B, 18-72Vin to 5V, 25A
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-C, 18-72Vin to 12V, 10A
Design files for this circuit board are avail
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 30A
34V
Maximum Input Voltage
IOUT = 0A to 30A
75V
VOUT
VIN = 34V to 75V, IOUT = 0A to 30A
3.3V ±3%
Typical Output Ripple VOUT
VIN = 34V to 75V, IOUT = 0A to 30A
50mVP–P
Nominal Switching Frequency
300kHz
QUICK START PROCEDURE
PROCEDURE
Demonstration circuit 1317 is easy to set up to evaluate the performance of LT1952 circuit. Refer to FigFig-
ure 1 for proper measurement equipment setup
and follow the procedure below:
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-A
ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A DC/DC POWER CONVERTER
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.
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 75V.
3.
Check for the proper output voltage.
Vout = 3.3V.
Figure 1. Proper
Proper Measurement Equipment Setup
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-A
ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A DC/DC POWER CONVERTER
Rip
p ple
Figure 2. Scope Probe Placement for Measuring Input or Output Ri
OPTIONAL PRIMARY MOSFET
MOSFET DRIVER LTC4440
ACTIVE RESET CIRCUIT
The Active Reset circuit on DC1317A-A 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 is suitable for driving
the secondary synchronous MOSFET rectifier Q3.
Beware that the gate voltage of Q3 depends on the
reset circuit Q13 and transformer turns ratio.
The main benefit of active reset circuit in the case of
DC1317A-A demo board is high efficiency (shown
in Figure 3)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.
94%
93%
Efficiency
The DC1317 has an optional LTC4440 MOSFET
driver U2. The LTC4440 can be used if the efficiency
is important and large MOSFET is used. The efficiency gain is usually in the 0.5%-1% range when
LTC4440 is used. If required, please contact LT factory for assistance.
DC1317A-A (LT1952) 48Vin to 3.3V out
Efficiency
92%
91%
90%
89%
88%
0
10
20
30
Iout [A]
Figure 3. High efficiency of DC1317ADC1317A-A al
allows
the board to be used in thermally critical appliapplications
OUTPUT LOAD STEP RESPONSE
The load step response of DC1317A-A is very fast
even though relatively small amount of output capacitance is present (200uF 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.
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-A
ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A 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 resistor is used in a place holder for
a capacitor such as in the 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
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.
Place sensitive lines on the inner layers that will be
shielded by grounds on layers 2 and n-1.
DEBUGGING AND TESTING
TESTING
Keep the loop formed by Q1, RCS1, Cin and T1 tight.
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 Q2, Q3 and T1 tight.
Keep noise sensitive nodes like SD/VSEC, ROSC, FB,
COMP, ISENSE, BLANK and DELAY as small as posible
4
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-A
ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A DC/DC POWER CONVERTER
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-A
ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A DC/DC POWER CONVERTER
Q10
PBSS8110 Vu1
L1
1
D3
BAS516
+Vr2
Cin
2x2.2uF
R11
82k
2, 3
+Vin
4.7
2
Q12
BC856T
R15
115k 3
4
SS
C10
0.1u
5
6
R22
7
13.3k
8
R32
332k
R28
442k
+Vr2 +Vb
Comp
Rcs1
0.015R
Vu1
Sout
FB=1.23V
Vin
Rosc
Out
Sync
PGND
MaxDC
Delay
Vr=2.5V
OC
SD
Isense
GND
Blank
16
U6
PS2801-1
R8
2.2R
C16
0.22uF
D10
13
C9
12
100p
11
10
R23 1.2k
9
R33
470k
C13
.47u
R24
39K
R27
470
D6
B0540W
2
3
R30
1.2k
C19
1uF
15
14
D11
BAS516
1
R26
220R
C23
1uF
U1
LT1952-1
SS
R29
22K
R50
2.2R
Vfb
BAT760
1
+
CS
D14
BAS516
Vfb
Q3
Q1
Si7430
R45
10k
R14
33K
PA0861.004
HAT2165
4, 5
Q13
Si2325
D17
BAS516
Q2
GND
C25
10n
C33
0.1u
T1
R54
C34
0.22uf
R13
22K
9, 10, 11
6
PA1671.650
R49
2.2R
D5
PDZ10B
-Vin
R53
200
+Vout
D2
L2
1.5mH
2.2R
7, 8
470uF, 6.3V
+Vin
Csys
+Vb
R1
Co1
2x100uF
+Vin
Vcc
Opto
GND
Comp
SS
FB
U4
LT4430
C15
2.2nF, 2kV
Cu1
4.7u
C17
10n
R34
4.75k
6
5
R35
82.5k
4
C24
47p
R38
18.2K
R20
174k
Demo Board DC1317A-A schematic
CS
NOTE:
This schematic shows only the components required for operation of -A 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-A schematic to decide if any of the optional
components should be included in your design.
6
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-A
ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A DC/DC POWER CONVERTER
7
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 1317A-A
ACTIVE RESET ISOLATED 48V INPUT TO 3.3V @30A DC/DC POWER CONVERTER
8
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