DC185A - Demo Manual

DEMO MANUAL DC185
NO-DESIGN
SWITCHER
DEMO
MANUAL
DC185
DESCRIPTIO
LT1370 6A Switch
2.7V to 12V Input
5V or 12V Output
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Demonstration board DC185 is a complete DC/DC stepdown regulator using the LT ®1370 constant frequency,
high efficiency converter in a 7-pin DD package. High
frequency switching allows the use of small inductors,
making this all surface mount solution ideal for spaceconscious systems.
, LTC and LT are registered trademarks of Linear Technology Corporation.
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PERFOR A CE SU
ARY
TA = 25°C, VIN = 5V, ILOAD = 1A, VOUT = 12V (jumper J1 removed), S/D pin open, unless otherwise specified.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Output Voltage
Jumper J1 Removed (Note 1)
Jumper J1 Inserted
11.6
4.85
12.0
5.00
12.4
5.17
V
V
6
8
(Note 2)
2.7
Maximum ISW
Input Voltage Range
Switching Frequency
440
Output Ripple Voltage
500
10
A
12
V
580
80
kHz
mVP-P
Line Regulation
VIN = 2.7V to 11V, ILOAD = 0.5A
20
mV
Load Regulation
ILOAD = 10mA to 1.75A
18
mV
S/D Shutdown Threshold
0.6
S/D Synchronization Range
600
Supply Current
S/D = 0V, ILOAD = 0A (Note 3)
Note 1: Output voltage variations include ±1% tolerance of feedback
divider network. For tighter voltage range, use lower tolerance resistors.
Note 2: With the boost topology, input voltage must always be lower than
output voltage. See the LT1370 data sheet for maximum device ratings.
1.3
2
V
800
kHz
µA
100
Note 3: The boost topology provides a path from input to output even with
the LT1370 in shutdown. Applications are available that remove this direct
path and reduce shutdown supply current to 12µA, independent of
loading.
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TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO
Maximum Load Current vs Input Voltage
Output Efficiency
90
5.5
VIN = 5V
VOUT = 12V
88
5.0
4.5
LOAD CURRENT (A)
86
EFFICIENCY (%)
Component Side
VIN = 3.3V
VOUT = 5V
84
82
80
VOUT = 5V
4.0
3.5
3.0
VOUT = 12V
2.5
2.0
1.5
78
1.0
76
0.5
0
0.5
1.0
1.5
2.0
LOAD CURRENT (A)
2.5
3.0
DM185 G01
2
3
4
9
5
7
8
6
INPUT VOLTAGE (V)
10
11
DC185 BP
DM185 G02
1
DEMO MANUAL DC185
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PACKAGE A D SCHE ATIC DIAGRA SM
R4
C7
10Ω 1000pF
5%
E1
VIN
L1
6.8µH
VIN
1
+
C1
33µF
16V
6
7
NFB
E2
S/D
1
S/D 3
S/S
VIN
VSW
U1
LT1370CR
FB
GND
E3
GND
1
E4
GND
1
D1
MBRD835L
5
2
C5
0.1µF
+
C2
100µF
16V
+
C3
100µF
16V
E5
VOUT
C6
4.7µF
DM185 F01
R1
6.19k
1%
1
R4
470Ω
5%
R3
28.7k
1%
FRONT VIEW
VC
4
R2
53.6k
1%
J1
5V/12V
LINK
7
6
5
4
3
2
1
C4
OPTIONAL
VIN
NFB
VSW
GND
S/S
FB
VC
R PACKAGE
7-LEAD PLASTIC DD
Figure 1. 5V/12V Output Boost Converter
LT1370CR
PARTS LIST
REFERENCE
DESIGNATOR
C1
C2, C3
C4
C5
C6
C7
D1
E1 to E5
R1
R2
R3
R4
R5
L1
J1
J1
U1
QUANTITY
1
2
1
1
1
1
1
5
1
1
1
1
1
1
1
1
1
PART NUMBER
T495D336M016AS
T495X107M016AS
Optional
08055C104MAT3S
1206YG475MAT3S
08053A102KAT
MBRD835L
2501-2
CR10-6191F-T
CR10-5362F-T
CR10-2872F-T
CT10-471J-T
CR10-100J-T
501-0726
2802S-02-G2
CCIJ2MM-138-G
LT1370CR
DESCRIPTION
33µF 16V Tantatum Capacitor, Case-D
100µF 16V Tantalum Capacitor, Case-D
VENDOR
Kemet
Kemet
TELEPHONE
(714) 640-9320
(714) 640-9320
0.1µF 50V X7R Chip Capacitor, 0805
4.7µF 16V Y5V Chip Capacitor, 1206
1000pF, 25V NPO Chip Capacitor, 0805
SMT Diode, D-Pak
Pad Turret, PAD.092
6.19k 1/8W 1% Chip Resistor, 0805
53.6k 1/8W 1% Chip Resistor, 0805
28.7k 1/8W 1% Chip Resistor, 0805
470Ω 1/8W 5% Chip Resistor, 0805
10Ω 1/8W 5% Chip Resistor, 0805
6.8µH 20% Inductor, Qtr-Pak
0.079" Center 2-Pin Header
0.079" Center 2-Pin Shunt
7-Lead DD IC
AVX
AVX
AVX
Motorola
Mill-Max
TAD
TAD
TAD
TAD
TAD
BH-Elec
Comm Con
Comm Con
LTC
(803) 946-0362
(803) 946-0362
(803) 946-0362
(602) 244-3576
(516) 922-6000
(800) 508-1521
(800) 508-1521
(800) 508-1521
(800) 508-1521
(800) 508-1521
(612) 894-9590
(818) 301-4200
(818) 301-4200
(408) 432-1900
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OPERATIO
DC185 Operation
The DC185 demonstration board is intended for evaluating the LT1370 switching regulator in a typical step-up
application. Solid turret terminals are provided for easy
connection to test equipment. A device pinout and board
schematic are shown in Figure 1. Please refer to the
2
LT1370 data sheet for additional specifications and applications information. You may find Linear Technology’s
SwitcherCADTM software helpful for creating your own
designs.
SwitcherCAD is a trademark of Linear Technology Corporation.
DEMO MANUAL DC185
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OPERATIO
Hook-Up
Connect the input supply and measurement instruments
to the VIN and GND terminals. The S/D pin (synchronization/shutdown) can be connected to VIN or left open.
Connect the output load and measurement instruments to
the VOUT and GND terminals.
LT1370 Operation
The LT1370 is a monolithic, high frequency, current mode
switcher. The part can operate from an input supply range
of 2.7V to 30V (DC185 maximum VIN = 12V) and draws
only 4.5mA quiescent current. The on-chip current limited
power switch is guaranteed to 6A minimum switch current with a 0.065Ω typical “on” resistance and a 35V
minimum breakdown voltage. The switch, which operates
at a fixed frequency of 500kHz, can also be easily synchronized to a higher frequency by driving the S/D pin with a
logic-level source. Shutdown is activated by holding the
S/D pin below 0.6V, which reduces device supply current
to 40µA maximum.
mode power supply applications. At these high frequencies, input and output ripple voltages are more a function
of the ESR of the capacitor than of the capacitance value.
For example, at 500kHz a 100µF capacitor has a capacitive
reactance of only 0.003Ω, which is much lower than the
limiting 0.1Ω maximum ESR of the capacitors used.
Therefore, if a reduction in input or output ripple voltage
is required, use two or more capacitors in parallel instead
of a larger value capacitor. If very low output ripple voltage
is needed, adding an output LC filter may be a cheaper
solution. The output contains very narrow voltage spikes
because of the parasitic inductance of the output capacitor. Due to their high frequency nature, the amplitude of
the spikes is determined by the ESL (effective series
inductance) of the output capacitor. But this also makes
them easy to filter. Small 0.1µF ceramic chip capacitors
work well in reducing the spikes. If trace connections to
the load are a few inches or more in length, the parasitic
inductance, combined with any local load bypass capacitor, will virtually eliminate the spikes at the load.
Under normal operating conditions, a 1.245V reference
voltage is developed at the Feedback pin. The output
voltage is set by R1 and R2, where VOUT = VREF (1 +
R2/R1). Although not used in this application, the part
also has a Negative Feedback pin (NFB), which can be
used to set the output voltage of positive-to-negative
converters. When in use, a – 2.48V reference voltage is
developed at the NFB pin.
Snubber
The VC pin is the output of the error amplifier. During
normal regulator operation, this pin sits at a voltage
between 1V (low output current) and 1.9V (high output
current). Loop frequency compensation is performed at
the VC pin via an RC network to ground.
Diodes
COMPONENTS
Inductor
The inductor is a BH Electronics 501-0726, a 6.8µH
toroidal ferrite unit. It was selected for its small size, low
EMI, low DCR and 5A ISAT rating.
Capacitors (and Input/Output Ripple Voltage)
The capacitors on this board are low ESR (effective series
resistance) tantalum units specifically designed for switch
R4 and C7 form a snubber network across the catch diode,
D1. This reduces the spikes seen on the output due to
ringing of the catch diode on switching edges. The snubber reduces efficiency typically by 0.5%. Trace inductance
and decoupling capacitors on the application board may
remove the need for a snubber network.
Use diodes designed for switching applications, with
adequate current rating and fast turn-on times, such as
Schottky or ultrafast diodes. In selecting a diode, the basic
parameters of interest are forward voltage, maximum
reverse voltage, average operating current and peak current. Lower forward voltage yields higher circuit efficiency
and lower power dissipation in the diode. The worst-case
reverse voltage is equal to the output voltage. The average
diode current will be equal to the output current, but the
peak diode current can be many times higher than the
output current. Except for output short-circuit conditions,
peak diode current is limited to the switch current limit of
7.5A maximum.
Information furnished by Linear Technology Corporation is believed to be accurate and reliable.
However, no responsibility is assumed for its use. Linear Technology Corporation makes no representation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
3
DEMO MANUAL DC185
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OPERATIO
there are a few things to be aware of with high frequency
converter layouts. Keep the traces connecting the Switch
(Pin 5), output diode, output capacitor and ground return
path (Pin 4 and Tab) as short as possible. This will reduce
RFI and limit the voltage spikes caused by parasitic
inductance. Keep the more sensitive components, mainly
the feedback resistors and VC pin network, away from the
high current switching components.
Thermal Considerations
Care should be taken to ensure that the worst-case input
voltage and load current conditions do not cause excessive die temperatures. Please consult the LT1370 data
sheet or Linear Technology’s SwitcherCAD software for
more information.
PCB Layout
In many cases, the circuit area traces of the demonstration
board may be dropped directly into your PCB layout. If not,
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PCB LAYOUT A D FIL
Silkscreen Top
Component Side
Solder Mask Top
Solder Side
Solder Mask Bottom
Paste Mask Top
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PC FAB DRAWI G
SYMBOL
DIAMETER
# OF HOLES
PLATED
A
0.020
58
Yes
B
0.037
2
Yes
C
0.025
3
Yes
D
0.072
2
No
E
0.095
5
Yes
TOTAL HOLES
2.000
NOTES: UNLESS OTHERWISE SPECIFIED
D
A
E
C
B
E
A
A
70
E
A
E
D
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1. MATERIAL: FR4 OR EQUIVALENT EPOXY, 2 OZ COPPER CLAD
THICKNESS 0.062 ±0.006 TOTAL OF 2 LAYERS
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Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417 ● (408) 432-1900
FAX: (408) 434-0507● TELEX: 499-3977 ● www.linear-tech.com
2.000
2. FINISH: ALL PLATED HOLES 0.001 MIN/0.0015 MAX COPPER
PLATE ELECTRODEPOSITED TIN-LEAD COMPOSITION
BEFORE REFLOW, SOLDER MASK OVER BARE COPPER
(SMOBC)
3. SOLDER MASK: BOTH SIDES USING GREEN PC-401 OR
EQUIVALENT
C
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4. SILKSCREEN: USING WHITE NONCONDUCTIVE EPOXY INK
5. ALL DIMENSIONS ARE IN INCHES
dc185f LT/TP 0398 500 • PRINTED IN USA
 LINEAR TECHNOLOGY CORPORATION 1998
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