DEMO MANUAL DC093
NO-DESIGN SWITCHER
DEMO MANUAL DC093
LT1371 5V to 12V
Step-Up Converter
DESCRIPTIO
Demonstration board DC093A is a complete DC/DC step-
up switching regulator using the LT
®
1371 constant fre-
quency, high efficiency converter in a 7-pin DD package.
PERFOR A CE SU
PARAMETER
Output Voltage
Output Current
Input Voltage Range
Switching Frequency
Output Ripple Voltage
Supply Current
Shutdown Supply Current
Note 1:
The reference voltage tolerance of the LT1371 is
±1.6%
over
temperature. Output voltage is a worst-case summation of R2, R3 and
reference tolerances, plus feedback input current times R3. For a tighter
output voltage range, use lower tolerance feedback resistors, or a fixed
voltage version of the LT1371 (consult Linear Technology Marketing).
Note 2:
Increase L1 to 15µH for V
IN
< 3.3V.
TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO
12V Output Efficiency
100
V
IN
= 5V
MAXIMUM OUTPUT CURRENT (A)
Maximum Output Current vs Input Voltage*
2.50
2.25
2.00
1.75
1.50
1.25
1.00
0.75
0.50
V
OUT
= 12V
90
EFFICIENCY (%)
80
70
60
50
0.01
0.1
OUTPUT CURRENT (A)
1
DM093A • TA01
0.25
2
3
4
9
7
5
6
8
INPUT VOLTAGE (V)
10
DM093A • TA02
*INCREASE L1 TO 15µH FOR V
IN
< 3.3V
U
WW
U W
U
High frequency switching allows the use of small induc-
tors, making this all surface mount solution ideal for space
conscious systems.
, LTC and LT are registered trademarks of Linear Technology Corporation.
U W
ARY
T
A
= 25°C, V
IN
= 5V, S/S pin open, unless otherwise specified.
MIN
11.60
800
2.7
500
140
5
100
11
TYP
12.04
MAX
12.50
UNITS
V
mA
V
kHz
mV
P-P
mA
µA
CONDITIONS
R2 = R3 = 1% (Note 1)
V
IN
= 5V
(Note 2)
I
LOAD
= 800mA
I
LOAD
= 0A
I
LOAD
= 0A, V
S/S
= 0V (Note 3)
Note 3:
Single inductor step-up converters have a direct path from the
input supply to the output, and therefore draw some supply current even
when the LT1371 is in shutdown. Shutdown supply current will also
increase with the addition of an output load. Applications are available that
remove this direct path and reduce shutdown supply current to 30µA
maximum, independent of loading.
Component Side
11
DC093A BP
1
DEMO MANUAL DC093
PACKAGE A D SCHE ATIC DIAGRA SM
E3
V
IN
FRONT VIEW
7
6
5
4
3
2
1
R PACKAGE
7-LEAD PLASTIC DD
V
IN
S/S
V
SW
GND
NFB
FB
V
C
TAB
IS
GND
E4
S/S
6
S/S
1
V
C
NFB
3
C2
0.047µF
C2
0.0047µF
R3
2K
1/8W
1%
LT1371CR
Figure 1. Switching Regulator 5V to 12V, 0.25A
PARTS LIST
REFERENCE
DESIGNATOR
C1, C4, C5
C2
C3
C6
D1
E1, E2, E3, E4, E5
L1
R1
R2
R3
U1
QUANTITY
3
1
1
1
1
4
1
1
1
1
1
1
PART NUMBER
TPSD226M025R0200
08055G473MATIA
08055G472MATIA
1206YG225ZATMAM
MBRS330T3
1502-2
CD104-100MC
CR215362FT
CR216191FT
CR212001FT
LT1371CR
216-40CT
DESCRIPTION
22µF, 25V, 20%, Tantalum Capacitor
0.047µF, 50V, 20%,Capacitor
0.0047µF, 50V, 20%, Capacitor
2.2µF, 16V, 20%, Capacitor
MBRS330, Diode
Turret
10µH, Inductor
53.6k, 1/8W, 1%, Resistor
6.19k, 1/8W, 1%, Resistor
2k, 1/8W, 1%, Resistor
Switching Regulator IC
Heat Sink, Optional
VENDOR
AVX
AVX
AVX
AVX
Motorola
Keystone
Sumida
AVX
AVX
AVX
LTC
Wakefield Eng.
TELEPHONE
(803) 448-9411
OPERATIO
DC093A Operation
This DC093A demonstration board is intended for evalu-
ating the LT1371 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 LT1371
data sheet for additional specifications and applications
information. You may find Linear Technology’s SwitcherCAD
software helpful for creating your own designs.
2
W
V
IN
W
U
L1
10µH
100M
C1
22µF
25V
D1
MBRS330
+
7
V
SW
5
U1
LT1371
GND
4
FB
TAB
8
2
R1
53.6K
1/8W
1%
R2
6.19K
1/8W
1%
E2
V
OUT
+
C4
22µF
25V
+
C5
22µF
25V
C6
2.2µF
E2
GND
DB093A • SCEMATIC
(602) 244-5768
(718) 950-8900
(708) 956-0666
(408) 432-1900
(617) 245-5900
U
Hook-Up
Connect the input supply and measurement instruments
to the V
IN
and GND terminals. The S/S pin (synchroniza-
tion/shutdown) can be connected to V
IN
or left open.
Connect the output load and measurement instruments to
the V
OUT
and GND terminals.
DEMO MANUAL DC093
OPERATIO
LT1371 Operation
The LT1371 is a monolithic, high frequency, current mode
switcher. The part can operate from an input supply range
of 2.7V to 25V (DC093A maximum V
IN
= 11V) and draws
only 4mA quiescent current. The on-chip current limited
power switch is guaranteed to 3A minimum switch current
with a 0.25Ω typical “on” resistance and a 35V minimum
breakdown voltage. Operating at a fixed frequency of
500kHz, switching can also be easily synchronized to a
higher frequency by driving the S/S pin with a logic level
source. Shutdown is activated by pulling the S/S pin below
0.6V, which reduces device supply current to 30µA maxi-
mum.
Under normal operating conditions, a 1.245V reference
voltage is developed at the Feedback pin. The output
voltage is set by R2 and R3, where V
OUT
= V
REF
(1 + R3/R2).
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 –2.49V reference voltage is developed at the NFB pin.
The V
C
pin is the output of the error amplifier. During
normal regulator operation this pin sits at a voltage be-
tween 1V (low output current) and 1.9V (high output
current). Loop frequency compensation is also performed
at the V
C
pin via an RC network to ground.
COMPONENTS
Inductors
The inductor is a Sumida CD104-100MC, a 10µH unshielded
ferrite unit. It was selected for low cost and small physical
size. Similar units are available from other manufacturers.
An inductor with a closed magnetic path (i.e., an E-core or
toroid) may also be chosen to reduce the RFI/EMI of the
circuit.
Capacitors (and Input/Output Ripple Voltage)
The capacitors on this board are low ESR (Effective Series
Resistance) tantalum units specifically designed for switch-
mode power supply applications. At these high frequen-
cies, 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 22µF capacitor has a capacitive
U
reactance of only 0.014Ω, which is much lower than the
limiting 0.2Ω 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 capaci-
tor. 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, and if the traces connecting to the
load are a few inches or more, the parasitic inductance of the
traces combined with any local load bypass capacitor will
virtually eliminate the spikes at the load.
Diodes
Use diodes designed for switching applications with ad-
equate current rating and fast turn-on times, such as
Schottky or ultra-fast diodes. In selecting a diode, the
basic parameters of interest are forward voltage, maxi-
mum reverse voltage, average operating current and peak
current. Lower forward voltage yields higher circuit effi-
ciency 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
conditions, peak diode current is limited to the switch
current limit of 4.8A maximum.
Thermal Considerations
Care should be taken to ensure that the worst-case input
voltage and load current conditions do not cause exces-
sive die temperatures. Please consult the LT1371 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,
there are a few things to be aware of with high frequency
converter layouts. Keep the traces connecting the Switch
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 represen-
tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
3
DEMO MANUAL DC093
OPERATIO
(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 induc-
PCB LAYOUT A D FIL
Silkscreen Top
Paste Mask Top
PC FAB DRAWI G
2.00"
NOTES: UNLESS OTHERWISE SPECIFIED
1. MATERIAL: FR4 OR EQUIVALENT EPOXY, 2 OZ COPPER
CLAD THICKNESS 0.062"
±0.006
TOTAL OF 2 LAYERS
2. FINISH:
A.ALL PLATED HOLES 0.001" MIN/0.0015" MAX COPPER PLATE
B.ELECTRODEPOSITED TIN-LEAD COMPOSITION. BEFORE
REFLOW, SOLDER MASK OVER BARE COPPER (SMOBC)
C.SOLDER MASK: BOTH SIDES USING GREEN PC-401
OR EQUIVALENT
D.SILKSCREEN: USING WHITE NONCONDUCTIVE EPOXY INK
2.00"
3. LAYER SEQUENCE: COMPONENT SIDE = LAYER 1
SOLDER SIDE = LAYER 2
SYMBOL
DIAMETER # OF HOLES
0.025
6
0.095
5
TOTAL HOLES
11
LT/GP 1295 500 • PRINTED IN USA
4
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
q
FAX
: (408) 434-0507
q
TELEX
: 499-3977
W
U
U
U
tance. Keep the more sensitive components, mainly the
feedback resistors and V
C
pin network, away from the high
current switching components.
Component Side
Solder Mask Top
Solder Side
Solder Mask Bottom
©
LINEAR TECHNOLOGY CORPORATION 1995
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