DC053A - Demo Board

DEMO MANUAL DC053A
DEMONO-DESIGN
MANUAL SWITCHER
DC053A
LT1372/LT1377 5V to 12V
Step-Up Converters
DESCRIPTIO
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Demonstration board DC053A is a complete DC/DC stepup switching regulator using the LT ®1372 or the LT1377
constant frequency, high efficiency converter in an 8-pin
SOIC package. High frequency switching allows the use of
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PERFOR A CE SU
ARY
very small inductors, making this all surface mount solution ideal for space conscious systems.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TA = 25°C, VIN = 5V, S/S pin open, unless otherwise specified.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Output Voltage
R2 = R3 = 1% (Note 1)
11.60
12.04
12.50
Output Current
VIN = 5V
250
Input Voltage Range
(Note 2)
2.7
Switching Frequency
LT1372
LT1377
500
1
kHz
MHz
Output Ripple Voltage
ILOAD = 250mA
ILOAD = 250mA (Note 3)
VOUT2, ILOAD = 250mA
150
80
3
mVP-P
mVP-P
mVP-P
V
mA
11
V
Supply Current
ILOAD = 0A
4.5
mA
Shutdown Supply Current
ILOAD = 0A, VS/S = 0V (Note 4)
100
µA
Note 1: The reference voltage tolerance of the LT1372/LT1377 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 LT1372/LT1377 (consult Linear Technology
Marketing).
Note 2: Increase L1 to 10µH for VIN < 4.75V or to 15µH for VIN < 3.3V.
Note 3: To reduce output ripple voltage, change C7 to a 2.2µF ceramic
chip capacitor (Tokin 1E225ZY5U-C203).
Note 4: 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 LT1372/LT1377 is in shutdown. Shutdown supply current will
also increase with the addition of an output load. Applications are
available which remove this direct path and reduce shutdown supply
current to 30µA maximum, independent of loading.
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TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO
12V Output Efficiency
Maximum Output Current vs Input Voltage*
VIN = 5V
VOUT = 12V
0.9
90
EFFICIENCY (%)
Component Side
1.0
MAXIMUM OUTPUT CURRENT (A)
100
80
70
60
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
50
0.01
0.1
OUTPUT CURRENT (A)
1
DC053A G01
0
2
3
4
9
5
7
8
6
INPUT VOLTAGE (V)
10
11
DC053A BP
DC053A G02
*INCREASE L1 TO 10µH FOR VIN < 4.75V
OR TO 15µH FOR VIN < 3.3V
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DEMO MANUAL DC053A
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PACKAGE A D SCHE ATIC DIAGRA SM
VIN
5V
L1*
4.7µH
E2
+
OPTIONAL
OUTPUT FILTER
L2**
1µH
C3
22µF
25V
+
E1
S/S
4
S/S
NC
3
1
C1
0.047µF
C2
0.0047µF
5
VIN
8
VSW
NFB
U1
LT1372/LT1377
FB
VC
GNDS
GND
6
R1
2k
2
7
D1
MBRS130
C6
4.7µF
25V
E4 VOUT
12V
0.25A
R3
53.6k, 1%
R2
6.19k
1%
TOP VIEW
E6 VOUT2
12V
0.25A
+
C4
22µF
25V
+
C5
OMIT
VC 1
8
VSW
FB 2
7
GND
NFB 3
6
GNDS
S/S 4
5
VIN
S8 PACKAGE
8-LEAD PLASTIC SO
LT1372CS8
LT1377CS8
C7
0.1µF
(NOTE 4)
E3
E5
GND
GND
*SUMIDA CD43-4R7KC
**MILLER PM20-1R0K
NOTES: UNLESS OTHERWISE SPECIFIED
1. ALL RESISTOR VALUES OHMS, 1/8W, 5%
2. ALL CAPACITOR VALUES µF, 50V, 20%
3. ALL POLARIZED CAPACITOR AVX TPS SERIES OR EQUIVALENT
4. PLACE C7 AT THE LOAD
DC053A F01
Figure 1. Switching Regulator 5V to 12V, 0.25A; 500kHz for the LT1372 and 1MHz for the LT1377
PARTS LIST
REFERENCE
DESIGNATOR
QUANTITY PART NUMBER
DESCRIPTION
VENDOR
TELEPHONE
C1
1
AVX 12065C473MAT2A
0.047µF, 50V, 20%, X7R Capacitor
AVX
C2
1
AVX 12065C472MAT2A
0.0047µF, 50V, 20%, X7R Capacitor
AVX
(803) 946-0362
C3, C4
2
AVX TPSD226M025R0200
22µF, 25V, 20%, Tantalum Capacitor
AVX
(207) 282-5111
AVX 12065C104MAT2A
0.1µF, 50V, 20%, X7R Capacitor
AVX
(803) 946-0362
C5, C6
0
C7
1
(803) 946-0362
Capacitor, Optional (See Text)
D1
1
MBRS130LT3
30V, 1A, Schottky Diode
Motorola
(602) 244-5768
E1 to E5
5
1502-2
2-Turret, 0.092 Terminal
Keystone
(718) 956-8900
E6
0
L1
1
CD43-4R7KC
4.7µH, SMT Inductor
Sumida
(708) 956-0666
2k, 5%, SMT1206 Resistor
AVX
(803) 946-0524
Terminal, Optional (See Text)
L2
0
R1
1
AVX CR32-202J-T
Inductor, Optional (See Text)
R2
1
AVX CR32-6191F-T
6.19k, 1%, SMT 1206 Resistor
AVX
(803) 946-0524
R3
1
AVX CR32-5362F-T
53.6k, 1%, SMT-1206 Resistor
AVX
(803) 946-0524
U1*
1
LT1372CS8
SO-8, LT1372, Switching Regulator IC
LTC®
(408) 432-1900
U1*
1
LT1377CS8
SO-8, LT1377, Switching Regulator IC
LTC
(408) 432-1900
*The two demo board versions are:
DC53A-A: U1 = LT1372CS8
DC53A-B: U1 = LT1377CS8
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DEMO MANUAL DC053A
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OPERATIO
DC053A Operation
This DC053A demonstration board is intended for evaluating the LT1372/LT1377 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
LT1372/LT1377 data sheet for additional specifications
and applications information. Also useful is Linear
Technology’s SwitcherCAD software when creating your
own designs.
tween 1V (low output current) and 1.9V (high output
current). The VC pin is also where loop frequency compensation is performed with an RC network to ground.
COMPONENTS
Inductors
Connect the input supply and measurement instruments
to the VIN and GND terminals on the left side of the board.
The S/S pin (synchronization/shutdown) can be connected to VIN or left open. Connect the output load and
measurement instruments to the VOUT and GND terminals
on the right side of the board. VOUT2 is for evaluating an
optional output filter and can be left open.
The inductor is a Sumida CD43-4R7KC, which is a 4.7µH
unshielded ferrite unit. It was selected for low cost and
small physical size. Similar units are available from other
manufacturers. There are benefits to higher frequency
switching (1MHz LT1377 versus 500kHz LT1372) and
higher value inductors. Both higher frequency switching
and higher value inductors allow more output current
because they reduce peak current in the switch. Both also
reduce input ripple voltage and output ripple voltage. An
inductor with a closed magnetic path (i.e., E-core or
toroid) may also be chosen to reduce the RFI/EMI of the
circuit.
LT1372/LT1377 Operation
Capacitors (and Input/Output Ripple Voltage)
The LT1372/LT1377 are monolithic high frequency current mode switchers. Each device can operate from an
input supply range of 2.7V to 25V (DC053A maximum
VIN = 11V), and draws only 4mA quiescent current. The onchip current limited power switch is guaranteed to 1.5A
minimum switch current with a 0.5Ω typical “on” resistance and a 35V minimum breakdown voltage. Running at
a fixed frequency of 500kHz (LT1372) or 1MHz (LT1377),
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 maximum.
The capacitors on this board are low ESR (Effective Series
Resistance) tantalum units specifically designed for switchmode power supply applications. At these high frequencies, input and output ripple voltages are more a function
of the ESR of the capacitor than the capacitance value. For
example, at 500kHz a 22µF capacitor has a capacitive
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 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, 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.
Hook-Up
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 VOUT = VREF (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 VC pin is the output of the error amplifier. During
normal regulator operation this pin sits at a voltage be-
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.
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DEMO MANUAL DC053A
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OPERATIO
Diodes
sive die temperatures. Please consult the LT1372/LT1377
data sheet or Linear Technology’s SwitcherCAD software
for more information.
Use diodes designed for switching applications with adequate 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, 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
conditions, peak diode current is limited to the switch
current limit of 2.4A maximum.
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
(Pin 8), output diode, output capacitor and Ground pin
(Pin 7) 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 exces-
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PCB LAYOUT A D FIL
Component Side Silkscreen
Component Side
Solder Side
Component Mask
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PC FAB DRAWI G
2.000
B
A
A
NOTES:
1. FINISHED MATERIAL IS FR4, 0.062 THICK, 2-OZ COPPER
2. PCB WILL BE DOUBLE-SIDED WITH PLATED THROUGH-HOLES
3. PTH SIZES AFTER PLATING, 0.001 MIN WALL THICKNESS
4. SOLDER MASK BOTH SIDES USING PC401 OR EQUIVALENT
5. SILKSCREEN COMPONENT SIDE USING WHITE NONCONDUCTIVE INK
6. ALL DIMENSIONS IN INCHES, ±0.005
7. ALL HOLE SIZES AFTER PLATING, – 0 TO 0.003 MAX
2.000
HOLE CHART
SYMBOL DIAMETER QTY PLT
A
A
A
0.200
B
Solder Mask
4
Linear Technology Corporation
A
NONE
0.020
3 YES
A
0.094
6 YES
0.062
2
B
NO
TOTAL HOLES 11
0.400
DC053A FAB
LT/GP 0895 500 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900 ● FAX: (408) 434-0507 ● TELEX: 499-3977
 LINEAR TECHNOLOGY CORPORATION 1995
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