1
DEMO MANUAL DC053A
PARAMETER CONDITIONS MIN TYP MAX UNITS
Output Voltage R2 = R3 = 1% (Note 1) 11.60 12.04 12.50 V
Output Current V
IN
= 5V 250 mA
Input Voltage Range (Note 2) 2.7 11 V
Switching Frequency LT1372 500 kHz
LT1377 1 MHz
Output Ripple Voltage I
LOAD
= 250mA 150 mV
P-P
I
LOAD
= 250mA (Note 3) 80 mV
P-P
V
OUT2
, I
LOAD
= 250mA 3 mV
P-P
Supply Current I
LOAD
= 0A 4.5 mA
Shutdown Supply Current I
LOAD
= 0A, V
S/S
= 0V (Note 4) 100 µA
DEMO MANUAL DC053A
LT1372/LT1377 5V to 12V
Step-Up Converters
NO-DESIGN SWITCHER
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.
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 V
IN
< 4.75V or to 15µH for V
IN
< 3.3V.
TYPICAL PERFOR A CE CHARACTERISTICS A D BOARD PHOTO
UU
W
INPUT VOLTAGE (V)
2
MAXIMUM OUTPUT CURRENT (A)
1.0
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
46711
DC053A G02
35 8
9
10
V
OUT
= 12V
*INCREASE L1 TO 10µH FOR V
IN
< 4.75V
OR TO 15µH FOR V
IN
< 3.3V
DC053A BP
OUTPUT CURRENT (A)
0.01
50
EFFICIENCY (%)
60
70
80
90
0.1 1
DC053A G01
100 V
IN
= 5V
Maximum Output Current vs Input Voltage*
12V Output Efficiency
PERFOR A CE SU ARY
UWWW
T
A = 25°C, VIN = 5V, S/S pin open, unless otherwise specified.
DESCRIPTIO
U
Demonstration board DC053A is a complete DC/DC step-
up 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
, LTC and LT are registered trademarks of Linear Technology Corporation.
very small inductors, making this all surface mount solu-
tion ideal for space conscious systems.
Component Side
2
DEMO MANUAL DC053A
PARTS LIST
REFERENCE
DESIGNATOR QUANTITY PART NUMBER DESCRIPTION VENDOR TELEPHONE
C1 1 AVX 12065C473MAT2A 0.047µF, 50V, 20%, X7R Capacitor AVX (803) 946-0362
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
C5, C6 0 Capacitor, Optional (See Text)
C7 1 AVX 12065C104MAT2A 0.1µF, 50V, 20%, X7R Capacitor AVX (803) 946-0362
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 Terminal, Optional (See Text)
L1 1 CD43-4R7KC 4.7µH, SMT Inductor Sumida (708) 956-0666
L2 0 Inductor, Optional (See Text)
R1 1 AVX CR32-202J-T 2k, 5%, SMT1206 Resistor AVX (803) 946-0524
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
PACKAGE A D SCHE ATIC DIAGRA SM
W UW
U1
LT1372/LT1377
V
IN
V
C
V
IN
5V
1
38
5
4
67
*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
GND
GND
GND
DC053A F01
GNDS
NFB
NC
FB
V
SW
S/S
S/S
E2
D1
MBRS130
C3
22µF
25V
C1
0.047µF
C2
0.0047µFR1
2k
R3
53.6k, 1%
R2
6.19k
1%
V
OUT
12V
0.25A
C6
4.7µF
25V
C4
22µF
25V
V
OUT2
12V
0.25A
2
L1*
4.7µH
L2**
1µH
OPTIONAL
OUTPUT FILTER
+
+
+
C5
OMIT
+
C7
0.1µF
(NOTE 4)
E1
E4
E6
E5E3
Figure 1. Switching Regulator 5V to 12V, 0.25A; 500kHz for the LT1372 and 1MHz for the LT1377
1
2
3
4
8
7
6
5
TOP VIEW
V
C
FB
NFB
S/S
V
SW
GND
GNDS
V
IN
S8 PACKAGE
8-LEAD PLASTIC SO
LT1372CS8
LT1377CS8
3
DEMO MANUAL DC053A
OPERATIO
U
DC053A Operation
This DC053A demonstration board is intended for evalu-
ating 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.
Hook-Up
Connect the input supply and measurement instruments
to the V
IN
and GND terminals on the left side of the board.
The S/S pin (synchronization/shutdown) can be con-
nected to V
IN
or left open. Connect the output load and
measurement instruments to the V
OUT
and GND terminals
on the right side of the board. V
OUT2
is for evaluating an
optional output filter and can be left open.
LT1372/LT1377 Operation
The LT1372/LT1377 are monolithic high frequency cur-
rent mode switchers. Each device can operate from an
input supply range of 2.7V to 25V (DC053A maximum
V
IN
= 11V), and draws only 4mA quiescent current. The on-
chip current limited power switch is guaranteed to 1.5A
minimum switch current with a 0.5Ω typical “on” resis-
tance 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.
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). The V
C
pin is also where loop frequency compen-
sation is performed with an RC network to ground.
COMPONENTS
Inductors
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.
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 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 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 connect-
ing 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.
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.
4
DEMO MANUAL DC053A
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7487
(408) 432-1900
●
FAX
: (408) 434-0507
●
TELEX
: 499-3977
LT/GP 0895 500 • PRINTED IN USA
LINEAR TECHNOLOGY CORPORATION 1995
OPERATIO
U
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 2.4A 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 LT1372/LT1377
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
(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 V
C
pin network, away from the high current
switching components.
PCB LAYOUT A D FIL
UW
Component Side
Solder Mask
PC FAB DRAWI G
U
A
A
AA
A
A
B
B
2.000
0.200
0.400
2.000
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
 HOLE CHART
SYMBOLDIAMETER QTY PLT
NONE 0.020 3 YES
A 0.094 6 YES
B 0.062 2 NO
TOTAL HOLES 11
DC053A FAB
Component Mask Solder Side
Component Side Silkscreen