DC502A - Demo Manual

QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 502
1.25MHZ WIDE INPUT RANGE STEP DOWN DC/DC CONVERTER
LT1767
DESCRIPTION
Demonstration
circuit
502
is
a
1.25MHz 1.5A monolithic step-down
DC/DC switching converter using the
LT1767 buck regulator. With its fast
switching speed, 1.5A internal power
switch, and wide input voltage range,
the LT1767 is a very versatile and
powerful IC for DC/DC converters that
require compact space and a wide variety of input voltage ranges. The
constant 1.25MHz switching frequency
allows all of the components to be
very small, surface mount devices.
The current-mode control topology
creates fast transient response and
good loop stability with a minimum
number of external compensation components and ceramic input and output
capacitors. The low resistance internal power switch (0.22Ω) maintains
high efficiencies >80% and up to 90%.
The SHDN pin and 6uA shutdown current
extends battery life. The wide VIN
range of the LT1767 allows step-down
configurations from 3Vin up to 25Vin.
Synchronization of switching frequencies up to 2MHz is possible.
Demonstration Circuit 502 is a stepdown converter using the LT1767EMS8E.
The circuit is designed for 6.6-25V
input to 5.0V output @1A or for 4.525V† input to 3.3V output @1A for cable modem, handheld, automotive, and
desktop computer applications. The
output voltage is jumper selectable
(5V or 3.3V). This board was designed
for wide input voltage range applications where simplicity, small circuit
size, and low component count are important as well as up to 1A of load
current. The use of ceramic capacitors not only demonstrates small size
and low cost, but the advantage of
current-mode control in step-down applications with a simple compensation
network and a place-holder for a
feedforward capacitor for more rugged
stability and optimal transient response if required.
Design files for this circuit board
are available. Call the LTC factory.
†
Higher input voltages may pulse-skip due to
minimum on-time restrictions. Compensation
component changes may be necessary to optimize pulse-skipping during high-temperature,
high-voltage conditions and maintain control
of switch current.
Table 1. Typical Performance Summary
PARAMETER
CONDITION
VALUE
Input Voltage Range
Vout = 5V (Jumper Selection)
6.6V–25V
Input Voltage Range
Vout = 3.3V (Jumper Selection)
4.5V–18V
Vout
Vout = 5V (Jumper Selection)
5V ±3%
Vout
Vout = 3.3V (Jumper Selection)
3.3V ±3%
Maximum Output Current
1A
Typical Switching Frequency
1.25MHz
Typical Efficiency
Vin = 12V, Vout = 5V, Iout = 1A 84%
1
1
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 502
1.25MHZ WIDE INPUT RANGE STEP DOWN DC/DC CONVERTER
QUICK START PROCEDURE
Demonstration circuit 502 is easy to
set up to evaluate the performance of
the LT1767. Refer to Figure 1 for
proper measurement equipment setup
and follow the procedure below:
4. Connect
an ammeter in series with
output load to measure output current.
5. Connect a voltmeter across the Vin
and Gnd terminals to measure input
voltage.
NOTE: Make sure that the input voltage
does not exceed 25V.
6. Connect a voltmeter across the Vout
1. Connect the 7V–25V or 4.5V–18V in-
and Gnd terminal to measure output
voltage.
put power supply to the Vin and Gnd
terminals on the board.
7. After
all connections are made,
turn on input power and verify that
the output voltage is either 5.0V
or 3.3V (the output voltage jumper
setting).
2. Connect
an ammeter in series with
the input supply to measure input
current.
3. Connect
either power resistors or
an electronic load to the Vout and
Gnd terminals on the board.
–
8. The
synchronization and shutdown
functions are optional and their
pins can be left floating (disconnected) if their functions are not
being used.
+ +
+
–
–
LTC1767EMS8E
1.25MHz Wide Input Range
Step Down DC/DC Converter
Demo Circuit 502
Linear Technology
(408) 432-1900
www.linear.com
Vin
GND
–
Vout
SHDN
GND
SYNC
+
VOUT
3.3V 5V
+
+
–
–
+
–
LOAD
Figure 1. Proper Measurement Equipment Setup
2
2
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 502
100
100
90
90
80
80
5VOUT EFFICIENCY (%)
3.3VOUT EFFICIENCY (%)
1.25MHZ WIDE INPUT RANGE STEP DOWN DC/DC CONVERTER
70
60
50
5VIN
40
8VIN
30
12VIN
18VIN
20
60
50
8VIN
40
12VIN
30
18VIN
24VIN
20
10
10
0
0.01
70
0
0.1
1
0.01
LOAD CURRENT (mA)
Figure 2. Efficiency for VOUT = 3.3V
MINIMUM INPUT VOLTAGE
The minimum LT1767 operating input
voltage is 3.0V. However, a DC/DC
buck converter needs to have an input
voltage greater than the output voltage by a certain margin in order to
provide the desired regulated output
voltage. Maximum duty cycle, switch
on-resistance, and inductor and diode
DC losses all play a part in determining the minimum input voltage for
a selected output over the full current range of the application. For
this demonstration board, with up to
1A output current, the minimum input
voltages required to maintain regulated output voltages is listed below. Customizable output voltages
2.5V and 1.8V are very common and are
thus additionally listed in the table
(see Customizing the Board below). If
the input voltage falls below the
minimum input voltage listed below,
the output voltage can drop accordingly from the programmed output
0.1
1
LOAD CURRENT (mA)
Figure 3. Efficiency for VOUT = 5V
voltage. This mode is called maximum
duty cycle drop-out.
Table 2. Minimum Input Voltage for Regulated
Output
VOUT
VIN (MINIMUM)
5.0V
6.6V
3.3V
4.5V
2.5V
3.5V
1.8V
3.0V
CUSTOMIZING THE BOARD
The components built on the board are
optimized for a wide input voltage
range. The bandwidth can be increased
for more specific input voltages such
as 12V ±10% or 5V ±10% if desired.
Some typical applications with typical input voltage ranges that are
smaller than the wide input voltage
range of the part are included below.
The adjustable feedback resistors allow the output voltage to be customized. For output voltages below 3.0V,
the boost diode should be moved from
D2 to D3 to provide the minimum boost
3
3
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 502
1.25MHZ WIDE INPUT RANGE STEP DOWN DC/DC CONVERTER
voltage required for the internal
power switch. Make sure that the
boost capacitor (C8) has a voltage
rating greater than or equal to the
output voltage for applications where
the boost diode is placed in D2. However, the boost capacitor must have a
voltage rating greater than the input
voltage whenever the boost diode is
placed in position D3.
12V +/-10%
5V @1A
Vin
LT1767EMS8E
Vin
C2
2.2uF 25V X7R 1206
Boost
U1
C8
0.1uF
Vout
L1
Vsw
CDRH5D18-5R4
Sync
/Shdn
Ceramic
D2 CMDSH-3
R1
FB
Vc
31.6k
Gnd
C3
1.5nF
R3
C4
100pF
D1
R2
10.0k
UPS120
C5
4.7uF 6.3V X5R 0805
Ceramic
4.7k
12V +/-10%
3.3V @1A
Vin
LT1767EMS8E
Vin
C2
2.2uF 25V X7R 1206
Boost
U1
C8
0.1uF
Vout
L1
Vsw
CDRH4D28-4R7
Sync
/Shdn
Ceramic
D2 CMDSH-3
R1
FB
Vc
17.4k
Gnd
C3
2.2nF
R3
C4
100pF
D1
R2
10.0k
UPS120
C5
4.7uF 6.3V X5R 0805
Ceramic
3.3k
5V +/-10%
2.5V @1A
Vin
D3 CMDSH-3
LT1767EMS8E
Vin
C2
2.2uF 10V X5R 0805
Boost
U1
L1
Vsw
1008PS-272M
Sync
/Shdn
Ceramic
Vout
C8
0.1uF
R1
FB
Vc
1.5nF
R3
3.3k
10.7k
Gnd
C3
C4
100pF
D1
UPS120
R2
10.0k
C5
4.7uF 6.3V X5R 0805
Ceramic
4
4
QUICK START GUIDE FOR DEMONSTRATION CIRCUIT 502
1.25MHZ WIDE INPUT RANGE STEP DOWN DC/DC CONVERTER
3-5.5V
1.8V @1A
Vin
D3 CMDSH-3
LT1767EMS8E
Vin
C2
2.2uF 10V X5R 0805
Boost
U1
L1
Vsw
1008PS-272M
Sync
/Shdn
Ceramic
Vout
C8
0.1uF
R1
FB
Vc
1.5nF
R3
2.2k
4.99k
Gnd
C3
C4
100pF
D1
UPS120
R2
10.0k
C5
4.7uF 6.3V X5R 0805
Ceramic
5
5
5
4
3
2
D3
D
D2
CMDSH-3
OPT.
Vin
C8
0.1uF
L1
BOOST
2
VIN
8
SYNC
VSW
C
C1
2.2uF
25V
5
SYNC
FB
Vout
[email protected]
Vout
3
CDRH5D18-5R4
E1
C6
TAJ
OPT.
D
CMDSH-3
U1
LT1767EMS8E 1
* 3V-25V
1
E2
R2
6
C7
0805
OPT.
31.6k
SHDN
GND
VC
4
7
C5
Vfb
C
100pF
OPT.
E4
R5
100k
OPT.
D1
UPS140
C3
6800pF
SHDN
R1
10.0k
C2
10uF
6.3V
C4
100pF
E5
R3
2.2k
GND
GND
E3
E6
EXPOSED PAD SOLDER TO GROUND
B
B
2
Vfb
Vout
JP1
1
3
5.0V 3.3V
* VIN
MINIMUM
A
39.2k
VOUT
CONTRACT NO.
6.6
5
4.5
3.3
3.5
2.5
DRAWN
3
1.8
CHECKED
APPROVALS
June Wu
DATE
2/12/02
See Quick-Start Guide.
ENGINEER
Keith S.
Tuesday, August 06, 2002
3
TITLE
A
DESIGNER
4
TECHNOLOGY
1630 McCarthy Blvd.
Milpitas, CA 95035
Phone: (408)432-1900
Fax: (408)434-0507
LT1767EMS8E, 1.25MHz Wide Input Range Step Down DC/DC Converter
APPROVED
5
R4
2/12/02
SIZE CAGE CODE
DWG NO
REV
A
DC502A
SCALE:
FILENAME:
2
SHEET
1
1
OF
1
Bill Of Material
Demo Bd. #502A
Linear Technology Corporation
LT1767EMS8E
6/17/2005
Item Qty Reference
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
1
1
1
1
0
0
0
1
1
1
0
6
2
1
1
1
1
1
1
0
1
1
C1
C2
C3
C4
C5 (OPT.)
C6 (OPT.)
C7 (OPT.)
C8
D1
D2
D3 (OPT.)
E1-E6
JP1,JP2
JP1
L1
R1
R2
R3
R4
R5 (OPT.)
U1
Part Description
CAP., X7R, 2.2uF, 25V, 10% 1206
CAP., X5R, 10uF, 6.3V, 20% 0805
CAP., X7R, 6800pF, 50V, 20% 0603
CAP., NPO, 100pF, 50V, 10% 0603
CAP., 100pF,
0603
Manufacture / Part #
TDK, C3216X7R1E225K
TDK, C2010X5R0J106M
AVX, 06035C682MAT2A
AVX, 06035A101KAT2A
CAP.,
0805
CAP., X7R, 0.1uF, 16V, 20% 0603
Taiyo Yuden, EMK107BJ104MA
Schottky Barrier REC., UPS140
MICROSEMI., UPS140
DIODE, CMDSH-3,
SOD-323
CENTRAL SEMI., CMDSH-3
DIODE, CMDSH-3,
SOD-323
CENTRAL SEMI., CMDSH-3
TURRET,
MILL-MAX 2501-2
0.079 SINGLE ROW HEADER, 3 PIN
COMM CON, 2802S-03-G1
SHUNT,
COMM CON, CCIJ2MM-138G
INDUCTOR, 5.4uH
SUMIDA, CDRH5D18-5R4
RES.,CHIP, 10.0K, 1/16W, 5% 0603
AAC, CR16-103JM
RES.,CHIP, 31.6K, 1/16W, 1% 0603
AAC, CR16-3162FM
RES.,CHIP, 2.2K, 1/16W, 5% 0603
AAC, CR16-222JM
RES.,CHIP, 39.2K, 1/16W, 5% 0603
AAC, CR16-3922FM
RES., CHIIP
0603
I.C., LT1767EMS8E MS8 Exposed
Linear Tech. LT1767EMS8E
PRINTED CIRCUIT BOARD
DEMO BOARD DC502A
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