DEMO MANUAL DC355/DC356 LT1959 Monolithic 4A Switcher 5V to 15V Input 1.8V Output

DEMO MANUAL DC355/DC356
NO-DESIGN SWITCHER
LT1959 Monolithic 4A Switcher
5V to 15V Input
1.8V Output
U
DESCRIPTIO
Demonstration circuits DC355 and DC356 are complete
DC/DC step-down regulators using the LT®1959 constant
frequency, high efficiency converter in 7-pin DD (DC356)
and SO-8 (DC355) packages. These circuits are primarily
used in personal computers, disk drives, portable
handheld devices and, in larger systems, as local onboard
regulators. High frequency switching allows the use of
small inductors, making this all surface mount solution
ideal for space conscious systems.
, LTC and LT are registered trademarks of Linear Technology Corporation.
WW
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PERFOR A CE SU
ARY
TA = 25°C, VIN = 5V, ILOAD = 2A, VOUT = 1.8V, SHDN and SYNC pins open, unless otherwise specified.
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
Output Voltage
(Note 1)
1.75
1.8
1.85
V
Maximum ILOAD
(Note 2)
15
V
540
kHz
4.3
Input Voltage Range
4.5
Switching Frequency
460
Output Ripple Voltage
A
500
25
mVP-P
Line Regulation
5V to 15V
4
mV
Load Regulation
ILOAD = 10mA to 4A
10
mV
SHDN Lockout Threshold
2.3
2.38
2.46
V
SHDN Shutdown Threshold
0.15
0.37
0.6
V
Synchronization Range
DC355 Only
Supply Current
SHDN = 0V
580
1000
20
kHz
µA
Note 1: Output voltage variations include ±1% tolerance of feedback
divider network.
Note 2: For DC355, additional thermal restrictions apply.
BOARD PHOTOS
DC355 Component Side
DC356 Component Side
1
DEMO MANUAL DC355/DC356
NO-DESIGN SWITCHER
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TYPICAL PERFOR A CE CHARACTERISTICS
Temperature Rise vs Load Current
120
85
100
DIE TEMPERATURE RISE (°C)
EFFICIENCY (%)
1.8V Output Efficiency
90
5VIN
80
75
12VIN
70
65
60
VIN = 5V
VOUT = 1.8V
DC355
80
DC356
60
40
20
0
1
0
2
4
3
1
0
LOAD CURRENT (A)
2
4
3
LOAD CURRENT (A)
DC355/356 TA01
DC355/356 TA02
W
W
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PACKAGE A D SCHE ATIC DIAGRA SM
DC355
D2*
OPTIONAL
E1
VIN
5V TO 15V
C4
1µF
10V
D3*
MMBD914LT1
+
C3
10µF
25V
2
1
6
E2
SHDN
L1
6.8µH
BOOST
VIN
U1 SW
LT1959CS8
SHDN
SYNC
GND
FB
VC
E3
GND
8
7
3
D1
MBRD835L
+
C5
100µF
10V
R2
1.21k
1%
E6
SYNC
E2
SHDN
C3
10µF
25V
C4
1µF
10V
5
2
E3
GND
VIN
SW
U1
LT1959CR
SHDN
GND
4
*MOVE D3 TO POSITION D2
FOR OUTPUT VOLTAGES > 3.3V
FB
VC
VIN 1
E4
GND
3
7 SYNC
FB 3
6 SHDN
5 VC
S8 PACKAGE
8-LEAD PLASTIC SO
LT1959CS8
DC355 SCHEM
DC356
D1
MBRD835L
+
C5
100µF
10V
+
+
C7
OPTIONAL
R2
1.21k
1%
7
R3
2.49k
1%
1
R1
3.3k
C2
3.3nF
8 VSW
BOOST 2
GND 4
L1
6.8µH
6
BOOST
TOP VIEW
C1
OPTIONAL
D2*
OPTIONAL
+
C6
0.47µF
10V
E5
VOUT
3.3V/4A
R3
2.49k
1%
R1
3.3k
C2
3.3nF
D3*
MMBD914LT1
+
C7
OPTIONAL
5
4
*MOVE D3 TO POSITION D2
FOR OUTPUT VOLTAGES > 3.3V
E1
VIN
5V TO 15V
+
DC356 SCHEM
C1
OPTIONAL
C6
0.47µF
10V
E5
VOUT
3.3V/4A
E4
GND
FRONT VIEW
TAB
IS
GND
7
6
5
4
3
2
1
R PACKAGE
7-LEAD PLASTIC DD PAK
LT1959CR
2
FB
BOOST
VIN
GND
VSW
SYNC OR SHDN
VC
DEMO MANUAL DC355/DC356
NO-DESIGN SWITCHER
PARTS LISTS
DC355
REFERENCE
DESIGNATOR
QUANTITY
PART NUMBER
DESCRIPTION
VENDOR
TELEPHONE
C1
0
Optional Capacitor
C2
1
08055C332MAT2S
3300pF 50V X7R Chip Capacitor
AVX
(843) 946-0362
C3
1
GRM235Y5V106Z
10µF 25V Y5V Chip Capacitor
Murata
(770) 436-1300
C4
1
0805ZC105MAT2S
1µF 10V X7R Chip Capacitor
AVX
(843) 946-0362
C5
1
TPSD107M010R0080
100µF 10V TPS Tantalum Capacitor
AVX
(207) 282-5111
C6
1
0603ZG474MAT3S
0.47µF 10V Y5V Chip Capacitor
AVX
(843) 946-0362
C7
1
D1
1
MBRD835L
SMT Diode
ON Semiconductor
(602) 244-6600
D2
1
MMBD914LT1
1N914 Diode
ON Semiconductor
(602) 244-6600
Optional Capacitor
D3
1
E1 to E6
6
2501-2
Pad Turret
Optional Diode
Mill-Max
(516) 922-6000
R1
1
CR10-332JM
3.3k 1/8W 5% Chip Resistor
AAC
(714) 255-9186
R2
1
CR10-1821F-T
1.82k 1/8W 1% Chip Resistor
AAC
(714) 255-9186
R3
1
CR10-4991F-T
4.99k 1/8W 1% Chip Resistor
AAC
(800) 508-1521
L1
1
DO3316P-682
6.8µH 20% Inductor
Coilcraft
(847) 639-6400
U1
1
LT1959CS8
SO-8 Linear IC
LTC
(408) 432-1900
PART NUMBER
DESCRIPTION
VENDOR
DC356
REFERENCE
DESIGNATOR
QUANTITY
TELEPHONE
C1
0
C2
1
08055C332MAT2S
Optional Capacitor
3300pF 50V X7R Chip Capacitor
C3
1
GRM235Y5V106Z
C4
1
0805ZC105MAT2S
C5
1
C6
1
C7
1
D1
1
MBRD835L
D2
1
MMBD914LT1
D3
1
E1 to E6
6
2501-2
Pad Turret
Mill-Max
(516) 922-6000
R1
1
CR10-332JM
3.3k 1/8W 5% Chip Resistor
AAC
(714) 255-9186
R2
1
CR10-1821F-T
1.82k 1/8W 1% Chip Resistor
AAC
(714) 255-9186
R3
1
CR10-4991F-T
4.99k 1/8W 1% Chip Resistor
AAC
(800) 508-1521
L1
1
DO3316P-682
6.8µH 20% Inductor
Coilcraft
(847) 639-6400
U1
1
LT1959CR
7-Pin DD Pak Linear IC
LTC
(408) 432-1900
AVX
(843) 946-0362
10µF 25V Y5V Chip Capacitor
Murata
(770) 436-1300
1µF 10V X7R Chip Capacitor
AVX
(843) 946-0362
TPSD107M010R0080
100µF 10V TPS Tantalum Capacitor
AVX
(207) 282-5111
0603ZG474MAT3S
0.47µF 10V Y5V Chip Capacitor
AVX
(843) 946-0362
SMT Diode
ON Semiconductor
(602) 244-6600
1N914 Diode
ON Semiconductor
(602) 244-6600
Optional Capacitor
Optional Diode
3
DEMO MANUAL DC355/DC356
NO-DESIGN SWITCHER
U
OPERATIO
DC355 vs DC356 (Temperature vs Package Size)
The DC355 and DC356 demonstration boards are
intended for evaluation of the LT1959 switching regulator
in the SO-8 and 7-pin DD packages, respectively. The 7-pin
DD package used on DC356 has no SYNC pin. The primary
reason for choosing the SO-8 over the DD package is board
space. The DC356 (DD package) occupies an active board
area of approximately 0.75 square inches. By optimizing
the DC355 board, using a Sumida coil and removing the
layout options, a total active area of 0.4 square inches can
be achieved. The DD package is more suitable for higher
power or higher ambient temperature applications.
Although both boards will supply 4A of output current,
DC355 must be thermally derated to 3A continuous current at 22°C ambient to prevent excessive die temperatures. DC356 can run at 60°C ambient at 4A output current. However, the SO-8 package can be used for dynamic
loads up to the full rated switch current.
LT1959 Operation
The LT1959 data sheet gives a complete description of the
part, operation and applications information. The data
sheet should be read in conjunction with this demo manual.
Hook-Up
Solid turret terminals are provided for easy connection to
supplies and test equipment. Connect a 0V to 15V, 4.5A
power supply across the VIN and GND terminals and the
load across the VOUT and GND terminals. When measuring
load/line regulation, remember to Kelvin connect to the
turrets. Also, when measuring output ripple voltage with
an oscilloscope probe, the wire from the probe to the
ground clip will act as an antenna, picking up excessive
noise. For improved results, the test hook should be
removed from the tip of the probe. The tip should be
touched against the output turret, with the bare ground
shield pressed against the ground turret. This reduces the
noise seen on the waveform.
Shutdown
For normal operation, the SHDN pin can be left floating.
SHDN has two output-disable modes: lockout and
shutdown. When the pin is taken below the lockout
4
threshold, switching is disabled. This is typically used for
input undervoltage lockout. Grounding the SHDN pin
places the LT1959 in shutdown mode. This reduces total
board supply current to 20µA.
Synchronization
Synchronization is available on DC355 only. For normal
demo board operation, the SYNC pin can be left floating.
If it is not used in the application, it is advisable to tie this
pin to ground. To synchronize switching to an external
clock, apply a logic-level signal to the SYNC pin. The
amplitude must be from a logic low to greater than 2.2V,
with a duty cycle between 10% and 90%. The synchronization frequency must be greater than the free-running
oscillator frequency and less than 1MHz. Additional circuitry may be required to prevent subharmonic oscillation. Refer to the LT1959 data sheet for more details.
COMPONENTS
Inductor L1
The inductor is a Coilcraft DO3316P-682, a 6.8µH
unshielded ferrite unit. It was selected for its low cost,
small size and 4.6A ISAT rating. The equivalent Coiltronics
UP2-6R8 unit can be substituted. If board space is at a
premium and higher ripple current is acceptable, solder
pads are available for the Sumida CD43-1R8 inductor.
This 1.8µH unit has a 2.9A ISAT rating. Ripple at 5VIN is
±0.6A. This gives a maximum output current of
(4.5A – 0.6A) = 3.9A.
Input/Output Capacitors C3, C5, C6 and C7
The input capacitor C3 is a Tokin ceramic capacitor. It was
selected for its small size, high voltage rating and low ESR
(effective series resistance). The input ripple current for a
buck converter is high, typically IOUT/2. Tantalum capacitors become resistive at higher frequencies, requiring
careful ripple-rating selection to prevent excessive heating. Ceramic capacitors’ ESL (effective series inductance)
tends to dominate their ESR, making them less susceptible to ripple-induced heating.
DEMO MANUAL DC355/DC356
NO-DESIGN SWITCHER
U
OPERATIO
The output capacitor C5 is an AVX tantalum capacitor. A
ceramic is not recommended as the main output capacitor, since loop stability relies on a resistive characteristic
at higher frequencies to form a zero. The AVX TPS series
was specifically designed to have the low ESR required in
switch-mode power supplies. At switching frequencies,
ripple voltage is more a function of ESR than of absolute
capacitance value. If lower output ripple voltage is required, use the optional capacitor C7 to reduce ESR rather
than increasing the capacitance of C5. For very low ripple,
an additional LC filter in the output may be a less expensive
solution. The output contains very narrow voltage spikes
because of the parasitic inductance of C5. A small ceramic
capacitor, C6, removes these spikes on the demo board.
In application, trace inductance and local bypass capacitors will perform this function, negating the need for C6.
Catch Diode D1
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 lowers power dissipation in the diode. The MBRD835L
has a maximum forward drop of 0.4V at 3A. The reverse
voltage rating must be greater than the input voltage.
Average diode current is always less than output current,
but under a shorted output condition, diode current can
equal the switch current limit. If the application must
withstand this condition, the diode must be rated for
maximum switch current.
Compensation: C1, C2 and R1
A detailed discussion of frequency compensation can be
found in the LT1959 data sheet. R1 + C2 from VC to ground
give a stable loop response over a wide range of input
and output conditions. Optional capacitor C1 is included
for optimization of the dynamic response for a specific
application.
Boost Voltage: D2, D3 and C4
A boost voltage of at least 2.8V is required throughout the
on-time of the switch to guarantee that it remains saturated. For output voltages above 3.3V, diode D2 can
replace D3 and provide sufficient boost voltage to C4.
PCB LAYOUT
In many cases, the layout of the demonstration board
may be dropped directly into the application with minimal changes. If not, there are several precautions that
must be taken when laying out high frequency converter circuits. The high frequency switching path runs
from ground, through C3, to the VIN pin of the LT1959,
out of the SW pin, through D1 and back to ground. This
loop acts as an antenna and will radiate noise if not kept
as short as possible. Also, at higher switching currents,
the associated trace inductance can cause excessive
voltage spikes across the switch. The use of a ground
plane will reduce many noise problems. The ground pin
of the LT1959 contains some high frequency signal
currents, but more importantly, it is the 0V reference for
the output voltage. Connect the ground pin directly to
the ground plane. The FB and VC components should be
kept away from the power components as much as
possible. The ground for these components should be
separated from power grounds. Run a Kelvin sense line
to VOUT as required but keep the divider network close
to the LT1959 to prevent noise pickup on the FB node.
Noise pickup on the VC pin appears as various problems, including poor load regulation, subharmonic
oscillation and instability. Thermal management must
also be considered. The SO-8 package has a fused
ground pin. Soldering this pin to a large copper area will
significantly reduce its thermal resistance. Solder-filled
feedthroughs close to the ground pin provide a good
thermal path to the ground plane. For the DD package,
the grounded tab should be treated in the same manner.
For more information or advice, contact the LTC Applications department.
5
DEMO MANUAL DC355/DC356
NO-DESIGN SWITCHER
U
W
PCB LAYOUT A D FIL
6
(DC355)
Component Side Silkscreen
Component Side
Component Side Solder Mask
Component Side Paste Mask
Solder Side
Solder Side Solder Mask
DEMO MANUAL DC355/DC356
NO-DESIGN SWITCHER
U
W
PCB LAYOUT A D FIL
(DC356)
Component Side Silkscreen
Component Side
Component Side Solder Mask
Component Side Paste Mask
Solder Side
Solder Side Solder Mask
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.
7
DEMO MANUAL DC355/DC356
NO-DESIGN SWITCHER
U
PC FAB DRAWI GS
DC355
2.000"
C
A
D
D
A
B
2.000"
D
D
B
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: 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 SR1020 OR EQUIVALENT
4. SILKSCREEN: USING WHITE NONCONDUCTIVE EPOXY INK
5. ALL DIMENSIONS IN INCHES
6. SCORING
0.017
B
C
SYMBOL
DIAMETER
NUMBER
OF HOLES
A
0.020
38
B
0.025
7
C
0.072
2
D
0.095
6
TOTAL HOLES
53
DC355 FD
DC356
2.000"
B
A
C
C
A
C
2.000"
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: 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 SR1020 OR EQUIVALENT
4. SILKSCREEN: USING WHITE NONCONDUCTIVE EPOXY INK
5. ALL DIMENSIONS IN INCHES
6. SCORING
0.017
B
SYMBOL
DIAMETER
NUMBER
OF HOLES
A
0.020
30
B
0.072
2
C
0.095
5
TOTAL HOLES
37
DC356 FD
8
Linear Technology Corporation
dc3556f LT/TP 0701 500 • PRINTED IN USA
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408)432-1900 ● FAX: (408) 434-0507 ● www.linear-tech.com
 LINEAR TECHNOLOGY CORPORATION 2001
1
2
3
4
3
A
5
6
7
8
1
A
1
1
1
3
3
6
4
VIN
2
SHDN
B
1
1
1
BOOST
5
GND
VC
4
1
SW
3
FB
7
B
1
C
C
D
D
1
2
3
4
5
6
7
8
Bill Of Material
Demo Bd. #356A
Linear Technology Corporation
LT1959CR
6/16/2005
1:10 PM
Item Qty Reference
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
0
1
1
1
1
1
0
1
0
1
6
1
1
1
1
1
1
1
C1
C2
C3
C4
C5
C6
C7
D1
D2
D3
E1-E6
R1
R2
R3
L1
U1
Part Description
CAP., OPTIONAL
CAP., CHIP X7R .033uF 50V
CAP., CHIP Y5V 10uF 25V
CAP., CHIP X7R 1uf 10V
CAP., TANT TPS 100uF 10V
CAP., CHIP Y5V 0.47uF 10V
CAP., OPTIONAL
DIODE, SMT MBRD835L
DIODE, OPTIONAL
DIODE, 1N914
TURRET, PAD
RES., CHIP 3.3K 1/8W 5%
RES., CHIP 1.21K 1/8W 1%
RES., CHIP 2.49K 1/8W 1%
INDUCTOR, 6.8uH 20%
IC., LINEAR LT1959CR
PRINTED CIRCUIT BOARD
STENCIL
Page 1 - of - 1
Manufacture / Part #
AVX 08055C333MAT2S 0805
TAIYOYUDEN TMK325F106ZH 1210
AVX 0805ZC105MAT2S 0805
AVX TPSD107M010R0065 CASE-D
AVX 0603ZG474ZAT3S 0603
MOTOROLA MBRD835L
DPAK
MOTOROLA MMBD914LT1 SOT23
MILL-MAX 2501-2
PAD.092
AAC CR10-332JM
0805
AAC CR10-1211FM 0805
AAC CR10-2491FM
0805
COILCRAFT DO3316P-682
LINEAR LT1959CR
7LEAD-DD
DEMO BOARD DC356A
STENCIL DC356A

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