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1
LT3483
3483f
LCD Bias
Handheld Computers
Battery Backup
Digital Cameras
OLED Bias
3.6V to 8V DC/DC Converter
, LTC and LT are registered trademarks of Linear Technology Corporation.
Inverting Micropower
DC/DC Converter with
Schottky in ThinSOT Package
Internal 40V Schottky Diode
One Resistor Feedback (Other Resistor Inside)
Internal 40V, 200mA Power Switch
Generates Regulated Negative Outputs to 38V
Low Quiescent Current:
40A in Active Mode
<1A in Shutdown Mode
Low V
CESAT
Switch: 200mV at 150mA
Wide Input Range: 2.5V to 16V
Uses Small Surface Mount Components
Output Short-Circuit Protected
Available in a 6-Lead SOT-23 Package
Efficiency and Power Loss
ThinSOT is a trademark of Linear Technology Corporation.
Patent pending.
FEATURES
DESCRIPTIO
U
APPLICATIO S
U
TYPICAL APPLICATIO
U
The LT
3483 is a micropower inverting DC/DC converter
with integrated Schottky and one resistor feedback. The
small package size, high level of integration and use of tiny
surface mount components yield a solution size as small
as 40mm
2
. The device features a quiescent current of only
40A at no load, which further reduces to 0.1A in
shutdown. A current limited, fixed off-time control scheme
conserves operating current, resulting in high efficiency
over a broad range of load current. A precisely trimmed
10A feedback current enables one resistor feedback and
virtually eliminates feedback loading of the output. The
40V switch enables voltage outputs up to 38V to be
generated without the use of costly transformers. The
LT3483's low 300ns off-time permits the use of tiny low
profile inductors and capacitors to minimize footprint and
cost in space-conscious portable applications.
The LT3483 is available in the low profile (1mm) SOT-23
(ThinSOT
TM
) package.
SW
10H
D
LT3483
FB
4.7F
0.22F
V
IN
10
806k
5pF
2.2F
3483 TA01a
V
OUT
8V
25mA
V
IN
3.6V
SHDN
GND
LOAD CURRENT (mA)
0.1
55
EFFICIENCY (%)
POWER LOSS (mW)
60
65
70
75
0.1
1
10
100
V
IN
= 3.6V
POWER
LOSS
1000
1
10
3483 TA01b
100
EFFICIENCY
2
LT3483
3483f
(Note 1)
V
IN
Voltage ............................................................. 16V
SW Voltage ............................................................. 40V
D Voltage .............................................................. 40V
FB Voltage ............................................................. 2.5V
SHDN Voltage ......................................................... 16V
Operating Ambient Temperature Range
(Note 2) .................................................. 40C to 85C
Junction Temperature .......................................... 125C
Storage Temperature Range ................ 65C to 150C
Lead Temperature (Soldering, 10 sec)................. 300C
Consult LTC Marketing for parts specified with wider operating temperature ranges.
ABSOLUTE AXI U RATI GS
W
W
W
U
PACKAGE/ORDER I FOR ATIO
U
U
W
LT3483ES6
ORDER PART
NUMBER
S6 PART MARKING
LTBKX
T
JMAX
= 125C,
JA
= 256C/W IN FREE AIR
JA
= 120C/W ON BOARD OVER GROUND PLANE
SW 1
GND 2
FB 3
6 V
IN
5 D
4 SHDN
TOP VIEW
S6 PACKAGE
6-LEAD PLASTIC TSOT-23
PARAMETER
CONDITIONS
MIN
TYP
MAX
UNITS
V
IN
Operating Range
2.5
16
V
V
IN
Undervoltage Lockout
2
2.4
V
FB Comparator Trip Voltage to GND (V
FB
)
FB Falling
0
5
12
mV
FB Output Current (Note 3)
FB = V
FB
5mV
10.15
10
9.75
A
FB Comparator Hysteresis
FB Rising
10
mV
Quiescent Current in Shutdown
V
SHDN
= GND
1
A
Quiescent Current (Not Switching)
FB = 0.05V
40
50
A
I
FB
Line Regulation
2.5V V
IN
16V
0.07
%/V
Switch Off-Time
300
ns
Switch Current Limit
170
200
230
mA
Switch V
CESAT
I
SW
= 150mA to GND
200
mV
Switch Leakage Current
SW = 40V
1
A
Rectifier Leakage Current
D = 40V
4
A
Rectifier Forward Drop
I
D
= 150mA to GND
0.64
V
SHDN Input Low Voltage
0.4
V
SHDN Input High Voltage
1.5
V
SHDN Pin Current
6
10
A
The
denotes specifications which apply over the full operating temperature range, otherwise specifications are T
A
= 25C.
V
IN
= 3.6V, V
SHDN
= 3.6V unless otherwise specified.
ELECTRICAL CHARACTERISTICS
Note 1: Absolute Maximum Ratings are those values beyond which the life
of a device may be impaired.
Note 2: The LTC3483E is guaranteed to meet specifications from 0C to
70C. Specifications over the 40C to 85C operating temperature range
are assured by design, characterization and correlation with statistical
process controls.
Note 3: Current flows out of the pin.
3
LT3483
3483f
TYPICAL PERFOR A CE CHARACTERISTICS
U
W
V
FB
Current
TEMPERATURE (C)
50
V
FB
CURRENT (
A)
10.0
10.1
70
3483 G01
9.9
9.8
20
10
40
100
10.2
TEMPERATURE (C)
50
V
FB
VOLTAGE (mV)
6
9
70
3483 G02
3
0
20
10
40
100
12
TEMPERATURE (C)
50
SWITCH OFF TIME (ns)
150
200
250
40
100
3483 G03
100
50
0
20
10
70
300
350
400
V
FB
Voltage
Switch Off Time
Switch Current Limit
Quiescent Current
SHDN Pin Bias Current
TEMPERATURE (C)
50
170
SWITCH CURRENT LIMIT (mA) 180
190
200
210
220
230
20
10
40
70
3483 G04
100
TEMPERATURE (C)
50
QUIESCENT CURRENT (
A)
30
40
50
70
3483 G05
20
10
0
20
10
40
100
NOT SWITCHING
V
FB
= 0.05V
SHDN PIN VOLTAGE (V)
0
SHDN PIN BIAS CURRENT (
A)
4
6
16
3483 G06
2
0
4
8
12
10
T
A
= 25C
8
U
U
U
PI FU CTIO S
SW: Switch. Connect to external inductor L1 and positive
terminal of transfer capacitor.
GND: Ground.
FB: Feedback. Place resistor to negative output here. Set
resistor value R1 = V
OUT
/10A.
SHDN: Shutdown. Connect to GND to turn device off.
Connect to supply to turn device on.
D: Anode Terminal of Integrated Schottky Diode. Con-
nect to negative terminal of transfer capacitor and exter-
nal inductor L2 (flyback configuration) or to cathode of
external Schottky diode (inverting charge pump
configuration).
V
IN
: Input Supply. Must be locally bypassed with 1F or
greater.
4
LT3483
3483f
BLOCK DIAGRA
W
+
+
6
3
1
2
5
A3
300ns
DELAY
1.250V
REFERENCE
S
Q1
20mV
SW
D
L1B
L1A
C
FLY
C
OUT
V
OUT
0.1
0.1
GND
3483 BD
+
25mV
D1
Q
R
Q
A1
A2
125k
R1
R2
V
OUT
D
D2
V
IN
V
IN
FB
OPTIONAL CHARGE PUMP CONFIGURATION.
L1B REPLACED WITH:
V
OUT
OPERATIO
U
The LT3483 uses a constant off-time control scheme to
provide high efficiency over a wide range of output cur-
rents. Operation can be best understood by referring to the
Block Diagram. When the voltage at the FB pin is approxi-
mately 0V, comparator A3 disables most of the internal cir-
cuitry. Output current is then provided by external capacitor
C
OUT
, which slowly discharges until the voltage at the FB
pin goes above the hysteresis point of A3. Typical hyster-
esis at the FB pin is 10mV. A3 then enables the internal
circuitry, turns on power switch Q1, and the currents in
external inductors L1A and L1B begin to ramp up. Once the
switch current reaches 200mA, comparator A1 resets the
latch, which turns off Q1 after about 80ns. Inductor cur-
rent flows through the internal Schottky D1 to GND, charg-
ing the flying capacitor. Once the 300ns off-time has
elapsed, and internal diode current drops below 250mA
(as detected by comparator A2), Q1 turns on again and
ramps up to 200mA. This switching action continues until
the output capacitor charge is replenished (until the FB pin
decreases to 0V), then A3 turns off the internal circuitry
and the cycle repeats. The inverting charge pump topology
replaces L1B with the series combination D2 and R2.
5
LT3483
3483f
APPLICATIO S I FOR ATIO
W
U
U
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CHOOSING A REGULATOR TOPOLOGY
Inverting Charge Pump
The inverting charge pump regulator combines an induc-
tor-based step-up with an inverting charge pump. This
configuration usually provides the best size, efficiency and
output ripple and is applicable where the magnitude of
V
OUT
is greater than V
IN
. Negative outputs to 38V can be
produced with the LT3483 in this configuration. For cases
where the magnitude of V
OUT
is less than or equal to V
IN
,
use a 2-inductor or transformer configuration such as the
inverting flyback.
In the inverting charge pump configuration, a resistor is
added in series with the Schottky diode between the
negative output and the D pin of the LT3483. The purpose
of this resistor is to smooth/reduce the current spike in the
flying capacitor when the switch turns on. A 10 resistor
works well for a Li
+
to 8V application, and the impact to
converter efficiency is less than 3%. The resistor values
recommended in the applications circuits also limit the
switch current during a short-circuit condition at the
output.
Inverting Flyback
The inverting flyback regulator, shown in the 5V applica-
tion circuit, uses a coupled inductor and is an excellent
choice where the magnitude of the output is less than or
equal to the supply voltage. The inverting flyback also
performs well in a step-up/invert application, but it occu-
pies more board space compared with the inverting charge
pump. Also, the maximum |V
OUT
| using the flyback is less
than can be obtained with the charge pump--it is reduced
from 38V by the magnitudes of V
IN
and ringing at the
switch node. Under a short-circuit condition at the output,
a proprietary technique limits the switch current and
prevents damage to the LT3483 even with supply voltage
as high as 16V. As an option, a 0.47F capacitor may be
added between terminals D and SW of LT3483 to suppress
ringing at SW.
Inductor Selection
Several recommended inductors that work well with the
LT3483 are listed in Table 1, although there are many other
manufacturers and devices that can be used. Consult each
manufacturer for more detailed information and for their
entire selection of related parts. Many different sizes and
shapes are available. For inverting charge pump regula-
tors with input and output voltages below 7V, a 4.7H or
6.8H inductor is usually the best choice. For flyback
regulators or for inverting charge pump regulators where
the input or output voltage is greater than 7V, a 10H
inductor is usually the best choice. A larger value inductor
can be used to slightly increase the available output
current, but limit it to around twice the value recom-
mended, as too large of an inductance will increase the
output voltage ripple without providing much additional
output current.
Capacitor Selection
The small size and low ESR of ceramic capacitors make
them ideal for LT3483 applications. Use of X5R and X7R
types is recommended because they retain their capacitance
over wider voltage and temperature ranges than other di-
electric types. Always verify the proper voltage rating. Table
2 shows a list of several ceramic capacitor manufacturers.
Consult the manufacturers for more detailed information
on their entire selection of ceramic capacitors.
A 4.7F ceramic bypass capacitor on the V
IN
pin is
recommended where the distance to the power supply or
battery could be more than a couple inches. Otherwise, a
1F is adequate.
Table 1. Recommended Inductors
MAX
L
I
DC
DCR
HEIGHT
PART
(
H) (mA)
(
)
(mm)
MANUFACTURER
LQH2MCN4R7M02L
4.7
300
0.84
0.95
Murata
LQH2MCN6R8M02L
6.8
255
1.0
www.murata.com
LQH2MCN100M02L
10
225
1.2
SDQ12
10
980
0.72
1.2
Cooper Electronics
Coupled
15
780
1.15
Tech
Inductor
www.cooperet.com
744876
10
550
0.46
1.2
Wrth Elektronik
Coupled
www.we-online.com
Inductor
6
LT3483
3483f
APPLICATIO S I FOR ATIO
W
U
U
U
1
2
3
6
5
4
+
V
IN
GND
SHDN
C
FLY
C
OUT
3483 AI01
R1
L1
C
IN
V
OUT
Suggested Layout (SOT-23)
for Inverting Charge Pump
A capacitor in parallel with feedback resistor R1 is recom-
mended to reduce the output voltage ripple. Use a 5pF
capacitor for the inverting charge pump, and a 22pF value
for the inverting flyback or other dual inductor configura-
tions. Output voltage ripple can be reduced to 20mV in some
cases using this capacitor in combination with an appro-
priately selected output capacitor.
The output capacitor is selected based on desired output
voltage ripple. For low output voltage ripple in the inverting
flyback configuration, use a 4.7F to 10F capacitor. The
inverting charge pump utilizes values ranging from 0.22F
to 4.7F. The following formula is useful to estimate the
output capacitor value needed:
C
L I
V
V
OUT
SW
OUT
OUT
=
2
where I
SW
= 0.25A and V
OUT
= 30mV. The flying capaci-
tor in the inverting charge pump configuration ranges
from 0.1F to 0.47F. Multiply the value predicted by the
above equation for C
OUT
by 1/10 to determine the value
needed for the flying capacitor.
Conditions that increase inrush current include a larger,
more abrupt voltage step at V
IN
, a larger flying capacitor,
and an inductor with a low saturation current.
While the internal diode is designed to handle such events,
the inrush current should not be allowed to exceed 1.5A.
For circuits that use flying capacitors within the recom-
mended range and have input voltages less than 5V,
inrush current remains low, posing no hazard to the
device. In cases where there are large steps at V
IN
, inrush
current should be measured to ensure operation within the
limits of the device.
Board Layout Considerations
As with all switching regulators, careful attention must be
given to the PCB board layout and component placement.
Proper layout of the high frequency switching path is
essential. The voltage signals of the SW and D pins have
sharp rising and falling edges. Minimize the length and
area of all traces connected to the SW and D pins. In
particular, it is desirable to minimize the trace length to
and from the flying capacitor, since current in this capaci-
tor switches directions within a cycle. Always use a
ground plane under the switching regulator to minimize
interplane coupling.
Table 2. Recommended Ceramic Capacitor Manufacturers
MANUFACTURER
URL
AVX
www.avxcorp.com
Kemet
www.kemet.com
Murata
www.murata.com
Taiyo Yuden
www.tyuden.com
Setting the Output Voltage
The output voltage is programmed using one feedback
resistor according to the following formula:
R
V
A
OUT
1
10
=
Inrush Current
When V
IN
is increased from ground to operating voltage,
an inrush current will flow through the input inductor and
integrated Schottky diode to charge the flying capacitor.
7
LT3483
3483f
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.
U
PACKAGE DESCRIPTIO
S6 Package
6-Lead Plastic TSOT-23
(Reference LTC DWG # 05-08-1636)
1.50 1.75
(NOTE 4)
2.80 BSC
0.30 0.45
6 PLCS (NOTE 3)
DATUM `A'
0.09 0.20
(NOTE 3)
S6 TSOT-23 0302
2.90 BSC
(NOTE 4)
0.95 BSC
1.90 BSC
0.80 0.90
1.00 MAX
0.01 0.10
0.20 BSC
0.30 0.50 REF
PIN ONE ID
NOTE:
1. DIMENSIONS ARE IN MILLIMETERS
2. DRAWING NOT TO SCALE
3. DIMENSIONS ARE INCLUSIVE OF PLATING
3.85 MAX
0.62
MAX
0.95
REF
RECOMMENDED SOLDER PAD LAYOUT
PER IPC CALCULATOR
1.4 MIN
2.62 REF
1.22 REF
4. DIMENSIONS ARE EXCLUSIVE OF MOLD FLASH AND METAL BURR
5. MOLD FLASH SHALL NOT EXCEED 0.254mm
6. JEDEC PACKAGE REFERENCE IS MO-193
TYPICAL APPLICATIO
U
SW
L1
10H
D
LT3483
FB
C1
4.7F
C2
0.22F
D1
V
IN
10
R1
806k
C1: MURATA GRM219R61A475KE34B
C2: TAIYO YUDEN LMK107BJ224
C3: MURATA GRM219R61C225KA88B
D1: PHILIPS PMEG2005EB
L1: MURATA LQH2MCN100K02L
5pF
C3
2.2F
3483 TA04a
V
OUT
8V
25mA
V
IN
3.6V
SHDN
GND
3.6V to 8V DC/DC Converter
Low Profile, Small Footprint
Switching Waveform
V
OUT
20mV/DIV
I
SW
100mA/DIV
2s/DIV
3483 TA04b
8
LT3483
3483f
LINEAR TECHNOLOGY CORPORATION 2004
LT/TP 1004 1K PRINTED IN THE USA
RELATED PARTS
Linear Technology Corporation
1630 McCarthy Blvd., Milpitas, CA 95035-7417
(408) 432-1900
FAX: (408) 434-0507
www.linear.com
TYPICAL APPLICATIO S
U
3.6V to 22V DC/DC Converter
SW
L1
10H
D
LT3483
FB
C1
4.7F
C2
0.1F
D1
V
IN
R
S
30
R1
2.2M
C1: TAIYO YUDEN LMK316BJ475MD
C2: TAIYO YUDEN TMK107BJ104 (X5R)
C3: TAIYO YUDEN TMK316BJ105MD
D1: PHILIPS PMEG3002AEB
L1: MURATA LQH2MCN100K02L
C3
1F
5pF
3483 TA02a
V
OUT
22V
8mA
V
IN
3.6V
SHDN
GND
3.6V to 22V Converter Efficiency and Power Loss
5V DC/DC Converter
5V Efficiency
SW
10
L1A
10H
L1B
10H
D
LT3483
FB
C1
4.7F
1nF
V
IN
511k
22pF
C2
10F
3483 TA03a
V
OUT
5V
V
IN
SHDN
GND
C1: TAIYO YUDEN EMK316BJ475ML
C2: TAIYO YUDEN JMK316BJ106ML
L1A, L1B: WURTH 744876100
PART NUMBER
DESCRIPTION
COMMENTS
LT1617/LT1617-1
350mA/100mA (I
SW
) High Efficiency
V
IN
: 1.2V to 15V, V
OUT(MAX)
= 34V, I
Q
= 20A, I
SD
< 1A
Micropower Inverting DC/DC Converter
ThinSOT Package
LT1931/LT1931A
1A (I
SW
), 1.2MHz/2.2MHz, High Efficiency
V
IN
: 2.6V to 16V, V
OUT(MAX)
= 34V, I
Q
= 5.8mA, I
SD
< 1A
Micropower Inverting DC/DC Converter
ThinSOT Package
LT1945
Dual Output, Boost/Inverter, 350mA (I
SW
), Constant
V
IN
: 1.2V to 15V, V
OUT(MAX)
= 34V, I
Q
= 40A, I
SD
< 1A,
Off-Time, High Efficiency Step-Up DC/DC Converter
MS10 Package
LT3463
Dual Output, Boost/Inverter, 250mA (I
SW
), Constant
V
IN
: 2.3V to 15V, V
OUT(MAX)
= 40V, I
Q
= 40A, I
SD
< 1A
Off-Time, High Efficiency Step-Up DC/DC Converter
DFN Package
with Integrated Schottky Diodes
LT3464
85mA (I
SW
), High Efficiency Step-Up DC/DC Converter
V
IN
: 2.3V to 10V, V
OUT(MAX)
= 34V, I
Q
= 25A, I
SD
< 1A
with Integrated Schottky and PNP Disconnect
ThinSOT Package
LT3472
Boost (350mA) and Inverting (400mA) DC/DC Converter
V
IN
: 2.3V to 15V, V
OUT(MAX)
= 40V, I
Q
= 2.8mA, I
SD
< 1A
for CCD Bias with Integrated Schottkys
DFN Package
LOAD CURRENT (mA)
0.1
EFFICIENCY (%)
POWER LOSS (mW)
65
70
EFFICIENCY
10
3483 TA02b
60
55
1
75
10
100
POWER
LOSS
1
0.1
1000
LOAD CURRENT (mA)
0.1
55
EFFICIENCY (%)
60
65
70
75
1
10
3483 TA03b
100
V
IN
= 5V
V
IN
= 12V
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