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PDF LT3463A Data sheet ( Hoja de datos )
| Número de pieza | LT3463A | |
| Descripción | Dual Micropower DC/DC Converters | |
| Fabricantes | LINEAR | |
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FEATURES
s Generates Well-Regulated Positive and
Negative Outputs
s Low Quiescent Current:
20µA (per Converter) in Active Mode
<1µA in Shutdown Mode
s Internal 42V Power Switches
s Internal 42V Schottky Diodes
s Low VCESAT Switch: 180mV at 150mA
s Input Voltage Range: 2.4V to 15V
s High Output Voltages: Up to ±40V
s Low Profile (0.8mm) 3mm x 3mm DFN Package
U
APPLICATIO S
s CCD Bias
s LCD Bias
s Handheld Computers
s Digital Cameras
LT3463/LT3463A
Dual Micropower
DC/DC Converters
with Schottky Diodes
DESCRIPTIO
The LT®3463/LT3463A are dual micropower DC/DC con-
verters with internal Schottky diodes in a 10-lead 3mm ×
3mm DFN package. Negative and positive LT3463 con-
verters have a 250mA current limit. The LT3463A positive
converter also has a 250mA limit, while the negative
converter has a 400mA limit. Both devices have an input
voltage range of 2.4V to 15V, making them ideal for a wide
variety of applications. Each converter features a quies-
cent current of only 20µA, which drops to under 1µA in
shutdown. A current limited, fixed off-time control scheme
conserves operating current, resulting in high efficiency
over a broad range of load current. The 42V switch enables
high voltage outputs up to ±40V to be easily generated
without the use of costly transformers. The low 300ns off-
time permits the use of tiny, low profile inductors and
capacitors to minimize footprint and cost in space-con-
scious portable applications.
, LTC and LT are registered trademarks of Linear Technology Corporation.
TYPICAL APPLICATIO
VIN
2.7V
TO 5V
4.7µF
CCD Bias Supply (15V, –8V)
10µH
VIN SW1 VOUT1
SHDN1
FB1
LT3463A VREF
SHDN2
GND SW2
FB2
D2
1M
90.9k
154k
VOUT1
15V
10mA
2.2µF
10µH
1µF
1M
4.7µF
10pF
VOUT2
–8V
50mA
3463 TA01a
Efficiency and Power Loss
80
15V EFFICIENCY
75
240
VIN = 3.6V
200
70
–8V EFFICIENCY
160
65 120
60
55
50
0.1
15V LOSS
–8V LOSS
80
40
1 10
LOAD CURRENT (mA)
0
100
3463 TA01b
3463f
1
1 page  
LT3463/LT3463A
APPLICATIO S I FOR ATIO
Choosing an Inductor
Several recommended inductors that work well with the
LT3463 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. Use the equations and recommenda-
tions in the next few sections to find the correct inductance
value for your design.
Table 1. Recommended Inductors
PART
CMD4D06
MAX MAX HEIGHT
L (µH) IDC (mA) DCR(Ω) (mm) MANUFACTURER
4.7 750 0.22 0.8 Sumida
10 500 0.46
(847) 956-0666
22 310 1.07
www.sumida.com
CDRH3D16
10 500 0.19 1.8 Sumida
22 310 0.36
LPO4812
4.7 600 0.16 1.2 Coilcraft
10 400 0.30
(847) 639-6400
22 280 0.64
www.coilcraft.com
LQH32C
10 450 0.39 1.8 Murata
15 300 0.75
(714) 852-2001
22 250 0.92
www.murata.com
LQH31C
4.7 340 0.85 1.8 Murata
Inductor Selection—Boost Regulator
The formula below calculates the appropriate inductor
value to be used for a boost regulator using the LT3463 (or
at least provides a good starting point). This value pro-
vides a good tradeoff in inductor size and system perfor-
mance. Pick a standard inductor close to this value. A
larger value can be used to slightly increase the available
output current, but limit it to around twice the value
calculated below, as too large of an inductance will in-
crease the output voltage ripple without providing much
additional output current. A smaller value can be used
(especially for systems with output voltages greater than
12V) to give a smaller physical size. Inductance can be
calculated as:
( )VOUT − VIN MIN + VD
L = ILIM tOFF
where VD = 0.5V (Schottky diode voltage), ILIM = 250mA
(or 400mA) and tOFF = 300ns; for designs with varying VIN
such as battery powered applications, use the minimum
VIN value in the above equation. For most regulators with
output voltages below 7V, a 4.7µH inductor is the best
choice, even though the equation above might specify a
smaller value.
For higher output voltages, the formula above will give
large inductance values. For a 3V to 20V converter (typical
LCD Bias application), a 21µH inductor is called for with
the above equation, but a 10µH inductor could be used
without much reduction in the maximum output current.
Inductor Selection—Inverting Regulator
The formula below calculates the appropriate inductor
value to be used for an inverting regulator using the
LT3463 (or at least provides a good starting point). This
value provides a good tradeoff in inductor size and system
performance. Pick a standard inductor close to this value
(both inductors should be the same value). A larger value
can be used to slightly increase the available output
current, but limit it to around twice the value calculated
below, as too large of an inductance will increase the
output voltage ripple without providing much additional
output current. A smaller value can be used (especially for
systems with output voltages greater than 12V) to give a
smaller physical size. Inductance can be calculated as:
VOUT + VD
L = 2 ILIM
tOFF
where VD = 0.5V (Schottky diode voltage), ILIM = 250mA
(or 400mA) and tOFF = 300ns.
For higher output voltages, the formula above will give
large inductance values. For a 3V to 20V converter (typical
LCD bias application), a 49µH inductor is called for with
the above equation, but a 10µH or 22µH inductor could be
used without much reduction in the maximum output
current.
Inductor Selection—Inverting Charge Pump Regulator
For the inverting regulator, the voltage seen by the internal
power switch is equal to the sum of the absolute value of
the input and output voltages, so that generating high
3463f
5
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| PDF Descargar | [ Datasheet LT3463A.PDF ] | |
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