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PDF LTC3443 Data sheet ( Hoja de datos )
| Número de pieza | LTC3443 | |
| Descripción | High Current Micropower 600kHz Synchronous Buck-Boost DC/DC Converter | |
| Fabricantes | Linear Technology | |
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LTC3443www.DataSheet4U.com
High Current Micropower
600kHz Synchronous Buck-Boost
DC/DC Converter
FEATURES
■ Regulated Output with Input Above, Below or Equal
to the Output
■ Single Inductor, No Schottky Diodes
■ High Efficiency: Up to 96%
■ 28µA Quiescent Current in Burst Mode® Operation
■ Up to 1.2A Continuous Output Current from a Single
Lithium-Ion
■ True Output Disconnect in Shutdown
■ 2.4V to 5.5V Input Range
■ 2.4V to 5.25V Output Range
■ 600kHz Fixed Frequency Operation
■ Synchronizable Oscillator
■ Selectable Burst Mode or Fixed Frequency Operation
■ <1µA Quiescent Current in Shutdown
■ Small, Thermally Enhanced 12-Lead
(4mm × 3mm × 0.8mm) DFN package
U
APPLICATIO S
■ Handheld Computers
■ Handheld Instruments
■ MP3 Players
■ Digital Cameras
, LTC and LT are registered trademarks of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
U.S. Patent #’s 6404251, 6166527
DESCRIPTIO
The LTC®3443 is a high efficiency, fixed frequency, buck-
boost DC/DC converter that operates from input voltages
above, below or equal to the output voltage. The part is pin
for pin compatible with its predecessor, the LTC3441, with
a lower operating frequency (600kHz), and a VC pin clamp
circuit during Burst Mode operation. The topology incor-
porated in the IC provides a continuous transfer function
through all operating modes, making the product ideal for
single Lithium Ion or multicell applications where the out-
put voltage is within the battery voltage range.
The device includes two 0.10Ω N-channel MOSFET
switches and two 0.11Ω P-channel switches. External
Schottky diodes are optional, and can be used for a
moderate efficiency improvement. The operating frequency
is internally set to 600kHz and can be synchronized up to
1.2MHz. Quiescent current is only 28µA in Burst Mode
operation, maximizing battery life in portable applications.
Burst Mode operation is user controlled and can be
enabled by driving the MODE/SYNC pin high. If the MODE/
SYNC pin is driven low or with a clock, then fixed fre-
quency switching is enabled.
Other features include a 1µA shutdown, soft-start control,
thermal shutdown and current limit. The LTC3443 is
available in a thermally enhanced 12-lead (4mm × 3mm)
DFN Package.
TYPICAL APPLICATIO
VIN
2.5V
TO 4.2V
Li-Ion
Li-Ion to 3.3V at 1A Buck-Boost Converter
6µH
10µF
SW1 SW2
PVIN
VOUT
LTC3443
VIN FB
SHDN/SS
VC
MODE/SYNC GND
PGND
PGND
340k
220pF
2.2k
15k
560pF
200k
VOUT
3.3V
1A
44µF
(2 × 22µF)
3443 TA01
Efficiency vs VIN
100
IOUT = 200mA
95
90
85 IOUT = 1A
80
75
70
65
60
55
VOUT = 3.3V
50
2.7 3.2 3.7
4.2
VIN (V)
4.7
5.2
3443 TA02
sn3443 3443fs
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LTC3443www.DataSheet4U.com
TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25°C unless otherwise specified)
Error Amp Sink Current
400
VIN = VOUT = 3.6V
Output Frequency
0.70
VIN = VOUT = 3.6V
Current Limit
3.4
VIN = VOUT = 3.6V
350 0.65
3.2
300 0.60
3.0
250 0.55
200
–55 –25
5
35 65
TEMPERATURE (°C)
NMOS RDS(ON)
0.15
VIN = VOUT = 3.6V
SWITCHES B AND C
0.13
95 125
3443 G12
0.11
0.09
0.07
0.05
–55 –25
5
35 65
TEMPERATURE (°C)
95 125
3443 G15
0.50
–55 –25
5
35 65
TEMPERATURE (°C)
PMOS RDS(ON)
0.15
VIN = VOUT = 3.6V
SWITCHES A AND D
0.13
95 125
3443 G13
0.11
0.09
0.07
0.05
–50 –25
5
35 65
TEMPERATURE (°C)
95 125
3443 G16
2.8
–55
–25 5 35 65
TEMPERATURE (°C)
Minimum Start Voltage
2.30
95 125
3443 G14
2.25
2.20
2.15
2.10
–55 –25
5
35 65
TEMPERATURE (°C)
95 125
3443 G17
PI FU CTIO S
SHDN/SS (Pin 1): Combined Soft-Start and Shutdown.
Applied voltage < 0.4V shuts down the IC. Tie to >1.4V to
enable the IC and >2.4V to ensure the error amp is not
clamped from soft-start. An RC from the shutdown com-
mand signal to this pin will provide a soft-start function by
limiting the rise time of the VC pin.
GND (Pin 2): Signal Ground for the IC.
PGND (Pins 3, 6, 13 Exposed Pad): Power Ground for the
Internal NMOS Power Switches. The exposed pad must be
soldered to PCB ground for optimal thermal performance.
SW1 (Pin 4): Switch pin where the internal switches A and
B are connected. Connect inductor from SW1 to SW2. An
optional Schottky diode can be connected from this SW1
to ground. Minimize trace length to keep EMI down.
SW2 (Pin 5): Switch pin where the internal switches C
and D are connected. An optional Schottky diode can be
connected from SW2 to VOUT (it is required where
VOUT > 4.3V). Minimize trace length to keep EMI down.
MODE/SYNC (Pin 7): Burst Mode Select and Oscillator
Synchronization.
MODE/SYNC = High: Enable Burst Mode Operation.
During the period where the IC is supplying energy to
the output, the inductor peak inductor current will reach
0.8A and return to zero current on each cycle. In Burst
Mode operation the operation is variable frequency,
which provides a significant efficiency improvement at
light loads. The Burst Mode operation will continue until
the pin is driven low.
sn3443 3443fs
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LTC3443www.DataSheet4U.com
APPLICATIO S I FOR ATIO
COMPONENT SELECTION
1 SHDN/SS
2 GND
3 PGND
4 SW1
5 SW2
6 PGND
FB 12
VC 11
VIN 10
PVIN 9
VOUT 8
MODE 7
VIN
VOUT
GND
3443 F06
MULTIPLE VIAS
Figure 6. Recommended Component Placement. Traces Carrying
High Current are Direct. Trace Area at FB and VC Pins are Kept
Low. Lead Length to Battery Should be Kept Short. VOUT and VIN
Ceramic Capacitors Close to the IC Pins
Inductor Selection
The high frequency operation of the LTC3443 allows the
use of small surface mount inductors. The inductor cur-
rent ripple is typically set to 20% to 40% of the maximum
inductor current. For a given ripple the inductance terms
are given as follows:
( )L
>
VIN(MIN)2 • VOUT – VIN(MIN) • 100
f • IOUT(MAX) • %Ripple • VOUT2
H,
( )L > VOUT • VIN(MAX) – VOUT • 100 H
f • IOUT(MAX) • %Ripple • VIN(MAX)
where f = operating frequency, Hz
%Ripple = allowable inductor current ripple, %
VIN(MIN) = minimum input voltage, V
VIN(MAX) = maximum input voltage, V
VOUT = output voltage, V
IOUT(MAX) = maximum output load current
For high efficiency, choose an inductor with a high fre-
quency core material, such as ferrite, to reduce core loses.
The inductor should have low ESR (equivalent series
resistance) to reduce the I2R losses, and must be able to
handle the peak inductor current without saturating. Molded
chokes or chip inductors usually do not have enough core
to support the peak inductor currents in the 1A to 2A
region. To minimize radiated noise, use a toroid, pot core
or shielded bobbin inductor. See Table 1 for suggested
components and Table 2 for a list of component suppliers.
Table 1. Inductor Vendor Information
SUPPLIER PHONE
FAX
WEB SITE
Coilcraft (847) 639-6400 (847) 639-1469 www.coilcraft.com
Coiltronics (561) 241-7876 (561) 241-9339 www.coiltronics.com
Murata
USA: USA:
(814) 237-1431 (814) 238-0490
(800) 831-9172
www.murata.com
Sumida
USA:
(847) 956-0666 (847) 956-0702
Japan:
81(3) 3607-5111 81(3) 3607-5144
www.japanlink.com/
sumida
Output Capacitor Selection
The bulk value of the capacitor is set to reduce the ripple
due to charge into the capacitor each cycle. The steady
state ripple due to charge is given by:
( )%Ripple
_
Boost
=
IOUT(MAX) • VOUT – VIN(MIN)
COUT • VOUT2 • f
• 100
%
( )%Ripple _Buck = IOUT(MAX) •
VIN(MAX) – VOUT
• 100
%
COUT • VIN(MAX) • VOUT • f
where COUT = output filter capacitor, F
The output capacitance is usually many times larger in
order to handle the transient response of the converter.
For a rule of thumb, the ratio of the operating frequency to
the unity-gain bandwidth of the converter is the amount
the output capacitance will have to increase from the
sn3443 3443fs
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11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC3443.PDF ] | |
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