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PDF LTC3441 Data sheet ( Hoja de datos )
| Número de pieza | LTC3441 | |
| Descripción | High Current Micropower Synchronous Buck-Boost DC/DC Converter | |
| Fabricantes | Linear Technology | |
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Features
n Regulated Output with Input Above, Below or Equal
to the Output
n Single Inductor, No Schottky Diodes
n High Efficiency: Up to 95%
n 25µA Quiescent Current in Burst Mode® Operation
n Up to 1.2A Continuous Output Current from a Single
Lithium-Ion
n True Output Disconnect in Shutdown
n 2.4V to 5.5V Input Range
n 2.4V to 5.25V Output Range
n 1MHz Fixed Frequency Operation
n Synchronizable Oscillator
n Selectable Burst Mode or Fixed Frequency Operation
n <1µA Quiescent Current in Shutdown
n Small, Thermally Enhanced 12-Lead (4mm × 3mm)
DFN package
Applications
n Handheld Computers
n Handheld Instruments
n MP3 Players
n Digital Cameras
L, LT, LTC, LTM, Linear Technology, Burst Mode and the Linear logo are registered trademarks
and ThinSOT is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners.
LTC3441
High Current Micropower
Synchronous Buck-Boost
DC/DC Converter
Description
The LTC®3441 is a high efficiency, fixed frequency, buck-
boost DC/DC converter that operates efficiently from input
voltages above, below or equal to the output voltage. The
topology incorporated in the IC provides a continuous
transfer function through all operating modes, making
the product ideal for single lithium ion or multicell ap-
plications where the output 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 mod-
erate efficiency improvement. The operating frequency
is internally set to 1MHz and can be synchronized up to
1.7MHz. Quiescent current is only 25µA in Burst Mode
operation, maximizing battery life in portable applica-
tions. 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
frequency switching is enabled.
Other features include a 1µA shutdown, soft-start con-
trol, thermal shutdown and current limit. The LTC3441 is
available in a thermally enhanced 12-lead (4mm × 3mm)
DFN package.
Typical Application
Li-Ion to 3.3V at 1A Buck-Boost Converter
L1
4.7µH
4 SW1
SW2 5
Li-Ion
2.5V TO 4.2V
*
CIN
10µF
9
10
1
7
3
PVIN
VOUT
VIN LTC3441 FB
SHDN/SS
VC
MODE/SYNC GND
PGND
PGND
8
12
11
2
6
15k
1.5nF
340k
200k
VOUT
3.3V
1A
COUT
22µF
*1 = Burst Mode OPERATION
0 = FIXED FREQUENCY
CIN: TAIYO YUDEN JMK212BJ106MG
COUT: TAIYO YUDEN JMK325BJ226MM
L1: TOKO A916CY-4R7M
3441 TA01
Efficiency vs VIN
100 VOUT = 3.3V
95
IOUT = 200mA
90
85
80
IOUT = 1A
75
70
65
60
55
50
2.5 3 3.5 4 4.5 5 5.5
VIN (V)
3441 TA02
For more information www.linear.com/LTC3441
3441fb
1
1 page  
Typical Performance Characteristics
LTC3441
NMOS RDS(ON)
0.15
VIN = VOUT = 3.6V
SWITCHES B AND C
0.13
0.11
0.09
0.07
0.05
–55 –25
5
35 65
TEMPERATURE (°C)
95 125
3441 G14
PMOS RDS(ON)
0.15
0.14
VIN = VOUT = 3.6V
SWITCHES A AND D
0.13
0.12
0.11
0.10
0.09
0.08
0.07
0.06
0.05
–50 –25
5
35 65
TEMPERATURE (°C)
95 125
3441 G15
Minimum Start Voltage
2.30
2.25
2.20
2.15
2.10
–55 –25
5
35 65
TEMPERATURE (°C)
95 125
3441 G16
pin functions
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
light loads. The Burst Mode operation will continue until
the pin is driven low.
MODE/SYNC = Low: Disable Burst Mode operation
and maintain low noise, constant frequency operation .
MODE/SYNC = External CLK : Synchronization of the
internal oscillator and Burst Mode operation disable. A
clock pulse width between 100ns and 2µs and a clock
frequency between 2.3MHz and 3.4MHz (twice the
desired frequency) is required to synchronize the IC.
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
fOSC = fSYNC/2
VOUT (Pin 8): Output of the Synchronous Rectifier. A filter
capacitor is placed from VOUT to GND. A ceramic bypass
capacitor is recommended as close to the VOUT and GND
pins as possible.
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.
PVIN (Pin 9): Power VIN Supply Pin. A 10µF ceramic ca-
pacitor is recommended as close to the PVIN and PGND
pins as possible
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
VIN (Pin 10): Input Supply Pin. Internal VCC for the IC.
VC (Pin 11): Error Amp Output. A frequency compensa-
tion network is connected from this pin to the FB pin to
compensate the loop. See the section “Compensating the
Feedback Loop” for guidelines.
FB (Pin 12): Feedback Pin. Connect resistor divider tap
here. The output voltage can be adjusted from 2.4V to
5.25V. The feedback reference voltage is typically 1.22V.
3441fb
For more information www.linear.com/LTC3441
5
5 Page 
LTC3441
applications Information
Input Capacitor Selection
Since the VIN pin is the supply voltage for the IC it is
recommended to place at least a 4.7µF, low ESR bypass
capacitor.
Table 2. Capacitor Vendor Information
SUPPLIER PHONE
FAX
AVX (803) 448-9411 (803) 448-1943
Sanyo
(619) 661-6322 (619) 661-1055
Taiyo Yuden (408) 573-4150 (408) 573-4159
WEB SITE
www.avxcorp.com
www.sanyovideo.com
www.t-yuden.com
Optional Schottky Diodes
The Schottky diodes across the synchronous switches B
and D are not required (VOUT < 4.3V), but provide a lower
drop during the break-before-make time (typically 15ns) of
the NMOS to PMOS transition, improving efficiency. Use a
Schottky diode such as an MBRM120T3 or equivalent. Do
not use ordinary rectifier diodes, since the slow recovery
times will compromise efficiency. For applications with an
output voltage above 4.3V, a Schottky diode is required
from SW2 to VOUT.
Output Voltage < 2.4V
The LTC3441 can operate as a buck converter with out-
put voltages as low as 0.4V. The part is specified at 2.4V
minimum to allow operation without the requirement of a
Schottky diode. Synchronous switch D is powered from
VOUT and the RDS(ON) will increase at low output voltages,
therefore a Schottky diode is required from SW2 to VOUT
to provide the conduction path to the output.
Output Voltage > 4.3V
A Schottky diode from SW to VOUT is required for output
voltages over 4.3V. The diode must be located as close to
the pins as possible in order to reduce the peak voltage
on SW2 due to the parasitic lead and trace inductance.
Input Voltage > 4.5V
For applications with input voltages above 4.5V which
could exhibit an overload or short-circuit condition, a
2Ω/1nF series snubber is required between the SW1 pin
and GND. A Schottky diode from SW1 to VIN should also
be added as close to the pins as possible. For the higher
input voltages, VIN bypassing becomes more critical;
therefore, a ceramic bypass capacitor as close to the VIN
and GND pins as possible is also required.
Operating Frequency Selection
Additional quiescent current due to the output switches
GATE charge is given by:
Buck: 800e–12 • VIN • f
Boost: 400e–12 • (VIN + VOUT) • f
Buck/Boost: f • (1200e–12 • VIN + 400e–12 • VOUT)
where f = switching frequency
Closing the Feedback Loop
The LTC3441 incorporates voltage mode PWM control. The
control to output gain varies with operation region (Buck,
Boost, Buck/Boost), but is usually no greater than 15. The
output filter exhibits a double pole response is given by:
fFILTER_POLE = 2 • π •
1
L •COUT
Hz
(in buck mode)
fFILTER_POLE
=
2
•
VOUT
•
VIN
π•
L •COUT
Hz
(in boost mode)
Where L is in Henries and COUT is the output filter capaci-
tor in Farads.
The output filter zero is given by:
fFILTER
_
ZERO
=
2
•
π
•
1
RESR
•
COUT
Hz
where RESR is the capacitor equivalent series resistance.
A troublesome feature in Boost mode is the right-half
plane zero (RHP), and is given by:
fRHPZ
=
2
•
π
•
VIN2
IOUT • L
•
VOUT
Hz
The loop gain is typically rolled off before the RHP zero
frequency.
For more information www.linear.com/LTC3441
3441fb
11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet LTC3441.PDF ] | |
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