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PDF LTC3442 Data sheet ( Hoja de datos )
| Número de pieza | LTC3442 | |
| Descripción | Micropower Synchronous Buck-Boost DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3442www.DataSheet4U.com
Micropower Synchronous
Buck-Boost DC/DC Converter with
Automatic Burst Mode Operation
FEATURES
DESCRIPTIO
■ Regulated Output with Input Voltages Above,
Below, or Equal to the Output
■ Single Inductor, No Schottky Diodes Required
■ Manual or Programmable Automatic Burst Mode®
Operation
■ Programmable Average Input Current Limit
■ Up to 1.2A Continuous Output Current from a Single
Lithium-Ion Cell
■ High Efficiency: Up to 95%
■ Output Disconnect in Shutdown
■ 2.4V to 5.5V Input Range
■ 2.4V to 5.25V Output Range
■ 35µA Quiescent Current in Burst Mode Operation
■ Programmable Frequency from 300kHz to 2MHz
■ <1µA Shutdown Current
■ Small, Thermally Enhanced 12-Lead (4mm × 3mm)
DFN Package
U
APPLICATIO S
■ PDA/‘SMART’ Phones
■ Handheld Computers
■ MP3 Players
■ Handheld Instruments
■ Digital Cameras
■ Wireless Handsets
■ USB Peripherals
The LTC®3442 is a highly efficient, fixed frequency, Buck-
Boost DC/DC converter, which operates from input volt-
ages above, below, and 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 a single Lithium-Ion or multicell alkaline
applications where the output voltage is within the battery
voltage range.
The device includes two 0.10Ω N-channel MOSFET
switches and two 0.10Ω P-channel switches. Operating
frequency and average input current limit can each be
programmed with an external resistor. Quiescent current
is only 35µA in Burst Mode operation, maximizing battery
life in portable applications. Automatic Burst Mode opera-
tion allows the user to program the load current for Burst
Mode operation, or to control it manually.
Other features include 1µA shutdown current, program-
mable soft-start, peak current limit and thermal shutdown.
The LTC3442 is available in a low profile, thermally en-
hanced 12-lead (4mm × 3mm × 0.75mm) DFN package.
, LTC and LT are registered trademarks of Linear Technology Corporation. Burst Mode
is a registered trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Protected by U.S. Patents, including 6404251, 6166527.
TYPICAL APPLICATIO
4.7µH
VIN
2.5V TO
4.2V
Li-Ion
10µF
1M
0.01µF
71.5k
SW1 SW2
VIN VOUT
LTC3442
SHDN/SS
FB
RLIM
VC
RT
SGND
BURST
PGND
340k
2.2k
VOUT
3.3V
1.2A
15k
470pF
220pF
22µF
0.01µF
200k
200k
3442 TA01a
Efficiency vs VIN
100
300mA LOAD
90
1A LOAD
80
70
60 VOUT = 3.3V
L = 4.7µH
F = 600kHz
50
2.5 3.0 3.5 4.0 4.5 5.0 5.5
VIN (V)
3442 • TA01b
3442fa
1
1 page  
LTC3442www.DataSheet4U.com
TYPICAL PERFOR A CE CHARACTERISTICS (TA = 25°C unless otherwise specified).
Switch Pins in Buck-Boost Mode
SW1
2V/DIV
SW2
2V/DIV
Switch Pins Entering
Buck-Boost Mode
SW1
2V/DIV
SW2
2V/DIV
50ns/DIV
VIN = 3.3V
VOUT = 3.3V AT 500mA
3442 G16
50ns/DIV
VIN = 4.2V
VOUT = 3.3V AT 500mA
Output Ripple at 1A Load
VIN = 2.7V
VIN = 3.3V
VIN = 4.2V
3442 G17
VOUT
20mV/DIV
AC COUPLED
1µs/DIV
3442 G18
Load Transient Response in Fixed
Frequency Mode, No Load to 1A
Load Transient Response in Auto
Burst Mode Operation, No Load to 1A
Burst Mode Operation
VOUT
100mV/DIV
VOUT
100mV/DIV
VOUT
50mV/DIV
LOAD
0.5A/DIV
100µs/DIV
VIN = 3.6V
VOUT = 3.3V
COUT = 47µF, X5R CERAMIC
LOAD
0.5A/DIV
INDUCTOR
CURRENT
0.5A/DIV
3442 G19
100µs/DIV
VIN = 3.6V
VOUT = 3.3V
COUT = 47µF, X5R CERAMIC + 100µF
LOW ESR TANTALUM
3442 G20
20µs/DIV
COUT = 100µF
LOW ESR TANTALUM
Transition from Burst Mode
Operation to Fixed Frequency Mode
VOUT
50mV/DIV
INDUCTOR
CURRENT
0.5A/DIV
200µs/DIV
COUT = 100µF
LOW ESR TANTALUM
3442 G22
Pulsed Overload Using Average
Input Current Limit
VOUT
2V/DIV
RLIM PIN
0.5V/DIV
INDUCTOR
CURRENT
0.5A/DIV
RLIM = 133k
CLIM = .001µF
1ms/DIV
3442 G23
3442 G21
3442fa
5
5 Page 
U
OPERATIO
current in Amps. Do not use values of RBURST greater than
250k.
For automatic operation, a filter capacitor should also be
connected from BURST to ground to prevent ripple on
BURST from causing the IC to oscillate in and out of Burst
Mode operation. The equation for the minimum capacitor
value is:
CBURST(MIN)
≥
COUT • VOUT
60,000
where CBURST(MIN) and COUT are in µF
In the event that a load transient causes the feedback pin
to drop by more than 4% from the regulation value while
in Burst Mode operation, the IC will immediately switch to
fixed frequency mode and an internal pull-up will be
momentarily applied to BURST, rapidly charging the
BURST cap. This prevents the IC from immediately re-
entering Burst Mode operation once the output achieves
regulation.
Manual Burst Mode Operation
For manual control of Burst Mode operation, the RC
network connected to BURST can be eliminated. To force
fixed frequency mode, BURST should be connected to
VOUT. To force Burst Mode operation, BURST should be
grounded. When commanding Burst Mode operation
manually, the circuit connected to BURST should be able
to sink up to 2mA.
LTC3442www.DataSheet4U.com
For optimum transient response with large dynamic loads,
the operating mode should be controlled manually by the
host. By commanding fixed frequency operation prior to a
sudden increase in load, output voltage droop can be
minimized. Note that if the load current applied during
forced Burst Mode operation (BURST pin is grounded)
exceeds the current that can be supplied, the output
voltage will start to droop and the IC will automatically
come out of Burst Mode operation and enter fixed fre-
quency mode, raising VOUT. Once regulation is achieved,
the IC will then enter Burst Mode operation once again,
and the cycle will repeat, resulting in about 4% output
ripple. Note that Burst Mode operation is inhibited during
soft-start.
Burst Mode Operation to Fixed Frequency Transient
Response
In Burst Mode operation, the compensation network is not
used and VC is disconnected from the error amplifier.
During long periods of Burst mode operation, leakage
currents in the external components or on the PC board
could cause the compensation capacitor to charge (or
discharge), which could result in a large output transient
when returning to fixed frequency mode of operation, even
at the same load current. To prevent this, the LTC3442
incorporates an active clamp circuit that holds the voltage
on VC at an optimal voltage during Burst Mode operation.
This minimizes any output transient when returning to
fixed frequency mode operation. For optimum transient
3442fa
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11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC3442.PDF ] | |
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