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PDF LTC3444 Data sheet ( Hoja de datos )
| Número de pieza | LTC3444 | |
| Descripción | Micropower Synchronous Buck-Boost DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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Hay una vista previa y un enlace de descarga de LTC3444 (archivo pdf) en la parte inferior de esta página. Total 20 Páginas | ||
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LTC3444
Micropower Synchronous
Buck-Boost DC/DC Converter
for WCDMA Applications
FEATURES
■ Optimized Features for WCDMA Handsets
■ Regulated Output with Input Voltages
Above, Below, or Equal to the Output
■ 0.5V to 5V Output Range
■ Up to 400mA Continuous Output Current From
a Single Lithium-Ion Cell
■ Minimal External Components
■ 1.5MHz Fixed Frequency Operation
■ Internal Loop Compensation for Fast Response
<25μs Full Scale Output Slewing; COUT 4.7μF
■ Output Disconnect in Shutdown
■ 2.75V to 5.5V Input
■ <1μA Shutdown Current
■ Internal Soft-Start
■ Output Overvoltage Protection
■ Single Inductor, No Schottky Diodes Required
■ Small, Thermally Enhanced 8-Lead (3mm × 3mm)
DFN Package
U
APPLICATIO S
■ WCDMA Applications–3G Handsets with High Speed
Data Rate Capability
■ MP3 Players
■ Digital Cameras
DESCRIPTIO
The LTC®3444 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 multi-cell
applications where the output voltage can vary over a wide
range.
The LTC3444 has been optimized for use in 3G WCDMA
applications. A unique design yields high efficiency at
very low output voltages while also eliminating external
components. The high speed error amplifier provides the
fast transient response required to slew the RF power
amplifier from standby to transmit and transmit to stand
by power levels. Output overvoltage protection protects
the RF power amplifier.
Operating frequency is internally set to 1.5MHz to mini-
mize external component size while maximizing efficiency.
Other features include <1μA shutdown current, internal
soft-start, peak current limit and thermal shutdown. The
LTC3444 is available in a small, thermally enhanced
8-lead (3mm × 3mm) DFN package.
, LT, LTC and LTM are registered trademarks of Linear Technology Corporation.
All other trademarks are the property of their respective owners.
Protected by U.S. Patents including 6404251, 6166527.
TYPICAL APPLICATIO
2.2μH
3.1V TO 4.2V
4.7μF
+
Li-Ion
LTC3444
SW1 SW2
VIN
SHDN
VOUT
FB
GND VC
DAC
340k
VOUT
0.8V TO 4.2V
4.7μF
205k
267k
VCONTROL
3444 TA01
LTC3444 Dynamic Response
VOUT
VCONTROL
10μs/DIV
VIN = 3.6V, VOUT = 0.8V TO 4.2V
VCONTROL = 2.36V TO 0.28V, ILOAD = 100mA
3444 G16a
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1
1 page  
LTC3444
PI FU CTIO S
SHDN (Pin 1): Shutdown Function. A logic low input shuts
down the IC. A logic high input enables the IC and starts
the internal soft-start function by limiting the rise time of
the internal PWM command.
SW1 (Pin 2): 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 ground
to SW1 for a moderate efficiency improvement. Minimize
trace length to minimize EMI.
GND (Pin 3): Ground Pin for the IC.
SW2 (Pin 4): Switch Pin Where the Internal Switches C
and D are Connected. An optional Schottky diode can be
connected from SW2 to VOUT for a moderate efficiency
improvement. Minimize trace length to keep EMI down.
VOUT (Pin 5): 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.
VIN (Pin 6): Input Supply Pin. Internal VCC for the IC. A
4.7μF ceramic capacitor is recommended as close to VIN
and GND as possible.
VC (Pin 7): Error Amp Output. Pull VC to ground to select
internal loop compensation. External compensation may
be connected from VC to FB. Internal compensation will be
disabled if VC is tied to an external compensation network.
FB (Pin 8): Feedback Pin. Connect resistive divider tap
here. The output voltage can be adjusted from 0.5V to 5V.
The feedback reference voltage is typically 1.22V.
GND (Pin 9, Exposed Pad): Solder to Board GND.
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5 Page 
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OPERATIO
Buck Region (VIN > VOUT)
Switch D is always on and switch C is always off during this
mode. When the internal control voltage, VCI, is above
voltage V1, Switch A is on. During the off time of switch A,
synchronous switch B turns on for the remainder of the
time. Switches A and B will alternate similar to a typical
synchronous buck regulator. As the control voltage in-
creases, the duty cycle of switch A increases until the
maximum duty cycle of the converter in buck mode
reaches DMAX_BUCK, given by:
DMAX_BUCK = 100% – D4SW
where D4SW = duty cycle % of the four switch range.
D4SW = (125ns • f) • 100 %
where f = operating frequency, Hz.
Beyond this point the “four switch,” or Buck-Boost region
is reached.
LTC3444www.DataSheet4U.com
Buck-Boost or Four Switch (VIN ~ VOUT)
When the internal control voltage, VCI, is above voltage V2,
but below V3, switch pair AD remain on for duty cycle
DMAX_BUCK, and the switch pair AC begins to phase in.
As switch pair AC phases in, switch pair BD phases out
accordingly. When the VCI voltage reaches the edge of the
buck-boost range, at voltage V3, the AC switch pair
completely phase out the BD pair, and the boost phase
begins at duty cycle D4SW. The input voltage, VIN, where
the four switch region begins is given by:
VIN
=
1–
VOUT
(125ns
•
f)
V
The point at which the four switch region ends is given by:
VIN = VOUT(1–D) = VOUT(1–125ns • f) V
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11 Page | ||
| Páginas | Total 20 Páginas | |
| PDF Descargar | [ Datasheet LTC3444.PDF ] | |
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