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PDF LTC3455EUF Data sheet ( Hoja de datos )
| Número de pieza | LTC3455EUF | |
| Descripción | Dual DC/DC Converter with USB Power Manager and Li-Ion Battery Charger | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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FEATURES
s Seamless Transition between Input Power Sources:
Li-Ion Battery, USB, and 5V Wall Adapter
s Accurate USB Current Limiting (500mA/100mA)
s Two High Efficiency DC/DC Converters: Up to 96%
s Thermal Regulation Maximizes Battery Charge
Rate without Risk of Overheating*
s Full-Featured Li-Ion Battery Charger
s Hot Swap™ Output for SDIO and Memory Cards
s Pin-Selectable Burst Mode® Operation
s Output Disconnect: All Outputs Discharged to
Ground During Shutdown
s Available in a 4mm × 4mm × 0.8mm 24-Pin
QFN Package
U
APPLICATIO S
s Handheld Computers
s Digital Cameras
s MP3 Players
LTC3455
Dual DC/DC Converter
with USB Power Manager
and Li-Ion Battery Charger
DESCRIPTIO
The LTC®3455 is a complete power management solution
for a variety of portable applications. The device contains
two synchronous step-down DC/DC converters, a USB
power controller, a full-featured Li-Ion battery charger, a
Hot Swap output, a low-battery indicator, and numerous
internal protection features. The LTC3455 provides a
small, simple solution for obtaining power from three
different power sources: a single-cell Li-Ion battery, a USB
port, and a wall adapter. Current drawn from the USB bus
is accurately limited under all conditions. Whenever a USB
or a wall adapter is present, the battery charger is enabled
and all internal power for the device is drawn from the
appropriate external power source. All outputs are dis-
charged to ground during shutdown to provide complete
output disconnect. The device is available in a
4mm × 4mm 24-pin exposed-pad QFN package.
, LTC and LT are registered trademarks of Linear Technology Corporation.
Hot Swap is a trademark of Linear Technology Corporation.
Burst Mode is a registered trademark of Linear Technology Corporation.
*U.S. Patent 6,522,118
TYPICAL APPLICATIO
USB 5V
1Ω
4.7µF
USB
CONTROLLER
8
6
5
WALL 5V
1Ω
1µF
10
10µF
3.32k
1.24k
1k
0.1µF
4
11
3
2
2.49k
9
SINGLE
CELL Li-ION
+
3.3V TO 4.2V
4.7µF
1.8V
1M
LBO
VBAT
2.49M
17
16
806k
USB
SUSPEND
USBHP
VMAX
MODE
HSON
ON2
PWRON
RST
PBSTAT
21
15
19
22
20
23
µC
LTC3455
CHRG
WALLFB
TIMER
PROG
VBAT
AO
AI
1M 1M
1.8V
24
ON
14
HSO
ON/OFF
3.3V, HS
1µF
13
HSI
12 4.7µH
SW2
18
FB2
10pF
249k
80.6k
7
SW1
1
FB1
25
GND
3455 TA01a
4.7µH
10pF
100k
80.6k
3.3V
0.5A
10µF
1.8V
0.4A
10µF
Efficiency
100
SWITCHER 2
95 VOUT2 = 3.3V
90
85
SWITCHER 1
VOUT1 = 1.8V
80
75
70
65
60 VBAT = 3.6V
1 10
100
LOAD CURRENT (mA)
1000
3455 TA01b
3455f
1
1 page  
TYPICAL PERFOR A CE CHARACTERISTICS
LTC3455
Feedback Pins (FB1, FB2)
and AI Pin Voltage
815
810
805 AI
800
FB1
FB2
795
790
785
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3455 G04
Switching Regulator Oscillator
Frequency
2.0
1.5
FOR BOTH SWITCHERS
1.0
0.5
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3455 G05
Switching Regulator Current Limit
1000
SWITCHER 2
800
600 SWITCHER 1
400
200
0
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3455 G06
USB Pin Current Limit
500
USBHP = 2V
400
300
200
100
USBHP = 0V
VUSB = 5V
0
–50 –25 0
25 50
75
TEMPERATURE (°C)
100 125
3455 G07
VMAX Pin Current Limit
5.0
4.5
NORMAL OPERATION
4.0
3.5
3.0
2.5
2.0
1.5
1.0 STARTUP
0.5
0
–50 –25
0 25 50 75 100 125
TEMPERATURE (°C)
3455 G08
HSO Pin Current Limit
200
150
100
50
VHSI = 3.3V
VHSO = 2.5V
0
–50 –25 0
25 50
75
TEMPERATURE (°C)
100 125
3455 G09
Battery Undervoltage Lockout
4.00
3.75
3.50
3.25
RISING
3.00
2.75
2.50
–50 –25
FALLING
0 25 50 75
TEMPERATURE (°C)
100 125
3455 G10
USB Undervoltage Lockout
4.00
3.75
FALLING
RISING
3.50
3.25
3.00
2.75
2.50
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3455 G11
WALLFB Trip Voltage
1.26
1.24
RISING
1.22
1.20
1.18
FALLING
1.16
1.14
1.12
1.10
–50 –25
0 25 50 75
TEMPERATURE (°C)
100 125
3455 G12
3455f
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5 Page 
LTC3455
APPLICATIO S I FOR ATIO
Operation When No Battery Is Present
As long as USB or wall power is available, the LTC3455 will
operate with no battery present, a crucial requirement for
systems with a removable battery. Keep in mind, however,
that if the LTC3455 is USB powered and the battery is not
present, absence of the battery means that there is no
reservoir if the system needs more power than the USB
port can supply. Similarly, if external power is available,
the LTC3455 will operate even if the battery is bad or in
deep-discharge.
The LTC3455 is also a good choice for systems that are
always powered by a USB supply or wall adapter. The
charger can then be used to charge a large capacitor or
backup battery, which can briefly provide power to the
system after the external power has been removed. This
gives the microcontroller enough time to follow proper
shutdown procedures even after the main power source is
abruptly removed. If USB powered, the large capacitor or
backup battery will also be used to provide additional
current if the system briefly needs more power than the
USB bus can provide.
Concerns When Wall Adapter Powered
Always choose a wall adapter that can provide power for
all load and battery charging requirements. Choosing a
wall adapter with a power rating that is too small will result
in very long charge times and erratic system operation. If
the total current needed (load and battery charging) ex-
ceeds what the adapter can provide, the voltage on the
VMAX pin will begin to droop. If it droops close enough to
the battery voltage (the VBAT pin), the charge current
decreases and eventually reduces to zero. If the load
current is still too much for the wall adapter to provide, the
wall adapter will provide what it can and the battery will
provide the rest. When wall powered, this operation is
intended only for surviving fault conditions and should not
be a normal mode of operation.
Concerns When USB Powered
The popularity of USB (Universal Serial Bus) makes it an
attractive choice for transferring data in a variety of por-
table devices. Therefore, utilizing the USB port to power
these portable devices while charging their battery is very
desirable, but it is not necessarily an easy task. As the
performance of digital cameras, handheld computers, and
MP3 players increases, the power needed to operate them
also increases. The power available from a single USB port
(maximum 2.5W) is barely enough to support the peak
power needed by many full-featured portable devices,
even without the power needed to quickly charge their
batteries.
To further complicate matters, a USB port is not the ideal
power source. Each device can draw a maximum of
500mA (in high power mode), but the voltage provided to
the portable device can vary quite significantly. Although
a USB power supply has a 5V nominal rating, when you
include normal supply variations, cable losses, and tran-
sient conditions, the USB voltage showing up at the
portable device is typically much lower—often falling to
only 4V. Since the USB port has a strict current limit of
500mA, this means the amount of power available to the
portable device can be as low as 2W. The reduced USB
voltage also presents problems when trying to fully charge
a single-cell Lithium-Ion battery (that has a 4.2V final
charge voltage) when the USB voltage may itself be below
or near 4.2V.
The LTC3455 is specifically designed to alleviate these
problems and make the most of the power the USB port
has to offer. See the sections entitled ”Large Transient
Loads when USB powered” and ”Special Charger Features
when USB powered” for more detailed discussions of the
LTC3455’s special USB features.
USB High Power/Low Power/Suspend Modes
There are three basic modes for the USB power manager:
high power, low power, and suspend. High power mode
allows the LTC3455 to draw up to 500mA from the USB
port, and is selected by pulling the USBHP pin high. Low
power mode reduces the allowable current drawn to
100mA, and is selected by pulling the USBHP pin low. The
USBHP pin has a weak internal pulldown current source to
ensure that the LTC3455 always starts up in USB low
power mode. The SUSPEND pin will disable the USB
power manager completely, reducing the USB pin current
to under 20µA.
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11
11 Page | ||
| Páginas | Total 24 Páginas | |
| PDF Descargar | [ Datasheet LTC3455EUF.PDF ] | |
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