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PDF LTC3455 Data sheet ( Hoja de datos )
| Número de pieza | LTC3455 | |
| Descripción | Dual DC/DC Converter | |
| Fabricantes | Linear Technology | |
| Logotipo |  |
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LTC3455/LTC3455-1
Dual DC/DC Converter
with USB Power Manager
and Li-Ion Battery Charger
FEATURES
DESCRIPTION
n Seamless Transition between Input Power Sources:
Li-Ion Battery, USB, and 5V Wall Adapter
n Accurate USB Current Limiting (500mA/100mA)
n Two High Efficiency DC/DC Converters: Up to 96%
n Thermal Regulation Maximizes Battery Charge
Rate without Risk of Overheating
n Full-Featured Li-Ion Battery Charger with 4.2V Float
Voltage for LTC3455 and 4.1V for LTC3455-1
n 4.1V Float Voltage (LTC3455-1) Improves Battery Life
and High Temperature Safety Margin
n Hot Swap™ Output for SDIO and Memory Cards
n Pin-Selectable Burst Mode® Operation
n Output Disconnect: All Outputs Discharged to Ground
During Shutdown
n Available in a 4mm × 4mm × 0.75mm 24-Pin
QFN Package
APPLICATIONS
n Handheld Computers
n Digital Cameras
n MP3 Players
The LTC®3455/LTC3455-1 are complete power manage-
ment solutions for a variety of portable applications.
These devices contain 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/LTC3455-1 provide 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 discharged to ground during
shutdown to provide complete output disconnect. These
devices are available in a 4mm × 4mm 24-pin exposed-
pad QFN package.
L, LT, LTC, LTM and Burst Mode are registered trademarks of Linear Technology Corporation.
Hot Swap is a trademark of Linear Technology Corporation. All other trademarks are the
property of their respective owners. Protected by U.S. Patents including 6522118.
TYPICAL APPLICATION
USB 5V
1Ω
4.7μF
WALL 5V
1Ω
4.7μF
USB
5.6V CONTROLLER
10μF
3.32k
1k
1.24k
0.1μF
2.49k
SINGLE
CELL Li-ION
+
3.3V TO 4.2V
4.7μF
1.8V
1M
LBO
VBAT
2.49M
806k
USB
SUSPEND
USBHP
VMAX
MODE
HSON
ON2
PWRON
RST
PBSTAT
LTC3455/LTC3455-1
CHRG
WALLFB
TIMER
PROG
ON
HSO
HSI
VBAT
SW2
FB2
AO
SW1
AI FB1
GND
3455 TA01a
μC
1M 1M
1.8V
ON/OFF
3.3V, HS
1μF
4.7μH
10pF
4.7μH
10pF
249k
80.6k
3.3V
0.5A
10μF
100k
80.6k
1.8V
0.4A
10μF
Efficiency
100
SWITCHER 2
95 VOUT2 = 3.3V
1000
90
85
SWITCHER 1
100
VOUT1 = 1.8V
80
75
70 10
POWER LOSS FOR
65 BOTH OUTPUTS
60
55
1
VBAT = 3.6V 1
10 100 1000
LOAD CURRENT (mA)
3455 TA01b
3455fc
1
1 page  
TYPICAL PERFORMANCE CHARACTERISTICS
LTC3455/LTC3455-1
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 (oC)
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
TEMPERATURE (°C)
100 125
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
3455fc
5
5 Page 
LTC3455/LTC3455-1
APPLICATIONS INFORMATION
Operation When No Battery Is Present
As long as USB or wall power is available, the LTC3455/
LTC3455-1 will operate with no battery present, a crucial
requirement for systems with a removable battery. Keep
in mind, however, that if the LTC3455/LTC3455-1 are 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. This is espe-
cially a problem when starting up the LTC3455/LTC3455-1
in USB low power mode with no battery present, which
is discussed in greater detail on the next page, in the
section entitled “Startup Issues in USB Low Power Mode
When No Battery is Present”. Similarly, if external power
is available, the LTC3455/LTC3455-1 will operate even if
the battery is bad or in deep-discharge.
The LTC3455/LTC3455-1 are 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) exceeds
what the adapter can provide, the voltage on the VMAX pin
will begin to droop. If it droops close enough to the bat-
tery 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
portable 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 por-
table device can vary quite significantly. Although a USB
power supply has a 5V nominal rating, when you include
normal supply variations, cable losses, and transient
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 when the USB voltage may itself be
below or near the float voltage.
The LTC3455/LTC3455-1 are specifically designed to al-
leviate 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/LTC3455-1’s special USB features.
3455fc
11
11 Page | ||
| Páginas | Total 28 Páginas | |
| PDF Descargar | [ Datasheet LTC3455.PDF ] | |
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