LTC3455EUF-1#PBF Linear Technology, LTC3455EUF-1#PBF Datasheet - Page 10

• Manufacturer Part Number: LTC3455EUF-1#PBF
• Description: IC DC/DC CONV DUAL CHRG 24-QFN
• Manufacturer: Linear Technology

Specifications of LTC3455EUF-1#PBF

• Applications: Handheld/Mobile Devices
• Voltage - Supply: 3 V ~ 6 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-QFN
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Current - Supply: -

OPERATION
LTC3455/LTC3455-1
The LTC3455/LTC3455-1 are designed to be a complete
power management solution for a wide variety of portable
systems. The device incorporates two current mode step-
down switching regulators, a full-featured battery charger,
a USB power controller, a Hot Swap output, a low-battery
comparator (which can also be confi gured as an LDO)
and numerous protection features into a single package.
When only battery power is available, the battery PMOS
switch connects the V
power to both switching regulators (and any other devices
powered from V
APPLICATIONS INFORMATION
Undervoltage Lockout (UVLO)
If no external power is present, the LTC3455/LTC3455-1 will
start only if the battery voltage is above 3.0V. This prevents
starting up with a battery that is too close to deep discharge.
Once started, the battery must drop below 2.6V before the
LTC3455/LTC3455-1 will shut off. This hysteresis is set
intentionally large to prevent the LTC3455/LTC3455-1 from
turning off at an inappropriate time, like during the read- or
write-cycle of a hard-disk drive (which could potentially
damage the drive). The internal UVLO is meant only as a
last chance safety measure to prevent running the battery
voltage too low and damaging it. An accurate, user-settable
low-battery threshold can be implemented using the gain
block (see the “Gain Block” section for details) which gives
the microcontroller complete control over the timing of a
shutdown due to a low-battery condition.
If external power is present and the battery voltage is less
than 3.0V, the V
for the LTC3455/LTC3455-1 to start, and once started, the
V
running.
Selecting the Input Power Source
The priority for supplying power to both DC/DC convert-
ers, all internal circuitry, and the V
USB, battery.
10
MAX
pin must stay above 3.1V for the device to continue
MAX
MAX
pin voltage must be greater than 3.9V
). When external power is applied, the
MAX
pin to the V
MAX
pin is: Wall adapter,
BAT
pin to provide
LTC3455/LTC3455-1 seamlessly transition from battery
power (a single-cell Li-Ion cell) to either the USB supply or
a wall adapter. The battery PMOS switch is turned off, the
charger is activated and all internal power for the device
is drawn from the appropriate external power source.
Maximum charge current and charge time are programmed
using an external resistor and capacitor, respectively. The
USB power manager provides accurate current limiting for
the USB pin under all conditions. The Hot Swap output is
ideal for powering memory cards and other devices that
can be inserted while the system is fully powered.
Whenever the WALLFB pin is above 1.23V, system power
is drawn from the wall adapter via the V
battery charger is active. The 5V wall adapter output is
connected to the V
a resistor divider from the 5V wall input is connected to
the WALLFB pin to signal the LTC3455/LTC3455-1 that
wall power is present. A higher voltage adapter can also
be used, but the 6V maximum rating on the V
requires the use of an additional regulator to step down
the voltage.
If USB power is present and above 3.9V (and wall power
is not available), system power is drawn from the USB pin.
The battery charger is active, but charge current will be
held off until the USB pin increases above 4.0V to prevent
the battery charger from further loading down an already
low USB supply. As long as the USB pin stays above 3.9V,
the USB port supplies all other system power.
If the system needs more power than the USB bus can
supply, the charger turns off completely, the USB power
controller becomes a 500mA (or 100mA) current source
and the V
to decrease, eventually the battery will provide the additional
current needed. This allows the LTC3455/LTC3455-1 to
withstand load current transients that briefl y require more
power than the USB power supply can provide.
MAX
voltage begins to decrease. If V
MAX
pin through a Schottky diode, and
MAX
MAX
pin, and the
continues
MAX
3455fc
pin