LTC3455EUF#PBF Linear Technology, LTC3455EUF#PBF Datasheet - Page 15

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

Specifications of LTC3455EUF#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: -

APPLICATIONS INFORMATION
Startup and Shutdown When USB or Wall Powered
Whenever USB or wall power is present (as sensed by
the USB and WALLFB pins), Switcher 1 and the battery
charger will always be enabled. If the LTC3455/LTC3455-1
are off and external power is applied, both the charger and
Switcher 1 will start independent of the state of the ON and
PWRON pins. This provides maximum battery run-time by
always allowing the battery to charge whenever external
power is available, and ensures that the microcontroller
is always alive when external power is available (this is
important for designs that utilize coulomb-counting or
other battery monitoring techniques). Switcher 2 starts
only if ON2 is also pulled high. Figure 3 shows the turn-on
logic diagram for the LTC3455/LTC3455-1.
Starting Switcher 2/Power Supply Sequencing
Switcher 2 can operate only when Switcher 1 is also
enabled and in regulation. The ON2 pin can be driven by
a logic signal for independent control of Switcher 2. If
both outputs always operate together, tie the ON2 pin to
the V
of Switcher 1 has reached 90% of its fi nal value. This
power-up delay ensures proper supply sequencing and
reduces the peak battery current at startup. Figure 4 shows
MAX
pin. This will enable Switcher 2 after the output
SUSPEND
WALLFB
PBSTAT
PWRON
V
ON2
USB
BAT
ON
19
23
24
22
11
9
8
6
1.23V
3.9V
3V
+
–
+
–
+
–
Figure 3. Turn-On Logic Diagram
the output sequencing when both switchers are enabled
at startup with the ON2 pin tied to V
both switchers is always delayed until the V
reached the V
Reset Signal (RST)
A 200ms reset signal (the RST pin is pulled low) is provided
for proper initialization of a microcontroller whenever the
LTC3455/LTC3455-1 are fi rst turned on, either by the ON
or PWR pins, or by the application of external power. The
RST signal is also pulled low whenever the entire LTC3455/
LTC3455-1 are in shutdown, ensuring no false starts for
the microcontroller as the output voltages are rising or
collapsing.
PWRON/ON2
V
V
OUT1
OUT2
Figure 4. Sequencing for Switcher 1 and 2 Outputs
2V/DIV
2V/DIV
2V/DIV
2V/DIV
(1.8V)
(3.3V)
V
MAX
BAT
LTC3455/LTC3455-1
LTC3455/LTC3455-1
pin voltage.
SWITCHER 2
ENABLED
SWITCHER 1
ENABLED
CHARGER
ENABLED
USB POWER
CONTROLLER
ENABLED
3455 F03
100μs/DIV
MAX
. The turn-on of
MAX
3455 F04
15
pin has
3455fc