LTC3456_15 Datasheet, PDF (18/28 Pages) Linear Technology – 2-Cell, Multi-Output DC/DC Converter with USB Power Manager

LTC3456
U
OPERATIO
PWRKEY
V_CORE
RESET
PWRON
PWRKEY
PULLED LOW
PWRKEY
RELEASED
262ms
TIMEOUT
PBSTAT
POWER-ON SEQUENCE
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POWER-OFF SEQUENCE
Figure 8. Power-On/Power-Off Sequence
RESET
The LTC3456 contains a RESET circuitry that is active
during both power-up and shutdown. The RESET pin is
held low during initial power-up. When both the V_INT and
Core outputs come into regulation, a reset delay timer gets
activated. There is a full 262ms timeout before RESET is
released. During power-off mode RESET is pulled low.
This prevents the microprocessor from entering into any
spurious operating mode.
MODE
The LTC3456 has a user selectable MODE pin. When the
MODE pin is pulled logic high and the LTC3456 is battery
powered, the device will automatically enter into Burst
Mode operation under light load current situations. If the
load current in either of the regulators falls below a
predetermined value, the regulator will enter into Burst
Mode operation independent of the other regulator. When
the MODE pin is connected to ground, continuous PWM
operation is selected. It provides the lowest output voltage
ripple and current ripple, albeit at the cost of lower
efficiency under light load conditions.
The Burst Mode operation is disabled when the device is
USB or wall powered. The device operates in forced PWM
mode when powered from USB or wall input (irrespective
of the state of the MODE pin). Also, at initial power up, the
device operates in forced PWM mode during the 262ms
initial delay timeout.
Figure 9 shows the Main and Core converters in Burst
Mode operation.
V_MAIN
100mV/DIV
(AC COUPLED)
I_L2
500mA/DIV
V_CORE
100mV/DIV
(AC COUPLED)
I_L1
100mA/DIV
V_BATT = 2.4V
I_MAIN = 37.5mA
I_CORE = 6.2mA
20µs/DIV
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Figure 9. The LTC3456 in Burst Mode Operation
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