LTC3577-4_15 Datasheet, PDF (43/52 Pages) Linear Technology – Highly Integrated Portable Product PMIC

LTC3577-3/LTC3577-4
OPERATION
Power-Up via Pushbutton Timing
The timing diagram, Figure 14, shows the LTC3577-3/
LTC3577-4 powering up through application of the external
pushbutton. For this example the pushbutton circuitry
starts in the POFF state with V_OUT not in UVLO and Buck1,
Buck2 and LDO2 disabled. Pushbutton application (ON
low) for 50ms transitions the pushbutton circuitry into the
PUP state which sequences up LDO2, Buck1 and Buck2
in that order. PWR_ON must be driven high before the 1
second PUP period is over to keep supplies up. If PWR_ON
is low or goes low after the 1 second PUP period Buck1,
Buck2, and LDO2 will be shut down together. PGOOD is
asserted once Buck1, Buck2 and LDO1 are within 8% of
their regulation voltage for 230ms.
Buck3 and LED backlight can be enabled and disabled at
any time via EN3 or I²C once in the PUP or PON states.
The PWR_ON input can be driven via a μP/μC or by one of
the sequenced outputs through a high impedance (100kΩ
typ). PBSTAT goes low 50ms after the initial pushbutton
application and will stay low for 50ms minimum. PBSTAT
will go high coincident with ON going high unless ON goes
high before the 50ms minimum low time.
Power-Up via PWR_ON Timing
The timing diagram, Figure 15, shows the LTC3577-3/
LTC3577-4 powering up by driving PWR_ON high. For
this example the pushbutton circuitry starts in the POFF
state with V_OUT not in UVLO and Buck1, Buck2 and LDO2
disabled. 50ms after PWR_ON goes high the pushbutton
circuitry transitions into the PUP state which sequences
up LDO2, Buck1 and Buck2 in that order. PWR_ON must
be driven high before the 1 second PUP period is over
to keep supplies up. If PWR_ON is low or goes low after
the 1 second PUP period Buck1, Buck2 and LDO2 will
be shut down together. PGOOD is asserted once Buck1,
Buck2 and LD01 are within 8% of their regulation voltage
for 230ms.
Buck3 and LED backlight can be enabled and disabled at
any time via EN3 or I²C once in the PUP or PON states.
Powering up via PWR_ON is useful for applications
containing an always on microcontroller. This allows the
microcontroller to power the application up and down
for house keeping and other activities outside the user’s
control.
V_OUT UVLO
ON (PB)
PBSTAT
LDO2
BUCK1
BUCK2
PGOOD
PWR_ON
STATE
POFF
50ms
14ms
230ms
PUP
Figure 14. Power-Up via Pushbutton
1 SEC
PON
35773 F14
V_OUT UVLO
ON (PB)
PBSTAT
PWR_ON
LDO2
BUCK1
50ms
14ms
BUCK2
PGOOD
STATE
POFF
1 SEC
230ms
PUP
35773 F15
PON
Figure 15. Power-Up via PWR_ON
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