LTC3554 Datasheet, PDF (27/36 Pages) Linear Technology – Micropower USB Power Manager with Li-Ion Charger and Two Step-Down Regulators

LTC3554
OPERATION
state. If a valid HRST event is present in PON, PDN2 or
POFF, then the state machine will transition to the PDN1
state and subsequently transition to the HR state one
second later.
Debounced Pushbutton Output (PBSTAT)
In the PON, PUP1, and PUP2 states, the PBSTAT open-
drain output pin outputs a debounced version of the ON
pushbutton signal. ON must be held low for at least 50ms
for the pushbutton interface to recognize it and cause
PBSTAT to go low. PBSTAT goes high impedance when
ON goes high, except the logic enforces a minimum pulse
width on PBSTAT. Once it goes low, it stays low for at
least 50ms.
In the HR, POFF, PDN1, and PDN2 states, PBSTAT remains
high impedance regardless of the state of ON.
Power-Up Via Pushbutton Press
Figure 7 shows the LTC3554 powering up through ap-
plication of the external pushbutton. For this example the
pushbutton circuitry starts in the POFF or HR state with a
battery connected and both bucks disabled. Pushbutton
application (ON low) for 400ms transitions the pushbutton
circuitry into the PUP state and powers up buck1 followed
by buck2. If either PWR_ON is low or goes low after the
5 second period the corresponding buck(s) will be shut
down. In the above example PWR_ON2 is low at the end
of the 5 second period and therefore buck2 is disabled
at the end of the 5 second period. PGOOD is asserted
once all enabled bucks are within 8% of their regulation
voltage for 230ms.
The PWR_ON inputs can be driven via a μP/μC or by one
of the buck outputs through a high impedance (100kΩ
1
BAT
0
1
V_BUS
0
1
ON (PB)
0
1
PBSTAT
0
1
BUCK1
0
1
BUCK2
0
1
PGOOD
0
1
PWR_ON1
0
1
PWR_ON2
0
STATE
POFF/HR
400ms
230ms
5s
PUP2/PUP1
PON
3554 TD01
Figure 7. Power-Up Via Pushbutton Press
3554p
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