LTC3554EPD datasheet(27/36 Pages) LINER

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LTC3554

3554f

BAT

VBUS

ON (PB)

PBSTAT

BUCK1

BUCK2

PGOOD

PWR_ON1

PWR_ON2

STATE

POFF/HR

PON

PUP2/PUP1

3554 TD01

230ms

400ms

Figure 7. Power-Up Via Pushbutton Press

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

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