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LTC3554

3554f

BAT

VBUS

ON (PB)

PBSTAT

BUCK1

BUCK2

PGOOD

PWR_ON1

PWR_ON2

STATE

PON

POFF

PDN2

3554 TD04

μC/μP CONTROL

50ms

μC/μP CONTROL

Figure 10. Power-Down Via PWR_ON De-Assertion

OPERATION

Power-Up Via Asserting PWR_ON Pins

Figure 9 shows the LTC3554 powering up by driving

PWR_ON1 high. For this example the pushbutton circuitry

starts in the POFF or HR state with a battery connected

and all bucks disabled. Once PWR_ON1 goes high, the

pushbutton circuitry enters the PON state and buck1

powers up. Once buck1’s output is within 8% of its regu-

lation voltage for 230ms, PGOOD is asserted. Similarly,

if PWR_ON2 is brought high at a later time, buck2 will

power up. The pushbutton circuitry remains in the PON

state. During the time that buck2 powers up, PGOOD will

be held low. PGOOD will be asserted again once buck2 is

within 8% of its regulation for 230ms.

Powering up via PWR_ON is useful for applications

containing an always-on μC that’s not powered by the

LTC3554 regulators. That μC can power the application

up and down for housekeeping and other activities not

needing the user’s control.

Power-Down Via PWR_ON De-Assertion

Figure 10 shows the LTC3554 powering down by μC/μP

control. For this example the pushbutton circuitry starts

in the PON state with a battery connected and all bucks

enabled. The user presses the pushbutton (ON low) for at

least 50ms, which generates a debounced, low impedance

pulse on the PBSTAT output. After receiving the PBSTAT

signal, the μC/μP software decides to drive the PWR_ON

inputs low in order to power down. After the last PWR_ON

pin goes low, the pushbutton circuitry will enter the PDN2

state. In the PDN2 state a one second wait time is initi-

ated after which the pushbutton circuitry enters the POFF

state. During this one second time, the ON and PWR_ON

inputs as well as external power application are ignored to

allow all LTC3554 generated supplies to go low. Though

the above assumes a battery present, the same operation

would take place with a valid external supply (VBUS) with

or without a battery present.

BAT

VBUS

ON (PB)

PBSTAT

BUCK1

BUCK2

PGOOD

PWR_ON1

PWR_ON2

STATE

POFF/HR

PON

3554 TD03

230ms

Figure 9. Power-Up Via Asserting PWR_ON Pins

LTC3554 Datasheet(PDF) 29 Page - Linear Technology

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