LP3941A datasheet(27/32 Pages) NSC

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Flowchart Operation (Continued)

passed. If LDO1 reaches 93%, the state machine advances

to the RESET OFF DELAY state. If 60 ms have passed

before the 93% level is achieved, the state machine returns

to the STANDBY state and waits for another wakeup source.

The RESET OFF DELAY state counts off 40 ms. If the

battery voltage drops below the UVLO threshold of 2.5V, the

state machine goes to the ENABLE RESET state and power

down sequence. If LDO1 output drops below 85% of the

nominal voltage the state machine returns to the TURNON

LDOs state in an attempt to restart the LDO. If neither of

these conditions occurs the state machine advances to the

PS_HOLD DETECT state.

In the PS_HOLD DETECT, RESET is deasserted and the

state machine waits 35 ms for the PS_HOLD signal to go

high. If PS_HOLD goes high within 35 ms of RESET going

low the state machine advances to the IDLE state. If

PS_HOLD in still low after 35 ms the state machine goes to

ENABLE RESET state and the power down sequence. If

battery voltage pins drops below the UVLO threshold, the

state machine advances to the ENABLE RESET state and

the power down sequence. If LDO1 output drops below its

85% point the state machine returns to the TURNON LDOs

state in an attempt to try restart the LDOs.

The state machine remains in the IDLE state until PS_HOLD

goes low for 35 ms. If PS_HOLD is low for less than 35 ms

the state machine remains in the IDLE state. If PS_HOLD

stays low for more than 35 ms, the state machine advances

to the ENABLE RESET state and the power down sequence.

If LDO1 output falls below its 85% point the state machine

returns to the TURNON LDOs state in an attempt to restart

the LDOs. The UVLO is disabled in the IDLE state. The

back-up battery charger is on.

In the ENABLE RESET state RESET is asserted. After

60 ms all LDOs are turned off. UVLO as well as the back-up

battery charger are on. Once LDO1 falls to its 85% point the

state machine returns to the STANDBY state.

The RTC_LDO is powered by the back-up battery and is

always on (unless specifically disabled via the I

2C interface).

LP3941A 数据表(PDF) 27 Page - National Semiconductor (TI)

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