900844 datasheet(53/118 Pages) FREESCALE

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Analog Integrated Circuit Device Data

Freescale Semiconductor

900844

FUNCTIONAL DEVICE OPERATION

POWER STATES AND CONTROL

No Power State

In this state, every source of power has been removed or is fully depleted:

•VBAT < VBATOFF: The input voltage is under the cutoff threshold, indicating that the main supply has been removed, or has

been isolated by its own protection circuitry, and

•VCOIN < VCOINOFF: The coin cell backup battery has been removed or has been isolated by the 900844 coin cell discharge

prevention circuitry (see Coin Cell Battery Backup/Charger)

The 900844 has lost any source of power to maintain the RTC and its keep alive registers, and all the internal circuits power

down and time of day cannot be kept.

RTC State

In this state, the 900844 has limited power. The VBOS is available and powers the RTC and the Keep Alive Registers.

However, the system does not have enough power to enter the active state:

•VCOIN > COINOFF: The backup battery is above the coin cell disconnect threshold.

•VPWR < VPWRUVF: The system voltage is less than the under-voltage falling threshold.

During this mode, all voltage regulators are off and cannot be powered. The RTC is operating (Real Time Clock (RTC)), and

the time of day and all keep alive registers are maintained.

Active State

In this state, the 900844 internal circuits are fully powered:

•VPWR > VPWRUVR: The system voltage, VPWR, is available and valid, and

•VBAT > VLOWBAT: The main input voltage is above a low battery condition.

All features of the 900844 are either operating or can be enabled, which is under the control of the System Control Unit (SCU)

within the Platform Controller Hub (PCH).

Power State Transitions

When power is applied to the 900844 for the first time, it goes from the No Power state into the Active state, with a brief

transition through the RTC state. The RTC and the Keep Alive Registers are powered, and the time of day is initialized to a factory

set value (See Real Time Clock (RTC)).

When VPWR crosses the under-voltage rising detection threshold (VPWRUVR), the internal supplies power on, the logic is

reset, the initial power sequence is performed, SPI communication is enabled, and an interrupt to the Platform Controller Hub is

generated. The PMIC enters the Active state and the system is under control of the SCU.

If VPWR crosses the under-voltage falling detection threshold (VPWRUVF), and at least one of the VBOS supplies (VCOIN or

VBAT) is still valid, the 900844 enters the RTC state. Only the RTC is operating and the RTC and Keep Alive registers are

maintained.

If the 900844 is in the RTC state, full operation is obtained when the voltage at VPWR crosses again the under-voltage rising

detection threshold (VPWRUVR).

TURN ON EVENTS

A turn on event occurs when a valid input voltage is present at VBAT (VBAT > VLOWBAT), and the system voltage goes above

the under-voltage rising threshold (VPWR > VPWRUVR). Otherwise, the 900844 is in the RTC or No Power State.

When a turn on event occurs, the BATDET interrupt bit is set. Reference Interrupt Controller for more information on the

different system interrupts.

900844 Datasheet(PDF) 53 Page - Freescale Semiconductor, Inc

900844 Datasheet(HTML) 53 Page - Freescale Semiconductor, Inc

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