SABRE-LL-I datasheet(33/141 Pages) STMICROELECTRONICS

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SABRE-LL-I

Power saving modes

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The StdByMode bit used to switch off V3v3 and switch on the power switch can be set to ‘1’

by writing the standby command in the StdByMode register. S.A.B.Re exits standby mode if

a reset event happens or “Low Power mode” is selected.

Because all internal low voltage circuitry powered by V3v3 are designed to work with a 3.3V

voltage rail, when the standby mode is used, VGPIOSpi is requested to be at 3.3V.

10.3

Hibernate mode

S.A.B.Re’s hibernate mode allows the firmware to switch off some (or all) selected System

Regulators leaving in on state only those necessary to resume S.A.B.Re to operative

condition when waked-up by an external signal.

Hibernate mode is selected when the firmware writes the command word in the

HibernateCmd register. When in hibernate mode S.A.B.Re will force regulators in the state

(on/off) selected by the firmware by writing in the HibernateCmd register and will force

nRESET pin low.

The exiting from hibernate mode is achieved by forcing at low level nAWAKE pin (or GPIO5

pin if S.A.B.Re is in Slave mode); S.A.B.Re will also exit from hibernate mode if an

undervoltage event happens on VSupply, VSupplyInt, VPump or V3v3.

When the exit from hibernate mode is due to an external command, S.A.B.Re sets to ‘1’ the

bit HibModeLth in the HibernateStatus register.

10.4

Low power mode

When in normal operating mode, the microcontroller can place S.A.B.Re in “Low Power

mode”.

In this condition S.A.B.Re sets all bridges outputs in high impedance, powers down all

regulators (including system regulators and charge pump) and disables almost all its circuits

including internal clock reducing as much as possible power consumption.

The only circuits that remain active are:

–V3V3 internal regulator.

–

nAWAKE pin current pull-up.

–

nRESET pin that will be pulled low.

–

POR circuit.

The entering in low power mode is obtained in different ways depending if S.A.B.Re is

configured as slave device or not. When S.A.B.Re is configured as slave device the low

power mode is directly controlled by nAWAKE pin that acts as an enable: if this pin is low for

a time longer then tAWAKEFILT, Low Power mode is entered; if this pin is high S.A.B.Re exits

from Low Power mode.

In all other start-up configurations, Low Power mode is entered by writing a Low Power

mode command in the PowerModeControl register; once S.A.B.Re is in Low Power mode it

starts checking the nAWAKE pin status: if it is found low for a time longer than tAWAKEFILT,

S.A.B.Re exits from Low Power mode and restarts its startup sequence. When the

nAWAKE pin is externally pulled low, the “AWAKE” event is stored and it is readable

through SPI. S.A.B.Re will also exit from Low Power mode if a POR event is found.

Note:

When in “Low power mode” VSupply is monitored only for its power on reset level.

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