L9679P datasheet(30/272 Pages) STMICROELECTRONICS

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Start-up and power control

L9679P

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DocID029275 Rev 1

6.2.1

POWER OFF mode

During the POWER-OFF Mode all supplies are disabled keeping the system in a quiescent

state with very low current draw from battery. As soon as WAKEUP>WU_mon the IC will

move to SLEEP Mode.

6.2.2

SLEEP mode

During the Sleep mode the VINT3V3 and CVDD internal regulators are turned on and the IC

is ready for full activation of all the other supplies. As soon as VIN voltage is over a minimum

threshold, all the other supplies are turned on and the IC enters the ACTIVE mode.

6.2.3

ACTIVE mode

This is the normal operating mode for the system.

All power supplies are enabled and the energy reserve boost converter starts to increase

the voltage at ERBOOST. Likewise, the SYNCBOOST boost converter continues to charge

and regulate to a nominal 12 V (default level at startup). Once the SYNCBOOST has

reached a good value, the SATBUCK regulator starts up. In turn, when SATBUCK has

ramped up, VCC regulator is enabled. Once the VCC buck regulator is in regulation, RESET

is released allowing the system microcontroller and other components to begin their power-

on sequence. Among these, also the ER charge current generator can be enabled by the

microcontroller via a dedicated SPI command.

The active mode can be left when either WAKEUP pin or VIN voltage drop down. For the

very first 9ms after having entered the active mode, the WAKEUP pin low would

immediately cause the IC to switch back to sleep mode. After that time, WAKEUP pin low

must be first confirmed by a μC SPI_SLEEP command prior to cause the system to switch

to passive mode. Passive mode is also entered in case of VIN voltage low.

6.2.4

PASSIVE mode

In this state, the reserve capacitor charge current and the ERBOOST boost converter are

disabled. When in passive mode the device activates both the COVRACT output pin and the

integrated ER switch to allow VIN to be connected to the ER capacitor. In this time, VIN is

supposed to be increased up to almost VER level and the system operation relies on energy

from the ER capacitor. Two scenarios are possible: high or low battery. If VIN < VINGOOD,

the device moved from RUN state in ACTIVE mode to the ER state. Here, the ER capacitor

is depleted while supplying all the regulators until the POR on internal regulator occurs. The

threshold to decide the ER switch activation is based on VIN, because VIN is the supply

voltage rail for ERBOOST regulator. If the device has still a good battery level, it entered the

POWERMODE SHUTDOWN thanks to a microcontroller command to switch off. In this

case, the VER node will be discharged down to approximately VIN level, which then will be

supplied out of the battery line. System will continue to run up to a dedicated SPI command

to disable the SATBUCK regulator, which will lead the device to enter the POWEROFF

state.

The wake-up pin is filtered to suppress undesired state changes resulting from transients or

glitches. Typical conditions are shown in the chart below and summarized by state.

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