L9678P datasheet(31/215 Pages) STMICROELECTRONICS

31 / 215 page

DS11626 Rev 9

31/216

L9678P, L9678P-S

Start-up power control

214

Pulse skipping mode is also present to prevent output voltage from rising too much in case

of light load (IO_ERBST<IO_ERBST_MIN).

It is activated through an overvoltage comparator (VERBOOST_OV) at the feedback node.

Normal run time power for the system is provided directly from the battery input, not from the

boost. Boost energy is available to the system through the energy reserve crossover switch

once battery is lost or a commanded system shutdown is initiated. By default, the ERBoost

regulator is switched off once entered in passive mode. To keep active the ERBoost also in

passive mode the SPI bit SYS_CFG(KEEP_ERBST_ON) must be set to 1.

Figure 11. ERBOOST control behaviour

4.3.2

Energy reserve capacitor charging circuit

The energy reserve capacitor connected to VER pin can be charged in an efficient way by

means of a current generator. Its capability is 30 mA nominal, so that for example a 2.2 mF

capacitor can be charged in approximately 2 s to 24 V. The current generator is activated or

deactivated by SPI command only while in ACTIVE mode. When not in ACTIVE mode, the

generator is always switched off in order to decouple ERBOOST node voltage from VER

reserve voltage.

GAPGPS01120

ER BST ON

Active_mode = 1

AND

VBATMON > VBGOOD

AND

VIN > VINGOOD

AND

SYS_CTL(ER _BST _EN)=1

AND

GNDBOOST_loss = 0

AND

ERBST _OT=0

AND

ERBST_DISABLE=0

Default SYS_CTL(ER_BST_EN) = 1

at POR = 1

ER BOOST

power mode control

ER BST OFF

ERBST _OT=1/

ER BST OT

SPI _FLTSR READ

AND

ERBST _OT=0

ER BST STBY

SPI _SYS_CTL(ER_BST_EN=1)

AND

ERBST _OT=0

POWER-OFF_MODE

OR SLEEP_MODE

[(Active_mode = 0 OR

VBATMON < VBBAD)

AND

(ER_state=0 OR

SYS_CFG(KEEP_ERBST_ON)=0)]

VIN < VINBAD

SYSCTL(ER_BST_EN) = 0

GNDBOOST_loss = 1

ERBST_DISABLE=1

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