L9680 datasheet(40/286 Pages) STMICROELECTRONICS

40 / 286 page

Start-up and power control

L9680

40/286

DS11615 Rev 7

is done through the System Control (SYS_CTL) register. Boost converter diagnostics

include over voltage and under voltage and the circuit is fully protected against shorts. Boost

fault status is available through the SPI in Fault Status Register (FLTSR). The integrated

FET featuring the boost switch is protected against short to battery by means of a thermal

shutdown circuit. When thermal fault is detected the FET is switched off and latched in this

state until the related fault flag ERBST_OT in the FLTSR register is read. In case of loss of

BSTGND ground the FET is not turned on. Loss of ground can be detected also when the

FET is off thanks to a pull-up current present on the BSTGND pin. The FET will be

automatically reactivated as soon as ground connection is restored. Over-voltage protection

from load dump and inductive flyback is provided via an active clamp and an ER_Boost

disable circuitry, see Figure 12.

Figure 12. ERBOOST regulator block diagram

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.

Comp

ERBST

Driver &

Control

CLAMP

erbst _en

ERBSTSW

ERBOOST

BSTGND

ERBST_CLAMP _ENTH

ERBST_DISABLE TH

VIN

GAPGPS02257

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