L9678P datasheet(29/203 Pages) STMICROELECTRONICS

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DocID029274 Rev 3

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L9678P, L9678P-S

Start-up power control

202

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 enetered 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.

Figure 12. ER cap charging circuit

L9678P bảng dữ liệu(PDF) 29 Page - STMicroelectronics