L9679P datasheet(44/272 Pages) STMICROELECTRONICS

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Start-up and power control

L9679P

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DocID029275 Rev 1

Figure 18. ER ESR measurement timing diagram

The ER CAP ESR can be calculated according to the following formula:

ESRERCAP

VC VB

–

GER_ESR IER_DISCHARGE_HIGH



-----------------------------------------------------------------------------------------

OFFER_ESR

6.6

ER switch and COVRACT pin

L9679P allows the system to run out of the reserve capacitor energy stored on VER node by

means of the charging boost regulator. In this way, an extended operation can take place

even in case of battery lost. The ER switch implements a connection from the VER pin to

the VIN node, supply input for the SYNCBOOST regulator and for internal power supplies.

The ER switch is automatically activated upon entering the PASSIVE mode. Voltage

difference between VIN and VER is monitored in order to prevent VER back-feeding when

VIN exceeds VER by VER_SW_OV_TH. The ER switch is automatically deactivated upon the

above mentioned overvoltage detection.

During PASSIVE mode the discrete digital output pin COVRACT is activated to allow for

external optional cross-over switch control (except during VINGOOD blanking state, where

the COVRACT is deactivated).

L9679P Fiches technique(PDF) 44 Page - STMicroelectronics