L9965P datasheet(53/104 Pages) STMICROELECTRONICS

53 / 104 page

Figure 27. ERBST management during ER cap diag

ERBST

BOOST

CTRL

tER_WKUP_FLT

0.9*VERBST_XXX

tDISCHARGE

VERBST_XXX

VER_WKUP_THX

tCHARGE

tER_WKUP_FLT

tDISCHARGE

BOOST

CTRL

E D

VSUPPLY

ΔVER

ER cap

diag

tER_WKUP_FLT

tDISCHARGE

tCHARGE

tER_WKUP_FLT

tDISCHARGE

ΔVDISCHARGE

ΔVER

The IC performs the sequence of measurements automatically and saves the calculations in the

CAP_VALUE[13:0] and ESR_VALUE[12:0] bit fields.

A timeout tER_CAP_DIAG_TO for diagnostic duration is present. If it is exceeded, the process is halted and the

ERCAP_DIAG_END_TO flag is set in the ERCAP register.

If the diagnostic ends within the timeout, the device saves the CAP_VALUE in ERCAP_DIAG_CAP_READ_0 and

ERCAP_DIAG_CAP_READ_1 registers, and the ESR_VALUE in ERCAP_DIAG_ESR_READ_0 and

ERCAP_DIAG_ESR_READ_1 registers.

At this point the IC automatically compares CAP_VALUE and ESR_VALUE with the thresholds previously saved

in NVM, respectively ERCAP_C_THR and ERCAP_ESR_THR.

The FAULTN line is asserted:

•

If CAP_VALUE[13:0] < (“00” & ERCAP_C_THR[7:0] & “0000”), and ERCAP_LOW_C flag is set in the

ERCAP register.

•

If ESR_VALUE[12:0] > (ERCAP_ESR_THR[6:0] & “0000”), and ERCAP_HIGH_ESR flag is set in the

ERCAP register.

Note:

A high threshold is defined for capacitance value and a low threshold for ESR since, due to aging and thermal

stress, an electrolytic capacitor over the years shows a decrease of the capacitance value and an increase of

the ESR.

Knowing RERDCHSW, the MCU can check C and ESR calculation values as follows:

C=CAP_VALUE13:0 ×LSBC× 1RERDCHSW

(6)

ESR=ESR_VALUE12:0 ×LSBESR×RERDCHSW

(7)

Once started, the ER capacitor diagnostic process can only be interrupted by a deployment request.

Once a request is over, to proceed with a new one the ER_CAP bit must be left at 1 and the DIAG_START bit in

the DIAG_CMD register must be set back to 1 (it returns automatically to 0).

The ER capacitor diagnostic step duration is dependent on the capacitor value, as specified by tER_CAP_DIAG1 and

tER_CAP_DIAG2.

The possible results of ER capacitor diagnostics are reported in the Table 29.

L9965P

Functional description

DS14702 - Rev 4

page 53/104

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