SPSB081 datasheet(24/137 Pages) STMICROELECTRONICS

24 / 137 page

If the fail-safe mode was entered, it keeps active until the fail-safe condition is removed and the fail-safe was read

by SPI. Depending on the root cause of the fail-safe operation, the actions to exit fail-safe mode are as shown in

the following table.

Table 9. Temporary failures conditions

Failure source

Failure condition

Diagnosis

Exit from fail-safe mode

Microcontroller

(oscillator)

Watchdog

Early write failure or expired

window

FS (global status byte) = 1

WDFAIL (SR1) = 1

WDFAIL_CNT_x (SR1) = n+1

TRIG = 1 during long open window read

and clear SR1

Undervoltage

FS (global status byte) = 1

V1UV (SR1) = 1(1)

V1FAIL (SR2) = 1(2)

V1 > VRTX

Read and clear SR1

Temperature

TJ > TSD2

FS (global status byte) = 1

TW (SR2) = 1

TSD1 (SR1) = 1

TSD2 (SR1) = 1

TJ < TSD2

Read and clear SR1

1. bit V1UV in SR1 is set for t > tuv1 (16 µs). Fail-Safe bit GSR/FS is set only after tRD (NRESET low pulse).

2. If V1 < V1FAIL (for t > tV1FAIL). The fail-safe bit is located in the global status register.

3.7.2

Non recoverable failures - Forced in VBAT_standby mode

If the fail-safe condition persists and all attempts to return to normal system operation fail, the SPSB081 is forced

into VBAT_standby mode to prevent damage to the system. The VBAT_standby mode can be terminated by any

wake-up source. The root cause of the VBAT_standby is indicated in the SPI status registers.

In VBAT_standby mode, all control registers are set to power on default.

The VBAT_standby mode is entered in case of:

•

Multiple watchdog failures: FORCED_SLEEP_WD = 1 (15x watchdog failure)

•

Multiple thermal shutdowns 2: FORCED_SLEEP_TSD2/V1SC = 1 (7x TSD2)

•

V1 short at turn-on (V1 < V1FAIL for t > tV1SHORT): FORCED_SLEEP_TSD2/V1SC (SR 1) = 1

•

Loss of ground: SGNDLOSS(SR6) = 1

Table 10. Non recoverable failures conditions

Failure source

Failure condition

Diagnosis

Exit from fail-safe mode

Microcontroller

(oscillator)

15 consecutive

watchdog failures

FS (global status byte) = 1

WDFAIL (SR 1) = 1

FORCED_SLEEP_WD (SR 1) = 1

Wake-up

TRIG = 1 during long open

window read and clear SR1

Short at turn-on

FS (global status byte) = 1

V1FAIL = 1

FORCED_SLEEP_TSD2/V1SC (SR 1) = 1

Wake-up

Read and clear SR1

Overvoltage

FS (global status byte) = 1

FORCED_SLEEP_V1OV (SR2) = 1

Wake-up

Read and clear SR1

Temperature

7 times TSD2

FS (global status byte) = 1

TW (SR 2) = 1

TSD1 (SR 1) = 1

TSD2 (SR 1) = 1

FORCED_SLEEP_TSD2/V1SC (SR 1) = 1

Wake-up

Read and clear SR1

SPSB081

Fail safe mode

DS14048 - Rev 3

page 24/137

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