SPSB100 datasheet(24/214 Pages) STMICROELECTRONICS

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3.6.2.2

Watchdog trig and FCCU monitor faults management

The watchdog is launched during the power-up sequence when the NRST pin is deasserted high, it starts with a

long open window timeout. After the power-Up sequence, the SPSB100 reaches RECOVERY-1 state which is

dedicated to watchdog and FCCU monitor faults management.

Figure 13. State machine details with WD trig and FCCU monitor faults management

ACTIVE

state

WD trigger OK*

LOW-POWER

mode

FULL-POWER

mode

SPI cmd

WD trigger OK*

(WD failed @ REC -1 & cnt = 8)*

Execute

Power-Up

sequence

Finished OK

INIT

state

REC-1

state

Execute

Power-Down

sequence

REC-2

state

(WD trigger fail & cnt = 8)*

NFSO asserted

WD trigger fail

OR FCCU fail

DEEP-SLEEP

state

Wake-up

event

Execute

Power-Down

sequence

(WD trigger fail & cnt ≥ 15)*

WD LOW trigger OK

AND error cleared

NRESET asserted 4ms

for WD fail or 6ms for

FCCU fail, then WD

restarted in L.O.W.*

NFSO &

NRESET

asserted,

FCCU

disabled

Execute Power -

Up sequence

(NRESET not

deasserted)

Finished OK

VFBB_OK_R < VFBB < VFBB_OV

* when LOW_SET = 1111, watchdog service is disabled

(WD trigger fail & cnt !=8,15)*

OR (FCCU enabled & fail)

While in RECOVERY-1 state, a read and clear of error flags and a proper trig of the watchdog in long open

window timeout will initiate a transition to ACTIVE state.

If the watchdog is triggered without clearing all flags, then the device remains in RECOVERY-1 state and the

watchdog runs with normal window timings.

In an ACTIVE state the watchdog runs with normal window timings. Proper trig of the watchdog maintains

SPSB100 in an ACTIVE state, while a failure in watchdog service or a fault detected on FCCU monitor will:

•

Increment the watchdog trig fault counter (only on watchdog trig fault);

•

Assert NRST pin low;

•

Disable and reset the FCCU monitor;

•

Initiate a power-up sequence: this is mandatory to power backup regulators that could have been switched

off by SPI.

Then the NRST pin remains asserted for 4 ms, at least, in case of watchdog trig fault, 6 ms at least, in case of

FCCU monitor fault, before being released, watchdog starts a long open window timeout and SPSB100 reaches

RECOVERY-1 state.

In case of successive faults in servicing the watchdog in a long open window the watchdog trig fault counter is

incremented, a power-up sequence is run, a 4 ms NRST pulse is generated and a long open window timeout is

restarted.

If the watchdog is properly served during the long open window, then the watchdog trig fault counter is reset and

SPSB100 enters in ACTIVE state.

The 8 successive watchdog trig faults force SPSB100 to initiate a power cycle through RECOVERY-2 and INIT

states. And in case of 15 successive watchdog trig faults SPSB100 will enter in a DEEP-SLEEP state.

Note:

In this specific case, the IVDS current consumption is higher (worst case 4.8 mA max) than expected (40 μA

max).

The FCCU monitor is disabled and its configuration reset after the first watchdog trig fault. FCCU monitor can be

reconfigured and enabled through SPI in RECOVERY-1 or ACTIVE state.

SPSB100

Functional description

DS14640 - Rev 1

page 24/214

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