stled325 STMicroelectronics, stled325 Datasheet - Page 13

• Manufacturer Part Number: stled325
• Description: I?c Interfaced, Advanced Led Controller/driver With Keyscan, Standby Power Management And Real Time Clock Rtc
• Manufacturer: STMicroelectronics

STLED325
3.6.2
3.7
Watchdog timer
Another watchdog timer is present in the Watchdog timer register at address 09h of the RTC
register map. This watchdog timer can be used to program timer values of greater than 15s.
Bits BMB4-BMB0 store a binary multiplier and the three bits RB2-RB0 select the resolution
where:
000 = 1/16 second (16 Hz);
001 = 1/4 second (4 Hz);
010 = 1 second (1 Hz);
011 = 4 seconds (1/4 Hz); and
100 = 1 minute (1/60 Hz).
The Watchdog timer is programmed by setting the desired timeout into the Watchdog
register, address 09h. The amount of timeout time is determined to be the multiplication of
the 5-bit multiplier value with the resolution values depicted by the watchdog resolution bits.
The Watchdog timer is disabled when its register is cleared by writing a value of 00h.
Hence the Watchdog function is not enabled upon power on. It is enabled when a non-zero
value is written into its register. The Watchdog timer is reset by performing a write to the
watchdog register, then the time-out period starts over.
If the processor does not reset the timer within the specified timeout period, and when the
timeout occurs, the watchdog flag is set. The watchdog timer of RTC is cleared by writing a
00 value and starts again whenever any new value is written to it.
The WatchDogEn Flag can be disabled or enabled by writing to the register bit and the reset
of watchdog timer is done by writing to the register.
Power-on-reset and soft-start
The device integrates two internal power-on-reset circuits which initialize the digital logic
upon power up. One circuit is for the V
soft-start circuit limits the inrush current and high peak current during power-up. This is done
by delaying the input circuit’s response to the external applied voltage. During soft-start, the
input resistance is higher which lowers the in-rush current when the supply voltage is
applied.
Doc ID 17576 Rev 1
CC
power and the other is for the V
Functional description
BAT
power. The
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