![](http://datasheet.mmic.net.cn/170000/R5109N151C-TR-FE_datasheet_9714731/R5109N151C-TR-FE_24.png)
R510xx
24
OPERATION
(1) When the power supply, the SENSE pin voltage becomes more than the released voltage (+VDET), after the
released delay time (or the power on reset time tPLH), the output of RESETB becomes "H" level.
(2) When the SCK pulse is input, the watchdog timer is cleared, and CTW pin mode changes from the discharge
mode to the charge mode. When the CTW pin voltage becomes higher than Vref2H, the mode will change into
the discharge mode, and next watchdog time count starts.
(3) Unless the SCK pulse is input, WDT will not be cleared, and during the charging period of CTW pin,
RESETB
="L".
(4) When the SENSE pin becomes lower than the detector threshold voltage (-VDET), RESETB outputs "L" after
the tPHL.
(5) If "L" signal is input to the INH pin, the RESETB outputs "H", regardless the SCK clock state.
(6) When the signal to the INH pin is set from "L" to "H", the watchdog starts supervising the system clock.
Watchdog Timeout period/Reset hold time
The watchdog timeout period and reset hold time can be set with an external capacitor to CTW pin.
The next equations describe the relation between the watchdog timeout period and the external capacitor
value, or the reset hold time and the external capacitor value.
tWD (s)
= 3.1 × 106 × C (F)
tWR (s)
= tWD/9
The watchdog timer (WDT) timeout period is determined with the discharge time of the external capacitor.
During the watchdog timeout period, if the clock pulse from the system is detected, WDT is cleared and the
capacitor is charged. When the charge of the capacitor completes, another watchdog timeout period starts
again. During the watchdog timeout period, if the clock pulse from the system is not detected, during the next
reset hold time RESETB pin outputs "L".
During the reset time, (while charging the external capacitor) and after starting the watchdog timeout period,
(just after from the discharge of the external capacitor) even if the clock pulse is input during the time period
"tWDI", the clock pulse is ignored.
tWDI (s)
= tWD/10
Released Delay Time (Power-on Reset delay time)
The released delay time can be set with an external capacitor connected to the CD pin. The next equation
describes the relation between the capacitance value and the released delay time (tPLH).
tPLH (s)
=3.7 × 106 × C (F)
The capacitor connected to CD pin determines tWD, tWR, and tPLH.
When the VDD voltage becomes equal or less than (-VDET), discharge of the capacitor connected to the CD pin
starts. Therefore, if the discharge is not enough and VDD voltage returns to (+VDET) or more, thereafter the delay
time will be shorter than tPLH which is expected.