Application Note : Reset ICs (Voltage Detectors)
The VDD pin on reset ICs in general also acts as the voltage detection pin (SENSE pin). if the input voltage to the VDD pin becomes lower than the minimum operating voltage, the reset IC becomes unstable operation and is unable to maintain the reset signal level.
As shown in the following figures, reset signal (VOUT) becomes unstable on CMOS output products and reset signal (VOUT) is equalized to the pull-up voltage in the Nch. open drain output products.
Since the reset IC with SENSE pin type separates the SENSE pin from the VDD pin, the reset signal can be maintained as long as voltage is supplied to the VDD pin even when the input voltage to the SENSE pin becomes lower then the minimum operating voltage.
Ricoh provides a reset IC with using a Manual Reset pin can reset manually.