Description Adafruit S-35710 Wake-up Timer Breakout - STEMMA QT / Qwiic

The Adafruit S-35710 Wake Up Timer is a low-power 'watchdog timer' chip. This chip can be programmed to sound a digitally configurable alarm ranging from 1 second to as many as 194 days, using a 24-bit seconds counter. This is an interesting alternative to a real-time clock or internal sleep timer, and can be useful for ultra-low-power projects that require a separate (and possibly separately powered) chip for timekeeping and alarms. We reviewed this part at EYE ON NPI and thought it would be a nice addition to the shop.

Usage is simple: when writing to the timer register via I2C, the chip starts counting from 0 seconds and the OUT pin goes high. When the count matches the timer register, the OUT pin goes low. Simple and very power efficient, consuming only 0.2µA. The output is open-drain and if you want to invert it, there is a switch that passes the signal through an N-channel FET so that the polarity is reversed.

An important point to note is that the OUT line is low by default at boot. This means that it is not suitable as a low-power sleep manager, but it is suitable for watchdog-like timings. So you cannot connect this chip to the reset or enable line of your microcontroller to shut down itself, as it will be powered down or reset at boot. Still, it can be a useful chip for users who want to signal after a long delay or have a more complex power management system.