We are looking for a ultra-low-power device that will monitor voltage between 3.3 and 2.4 VDC. It needs a 40s delay when it reaches 3.3v before it switches on. During operation, the voltage will fluctuate as follows: voltage drops from 3.3 to 2.48 in 20ms then rise from 2.48 to 3.3 in 225ms.
The only device we have that will do a 40s delay is the UCC3946. You will need to use a 12.6uF timing capacitor on the RP pin to get 40 seconds of delay. This capacitor will need to be low leakage current so stick with ceramics. The UCC3946 also has a watchdog function but this feature does not need to be used if it is not needed.
Thank you Scott,
This chip might work. The hysteresis is smaller then we need for our application but I think we can work around it.
You can increase the hysteresis by adding a resitor between the /RES output and the RTH pin. The attached app note explains how to do this. This works for most voltage supervisors that have an external resistor divider to set the reset threshold.
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