power managment with 40s delay to turn on.

David Waters

Other Parts Discussed in Thread: UCC3946, TL7712A

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.

Any suggestion?

over 15 years ago

0 Scot Lester over 15 years ago

TI__Expert 5640 points

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.

0 David Waters over 15 years ago in reply to Scot Lester

Prodigy 20 points

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.

0 Scot Lester over 15 years ago in reply to David Waters

TI__Expert 5640 points

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.

slva360.pdf

0 CaEngineer over 11 years ago in reply to David Waters

Mastermind 8615 points

David Waters said:

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.

Or using such SVM/S:

TL7712A

Power management

Power management forum

power managment with 40s delay to turn on.