need help about the power on reset

[wuwuwengong]

I have read some papers about the power on reset ,but the definition of reset time , when the reset pulse should be generated ,and the width of reset pulse should be are not clear yet. could anyone help me? could you please show me the figure of the result?

 

[ambreesh]

First: When is the reset pulse generated?
In my design for Vdd=2.5V I had generated thr reset-pulse when Vdd reached 2.48V. One of the Maxim application notes talks about it. Look in supervisory circuit their. Every supply has rating e.g. Rated supply±3%. This is usually specified in the specifications.
Second: Duration of reset pulse?
Again a specification provided by customer, depending on the application. But various factors on which it depends I'm listing. Others can please add to it if I miss some:
a> Time for clock to settle
b> Time for power supply to settle.
c> Time for loading of intial states. (this time would be after a & b are satisfied)

Hope that helps

 

[IanP]

Here is a proper POR IC, the DS1232:
**broken link removed**
The time you are after is called TRPU, page 6 ..

 

[wuwuwengong]

thank you for your help! they are useful to me.