Searching thru this forum provides some confusing statements regarding the TPS3808 and its delay time in regard to accuracy.
Calculating the delay time with the equation given in the datasheet is easy to find a nominal and min/max based solely on capacitor variance but does not take into account device tolerances like the current source or voltage reference.
In this post, it says that the min/max values listed in the table from the datasheet has a 20% tolerance on the capacitor and around a 40% total variance on the device INCLUDING the capacitor. It then states that if a 5% capacitor is used, a 30% tolerance can be assumed.
(+) TPS3808: td calculation - Power management forum - Power management - TI E2E support forums
In this post, it is implied that the delay times in the table uses ideal capacitance. The listed min/max times in the table show a ~40% variance. This implies that the device tolerance is 40% NOT taking into account capacitor tolerance.
Please answer each of these questions so a true worst case can be calculated:
1. Does the 40% tolerance in the datasheet table assume a 20% capacitor tolerance for min/max times or does the capacitor tolerance need added on top of that 40% range?.
2. What is the tolerance band on the 220nA current source used to charge the capacitor?
3. What is the tolerance range on the 1.23V reference internal to the TPS3808?
4. Are there other factors not listed in the datasheet (besides capacitor variance, the 220nA current source, the 1.23V reference, and parasitic capacitance) that could affect accuracy?
Thank you for your time and I look forward to hearing back from you.
