TPS3818_Delay time tolerance

Q: TPS3818_Delay time tolerance by 1300154

What is the delay time tolerance of TPS3818?

In this forum, I found out that there is a formula for calculating the delay time based on the CT pin charge current and threshold voltage.

Could someone please share me that formula?

Thank you in advance.


A: Re: TPS3818_Delay time tolerance by 10449

The TPS3818 delay time is defined by how long it takes the 220nA precision current source to charge the timing capacitor on the CT pin to 1.23V.  This is a simple I=C*(dV/dt) calculation.  The equation you are looking for is found by rearranging terms to make it dt=C*dV/I = C * 1.23V / 220nA.  The datasheet equation for calculating the Ct capacitor value looks a little more complicated because it combines terms and includes a 500us delay time.  The 500us delay time is insignificant in most applications and can be ignored to make the calculation a little easier.  The tolerance of the RESET pulse is a function of tolerances of the current source (which is specified in the datasheet) and the 1.23V comparator trip voltage (which is specified in the datasheet).  The remaining RESET pulse variation is a function of capacitor tolerance.  Note 3 on page 3 shows that the RESET time tolerance due to the 1.23V and 220nA tolerances is +/- 15%