TPS3808: td calculation

Ryoma Ohashi

Part Number: TPS3808

Hi team,

For the delay time calculation, in the datasheet, it says use td=Ct[nF]/175 + 0.5x10^(-3)

By using the equation, for Ct=100pF

td=100pF/175+0.5x10^(-3)=1.071429[ms]

But in the datasheet, the typical value for Ct=100pF is td=1.25[ms] (min 0.75[ms] and max 1.75[ms])

The question is:

Why does the value differs? (calculation result: 1.071429 and typ: 1.25)
What is the min, typ, max value for the "175" & "0.5" in the calculation fomula?

Regards,

Ohashi

+1 Trailokya Rai over 2 years ago

Hi Ohashi

The typical value in the table has been provided with 20% tolerence in the capacitor. However calculation is done with ideal cap with 0% tolerance.

You can expect around ± 40% variation in the delay with the capacitor.

Regards

Trailokya

0 Ryoma Ohashi over 2 years ago in reply to Trailokya Rai

Hi Trailokya,

Thanks for your support. I got the point.

There is one additional question.

I f the customer uses cap with 5% tolerance, how much should they expect for the variation in the delay?

About 30%?

Regards,

Ohashi

+1 Trailokya Rai over 2 years ago in reply to Ryoma Ohashi

Hi Ohashi

Customer can expect around 30% with that.

Regards

Trailokya

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