Hello,
I have one question regarding TPS22918 when I read the datasheet.
what's the difference between Turn on time (Ton) and Rising time (Tr) ? I think Ton value should be large than Tr , but it's opposite in the TPS22918 datasheet.
Can you give a waveform or picture to explain ? Thank you so much !
Hi,
This is a great question.
Ton is essentially the propagation delay from the rising edge of ON logic signal to VOUT reaching 50% of the final value.
tr, on the other hand, measures the rise time of the signal, which is considered as 10% to 90% of final value on VOUT..
Actually you are right, both values does depend on load condition as well as VIN. Values for both with different conditions are listed in the datasheet. but because Ton only measures to when Vout, is 50% of final value, Ton is less than Tr, because the propagation time from ON signal to the load switch conducting from VIN to VOUT is very quick, so the Ton is less than rise time.
Please see the timing diagram below which helpfully illustrates the different, from Section 7 of the datasheet.
If i've answered your question, please let me know by pressing the green button. And please, do let me know if you have any further questions on this!
Best
Dimitri
and just for extra information, note that rise time (and on-time as well) are controlled by the value of capacitor on CT pin, according to the formula in Section 8.3.3 of the datasheet.
I highlight the test condition for 5V corresponding for your comparison.
