SN74LVC2G17DCKR maximum output capacitance

Hey Dan,

Unfortunately the output capacitance of SN74LVC2G17 is not something that has been characterized so we don't have that value for you. Is there a specific reason that you need that value for that we can help you with?

Thanks,
Daniel

My customer is asking for their design - and I'm not sure what they are hooking up to it yet. Looking at the datasheet - it appears we do some tests with 50pF - and they were concerned that this was the maximum. I do see, however, that we show propagation delay vs output capacitance showing up to 300pF - so I figure they should at least be good to that amount. Aside from that it seems more an issue with inrush current (although long propagation delays would certainly be a concern). Would that be the main limitation?

Thanks,
Dan

Hey Dan,

The capacitance you seem to be talking about is the load capacitance and not the output capacitance. The output capacitance is when the output of a device is in High Z and is the capacitive part of the high Z value. As far as load capacitance is concerned there will be an increase in the propagation delay of the device as the load increases, but not a risk to the device.

Could you elaborate on the problem you see with the inrush current of the device as I am a bit confused on what you are talking about. Typically inrush current is talked about on the inputs of the device and not on the output side.

Thanks,
Daniel

Correct - I am talking about the load capacitance in this case. I see propagation delay spec'd up to 300pF load capacitance on the datasheet curve. Would propagation delay increase in a linear manner with more capacitance?
Inrush current is the instantaneous rush of current when a device is first turned on. In this case we're talking about the inrush of current into an output load capacitor when the switch transitions. The load capacitance will cause some sort of high current through the device and into the output (load) capacitor on first turn-on when the cap is discharged and Vin is high. This current will be a function of the difference of Vin/Vout and the resistance through the SN74LVC2G17DCKR, starting high and decreasing as the load capacitance charges (and Vout increases). While I don't anticipate the customer switching highly capacitive loads on this line, there has to be a limit somewhere. Let's assume 3.3V operation.
Thanks,
Dan

Hey Dan,

It is unlikely that the propagation delay will be linear outside of what that graph shows based on what we have seen from testing on other parts.

The inrush current will always be a problem for the device no matter what capacitor you use, it is just as the capacitors get bigger they need to run the max current of the device for longer as the device will limit your current to whatever can go through the device. Note that the max current that can go through the device is different than the max current our device specifications say and the max current that can go through the device will be bigger than what our specs say. To avoid going over the max spec I would suggest having a current limiting resistor on the output that will keep that current in max range.

Is there a specific customer application you have in mind that would need a higher than normal capacitive load? If so I would be interested in hearing it and seeing if there might be a better solution.

Thanks,
Daniel