Power sequencing is becoming more and more of an issue as we proliferate so many different power supply levels. Hi Ed, Thanks for your comments. Adjust the ohm resistor to account for the series resistance of your driver, in order to perfect the received signal size. The parallel combination of and 50 equals We do not believe it is practical to always control the sequence, or to control the state in which gates power up. Is this terminated by 50 ohm or by some other value?

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If I make the line sufficiently short, it might not need termination. One thing I’ve learned about problems like this is that when I suggest changing the transmission line impedance I usually discover the layout is “already done” and “cannot be changed”.

(PDF) 74S Datasheet PDF Download – Dual 4-Input NSND Line Driver

The maximum specified high drive current for any modern device that I know of is 24 ma 74ACs for example which only gets you to 1. These parts impose no power sequencing requirements. The series-terminated circuit in Figure 4 places all the attenuation at the source end of the line. Thanks very much, I lins confused however, The specs state: Adjust the ohm resistor to account for the series resistance of your driver, in order to perfect the received signal size. 74s410 you set R1 to zero for use with this part that still leaves you with zero noise margin.


An unrestricted version of this entire Collection, including all the movies, articles, and powerpoint source files for the seminars, is available on hard disk under a one-time, royalty-free license. I am thinking it may lins good to buffer the signals before sending them to the but that seems to be starting to make something quite complicated! This places a split end termination at the endpoint ohms to 3. I have just got of the kine and NI have confirmed that it is definitely 75 ohm.

Just last week I was called in to help fix two cases where parts were being “burned out” because of power sequencing problems and one more case the week before.

The surge happens because, during 74140 first roundtrip delay, the transmission line looks like 50 ohms to ground, so the driver has to drive 75 ohms in series with the parallel combination of and 50 ohms.

50 Ohm, 5v driver needed | Electronics Forums

Thanks for your thoughtful analysis. Is this terminated by 50 ohm or by some other value? I’m going to try a oine of different architectures to see what is good and bad about each one. For example, LVT 3. Enough series resistance must be included to prevent dangerous overdrive currents when powering up.


The 74FD, which can sink 64 mA to 0. Message 4 of The datasheet is in error. Power sequencing problems are some of the most perplexing design problems we encounter.

If the line is longer, then considering the power issue paramount, and assuming the signal quality were acceptable, I would prefer a simple, series-terminated driver.

Here are his comments.

74S140 Datasheet

Somehow this current has to come out of the driver. We just sliced the drive current requirement in half to only linee mA. Message 5 of What is the output impedance of the “out” pins?? OK, so now I’m really motivated to come up with a better solution.

74S140 CDIP14

Message 10 of Achieving both attenuation and termination requires two resistors. First, I ilne he was talking about going from a 5V logic device to a 3. I will have to terminate on the PCB. Johnson takes another shot at the problem: I suppose you could parallel CMOS outputs to get more drive.