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I'm new to online forum. I want to interface 74HC541(Buffer) to 74HC574(D-f/f). The thing is 100's of D-f/f parallel interface as shown in figure(Fig.1). Input and load capacitance limits it to 10 to 15 fanout. Fanout of buffer current wants to charge input capacitance of D-f/f. So increasing D-f/f increases charge time of input capacitance. My question is this can be overcome by giving more current to increase charge current to input capacitance by adding pullup resistor to input of D-f/f(Fig.2) or BJT emitter follower(Fig.3). This would correct or not...

Thanks in advance...

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Prakash
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    Time to advertise an answer of mine: http://electronics.stackexchange.com/a/236671/107479 – dim Jun 22 '16 at 07:29
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    You haven't spelled out the actual problem you are trying to solve, generally we don't need buffering to go between CMOS and CMOS. If you do indeed need to fanout to 100s of inputs, and need a certain speed which isn't delivered by the simple connection, then use a CMOS buffer tree to get a lower fanout. Usually discrete solutions are not good. The weakness of fig 1 is the pulldown resistor, that will not be improved by a pullup! – Neil_UK Jun 22 '16 at 07:30
  • Are there any alternative methods rather than CMOS buffer tree to increase fanout? – Prakash Jun 22 '16 at 08:12
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    Fanning out the same signal to hundreds of DFFs suggests that there is probably something else horribly wrong with the design. What about the clock? What about the space consumed by all these discrete buffers? How long is the wire to the most distant one? – pjc50 Jun 22 '16 at 09:21
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    I'm with @pjc50: feeding hundreds of discrete FF seems weird. This may be a case of [XY problem](http://xyproblem.info/). If you explain what you really want to do with your project, we may be able to give you more sensible advices. – LorenzoDonati4Ukraine-OnStrike Jun 22 '16 at 10:33
  • I want to control more no of solenoid to turn ON/OFF. I used D-f/f to give signal to solenoid. With the use of decoder, giving clock pulses to D-f/f. To drive D-f/f I used buffer here. – Prakash Jun 22 '16 at 12:59

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I would try to connect 10 buffers to the data source and then 10 74HC574 inputs to each buffer output. Think about a rack with a data bus to ten boards, each board has its own buffer for its internal data bus driving ten 74HC574. No problem with current and capacitance limits. Just avoid a common data bus to hundred HC574. It is possible to drive even a thousand 74HC574, connect 10 buffers to the data source and another 10 buffers to each buffer output of the first stage and then 10 74HC574 to each second stage buffer output.

Uwe
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