Open Collector IC Suggestions?

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#1
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Does anyone have a good open collector buffer IC that they can recommend?

I am having difficulty convincing the project lead to use an open drain part, and I have been unable to find any good open collector NON-INVERTING buffers.

The few I have found (i.e., SN7417D), have limited temperature range: 0 - 70C. I'd like at least -40 to 85C.

Alternatively, I'll accept any good arguments (that I haven't already tried) as points to use an open-drain part instead.

Science is not consensus. Science is numbers.

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You can do effectively open-drain by using a tri-state device.

Wire it up so that the input makes the output low, permanently. Then, use the tristate control pin as the input. Works nicely, especially with some of those single-gate devices. See Fairchild NC7SP126 as example. There are many others.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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Alas, my marching orders are to make the output physically open collector.

Hence my frustration.

Science is not consensus. Science is numbers.

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Why does it matter?

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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hobbss wrote:
Hence my frustration.

Science is not consensus. Science is numbers.

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Use a 2N3904 with logic of your choice. Leave the collector open.

Voila, open collector.

Jim

Jim Wagner Oregon Research Electronics, Consulting Div. Tangent, OR, USA http://www.orelectronics.net

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hobbss,

Can the
"good open collector buffer IC" you seek be either inverting or non-inverting? Do you have a preference?

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I would prefer non-inverting, as the lines are going multiple places (i.e., driving status LEDs and serving as binary alarm pins on a backplane connector). However, I can always invert them twice. However, the temperature range is fairly important. My system is currently spec'd for 0 to 60C, but that may expand. I do not want to use any components right at their operating range limit if I can help it. I am really looking for a -40 to 85C part.

Science is not consensus. Science is numbers.

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SN5407

:)

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Ha. Actually AVAILABLE parts.... :twisted:

Science is not consensus. Science is numbers.

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ULN2003

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Avnet and Arrow both show stock. Just need a lot of gold...

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... or I guess go discrete.

DRIVEn are driven from a 5V source.

Attachment(s): 

Science is not consensus. Science is numbers.

Last Edited: Thu. Oct 17, 2013 - 09:33 PM
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Why do you have pullup resistors to 5V if you want O/C outputs? :roll:

And what's wrong with the ULN2003 suggested above? Or ULN2803?

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Pullups won't be populated (not yet marked in attached image).

Nothing wrong with what was suggested above. I think actual discretes (not arrays) are better in this particular application, because it gives me more routing flexibility (attempting to do all routing on single layer for this board). I also don't need all that current. Is there anything in particular wrong w/ the component I chose? I haven't done many designs with BJT discretes since college...

Science is not consensus. Science is numbers.

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Changed attachment (above) to reflect true open collector - and added inverters to drive signals.

Science is not consensus. Science is numbers.

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It may be wise to use a pulldown resistor (100K??) on the DRIVE side of the resistors so that the transistor do not accidentally turn on during reset while the outputs are still undefined.

Not a big issue with BJTs but more with FETs.

John Samperi

Ampertronics Pty. Ltd.

www.ampertronics.com.au

* Electronic Design * Custom Products * Contract Assembly

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Good suggestion - thanks.

Science is not consensus. Science is numbers.

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If you want open collector and non-inverting then jump to 2013 and hop over to
http://www.nxp.com/products/bipo...

Look for complementary, which gives 39 choices at 100mA and 1 choice at 500mA.

Unless you really need 500mA, choose 100mA, and a higher Rb base value of 10~22k region, can give some hfe current limiting slip protection. (brief shorts survived)

Choose the package and resistor values you like. Done.

Or, if you can tolerate inverting, you can select double NPN and get 2x the packing density.

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Nice products. Size isn't critical in this design, but these are still good to know about.

Science is not consensus. Science is numbers.