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victorf
Joined: 01 Jan 2006
Posts: 342
Location: Schenectady, New York
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Posted: 25 February 2010, 20:56 PM Post subject: I2C interface 3.3V device to ZX-24 |
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To make it simple: How do I interface a 3.3V I2C device to a 5.0V ZX-24? The device is a SFE HM6343 BO.
Any enlightenment will be appreciated.
Vic |
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dkinzer
Site Admin
Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
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Posted: 25 February 2010, 22:47 PM Post subject: Re: I2C interface 3.3V device to ZX-24 |
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| victorf wrote: | | How do I interface a 3.3V I2C device to a 5.0V ZX-24? |
Since both SDA and SCL are bi-directional lines this is a more difficult case - you need a level translation circuit that is bi-directional also. I haven't used it but it appears that the ST2378E might fit the bill. I'm sure there are other candidates, too.
There is also a clever two-transistor circuit described here:
http://www.edn.com/archives/1996/110796/23DI_02.htm |
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victorf
Joined: 01 Jan 2006
Posts: 342
Location: Schenectady, New York
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Posted: 26 February 2010, 14:50 PM Post subject: |
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What about simply pulling up the I2C lines to 3.3V. Will the ZX be able to handle this or am I just asking for trouble?
Vic |
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dkinzer
Site Admin
Joined: 03 Sep 2005
Posts: 2499
Location: Portland, OR
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Posted: 26 February 2010, 16:17 PM Post subject: |
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| victorf wrote: | | What about simply pulling up the I2C lines to 3.3V. Will the ZX be able to handle this or am I just asking for trouble? |
The minimum voltage level to be recognized as a logic 1 by the ZX input is Vcc * 0.6 = 3.0 volts. Since I2C outputs are "open drain" the logic 1 level is going to be pretty close to 3.3V, giving you at least a 100mV margin. If your lines are kept short, you use strong pullups (say 2.2K), your 3.3V supply is not too far below 3.3 volts and your 5V supply is not too far above 5 volts you'll probably be OK. |
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mikep
Joined: 24 Sep 2005
Posts: 765
Location: Austin, TX
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Posted: 26 February 2010, 18:51 PM Post subject: |
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Here is the de facto standard white paper on I2C level conversion from Phillips: http://ics.nxp.com/support/documents/interface/pdf/an97055.pdf. The explanation of how the dual MOSFET solution works is in the application note.
I have successfully used this circuit and recommend it.
You can buy prebuilt breakout board from Sparkfun for $1.95. I created my own PCB anbd used a dual MOSFET and 4 resistor array - about 30 cents. |
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twesthoff
Joined: 17 Mar 2006
Posts: 191
Location: Fredericksburg, VA
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sturgessb
Joined: 25 Apr 2008
Posts: 246
Location: Norwich, UK
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Posted: 27 February 2010, 14:16 PM Post subject: |
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Yes, I can confirm this is a great solution, I use the 3002.
its brillo pads!
Ben |
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