Rank: Advanced Member
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Joined: 2/10/2009(UTC)
Posts: 299
Location: Italy
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I'm trying to understand the electronic works of I2C because I wan't to implement galvanic isolation using an ADUM1250 chip.
Should all devises on an I2C bus have pull-up resistor? Or only one? Or at least one?
In my volumite controlled dual-mono buffalo there seems to be pull-up resistors on all three devises 2K on the buffalo's and 3.32K on volumite (I know the latter are not needed). Why 2K on buffalo and 3.32K on volumite?
Any short guide lines about when to use pull-up resistors and at which values would be very appreciated! In the specific case with an ADUM1250 between volumite and buffalo I assume that I will not need pull-up resistors as these are already there in both ends but I'm not really sure......
Cheers,
Nic
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Rank: Member
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Joined: 11/9/2007(UTC)
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Location: usa
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One Vd connection for the bus, so only the pull up resistors that connect to the source voltage matters. The ADUM chip interfaces two I2C buses so you need Vd connection on each bus with the corresponding pull ups. 2K is the "typical" value for pull up, although I think the Atmel chips use > 20K pull ups. Some people claim they are "too weak" of a pull up resistor but they work fine. For complete isolation, the volumite will have its own Vd and Gnd separate from the Vd and Gnd of buffalo. That means a separate ps for volumite. Edited by user Thursday, March 3, 2011 9:21:58 AM(UTC)
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Rank: Advanced Member
Groups: Member
Joined: 2/10/2009(UTC)
Posts: 299
Location: Italy
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thanks glt,
I will actually have the volumite in a separate case and it will have a separate supply.
I'm also working on isolating the I2S and this seems a bit more complicated.
Cheers,
Nic
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