TCA9539: I2C input rise and fall time for FAST MODE

Daisuke Maeda

Guru 19895 points

Part Number: TCA9539

The minimal input rise time is 20 ns and the minimal input fall time is 20 x (VCC / 5.5 V) ns.

Are those specifications really correct for the SDA and SCL input terminals?

In the I2C-bus Specification, the minimal rise and fall time is the specification for the output terminals and the bus lines, and it does not seem to be the specification for the input terminals.

I2C-bus Specification, Version 6.0, 4th of April 2014
http://cache.nxp.com/documents/user_manual/UM10204.pdf

On our customer board, no problems have occurred but the minimal rise and fall time is approximately 2.4 ns. Is this minimal time allowed?

Best regards,

Daisuke

over 5 years ago

0 fhoude over 5 years ago

TI__Mastermind 18445 points

Hello Daisuke,
Our datasheet specifies it such that it matches with what is stated in the I2C standard, but having a faster rise time on the input is acceptable and our part will work below the min rise and fall times. I am not sure why they have a min rise and fall time in the standard. I believe there might be some history for that specification that I am not aware of. I will look into it more and get back to you.
-Francis Houde

0 Daisuke Maeda over 5 years ago in reply to fhoude

Guru 19895 points

Hi Francis-san,

Thank you for your reply.

I will tell the customer that the SDA and SCL inputs work below the min rise and fall times.

Please post here if you find anything why they have a min rise and fall time in the standard.

Best regards,

Daisuke

0 fhoude over 5 years ago in reply to Daisuke Maeda

TI__Mastermind 18445 points

Hello Daisuke-san,
I was told the their is a min rise and fall time to help mitigate EMI. It is not a hard standard that needs to be followed.
-Francis Houde

0 Daisuke Maeda over 5 years ago in reply to fhoude

Guru 19895 points

Hi Francis-san,

Thank you for your reply.

Best regards,

Daisuke

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TCA9539: I2C input rise and fall time for FAST MODE