SN65DSI84: I2C rise / fall time

Takahiro Saito

Part Number: SN65DSI84

Hi team,

My customer is seeing too short rise and fall time (~1ns) of SCL/SDA compared with the time (>20ns, fast mode) mentioned in I2C standard. Do you think this very short rise/fall time has no problem to communicate SN65DSI84 with I2C?

Regards,

Saito

over 7 years ago

0 Ikechukwu Anyiam over 7 years ago

TI__Mastermind 35130 points

Hi Saito-san,

The SN65DSI84 is compliant with I2C Bus Specification, Version 2.1, so your I2C interface should meet all the requirements in that specification to ensure no issues with SN65DSI84. As you mentioned, 1ns rise/fall time is out of specification so they should ensure the rise/fall time is at least 20ns minimum to be compliant with the spec.

Regards,
I.K.

0 Takahiro Saito over 7 years ago in reply to Ikechukwu Anyiam

TI__Expert 5465 points

Hi IK,

Thank you for your feedback.

So, they should adjust the rise/fall time to >20ns to meet the requiredment. How to acieve that? Do they need to increase the pull up resistor to slow down the rise/fall time?

Regards,

Saito

0 Ikechukwu Anyiam over 7 years ago in reply to Takahiro Saito

TI__Mastermind 35130 points

Yes that is one way to do it. You can use this document as reference: www.ti.com/.../slva689.pdf Just remember that the DSI84 I2C interface is 1.8V, not 3.3V.

Regards,
I.K.

0 Takahiro Saito over 7 years ago in reply to Ikechukwu Anyiam

TI__Expert 5465 points

Hi IK,

Thank you for your feedback. I will ask to customer to adjust the rise / fall time.

Regards,
Saito

0 Takahiro Saito over 7 years ago in reply to Takahiro Saito

TI__Expert 5465 points

Hi IK,

Customer will try to adjust the rise/fall time by the pullup resistor.

Could you tell me what problem will be happen when the rise/fall time is smaller than the minimum rise/fall time.

Regards,

Saito

0 Ikechukwu Anyiam over 7 years ago in reply to Takahiro Saito

TI__Mastermind 35130 points

Hi Saito,

From a functional standpoint I don't believe there would be issues, but if the rise/fall time is too fast then they may run into EMI issues.

Regards,
I.K.

0 Takahiro Saito over 7 years ago in reply to Ikechukwu Anyiam

TI__Expert 5465 points

Hi I.K,

Thanks for your reply.

Regards,
Saito

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SN65DSI84: I2C rise / fall time