TCA9617A: IIC/SMBUS signal rise time measure

Hi ,

Two question need your help:

1. What's the start point of IIC signa rise time ?   A point or B point in figure 10? 

or use the waveform no pedestal overshoot?

2.  Usually, signal rise time is 10%–90% stable high level, is this definition also suitable for IIC signal? if not, please give me the corrective IIC signal rise time measure method.

Thanks.

Kailyn Chen：

Hello，

1） The start point is A point which is the same with standard timing.

2) The rise time or fall time is based on 30%~70% instead of 10%~90%.you can find more info about rise/fall time here:

https://www.ti.com/lit/an/slva689/slva689.pdf

Any other questions, please contact me again.

,

Chambin Zhang：

Hi Kailyn,

Thanks for your support,

1. As you said the rise time or fall time base on 30%-70% VCC. if my VCC is 5V and tolerance is 5%, that mean my maximum rise time will from 

    0.3*5*0.95V to 0.7*5*1.05V?

but base on follow AC and DC definition:

Which definition is correct? because they will have different result.

2. The second question is how to get VILMAX  and VIH MIN value if we use TR and TF formula to calculate TR and TF?  measure the actual waveform or quote from DC table VILMAX=0.8V, VIH  MIN=5*1.05*0.7=3.675V?

3. The third question is if rise time start point from A point (before pedestal overshoot), but pedestal overshoot normal about 0.5V, lower than 0.8V and 0.3*VCC,  I am very confusion.

Thanks

,

Kailyn Chen：

Hi Champin，

thank you for your feedback. About your question, I need to spend time to confirm the definition, and I would reply you as soon as possible.

,

Kailyn Chen：

Sorry to reply you so late. I have confirmed with senior engineer, below is his answer: 

1. As you said the rise time or fall time base on 30%-70% VCC. if my VCC is 5V and tolerance is 5%, that mean my maximum rise time will from 

   0.3*5*0.95V to 0.7*5*1.05V?

A:   I2C uses the definition of 30% to 70% of Vcc for rise time. This pedastal usually doesn't fit within the 30% definition.

2.  Usually, signal rise time is 10%–90% stable high level, is this definition also suitable for IIC signal? if not, please give me the corrective IIC signal rise time measure method.  base on follow AC and DC definition,  it is 10%~90% rise time.

A: I2C standard states it is from 30% to 70% of Vcc.

3. The third question is how to get VILMAX  and VIH MIN value if we use TR and TF formula to calculate TR and TF?  measure the actual waveform or quote from DC table VILMAX=0.8V, VIH  MIN=5*1.05*0.7=3.675V?

A:  I'm not sure I follow. TCA9617 doesn't use a ViH level. It only looks at ViL/ViLc to determine a low (if the signal is above ViL/VILc then it turns off it's open drain driver). ViH in I2C is only used for I2C target devices and the high signal is generated by the external pull up resistor.