TAS2110: I2C fast mode minimum fall time

Kazuki Itoh

Genius 9425 points

Part Number: TAS2110
Other Parts Discussed in Thread: TCA9539

Hello team,

I found the TAS2110 D/S specifies the minimum I2C fall time (tf) as 20 + 0.1 x Cb ns at the fast mode.

I found my I2C signal from the SoC doesn't meet this specification.

Could you let us know the possible risk by violating the minimum fall time specification?

In the previous thread for TCA9539 here, it is mentioned that this is just for EMI and it should be OK.

Also, I wonder why the I2C minimum fall time is specified only for fast mode, but not for normal mode and fast mode plus.

Could you please elaborate on that?

Regards,

Itoh

over 3 years ago

0 Luis Fernando Rodriguez S. over 3 years ago

TI__Guru* 84915 points

Hi, Itoh-san,

Unfortunately, we cannot guarantee that the I2C communication will work if it doesn't respect the minimum fall time. Even if the TCA9539 I2C lines times can be violated (with an EMI noise tradeoff), we cannot recommend to use times outside the recommended values.

Is it possible to adjust the I2C lines capacitance on your application in order to adjust the time?

Best regards,
Luis Fernando Rodríguez S.

0 Kazuki Itoh over 3 years ago in reply to Luis Fernando Rodriguez S.

TI__Genius 9425 points

Hello Luis-san,

Unfortunately, I2C rise time in my system is already slow, so I'm struggling with the trade-off. When I added the capacitor, the rise time violated the specification. Do you have any other idea?

Also, Could you please comment why the I2C min. fall time is only specified for the fast mode in the datasheet section 6.6?

Regards,

Itoh

0 Luis Fernando Rodriguez S. over 3 years ago in reply to Kazuki Itoh

TI__Guru* 84915 points

Hi, Itoh-san,

Have you tried to use the I2C lines in standard mode? It seems that your I2C interface doesn't have capabilities to handle the fast mode.

Best regards,
Luis Fernando Rodríguez S.

0 Kazuki Itoh over 3 years ago in reply to Luis Fernando Rodriguez S.

TI__Genius 9425 points

Hello Luis-san,

Thank you so much, I'll check it.
In the meantime, could you please check the reason why the I2C minimum fall time is only specified for the fast mode but not for normal mode and fast mode plus?
I'd like to make sure if this specification is really mandatory. If this question is challenging to answer, please let me know.

Regards,

Itoh

0 Raphael Xu over 3 years ago in reply to Kazuki Itoh

TI__Intellectual 940 points

Hi Itoh,

Most engineers on vocation now and I'm trying to get the feedback from them and will give you feedback when I receive it.

Regards

Raphael

0 Kazuki Itoh over 3 years ago in reply to Raphael Xu

TI__Genius 9425 points

Hello Raphael-san,

No problem, thank you so much!

Regards,

Itoh

0 Luis Fernando Rodriguez S. over 3 years ago in reply to Kazuki Itoh

TI__Guru* 84915 points

Hi, Itoh-san,

The electrical characteristics for the fast-mode plus are mandatory. Any parameter violation may result in a wrong communication.

In case of normal mode, the fall time can be relaxed, so the minimum fall time is not specified.

Best regards,
Luis Fernando Rodríguez S.

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TAS2110: I2C fast mode minimum fall time