DS90UB954-Q1: DESER 954 I2C Speed

Delaney Berger

Part Number: DS90UB954-Q1

Hi Team,

Can you please help answer the follow question?

Looking at changing the i2c speed from 330kHz to 100kHz on the i2c bus on the deserializer. Does that change the back channel communication frequency? It was not clear to me from the datasheet if the back channel and i2c share a clock divider.

Also, for the 954 – 953 link, is it possible to have two different i2c speeds on the serializer and deserializer?

Thank you,

Delaney

over 3 years ago

0 Ryan Fleetham over 3 years ago

TI__Expert 6605 points

Hi Delaney,

Changing the I2C speed will not affect the back channel communication frequency. While both I2C and the back channel operate off of the same clock, the clock dividers are independent.

Yes, it is possible for the serializer and deserializer to have different I2C speeds. With the default settings, the 954 I2C is set to 100kHz while the 953 is set to 74kHz so no issues mixing and matching different speeds.

Please let me know if you have any additional questions or need clarification.

Sincerely,

Ryan

0 Delaney Berger over 3 years ago in reply to Ryan Fleetham

TI__Intellectual 2475 points

Thanks Ryan, this explanation is very clear and helpful!

Will let you know if any other questions come up.

Thank you,

Delaney

0 Delaney Berger over 3 years ago in reply to Delaney Berger

TI__Intellectual 2475 points

Hi Ryan,

One more question. The datasheet recommends 2kohm to 4.7kohm for the pullups. Customer wants to use <1kohm pullups. Would this be possible?

Thank you,
Delaney

0 Ryan Fleetham over 3 years ago in reply to Delaney Berger

TI__Expert 6605 points

Hi Delaney,

That will depend on the use case and exact value they want to use. Here is a guide to calculating the min (and max) pull-up resistor value for I2C: /cfs-file/__key/communityserver-discussions-components-files/138/7183.I2C-Bus-Pullup-Resistor-Calculation.pdf. Below is the equation for calculating the minimum resistor value:

The following table from the DS90UB954-Q1 datasheet has the parameters based on your use case:

Please let me know if you have any additional questions.

Sincerely,

Ryan

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DS90UB954-Q1: DESER 954 I2C Speed