TCA9548A: Clarification on Unused pins in TCA9548APWR IC and veriflying the Pull value for all the I2C lines

Vikas Bangera

Part Number: TCA9548A
Other Parts Discussed in Thread: PCA9306

Hi Team,

Please verify unsed I2c pins termination should it be NC or connected to ground.

I have attached image below please verify.

For each I2C lines what is the pull up value in below image i have calculated it through the datasheet is this vallue correct. Kindly confirm it

Regards,

Vikas

5 months ago

0 Clemens Ladisch 5 months ago

Guru 326760 points

499 Ω is much too strong. How did you calculate it? (In general, the total pull-up current for all enabled channels should not exceed 3 mA.)

Unused channels (Sx6/Sx7) can be left open. You can also add pull-up resistors. You must not use pull-down resistors (if those channels would ever get enabled accidentally, they would block all further I²C communication).

0 Vikas Bangera 5 months ago

Prodigy 60 points

Hi Clemens,

thank you for the response.

...

https://www.ti.com/lit/an/slva689/slva689.pdf?ts=1773648665267

In Pull-up resistor calculation the

R(max) = 300nF/338.92pF = 885ohm (max)

is this what in referring is incorrect. Please check on this PU value calculation

Kindly provide what would be the PU value for all the I2c lines.

Regards,

Vikas

0 Nir Gilgur 5 months ago in reply to Vikas Bangera

TI__Mastermind 27965 points

Hello Vikas,

I am not sure where you got the values for your calculation, but I followed the document you linked and got 2950ohms as the max value.

I would recommend using 3.3k or 3.6k pull ups for your application.

Thanks,

Nir

0 Vikas Bangera 5 months ago in reply to Nir Gilgur

Prodigy 60 points

Hi Nir,

for fast mode im calculating

this will come across 885ohm (max)

lease confirm is the right PU value. Or can you suggest the PU value to be use in design

Regards,

Vikas

0 Nir Gilgur 5 months ago in reply to Vikas Bangera

TI__Mastermind 27965 points

Hello Vikas,

I have recommended.
You can use 3.3k, or 3.6k pull up values.

Thanks,

Nir

0 Vikas Bangera 5 months ago in reply to Nir Gilgur

Prodigy 60 points

Hi Nir,

Is that formula for calculating I2C PU value is wrong what i did?

Regards,

Vikas

0 Nir Gilgur 5 months ago in reply to Vikas Bangera

TI__Mastermind 27965 points

Hello Vikas,

The formula itself is not wrong, but you need to use values according to the mux specifications, not the protocol.
Your "limit factor" will be the mux, since the signal is passing through it.

Specifically, you should have used the rise time of the mux, instead of the protocol.

Thanks,

Nir

0 Vikas Bangera 5 months ago in reply to Nir Gilgur

Prodigy 60 points

Hi Nir,

Can u tell me the rise of mux?
are you talking about power VCC rise time

Regards,

Vikas

0 Nir Gilgur 5 months ago in reply to Vikas Bangera

TI__Mastermind 27965 points

Hello Vikas,

I am talking about input rise time of the mux.
See below spec from the datasheet:

Thanks,

Nir

0 Vikas Bangera 5 months ago in reply to Nir Gilgur

Prodigy 60 points

Hi Nir,

Thank you for the response.

But 1000ns is for standard mode

Im looking into Fast mode.

Then how will be rise time same for bothmode?

below find the image of both requirement

Regards,

Vikas

0 Nir Gilgur 5 months ago in reply to Vikas Bangera

TI__Mastermind 27965 points

Hello Vikas,

I see, I missed that part.
The rise time is not the same, 300ns for fast mode and 1000ns for standard mode.

Then, yes for fast mode you can use 1k according to the calculation, but I would still recommend 3.3k.
The calculation is an estimation of the value you should use not an exact strict one that you have to meet.

Thanks,

Nir

0 Vikas Bangera 5 months ago in reply to Nir Gilgur

Prodigy 60 points

Hi Nir,

Thanks for the information it was very helpful.

while using PCA9306DCUR IC for GPIO signals level translation. what would be recommended circuit or termination.

Reagrds,

Vikas

0 Nir Gilgur 5 months ago in reply to Vikas Bangera

TI__Mastermind 27965 points

Hello Vikas,

I do not support the PCA9306DCUR.
I have looped in the appropriate team to help here.

Thanks,

Nir

0 Vikas Bangera 5 months ago in reply to Nir Gilgur

Prodigy 60 points

Hi Team,

while using PCA9306DCUR IC for GPIO signals level translation. what would be recommended circuit or termination.

Should PU have to be provided at both the level translation IO pins end?

Please share if u have any recommended circuit for GPIO translation using PCA9306DCUR IC

Regards,

0 Vikas Bangera 5 months ago in reply to Vikas Bangera

Prodigy 60 points

Hi,

Please provide update

Reagrds,

Vikas

0 Jack Guan 5 months ago in reply to Vikas Bangera

TI__Guru 61061 points

Hi Vikas,

Having pullups at the I/Os would depend on if the the GPIO signals are push-pull driver based or open drain. Section 3 of this app note covers this further in detail: https://www.ti.com/lit/an/scea144/scea144.pdf?ts=1774635835732

Regards,

Jack

0 Vikas Bangera 5 months ago in reply to Jack Guan

Prodigy 60 points

Hi Jack,

Thanks for information

unused pins can be left floated for SCL and SDA?

Regards,

Vikas

0 Jack Guan 5 months ago in reply to Vikas Bangera

TI__Guru 61061 points

Hi Vikas,

Yes they can be left floating. The outputs of the PCA9306 are open drain, so the default state would be low.
Regards,

Jack

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TCA9548A: Clarification on Unused pins in TCA9548APWR IC and veriflying the Pull value for all the I2C lines