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TCA9548A: TCA9548APWR VIH, VIL, VOl values of SD0-7, SC0-7 ports

syed S
Prodigy 110 points
Part Number: TCA9548A

Tool/software:

im using the TCA9548APWR with 1.8V VCC, 1.8V I2C on the SDA, SCL pin (VDPUM ) and using 8 i2c output ports with 1.8V and 3.3V. 

what is the SD, SC ports VIH, VIL, VOL values for 1.8V level and 3.3V level. can i use different i2c bus on the TCA9548APWR IC with different supply. i need the DC analysis values.

  • 0
    TI__Mastermind 35218 points

    Hi Syed,

    The VIH/VIL levels are in the datasheet:

    1.26V for VIH and 0.54V for VIL @1.8V. 

    VOL values are also in the datasheet:

    But you'll likely want to use pull-ups to get your output side to the correct voltage.


    And yes you can use different bus levels with the same supply (I'm not sure what you mean by different supply though). 
    Section 8.2.1 tells you how to do it properly with Vpass - also look at Figure 8-2. 
    The rule fo thumb though if you want to bypass reading the datasheet is to have your supply be the lowest bus value. So if you have a 1.8V bus and a few 3.3V buses, then set your supplies to 1.8V and then pull up all your 3.3V buses to the 3.3V supply you would have and you should be good.

    Thanks,
    Rami

  • 0 in reply to Rami Mooti1
    Prodigy 110 points

    Hi  ,

    Im using TCA9548A with SDA, SCL on 1.8V rails and VCC=1.8V, my other ports are having SD0, SC0 -1.8V levels and SD1,SC1-3.3V i2c bus with pull ups.

    i want to check the DC analysis of the SD/SC ports to devices connected on 1.8V rail and 3.3V rail. for that i need the VOH, VOL, VIH, VIL values of SD/SC pins of 8 channels.

    the datasheet has only the VIH, VIL values for SDA,SCL main bus not for SD/SC ports 0-7. how can i check the dc levels for the SD/SC ports to connected deviced with different i2c bus like 1.8, 3.3v

  • 0 in reply to Rami Mooti1
    Prodigy 110 points

    also what this Vo(sw) voltage refers can you explain mem does it refer the Vds voltage of the internal FET or drain voltage of the FET.

  • 0 in reply to syed S
    TI__Mastermind 35218 points

    Hi Syed,

    There is no VIH/VIL for those channels. Once the channel is turned on on the SDA/SCL side it acts as a passive FET so the signals will just communicate through. At that point, the VIH/VIL of your I2C controller and peripherals will be the specs that you care about for sending and receiving data. If you want to change the configuration of the TCA device then you'll one again care about the VIH/VIL levels of just the SDA/SCL again. 

    Vo(sw) refers to the drain voltage of the FET.

    Thanks,
    Rami

  • 0 in reply to Rami Mooti1
    Prodigy 110 points

    Hi Rami,

    What if the controller SDA/SCL vih,vil,voh,voL is not matching with the devices connected on these 8 ports. Since you are referring the DC levels of the controller which is connected on SDA,SCL DC levels should only match with the devices DC levels connected on ports.am I right

    How does it work if these two DC levels are not matching, then it did not fulfill the need of level translator right?

    Also what is the vcc value should be used if I use 3.3v and 1.8v ports on Sd/SC lines.

  • 0 in reply to syed S
    TI__Mastermind 35218 points

    Hi Syed,

    I'm not sure I follow. You should pull up the 8 ports side to the VIH/VIL level of those devices. Use a pull up resistor up to the voltage you need (I'm assumin this will be 3.3V). Each side will pull up to the pull up value that you have on that specific bus. 
    Set your VCC to your lowest bus voltage, so 1.8V in this case

    Thanks,
    Rami

  • 0 in reply to Rami Mooti1
    Prodigy 110 points

    Hi Rami,

    Let me clear this. I'm using AGX Orin SOM as main I2C bus with TCA9548 expander. And all other 8 ports have been used for various IC with their respective VCC(1.8V for 6 bus and 3.3V for 2 bus with Rpu).

    My concern here is, the Orin SOM has some VOH, VOL, VIH, VIL values and my 8 devices connected on Sd/Sc ports have different VIH,Vil,VoL values. While doing dc analysis these SoM and devices which have 3.3V I2C bus connection has failure in dc analysis.

    How to make sure that this TCA9548 can work for any devices on the 8-ports with the main I2C bus interms of dc analysis.

    Also only the vih,vil,vol values are given for SDA,SCL bus of the IC. Which I have checked with SoM values looks matching. But for output ports 8-channels looks mismatching. 

    With which values I need to check the DC analysis for 8-ports connexted on the IC.

    I have used the VCC-1.8V, main bus 1.8V, 

    Output ports Sd,sc-1.8V, 3.3V (mixed)

  • 0 in reply to syed S
    TI__Mastermind 35218 points

    Hi Syed,

    As mentioned, the TCA9548A will not have VIH/VIL on those 8 SDx/SCx pins. You can think of Vpass as the VIH in some ways. But the truth is that once you select the path, the TCA9548A will act as a pass FET.  Efectively it will be a resistor with the on resistance showns below:



    For your setup you will use 1.8V on VCC and hten pull up the main bus to 1.8V. 
    You will then pull SD0/SC0 to 1.8V, SD1/SC1 to 3.3V and so forth for all yoru bus voltages. 

    If the VIH/VIL/VOL values do not match then please share an schematic, highlight where your concern is and the actual values. But from the mux perspective, as long as the VIH/VIL matches the VOH/VOL of the AGX Orin SOM you mentioned that is driving the main bus, you will fine. 

    -Rami