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TS3A24159: Can I use it without I2C pull-up resistors?

Part Number: TS3A24159

Hello TI experts,

my customer considers TS3A24159 for their new product.

they will use it for I2C communication. and for some reason, they have pull-up resistors on COM1 and COM2 pins, and don't have on NCx and NOx pins.

could you confirm that this configuration is right or not? should we add pull-up resistors to NCx and NOx pins?

Best regards,

Chase

  • Hi Chase,

    For I2C communication there needs to be pull-ups on both COM and NC/NO pins to ensure the correct voltage is applied on both sides of the switch. This is due to the fact that a pull-up resistor is primarily used to pull-up 1 circuit node. Since the switch has resistance and capacitance it splits the I2C bus into multiple nodes. Each circuit node will need its own pull-up to ensure correct voltages.

    Please let me know if you have any other questions!

    Best,

    Parker Dodson

  • Dear parker,

    Thank you for your support.

    - I understand what you mean. then, is there any analog switch which don't need insert pull up resistors on both input and output? or all switches have similar characteristics?

    - here is the schematic of my customer, as you can see there are only pull up resistors on the input of U5, and don't have any other pull up on U6. customer thinks that if the switch is active, all the path is connected, so there need pull up only on input. please check that this scheme is right or not.

    sch_0001.pdf

    Best regards,

    Chase

  • But when a switch is not active, the disconnected bus segments are floating, which might results in malfunctions of the I²C devices on that segment.

    I²C devices need to be connected to some pull-up resistor at all times. (If you care about power usage: the resistors on the inactive segments do not need to have a low value.)

  • Hi Chase,

    Clemens is correct - its in the case of the disconnected bus and also we have had other customers experience issues in data transmission without the additional pull-up. Without pull-ups on both sides the system is being opened up to malfunction and errors.

    Best,

    Parker Dodson