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TCA9802: IILC vs. IEXT-O

user446310155
Intellectual 460 points
Part Number: TCA9802

Hi there supporter,

What's the difference between IEXT-O and IILC? As my understanding, input leakage may not exceed the IEXT-O maximum or else the TCA980x can interpret this excessive current as an external device transmitting a low. On the other hand, IILC is the minimum amount of current that external device must be sinking from TCA980x. Take TCA9802 as an example, at least 800uA sunk by external device so that a low will be relayed from B-side to A-side. Thus, any current sunk less than 800uA will not be accepted valid low, right? So why do I have to care IEXT-O's requirement?

Regards,

S.P. Lin

 

  • 0
    TI__Genius 17205 points

    Hello S.P.Lin,

    It is to deal with nodes that might have leakage current or a week pull ups or pull downs.  We simple state that if there is less than 200uA of current either going into our out of the pin it will not interfere with the devices logic recognition as long as you have a minimum of 800uA pulling low. 

    -Francis Houde

  • 0 in reply to fhoude
    Intellectual 460 points

    Hi Francis,

    To TCA980x, what is the difference between IEXT-O leakage current 200uA and sink current 200uA?

    As my understanding, both of them all indicate that there is an external device sinking 200uA. However, its datasheet says more than IEXT-O 200uA will make TCA980x recognize a device low is transmitting.

    So, I am confused which value is the minimum current threshold to detect a device low. Can you give me more detail clarification?

    Your kindly help will be appreciated.

    Regards,

    S.P. Lin 

  • 0 in reply to user446310155
    TI__Genius 16430 points

    S.P. Lin,

    Plesae take a look at the datasheet section 9.4.1.2: Input and output leakage current (IEXT-I/ IEXT-O) on page 14.

    This section provides visual examples of what the difference is.

    The idea here is that you should not place an external pull-up resistor on any of the B-side ports, because the TCA980x has its own internal current source, and uses this to detect what side is controlling the bus. It's how we achieve a low VOL to support 1.65V.

    Your understanding of IEXT-O is correct. MOre than 200 uA (this value will vary depending on which variant you are using) will make the device believe that something is transmitting a low. However, there are 2 specs that call this out. IEXT-O and IILC.

    These are very similar but different specs.

    IILC and IEXT-O are both measurements of the amount of current out of the B_side that will make the TCA980x think a device is transmitting a low. IEXT-O is a maximum external leakage allowable to safely ensure that you don't accidently transmit a low when you don't intend to (see the section i told you to look at at start of this post, there is a graphic that shows this). IILC is the minimum current that a I2C device should sink to ensure that a low gets successfully transmitted.

    I know these specs might be a little confusing, but to summarize it easily: If your I2C device you connect to the bus is able to pull down a 3 mA current source to 0.4V or lower (a VOL of 0.4 V or lower at 3 mA), the TCA980x will successfully transmit a low.