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TCA9517A: About power supply of VCCA and VCCB

Tsukui Yusuke
Guru 21930 points
Part Number: TCA9517A

Hi,

Let me talk about the power supply of VCCA and VCCB.
Customers separately supplied VCCA and VCCB power.
And customer has connected the rise time accelerators to the B-side.

This caused communication failure.
Customers want to know the cause.
(If you need waveform and circuit information please direct mail.
My email address is tsukui(dash)y(at)clv(dot)macnica(dot)co(dot)jp)

I understood that there are the following description in the data sheet and it should not do.
However, customers want to know why they should not do.
Could you give me advice on why it is prohibited?
And Please describe possible phenomena.


Best Regards,
Yusuke/Japan Disty





  • 0
    TI__Guru 62910 points
    Hello Yusuke-san,

    This device uses a static voltage offset on the "B" side in order to properly control the direction of the I2C data flow. This means that the B side has two different "low" levels possible - one very low level that occurs when the bus is being driven low by a device on the B side and one slightly higher level that occurs when the bus is being driven low by a device on the A side. (The low level is higher in this case so that the TCA9517A still detects it as a "high" level and does not drive it back to the A side, locking up the bus.)

    If the B side were to transition from the lower "low" level to the higher "low" level (static voltage offset), a rise time accelerator may detect this transition as the beginning of a full low-to-high bit transition. This would cause the bus to go high inadvertently, and communication errors would result.

    I hope this is all clear - please let me know if you have further questions.

    Regards,
    Max