TCA9801: The output when the B side is the master and the A side is the slave and the A side is open

Shinichi Inoue

Guru 21566 points

Part Number: TCA9801

Tool/software:

Dear Specialists,

My customer is considering TCA980x and has a question.

I would be grateful if you could advise.

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It is assumed that the A side of the TCA980x will be connected to the slave board and pulled up on the slave board.

In this case, if the slave board is not connected, there is no pull-up resistor.

Will this cause the B side to become undefined?

Or, since the B side has a built-in pull-up, is the output determined to be H/L even if the A side is left open?

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I appreciate your great help in advance.

Best regards,

Shinichi

0 Clemens Ladisch over 1 year ago

Guru 316440 points

If the I/O pins on the A side are floating, they might be read as low, and such a low signal would be transmitted to the B side.

Pull EN low, or add pull-up resistors on the main board (they do not need to be strong).

0 Shinichi Inoue over 1 year ago in reply to Clemens Ladisch

Guru 21566 points

Hi Clemens,

Thank you for your reply.

I'll share your suggestion with the customer.

When the customer has an additional question, I consult you again.

I appreciate your great help and cooperation.

Best regards,

Shinichi

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