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TCA9800: several question for this device

Kazuki Kitajima
Intellectual 1480 points

Part Number: TCA9800

Hello team,

I got the questions from the customer. Could you please check and support those?

1: For B-side, no need to add pull up resistor? Both A-side & B-side are 3.3V.

2: After enabling the device, low voltage is not 0V, and should be around 0.2V. Is this correct?

3: The customer is using a 30cm flat cable between the master device and EEPROM.

    In this case, generally which current source device should we choose?

    aside from the section 10.1, if your team has any comment I would like to inform that to the customer.

4: In the case above, which side should we add TCA980x? Is it better to add the master device side?

Thank you for your support.

Best Regards,

Kazuki Kitajima

  • 0
    TI__Guru* 78111 points

    Kazuki Kitajima said:

    Part Number: TCA9800

    Hello team,

    I got the questions from the customer. Could you please check and support those?

    1: For B-side, no need to add pull up resistor? Both A-side & B-side are 3.3V.

    [Bobby] Correct. B side has an internal current source.

    2: After enabling the device, low voltage is not 0V, and should be around 0.2V. Is this correct?

    [Bobby] The low in the datasheet specs A side to be about 40mV at IoL of 6mA and B side to be about 220mV (Using its own current source)

    3: The customer is using a 30cm flat cable between the master device and EEPROM.

        In this case, generally which current source device should we choose?

        aside from the section 10.1, if your team has any comment I would like to inform that to the customer.

    [Bobby] It depends on the expected capacitance of the cable and the max operating speed you would like to support.

    4: In the case above, which side should we add TCA980x? Is it better to add the master device side?

    [Bobby] Are you planning on buffering one side or both sides of the cable? Our device, doesn't care which side the master is on but for the cable I would probably place B side towards it since B side has a more steady di/dt which would help with driving inductive loads of a cable.

    Thank you for your support.

    Best Regards,

    Kazuki Kitajima

    Comments above

    -Bobby

  • 0 in reply to BOBBY
    TI__Intellectual 1480 points

    Hi Bobby-san,

    Thank you for your answer!

    Understood.

    One more question.

    Is it okay to plug out/in B-side while EN-OFF, inputting VCCB 3.3V?

    I assume that this might affect B-side load especially plugging in...

    Best Regards,

    Kazuki Kitajima

  • 0 in reply to Kazuki Kitajima
    TI__Guru* 78111 points

    Kazuki Kitajima said:

    Hi Bobby-san,

    Thank you for your answer!

    Understood.

    One more question.

    Is it okay to plug out/in B-side while EN-OFF, inputting VCCB 3.3V?

    [Bobby] That shouldn't be a problem. The device is disabled/held in reset until both VccA and VccB are above the Vpor. Holding the EN-OFF is just a nice extra safety feature to ensure glitches don't get shown from B side to A side.

    I assume that this might affect B-side load especially plugging in...

    [Bobby] The device will only care if you add external current sources on B side (like a pull up resistor) or if you accidentally/happen-to pull the line below GND or above its absolute max voltage. 

    Best Regards,

    Kazuki Kitajima

    -Bobby

  • 0 in reply to BOBBY
    TI__Intellectual 1480 points

    Bubby-san,

    Thank you for your help!

    Best Regards,

    Kazuki Kitajima