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ISO7840: Capacitance value at each pins and several questions about I/O logic

Hirotaka Matsumoto
Guru 27525 points
Part Number: ISO7840

Hi all

Would you mind if we ask ISO7840?

<Question1>
How much is the capacitance value at each pins?
If you have these data, could you give us as the reference?

<Question2>
On the datasheet Figure.17 P20, we guess that "Input (Device Without Suffix F)" and "Input  (Device With Suffix F)" are opposite.
Is it correct?

<Question3>
On the datasheet Figure.17 P20, about Enable, when VCCO connects to EN pin, EN current will be VCCO/1970.
Is it correct?

<Question4>
On the datasheet Figure.17 P20, about Output, there is description "20ohm".
Does it include FET Rds?
If no, how much is the FET Rds value?(For example; VOL=0.4V, IOL=2mA -> 200ohm)

Kind regards,

Hirotaka Matsumoto

  • 0
    TI__Intellectual 2900 points
    Hi Hirotaka san,

    Please find the required data below. Let me know if any additional clarifications are required.

    <Answer 1>
    Capacitance value is ~2pF. Please refer to section 6.9 of datasheet for additional details.

    <Answer 2>
    Device without Suffix F has an internal pull up resistor
    Device with Suffix F has an internal pull down resistor
    This basically controls the default state of the output. Please refer to section 8.4 of datasheet to get additional details regarding the functionality difference between 'F' and 'non-F' parts.

    <Answer 3>
    EN pin has an internal pull up resistor to VCCO. So if this pin is externally connected to VCCO there will be no current drawn by the pin.

    <Answer 4>
    No, this does not include the FET Rds.
    The total resistance including the FET Rds will come to about
    50ohm for VCC=5V and
    35ohm for VCC = 3.3V

    Regards,
    Anand Reghunathan