This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

  • TI Thinks Resolved

SN74AHC245: what is the input impedance of SN74AHC245QPWR

Intellectual 1390 points

Replies: 6

Views: 290

Part Number: SN74AHC245

What is the input impedance of SN74AHC245QPWR?  When I put an RC filter(100ohm+1nF) at the input. The high level and low level of input signal are 5V and 0V. But i can only see 4.1V after the resistor. So i am wondering if it is ok to add an RC filter at the input pin.

Regards,

Yangbo

  • Hi Yango,

    The input is high impedance. There is an input leakage spec which shows the max amount of current that will flow in or out of the device. I don't recommend using a filter at the input for another reason. That reason being, it will slow down the rise and fall times at the input which would most likely violate the input transition spec.

    Check out our new AXC family of Voltage Translators! 

    Watch the Introduction to AXC Family to find out more about the family.

  • In reply to Dylan Hubbard:

    Hi Dylan,

    Thank you for your reply.

    I still don't understand the connection between RC filter and leakage specs you mentioned as well as input transition spec. can you give an example or explain more detail?

    Regards,

    Yangbo

  • In reply to Yangbo:

    Hi Yangbo,

    Here are the specs I am talking about from the datasheet:

    Input Transition rate

    Input Leakage

    Check out our new AXC family of Voltage Translators! 

    Watch the Introduction to AXC Family to find out more about the family.

  • In reply to Dylan Hubbard:

    Hi Dylan,

    Thank, but it still can't explain the voltage drop on the 100 ohm resistor if the input impedance is high. 

    i know these two spes, what i want to learn from you is how the RC filter effect them. what will happen if i add a RC filter?

    Regards,

    Yangbo

  • In reply to Yangbo:

    Hi Yangbo,


    Could I get a schematic and scope measurements to better help me debug this? The RC filter will slow down the transition rate.

    Check out our new AXC family of Voltage Translators! 

    Watch the Introduction to AXC Family to find out more about the family.

  • In reply to Dylan Hubbard:

    Hi Yangbo,

    I haven’t heard back from you, I’m assuming you were able to resolve your issue. If not, just post a reply below (or create a new thread if the thread has locked due to time-out)

    Check out our new AXC family of Voltage Translators! 

    Watch the Introduction to AXC Family to find out more about the family.

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.