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AM26C32: Input Resistance to Ground Values.

Art Mecina
Genius 16645 points
Part Number: AM26C32

Hello Guys,

Good day.

Our customer wanted to know the following input resistance to ground values for AM26C32:

(1) With Vcc = 5V, What is the maximum Input resistance to ground? (ri). Datasheet specifies the minimum (12kΩ) and typical value (17kΩ) only.

(2) Without Vcc (power off), what would be the typical range of input resistance for a good AM26C32?

(3) If this part were to fail (internal short or open), what would this resistance measure?

Thanks in advance!

Art

  • 0
    TI__Mastermind 25705 points

    Art,

    1) The minimum input resistor decides the maximum leakage current of the input pin, which is critical to know the maximum node number on the bus. On the other hand, people usually don't care about the maximum resistance in the applications. May I know what your concern is about this?

    2) Without Vcc, the input resistance should always be larger than the ri spec.

    3) The equivalent schematic of section 8.2 represents the internal structure of the device. In general if the device failed, it would be more likely of having large resistance than 0Ohm.

    Regards,

    Hao

  • 0 in reply to Hao L
    TI__Genius 16645 points

    Thanks Hao!

    I will let you know if customer have additional inquiries

    Art

  • 0 in reply to Art Mecina
    TI__Genius 16645 points

    Hello Hao,

    See below for the response and follow-up comments from the customer:

    • Q1 – He is trying to implement a manual impedance check of these parts before turning the power on.  He's trying to come up with Min and Max Limits.
    • Q2 – According to ri from the spec, this part should always be >12kohms.
    • Q3 – Customer interpretation of the answer is, a typical failure would be a short, therefore the input resistance would be 0ohms.  Is he interpreting that correctly?  Reviewing section 8.2 of the spec, if the transistor failed as an open, would ri = 288kohms?

    Based on the above answers, hes's thinking of setting the following limits for a manual input resistance test to confirm the part is operational before applying power:  MIN = 10kohms & MAX = 100kohms.  Based on your experience with these parts, what are your thoughts?

    Thanks in advance!

    Art

  • 0 in reply to Art Mecina
    TI__Genius 16645 points

    Hello Hao,

    Any update regarding the follow-up inquiries?

    Thanks!

    Art

  • 0 in reply to Art Mecina
    TI__Mastermind 25705 points

    Art,

    I'm sorry I missed your message last week. I think it's more possible that the problematic device shows a high impedance (like 288kOhm) than a short (0Ohm).

    I think the idea of resistance testing should work. Does the customer want to use the test to screen the good parts from bad one? If so it might be better to give a wider range, especially for the maximum value. If the pin is close to 0V, the resistance could be very large.

    Regards,

    Hao

  • 0 in reply to Hao L
    TI__Genius 16645 points

    Hello Hao,

    No worries. I have informed the customer of your answer. I might direct customer on this thread if he has further inquiries, so that he can explain his use case better.

    Thanks!

    Art