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AM26C31: Unexpected Behavior

Ryuuichi machida
Guru 13020 points
Part Number: AM26C31
Other Parts Discussed in Thread: AM26C32

Hello,

I would like you to ask whether you have ever had an experience about following phenomenon.

* We rarely observe that output from "Y" pin and "Z" pin are same polarity.

According to datasheet, when "G" pin connect to GND and input low level signal to "Gn" pin, we must see following behavior.

* When "A" pin input is "low" level, "Y" pin output should be "low" level and "Z" pin output should be "high" level against common mode voltage.

However, we rarely observe when "A" pin input is "low" level, "Y" pin output is "low" level but "Z" pin output is also "low" level(This means we can not get inverted output.).

Q1, Have you ever observed same phenomenon ?

Q2, If answer of Q1 is yes, what was root cause ?

Q3, If answer of Q1 is no, what do you think I should investigate to understand root cause of this phenomenon ?

Best Regards,       

  • 0
    TI__Mastermind 25705 points

    Hi,

    When G is grounded, can you measure the Gn's voltage when input is low? G and Gn should follow the TTL logic. If both Y and Z are low, it is possible that the driver is not turned on and the output is high impedance. You can check it by using a large resistor to pull the node up.

    Regards,

    Hao

  • 0 in reply to Hao L
    Guru 13020 points

    Hello Hao-san,

    Thank you for your reply.

    When G is grounded, can you measure the Gn's voltage when input is low? G and Gn should follow the TTL logic. If both Y and Z are low, it is possible that the  driver is not turned on and the output is high impedance.

    In our case, we use all 4 driver output. And we observe this phenomenon only 2 driver output(1Y, 1Z and 2Y, 2Z), other driver output(3Y, 3Z and 4Y, 4Z) work correctly.

    If, this issue is related to enable, I think that we should see this phenomenon for all driver output. How do you think ?

    BR,

     

  • 0 in reply to Ryuuichi machida
    TI__Mastermind 25705 points

    I agree. Can you make these driver (1 and 2) work in any conditions? Is there any difference on the load between the channels?

    BTW, for sanity check, can you visit this page to check the marking?

    www.ti.com/.../partlookup.tsp

    Regards,

    Hao

  • 0 in reply to Hao L
    Guru 13020 points

    Hello,

    >Can you make these driver (1 and 2) work in any conditions? 

    I'm sorry, I could not understand meaning of above. Driver 3 and 4 work correclty but we see issue on only driver 1 and 2.

    >Is there any difference on the load between the channels?

    Just connect to several AM26C32

    >BTW, for sanity check, can you visit this page to check the marking?

    Parts number is "AM26C31IPWR". Is there any issue on specific parts number ?

    Best Regards

  • 0 in reply to Ryuuichi machida
    TI__Mastermind 25705 points

    Hi,

    I was curious if driver 1 and 2 work in any conditions. Since the behavior looks abnormal, I was wondering if you could first check if the parts are genuine.

    Regards,

    Hao

  • 0 in reply to Hao L
    Guru 13020 points

    Hello Hao-san,

    >I was curious if driver 1 and 2 work in any conditions.

    Which condition should we check ?

    (They confirmed that it seems that frequency of issue is not related to temperature.)

    Best Regards,

  • 0 in reply to Ryuuichi machida
    TI__Mastermind 25705 points

    Hi,

    I wanted to know what makes the difference between the channels. I was wondering 1) if the driver 1 and 2 would work in any conditions (with or without load, different data rate, etc); 2) if the driver 1 and 2 would behave same as the driver 3 and 4 given the same setup.

    Regards,

    Hao

  • 0 in reply to Hao L
    Guru 13020 points

    Hello,

    Sorry for my late response.

    Detail of customer's investigation, they confirmed they have issue on driver 3 and 4 as well.

    However, phenomenon is different. (I would like you ro share waveform internally later. can you accept my friendship request ?)

    While investigating, I have additional question.

    According to customer's waveform, there is possiblity that input voltage stay b/w Vil and Vih when data is latched.

    (According to datasheet, vil is defined as 0.8V but customer's waveform may be arround 1V.)

    In this case, is there possiblity that customer's following phenomenon will happen ?

    * We rarely observe that output from "Y" pin and "Z" pin are same polarity.

    Best Regards,

  • 0 in reply to Ryuuichi machida
    TI__Mastermind 25705 points

    Hi,

    The only scenario I can think of 'same polarity' is that the driver is not active and both Y and Z are high impedance. If this is the case, a load (current source or resistor) can be added to the output to check the output voltage vs. the output current. If light load like 10kOhm can change the output voltage level, the driver is probably not driving the pin.

    Regards,

    Hao