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SN75LBC175: SN75LBC175

Eric Cui13
Intellectual 920 points
Part Number: SN75LBC175

Hi,

We have been using the SN75LBC175AD chip before.


Description:


1. The last 60 ICs were purchased, but there are two batches: 51ADFFM and 5BA2GKM.

 

2. The problem that we are now facing is that we have unrecognized problems after we access the AES signal. The technical indicators we measure are unqualified.


3. The datasheet shows that the threshold voltage is 0.2V to identify the signal, but this batch of chips is very unstable, some are in 1V, and some even reach 3V.

 

4. The previously used chip can guarantee that our board AES minimum input voltage is 0.16-0.2V; this time the minimum input voltage of the purchase chip is 0.3V-3V.

    The threshold voltage of 75LBC175A is less than 0.2V, and the chip we purchased this time cannot reach 0.2V (even 3V phenomenon). It means that there is a problem with the chip. In addition, there are 2 batch numbers in the board.

 

5. But the problem disappears when we replace the previously purchased chip with the PCB board of the newly purchased chip.

 

6. Is there a problem with our use, or is there a problem with this batch of products. Or we did not notice those problems during use.


7. How to detect the quality of this chip?

 

Thank your for your help.

 

 

Regards,

Eric

  • 0
    TI__Guru 62920 points
    Hi Eric,

    From your description, what I understand is that the differential input threshold that you measure is not what you expected - i.e., it may take a signal lower than -200 mV to generate a "low" output and greater than +200 mV to generate a "high" output. Is that correct? If so, can you please give some more information how you measured this? Do you think you could show us waveform captures of the two halves of the differential input signal and the corresponding output so that we can confirm our understanding?

    If a chip is requiring >200 mV for the input and a new unit is behaving normally, my first inclination would be to suspect some kind of damage to the part. Is the older part showing any other strange behavior compared to the newer devices?

    Thanks,
    Max
  • 0 in reply to Miguel Robertson
    Intellectual 920 points
    Hi Max,

    We tested it this way:

    Make an AES signal source, when the voltage is 200 mV, check whether the chip is normally recognized.
    Now some chip voltages can reach 300 mV to recognize, and some even reach higher, but most of them are at 300 mV.
    In addition to this question, there are no other questions, so you can see whether there are problems with our measurements or problems with our use.

    1. I am not sure if our measurement method is correct.Do you have a measurement method recommended?

    2. Is there a way to measure the chip's specifications?

    3. Previously bought ICs can be used normally. The recently purchased batch is abnormal. And I replaced it with the old one and I can use it normally.


    Thanks,
    Eric
  • 0 in reply to Eric Cui13
    TI__Guru 62920 points
    Eric,

    Using a signal source with variable amplitude is usually a good way to determine the input threshold levels of a device. I'm not sure what your AES source looks like, though - do you think you could capture it on an oscilloscope? Also, it may make more sense to measure the threshold directly by seeing which input amplitude causes toggling on the corresponding chip output (rather than when the chip is recognized by some high-level function). This will give us a more direct understanding of how the hardware is functioning.

    I can try to look into the differences between batches to see if we can identify any relevant data. Do you have the date codes available?

    Max