LMV7219: oscillation process on the output

Hi Vladimir,

Some comments:

1. Scope photos: I did not see any pictures of the "ringing" waveform in your attachment. I only saw the schematic. Do you have the output waveform image to supply?

2. Output Isolation Resistor: You say you add RC to the LMV7219 but you did not show it on schematic and did not specify values. Can you specify these things? Adding an isolation resistor between LMV7219 output and DD1 input is what I'd recommend you try.

3. PCB Ground Plane: I assume your PCB has plenty of ground plane and when you probe the LMV7219 output, you are using a short scope probe ground lead. Can you please verify?

4. Input Bias Level: Your +IN (pin 3) is going below ground (-0.25V minimum). Have you tried to see if you change your Common Mode biasing (pin 4 connection currently tied to ground) to see that affects the "ringing"? For example, what if you biased pin 3, and 4 to 1V and see if the AC coupled signal onto +IN also causes output ringing? I'm not sure if this has any effect but I thought I ask if you've tried it?

5. Hysteresis: I've not seen your ringing photo images yet, but I thought I ask if you've tried any hysteresis (positive feedback from your output back onto IN+) on your LMV7219 comparator to see if that affects anything? This would only help if you are getting "chatter" from output transition (and not if the waveform is inherently ringing).

Please let me know.

Regards,

Hooman

5_Picture 5.docxDear Hooman, good morning

Thank you

Please, see attach

I want to find out how dangerous this transition process for chips?

3_Picture 3.docx

Good morning Vladimir,

I can see the waveform that you attached. You stated "Signal on the output of the DD1, DD2, DD3 is almost the same".

DD1 is a logic inverter and DD2 / DD3 are Flip-Flops. The LMV7219 output waveform should not "cause" these logic outputs to show the same ringing because these are not linear devices.

So, I'm beginning to think that the cause of the ringing is either in your "probing" / oscilloscope setup, grounding, or other similar causes and not the actual performance of the LMV7219.

As far device damage, I don't think you are violating anything in these devices in terms of excess input voltage  or current to cause damage. So, I don't believe you can damage DD1 - DD3 this way. For example, here is the Absolute Maximum Ratings for DD1 Inverter:

I don't think any of the above specs are violated by your waveform! 

I'm not entirely sure why the bottom of your waveform is "1-1.3V" above ground? Hopefully this does not bite into the inverter (DD1) logic thresholds?

I'll also post your question to the Logic Forum to make sure the experts on logic devices can also confirm that you don't have to worry about damaging DD1 / DD2 / DD3?

Regards,

Hooman

Hi Vladimir,

I've moved your post to the Logic Forum to see if the TI Logic devices experts / Forum users see any problem with device reliability / damage with the waveform you've shown on the Inverter or Flip-Flop input / output pins?

As I noted earlier, I don't think you would have any such issues but I wanted to double check to make sure.

Regards,

Hooman

Dear Hooman. Thank you. I'll try to send oscillograms of signals as soon as I get new PCB from our workshop