LM3880: FLAGx output behavior

Hi

Did you test on TI's LM3880 EVM or on your own design?

Could you share your sch?

Regards

Yihe 

hi yihe,

We tested our own design.

We have attached the test sketch.

Best Regards,

Hi

I tested on the EVM and it is very clean. is on the PCB or breadboard? 

You can refer LM3880 EVM.

Regards

Yihe 

hi yihe,

The device is mounted on a PCB and measured.

I would like to consider purchasing an EVM and measuring it.

Best Regards,

hi yihe,
I purchased the LM3880EVM and measured it under the same conditions as the PCB, but it also output a voltage below 0V.
You should be able to check this by setting the oscilloscope axis to around [1us].
Please tell me the cause of this phenomenon and how to solve it.


CH1:FLAG1 , CH4:EN

hi yihe,
I haven't received a response to my question, could you please answer it?
Best Regards,

Hi,

Sorry for the late response. Yihe has been out of office, and will not return for another 2 weeks.

I will check with the rest of the team about your issue, but we may not be able to provide a response until he returns.

Regards,

Troy

hi team,

It has been more than three weeks since your last reply, but I still haven't received an answer to my question.

Could you please answer it?

Best Regards,

Hi,

We apologize for the delay. Our expert on this part, Yihe, is still out and we have not been able to replicate the behavior seen without him. Could you please send us a photo of your setup and how you are taking these measurements? We would like to see what we are doing differently so that we can hopefully replicate the behavior you are seeing. 

Regards,

Maha

Hi Maha,
The measurements were taken using the configuration shown in the figure.
After powering on, the EN was changed to L-H using the SW, and the waveform of FLAG1 was measured.

Best Regards,

Hi,

Our expert is still out for another week. I have ordered some more EVMs so that I can replicate your setup and see what may be causing the negative Vout. However, the EVMs will not arrive to me for another week. 

Regards,

Maha

Hi Maha,
It's been about two weeks since your last reply, would you be able to give us a response?
Best Regards,

Hello,

Please make sure the FLAG1 scope channel ground is connected to GND test point on EVM.

Regards

hi,
The probe part is omitted in the figure, but of course the probe's GND is also connected to the EVM's GND.
Best Regards,

Hello,

I did bench test on our EVM and the negative voltage, of 0.5V during 10nS, is there. Does that affect the system?

Regards

Hi,
This will affect the system since it will be below the absolute rating of the connected IC.
What causes this to occur and how can it be reduced?
Best Regards,

Hello,

I'm not sure what causes it. I think small cap will reduce it.

Regards

Hi,
I understood that it was necessary to take measures using a separate external circuit.
Best Regards,