Hi Gavin:

You can measure the average current in the waveform after simulation. Below is a example with other device, just in my hand.

Firstly, zoom in the waveform to focus on the area which you interested. And then left click to choose it. 

Secondly…

Thanks Minqiu

I can't see these different modes explained anywhere in the datasheet?  Is there an applications note or similar that describes the behaviour, thresholds etc. in detail?

Regards

Jim

Hi Jim:

The FET for FB will turn on in switching phase. It has a sleep mode and turn off  for a short period if the load is light. So that the converter can achieve low Iq and high efficiency with light load. And it turns off during the disable status…

Hi Matilde:

As I catched you via email, please allow me close this post. Thanks for your kind understanding. 

Hi Mingiu,

matildemaria.pavese@studenti.polito.it is my email

Hope to hear back from you soon,

Matilde

Hi Matilde:

To simulate in LTspice, it need uncrypted model, which is not pubilic yet.

May you share email with me?  So that I can touch you and check if it's available. 

Hi Andrew:

Sorry for keep you waiting. I have checked with team and reproduced such similar phenomenon.

The P-FET in function block diagram is a simplified symbol. The real circuit is more complex, and it will cut off the route from Vout to VOSNS to reduce…

I still see the same behavior on both the Eval board from TI and my design

Hi Andrew:

I just arrived the office today. May I know if there any update in you side? If the phenomenon is the same as before, I will prepare the bench for the test in my side.

Hi Andrew:

The internal  FET has parasitic diode, so the VOSNS won't be zero when Vout is high enough.

Beside with FB signal, the SW signal is also wired. Have you observed same same phenomenon on EVM?

I would like to double check in our lab. But…

All our PCBs do the same thing.  I also purchased a TPS6109A eval board and it has the same behavior.  I did notice that in the block diagram in the datasheet there is a FET in the part connects VOS to VOUT.  It appears to be driven by the controller.  So…

Hi Andrew:

May you check the soldering and components healthy at first, and then share the schematic and layout for me to check?

The FB should follow the Vout as it only through the divided resistance.

Sorry,

1- SW

2- Fb

3- Vout

4- Vin

Hi Andrew:

I'm still confused.

May you confirm the signals once again. Otherwise, it's hard to believe the FB is so high.(If there is no soldering or damaged issue.)

1- SW

2- Vin

3- Fb

4- Vin

I was concerned about the square like behavior on the Fb pin.

Hi Andrew:

Sorry, I little confused with color. Just double check with you if the Channel 2 is the Vin or FB?

According to your previous post, the Vout is square, right?

And according to the SW signal, the converter seems not operate well. May you check…

The load is probably 12mA.

Blue is Switch, Green is Vin, Magenta is Vout, and Cyan is FB pin.

Hi Andrew:

What's the Vin and load condition? Is the issue exist with no load?

Please measure the Vin, SW together with Vout.