Gate-Source Signal

[matrino]

Figure 1: The Schematic

This is my buck converte schematic. I have designed to manage 24 watt (2 amper output),but I have a problem. The problem is the gate-source signal not proper and the circuit not working that I designed. When there is no load the output voltage is good (12.5V). If I connet a load the circuit, the circuit not working and the output voltage drops. Sometimes can maange 0.2 amper at 12.5 V, but If I reduce the load resistance value the circuit give zzzz sound (from tps40200) and the output voltage reduces. I think the problem cause the source-gate signal. I added the oscilloscope fotographe.

Figure 2: Source-Gate signal (pmos)

 

[dick_freebird]

If the output switch is PMOS then the gate waveform is "mostly on" when it should be about a 30% duty cycle.

That's not right. Can't see Y axis to judge further about levels etc.

 

[D.A.(Tony)Stewart]

I wonder how Vsg is limited in the IC. The example shows a 12V Zener shunt.

Your plot 5V/div, shows 3 to 8V and Vt= 1 to 3V, so why is it not getting at least 4.5V required makes me suspicious the GS is damaged
Verify the 40Vin and also the surge current on startup for the load.

 

[danadakk]

The zero ohm Gate R should be calculated -

https://toshiba.semicon-storage.com/info/docget.jsp?did=59460

Also, not that it should affect this particular probe point, but in high speed
circuits use 10X probe, not 1X, due to significant probe C when using 1 X
passive probes.


Regards, Dana.

 

[D.A.(Tony)Stewart]

What are all your specs on the 150 uH? Ferrite can have piezo audio effects.

The voltage ripple seems to ~ match the 300 ns RC current sense filter.

 

[matrino]

What are all your specs on the 150 uH? Ferrite can have piezo audio effects.

The voltage ripple seems to ~ match the 300 ns RC current sense filter.

The inductor is PE-53115NL.

https://www.ozdisan.com/passive-components/inductors/fixed-inductors/PE-53115NL