TPS55340: Boost Converter SW Node Ringing

Hi Desmond,

Please follow below items when performing the measurement:

• Make sure you are measuring with a ground springing.

• Use high sample rate (<1ns/pt) and >200MHz bandwidth
• Use scope full Y-axis scale

The switching node waveform is not stable. That means you may have a bad loop.

Please check the loop compensation with SLVC430 — TPS55340 Boost Design Excel Spreadsheet Tool.

Best Regards,
Feng

Thanks for the reply. I was indeed using ground spring for scope measurement.

Here is Bode plot from the current components (Rcomp = 10.7k, Ccomp = 33n, Chf = 47p, Cff = 120p):

And after tweaking the values using the application schematic from the datasheet (Fig. 8-1) (Rcomp = 2.55k, Ccomp = 150n, Chf = 150p, Cff = 120p):

Looking at total phase/gain, it looks more stable, as before 0dB gain occured near the knee of the phase plot. Lowering Rcomp seems to improve things even more. Is this sufficient? 

Thanks

Hi Desmond,

Both bode plot looks good. Can you share the design calculator? 

Is the audible noise gone with the new compensation?

Best Regards,

Feng

Hi, I haven't had a chance to solder on a new compensation network as I do not have the components for it yet.

Here is the Excel calculator: TPS55340 Parameter Calculation.xls

Is there too much parasitic inductance in the layout, or perhaps not enough output capacitance?

Thanks

Hi Desmond,

The loop looks good. However, it may not be real.

Please check the DC bias derating of the output ceramic capacitors as a first step.

Best Regards,
Feng

Hello,

The voltage rating for the 3x 22uF output capacitors is 35 V. However I will try adding an external capacitor.

Thanks

Hello, I added a 330 uF electrolytic to the output, and although the audible noise reduced considerably, the ringing on the SW node is still present.