TPS62933: SW signal has oscillations when no load

Steven Wang

Prodigy 230 points

Part Number: TPS62933

Hi, when TPS62933 has no load (Iout=0A), the SW signal has oscillations. Is this normal?

When there is a load (Iout>0A), the SW signal is nice clean PWM/square wave.

over 1 year ago

0 Daniel Li14 over 1 year ago

TI__Mastermind 27470 points

HI Steven:

yes , it is normal. it is because when inductor current is in discontinue mode, there will be a resonant voltage at SW node between the parasitic capacitor and output inductor.

0 Steven Wang over 1 year ago in reply to Daniel Li14

Prodigy 230 points

Hi Daniel, is there a rule of thumb or equation to qualify the oscillation (amplitude, frequency, damping rate, etc) is good or poor? Thanks

+1 Gui He over 1 year ago in reply to Steven Wang

TI__Mastermind 27276 points

Hi Steven

The oscillation is quite normal as this is under DCM mode, you can ignore this. When both the high side switch and the low side switch are turned off, the Cout and L cause the ringing. So the frequency is affected by the Cout and L value, the amplitude /damping is affected by the parasitic resistance like RDC of inductor and ESR of Cout.

Thanks and best regards.

Power management

Power management forum

TPS62933: SW signal has oscillations when no load