TPS62130A: SW waveform

Xuecheng Lu

Prodigy 20 points

Part Number: TPS62130A
Other Parts Discussed in Thread: TPS62130

Hello，we use TPS62130 on our board，and want to confirm the SW waveform is OK or not？

This is our schematic, input is 12V，and ouput is 1.8V/0.5A：

This is the original SW waveform：

Then we found the load capacitance is a little too much，the load consists of 7 filter circuits like this：

So we removed all 22uF befor beads，then the SW comes to this waveform：

But here is still some mistakes on loadchip， we want to confirm this SW waveform is OK or not？ And how can we optimize it？

over 1 year ago

0 Amod Vaze over 1 year ago

TI__Mastermind 23800 points

Yes additional output capacitance could be a problem and needs to be validated for stability by doing a load transient test. Given that, I do think the bottom waveform looks just fine to me.

Thanks,
Amod

0 Xuecheng Lu over 1 year ago in reply to Amod Vaze

Prodigy 20 points

Is the ringing in the waveform right? It doesn't look like a regular square wave for PWM, can be considered as a good waveform in power-save mode or not?

+1 Amod Vaze over 1 year ago in reply to Xuecheng Lu

TI__Mastermind 23800 points

Yes the device is operating in PFM and the SW waveform is normal. There are three phases - on time, off time and idle time where both FETs are off. The inductor current is almost zero and decays through the FET parasitics and inductor to cause this ringing during idle time. See figure 9-37 on page 24 of datasheet for a typical example. Note the idle time increases with decreasing load and vice versa to the point where it eventually does not exist with high enough output current and enters PWM operation.

Thanks,
Amod

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TPS62130A: SW waveform