TPS54302: SW waveform is oscillated.

Hank Chang1

Part Number: TPS54302
Other Parts Discussed in Thread: TPS54308

Hello ~
I have a question on TPS54302. The question is as below description,

Application information,
1).Vin=24V, Vout=5.0V
2).Iout=1.8A(typ.)

Q1:The SW pin output waveform is not quite as a square wave. It is disturbed. Especially on 500mA and 1.5A which compare with TPS54302 datasheet(Fig.23).

Q2:In the Iout=3.0A, Why does the high side SW width is not the same ?

I provide 4 conditions which are Iout=100 mA, 500 mA, 1.5A and 3.0A. Please refer attached file and let me know your opinions. Thank you in advance.TPS54302 SW waveform.pdf

over 4 years ago

0 Young Zhao over 4 years ago

TI__Genius 9540 points

Hi ,

Please see my comments below:

Q1:The SW pin output waveform is not quite as a square wave. It is disturbed. Especially on 500mA and 1.5A which compare with TPS54302 datasheet(Fig.23).

--It's in DCM mode , you can check the valley current of inductor waveform.

Q2:In the Iout=3.0A, Why does the high side SW width is not the same

--I think the LC is not good here, the circuit is not stable with current setup. Below are some action to fix it.

1. Please double check the Isat of inductor , better to select the Isat>5A.

2. please try to remove C144 and test again.

3. Try to add one more 22uF Cout cap and test again.

BRs,

Young

0 Hank Chang1 over 4 years ago in reply to Young Zhao

Prodigy 120 points

Hello Young,
Below is my reply. If you have any suggestion, please let me know. Thank you in advance.

1).The inductor Isat is 6.0A.

2).After removing C14,

Iout=500mA, the SW is still oscillating.

Iout=1.5A and 3.0A, there are no oscillation and the SW duty keep stable.

remove C144.pdf

3).After add Cout cap 47uF,

Iout=500mA, the SW is still oscillating.

Iout=1.5A and 3.0A, there are no oscillation and the SW duty is fixed.

add Cout 47uF.pdf

4).After removing C14 and add Cout cap 47uF,

Iout=500mA, there is no oscillation and the SW duty is fixed.

Iout=1.5A and 3.0A, there is no oscillation and the SW duty is fixed.

remove C14 and add Cout 47uF.pdf

Q:Please let me know "removing C14 and add Cout cap 47uF" is a property solution for my application ?

0 Andrew Xiong over 4 years ago in reply to Hank Chang1

TI__Expert 5470 points

Hi Hank,

Young will reply you after the holiday. Thanks.

Andrew

0 Young Zhao over 4 years ago in reply to Hank Chang1

TI__Genius 9540 points

Hi ,

what's the difference between 2) and 4) ?

BRs,

Young

0 Hank Chang1 over 4 years ago in reply to Young Zhao

Prodigy 120 points

Hello Young,

I make a clear for item 2) and 4) and please refer below updated.

2).After removing C144,

Iout=500mA, the SW is still oscillating.

Iout=1.5A and 3.0A, there are no oscillation and the SW duty keep stable.

1273.remove C144.pdf

4).After removing C14 and add Cout cap 47uF,

Iout=500mA, there is no oscillation and the SW duty is fixed.

Iout=1.5A and 3.0A, there is no oscillation and the SW duty is fixed.

remove C144 and add Cout 47uF.pdf

Please let me know "removing C144 and add Cout cap 47uF" is a property solution for my application ?

Best Regards

Hank Chang

0 Young Zhao over 4 years ago in reply to Hank Chang1

TI__Genius 9540 points

Hi ,

Yes, Please remove C144 and add larger Cout.

and 4) waveform looks good .

BRs,

Young

0 Hank Chang1 over 4 years ago in reply to Young Zhao

Prodigy 120 points

Hello Young,

Based on "remove C144 and add Cout 47uF", I have tested Iout=100mA, 200mA, 300mA, 400mA and 500mA different load current. The SW is still oscillation. Does TPS54302 operate in pulse skipping mode ? Do you have any idea to improve oscillation at Iout=200mA, 300mA and 400mA ? Please refer attached file for detail information. Thank you in-advance.

remove C144 and add Cout 47uF_0105.pdf

0 Young Zhao over 4 years ago in reply to Hank Chang1

TI__Genius 9540 points

Hi,

Pulse skipping initiates when the switch current falls to 500 mA typically.

Do you want to avoid the eco mode ? you can try TPS54308 which is FCCM mode if not care about the efficiency .

BRs,

Young

0 Hank Chang1 over 4 years ago in reply to Young Zhao

Prodigy 120 points

Hello Young,

Thanks for your information. From the datasheet of TPS54308 description, it is suitable for light load conditions. I will apply for TPS54308 sample to do testing again.

Best Regards,

Hank Chang

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TPS54302: SW waveform is oscillated.