TPS561208: Operating TPS561208 at 15V Vin

Rohit Thomas

Part Number: TPS561208
Other Parts Discussed in Thread: TPS561201

Hello,

So I needed to know if TPS561208 can be designed for supporting 15V Vin, as mentioned in the datasheet it can take upto 17V (recommended), 19V (Absolute Max), with the SW node supporting upto 19V and 21V of 10ns transient.

So in our design with the IC, at 15V Vin, the observed transient during switching is going upto about 19V for about 20ns at low loads and 16-17V at 0.5A load, it is also possible that the actual is lower given the probing error. Wanted to understand this behaviour better, why the switch node ringing reduces with load.

The typical load for our application would be less than 0.5A in which case the observed transient voltage at the SW node would be present, wherein there wouldn't be sufficient margin. Also in the datasheet some of the test conditions is mentioned to be at 15V Vin as well, wanted to know the reliability of the IC at this condition, possibility of failure especially when the Vin max is mentioned as 17V. From observing the SW node ringing at 15V Vin doubting whether it can be designed for the said 17V Vin.
Just to add, the layout was designed very similar to the recommended layout in the datasheet.

From the Datasheet was comparing the TPS561208 and TPS561201, and in TPS561201 has the pulse skipping at low loads and the TPS561208 doesn't, so does this reduce the SW node ringing ?

Could you please clarify the above mentioned points, please ?

Thanks & Regards,

Rohit.

over 2 years ago

0 Edwin Zang over 2 years ago

TI__Expert 6425 points

Hi Rohit,

Switch node ring is a little higher with higher loading. could you share how you test and test waveform?

TPS561201 and TPS561208 switching node ringing is same.

BRs,

Edwin.

0 Rohit Thomas over 2 years ago in reply to Edwin Zang

Prodigy 20 points

Hi Edwin,

So expected behaviour is higher switch node ringing with higher load, right ?

And I'm guessing the ringing would be similar between TPS561201 and TPS561208 even with the pulse skipping low load region in TPS561201.

Also would you recommend operating at 15V Vin, given the likelihood of Sw node transient ringing going above 20V ? datasheet mentions that the IC supports upto 17V Vin.

loading with Electronic load, switch waveforms given below.

At 13V Vin, 0A load

At 13V Vin, 0.5A load

Thanks & Regards,

Rohit.

0 Edwin Zang over 2 years ago in reply to Rohit Thomas

TI__Expert 6425 points

Hi Rohit,

Yes, you are right. But the differences is very small.

The ring is much bigger than our test in EVM board. Could you share schematic and layout to review? And want's your test way?

BRs,

Edwin.

0 Rohit Thomas over 2 years ago in reply to Edwin Zang

Prodigy 20 points

Hi Edwin,

Sharing the Schematic -

Layout, top layer -

Layout bot layer -

Can you suggest some points for improvements, to reduce the ringing ? So that can operate at 15V Vin.

Thanks & Regards,

Rohit.

0 Edwin Zang over 2 years ago in reply to Rohit Thomas

TI__Expert 6425 points

Hi Rohit,

Layout is not very good. If you can, please refer below guide. https://www.ti.com/lit/an/slva922/slva922.pdf?ts=1632361248998&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FTPS565201%253FkeyMatch%253DTPS565201%2526tisearch%253Dsearch-everything%2526usecase%253DGPN

Please have a try to change C38 to 0.1uF.

BTW, did you use a GND wire to test like below?

BRs,

Edwin.

0 Rohit Thomas over 2 years ago in reply to Edwin Zang

Prodigy 20 points

Hey Edwin,

Thanks for sharing the guide, yeah was more of following the recommended layout in the datasheet, missed out such details, will try to incorporate the improvements.
I will check after changing C38 to 0.1uF. Yes, used GND wire as you have shown to test.

Regards,

Rohit.

0 Edwin Zang over 2 years ago in reply to Rohit Thomas

TI__Expert 6425 points

Hi Rohit,

Please have a try with 0.1uF of C38 firstly. Another option is to add snubber circuit.

BRs,

Edwin.

0 Rohit Thomas over 2 years ago in reply to Edwin Zang

Prodigy 20 points

Hey Edwin,

So I tried with 0.1uF, ringing is the same only. Will probably have to try adding snubber circuit.

Regards,

Rohit.

0 Amod Vaze over 2 years ago in reply to Rohit Thomas

TI__Mastermind 21795 points

Hi Rohit,

Yes, as a reference for snubber design, you can refer to https://e2e.ti.com/cfs-file.ashx/__key/communityserver-discussions-components-files/198/1464.RC-Snubber.pdf You can possibly also consider adding a boot resistor in series with the boot cap to slow down SW slew rate and ringing. Please let us know how it goes.

Thanks,

Amod

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TPS561208: Operating TPS561208 at 15V Vin