TPS543B20: PVIN to GND(Pin25 to 27) capacitor

Yuto Sakai

Part Number: TPS543B20

Hi,

In PCN of TPS543B20 (Rev. A → Rev. B), it was added that the capacitor fromo Pin 25 (VIN) to Pin 27 (GND) is recommended.
Why is it recommended to add this capacitor?
What are the merits of adding this capacitor?

Best regards,
Yuto Sakai

over 7 years ago

0 JohnTucker over 7 years ago

TI__Guru**** 191445 points

Sakai-san,

A capacitor from pin 25 to 27 is recommended due to reduce the Vds of highside FET ringing during the turn-off. Merits: the peaking voltage and duration are reduced:

0 Yuto Sakai over 7 years ago in reply to JohnTucker

Mastermind 6100 points

Hi John-san,

Thank you for your reply.
Why are you recommending a small ceramic capacitor for PVIN - GND (Pin 25 - 27)?
Normally I think that it is recommended for PVIN - PGND (Pin 21 - 20) due to reducing the Vds of the high side FET ringing during turn off.
Please tell me why it is recommended not to add to Pin 20-21 but to Pin 25-27.

Best regards,
Yuto Sakai

0 JohnTucker over 7 years ago in reply to Yuto Sakai

TI__Guru**** 191445 points

Sakai-san,
If you refer back to your related post e2e.ti.com/.../706370
You can see there are small capacitors at both locations, C25 (from pin 25 to pin 27) and C8 (from pin 21 to pin 20).

0 Yuto Sakai over 7 years ago in reply to JohnTucker

Mastermind 6100 points

Hi John-san,

Thank you for your reply.
What I would like to know is why it is recommended to add it to Pin 25-27 (PVIN - GND).
If it is for "reducing the Vds of the high side FET ringing during turn off", I think it is normal to add it to Pin 21 - 20 (PVIN - PGND).
Please tell me about this reason.

Best regards,
Yuto Sakai

0 JohnTucker over 7 years ago in reply to Yuto Sakai

TI__Guru**** 191445 points

Sakai-san,
The answer above is what I got from the TPS543B20 team. It is based on extensive test results. You can see teh improvement with the added capacitor in the waveform I provided.

0 Yuto Sakai over 7 years ago in reply to JohnTucker

Mastermind 6100 points

Hi John-san,

What I would like to know is not the effect of placing a capacitor 25-27.
I would like to know why it is recommended to place capacitors on Pin 25-27.
For ringing reduction, I think that it is common to add it to PVIN - PGND. Why is Pin 25-27?

Best regards,
Yuto Sakai

0 JohnTucker over 7 years ago in reply to Yuto Sakai

TI__Guru**** 191445 points

Sakai-san,
From the above post from Tuesday:
"A capacitor from pin 25 to 27 is recommended due to reduce the Vds of highside FET ringing during the turn-off. Merits: the peaking voltage and duration are reduced". This statement came directly from the TPS543B20 development team. It is based on extensive testing. You can see from the waveform above that the ringing is reduced.

0 Yuto Sakai over 7 years ago in reply to JohnTucker

Mastermind 6100 points

Hi John-san,

I'm sorry for your bothering you again.
Why will not you check if the additional capacitor is Pin 25-27?
If you want to reduce ringing, I think that between PVIN and PGND is a reasonable place to add.

Best regards,
Yuto Sakai

0 JohnTucker over 7 years ago in reply to Yuto Sakai

TI__Guru**** 191445 points

Sakai-san,

Maybe I am misunderstanding. The reply above is directly from the support engineer that did the investigation:
"A capacitor from pin 25 to 27 is recommended due to reduce the Vds of highside FET ringing during the turn-off. Merits: the peaking voltage and duration are reduced".
Is there something not clear about it?

0 Yuto Sakai over 7 years ago in reply to JohnTucker

Mastermind 6100 points

HI John-san,

Thank you for your reply.
What I want to know is "why did you add it to Pin 25-27?"

Pin 25-27 capacitor was added in this PCN.
Even before Rev., small capacitors were recommended for PVIN-PGND to reduce ringing.
If it is for ringing reduction, I think that it may be added further to PVIN-PGND.
In addition to Pin 25-27, I am concerned that AGND will become noisy.

Is it more effective to add ringing to adding to Pin 25-27 than to PVIN - PGND?
Or was there any reason for a theoretical reason to add it to Pin 25-27?

I would like to know the background that we decided to add to Pin 25-27 with this PCN.

Best regards,
Yuto Sakai

0 JohnTucker over 7 years ago in reply to Yuto Sakai

TI__Guru**** 191445 points

Sakai-san,

All I know is that it was determined by extensive testing. I may be able to get more information, but the person who knows about it is not available for a while, so it may be a week or so before I can answer it. As I said before, for best results you shoulsd apply the small capacitor in BOTH locations.

0 Yuto Sakai over 7 years ago in reply to JohnTucker

Mastermind 6100 points

Hi John-san,

Thank you for your reply.
Please check with TPS543B20 team.
I'm looking forward to hearing from you.

Best regards,
Yuto Sakai

0 Henry Nguyen over 7 years ago in reply to Yuto Sakai

TI__Intellectual 2460 points

Hello Sakai-san,
I supported the same questions on the thread of TP543C20 (e2e.ti.com/.../706370).
If you need anything, please let me know. If not, can we close this tread?
Kit

0 Yuto Sakai over 7 years ago in reply to Henry Nguyen

Mastermind 6100 points

Kit-san,

I'm sorry for your late reply.
I close both threads.

Best regards,
Yuto Sakai

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TPS543B20: PVIN to GND(Pin25 to 27) capacitor