THS4631: About the NC pins of THS4631

Yatao Ling1

Part Number: THS4631

Dear TI expert,

I wonder for THS4631, if I can connect its pin 1 to Ground, pin 8 to VS+ (i.e., pin 7)? The datasheet says they are NC pins, and I'm not sure if connecting them to ground or positive supply will be ok?

Best regards

Yatao

over 3 years ago

0 Michael Steffes over 3 years ago

Guru 47485 points

Well Yatao, the drawing says no internal connection on those NC pins, should be ok to do as you suggest.

0 SimaJalaleddine over 3 years ago in reply to Michael Steffes

TI__Mastermind 22280 points

Hello Yatao,

Michael is correct, there is no internal die connection for the NC pins. You can connect the NC pins to any connection (including VS+, ground, or leave it floating).

Thank you,

Sima

0 Yatao Ling1 over 3 years ago in reply to Michael Steffes

Expert 1840 points

Hi Michael,

THANK YOU VERY MUCH!

Best Regards

Yatao

0 kai klaas69 over 3 years ago in reply to Yatao Ling1

Guru 140200 points

Hi Yatao,

keep in mind that pin 1 is close to the -input THS4631. An "excessive" grounding of pin 1 (sorry for my poor english :-)) could increase the stray capacitance to signal ground seen by the -input.

Kai

0 Yatao Ling1 over 3 years ago in reply to kai klaas69

Expert 1840 points

Dear Kai,

Thx for your kind tip.

But I've laid copper (connected to Ground) on the whole layer. And thus the -input and its tracks have already been surrounded by copper at Ground potential.

If pin 1 is conncted to ground, will this really harm the stability of 4631?

Best regards

Yatao

0 kai klaas69 over 3 years ago in reply to Yatao Ling1

Guru 140200 points

Hi Yatao,

can you give us a snippet of your layout showing the -input routing?

Kai

0 Yatao Ling1 over 3 years ago in reply to kai klaas69

Expert 1840 points

Dear Kai,

The PCB portion of the THS4631 is as the fig below. U1 is 4631. As can be seen, the large red area is the poured copper on the top layer and the copper is connected to Ground. And since pin1 is NC, I've connected pin1 to the Ground.

SInce 4631 is already surrounded by copper, can pin 1 cause unstability?

Best Regards

Yatao

0 kai klaas69 over 3 years ago in reply to Yatao Ling1

Guru 140200 points

Hi Yatao,

well, if it already works right now with the existing layout, then connecting pin 1 to the ground plane will not change very much. But please have a look at the figures 47, 48 and 49 of datasheet to see how the ground plane should be removed from the feedback components, not only in the same plane but also (and especially) in the planes below.

Kai

0 Yatao Ling1 over 3 years ago in reply to kai klaas69

Expert 1840 points

Hi Kai,

Thx for your tips!

Have a great day!

Best Regards

Yatao

0 kai klaas69 over 3 years ago in reply to Yatao Ling1

Guru 140200 points

You are welcome :-)

Kai

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THS4631: About the NC pins of THS4631