MSP430FR2676: Questions for layout guidelines

Koichiro Tashiro

Part Number: MSP430FR2676
Other Parts Discussed in Thread: CAPTIVATE-FR2676

Hi,

My customer is designing the board and referring "Capacitive Touch Design Flow for MSP430 MCUs with CapTIvate Technology" SLAA842B.
In section "Step 4b.5: Sensor Traces", it says;

Q1) "half of the panel thickness" means "half of PCB thickness"?
For example, if PCB thickness is 1.6mm, GND needs to be separated >0.8mm from TX or RX?
According to the customer, TI reference board does not meet it.

Q2) What is the purpose to keep such distance between GND and Tx (or Rx)?

Q3) Are these guidelines targeted for double sided boards or single sided boards or both?

Thanks and regards,
Koichiro Tashiro

over 2 years ago

0 Cash Hao11 over 2 years ago

TI__Mastermind 46765 points

Hi,

1. "half of the panel thickness" should means half of the arrylic layer thickness.

2. It uses to increase touch sensitivity.

3. For both.

Best regards,

Cash Hao

0 Koichiro Tashiro over 2 years ago in reply to Cash Hao11

TI__Mastermind 22945 points

Hi Cash,

Thanks for your quick reply!

Cash Hao11 said:
1. "half of the panel thickness" should means half of the arrylic layer thickness.

I see.
If there is no overlay on the electrode, do we have any recommended spacing between TX(or RX) line to GND?

Thanks and regards,
Koichiro Tashiro

0 Cash Hao11 over 2 years ago in reply to Koichiro Tashiro

TI__Mastermind 46765 points

Hi,

I would recommend 1mm for the space between TX(or RX) line to GND when there is no overlay.

Best regards,

Cash Hao

0 Koichiro Tashiro over 2 years ago in reply to Cash Hao11

TI__Mastermind 22945 points

Hi Cash,

It seems there was confusion between the customer and us.
Below figure is CAPTIVATE-FR2676 PCB top layout. This is the board FR2676 is mounted.

As you can see, signals are shielded by GND.
The customer is asking how much spacing is recommended between these signals and GND.
It looks less than 1mm.

Thanks and regards,
Koichiro Tashiro

0 Cash Hao11 over 2 years ago in reply to Koichiro Tashiro

TI__Mastermind 46765 points

Hi，

I checked with captivate expert, they says the spacing between on the TX/RX to the shield GND should be at least half of the arrylic layer thickness.

Best regards,

Cash Hao

0 Koichiro Tashiro over 2 years ago in reply to Cash Hao11

TI__Mastermind 22945 points

Hi Cash,

There is no acrylic layer on the customer's board.
In such case, how much spacing is recommended?

Thanks and regards,
Koichiro Tashiro

0 Cash Hao11 over 2 years ago in reply to Koichiro Tashiro

TI__Mastermind 46765 points

Hi,

Then 1mm is recommended. A bigger distance can resolve in a higher touch sensitivity.

Best regards,

Cash Hao

0 Koichiro Tashiro over 2 years ago in reply to Cash Hao11

TI__Mastermind 22945 points

Hi Cash,

Cash Hao11 said:
Then 1mm is recommended. A bigger distance can resolve in a higher touch sensitivity.

CAPTIVATE-FR2676 PCB does not have 1mm distance even these button boards are covered with acrylic layer.
Your answer implies a bigger distance(1mm) is recommended for no acrylic layer PCB compared to CAPTIVATE-FR2676.
Is this true? It does not make sense to me.

Thanks and regards,
Koichiro Tashiro

+1 Cash Hao11 over 2 years ago in reply to Koichiro Tashiro

TI__Mastermind 46765 points

Hi,

Yes. We do not have a strict rule for the distance when there is no acrylic layer on the top. And like I said before, use a bigger distance(use 1mm for example) can resolve in a higher touch sensitivity. You can always shorten the distance as you need because a higher sensitivity may also lead to a noise issue.

Best regards,

Cash Hao

0 Koichiro Tashiro over 2 years ago in reply to Cash Hao11

TI__Mastermind 22945 points

Hi Cash,

Thanks. This item is now closed.

Thanks and regards,
Koichiro Tashiro

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MSP430FR2676: Questions for layout guidelines