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MSP430FR2676: Adding an external driver on CAP TX signal.

Koichiro Tashiro

Mastermind 21550 points

Part Number: MSP430FR2676
Other Parts Discussed in Thread: SN74LV541A

Hi,

My customer is designing the system with MSP430FR2676.
In their system, mutual buttons are used and CAP TX signal needs to drive multiple sensors.
So customer is thinking to add an external driver(buffer) on CAP TX signal.
SN74LV541A is a candidate.

Q1) Is this OK to add an external driver on CapTIvate TX line?
Q2) Are there any recommendation or guidelines to select / use the driver with CapTIvate?

Thanks and regards,
Koichiro Tashiro

over 3 years ago

0 Eason Zhou over 3 years ago

TI__Mastermind 35570 points

Why customer need a buffer? Does the drive strength can't meet the requirement?

The voltage on TX pin may changes from 0.5V, 1.5V without enable DVCC charge.

0 Koichiro Tashiro over 3 years ago in reply to Eason Zhou

TI__Mastermind 21550 points

Hi Eason,

Customer found less sensitivity when he connected ~10 buttons on one TX pin.

Eason Zhou said:
The voltage on TX pin may changes from 0.5V, 1.5V without enable DVCC charge.

Do you mean TX pin voltage is dynamically changed and software does not know the change?

Thanks and regards,
Koichiro Tashiro

0 Eason Zhou over 3 years ago in reply to Koichiro Tashiro

TI__Mastermind 35570 points

The sensitivity change is not because of the drive strength.

It is because the base mutual cap is too large.

Make the TX and RX trace to be far away from each other can do some help. It can increase the detection distance. Hope this article can give you some idea from the principle side:https://www.ti.com/lit/ug/slau857/slau857.pdf?ts=1626097203051&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FMSP430FR2512%253FkeyMatch%253DMSP430FR2512%2526tisearch%253Dsearch-everything%2526usecase%253DGPN

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