TSC2007：About the X + and X- waveforms when lightly touched

?? ??

Other Parts Discussed in Thread: TSC2007

Hello.
I am considering using TSC2007 for my LCD.

I would like to know the behavior of TSC2007.
When touched normally, PENIRQ, X +, Y + instantly change to 0V. (Fig. 1)

However, when I lightly touch the touch panel, it takes time for X + and X- to change to 0V. (Fig. 2)

Since the coordinates can be recognized normally, there is no problem in operation, but the following points are uncertain.

(1) Is this behavior not supposed to occur due to the specifications of the IC?
(2) Is there a possibility that a problem may occur due to the slow fall? (For example, misrecognition of coordinates occurs)

Depending on the answers to the two questions, I think I have to change the circuit.

Please answer the above two questions

Fig.1

Fig.2

over 3 years ago

0 Arthur Brown over 3 years ago

TI__Mastermind 21775 points

Hi,

Can you share a schematic as well?

The slow fall may be due to the screen, and not the IC due to a weak connection between the X/Y screens with a weak touch.

I wouldn't expect this to cause an issue with the the coordinate reading

Regards,

Arthur

0 ?? ?? over 3 years ago

Prodigy 10 points

Sorry for the late reply.

Thank you for confirmation.

I will send you the schematic. (figure1)

"Not the IC due to a weak connection between the X / Y screens with a weak touch."

→ Due to the specifications of the IC, when PENIRQ is Low, shouldn't the potentials of X + and X- be 0V?

Is it the intended behavior of the IC that is changing at a halfway potential here? (figure2)

Thank you in advance.

figure1

figure2

0 Arthur Brown over 3 years ago in reply to ?? ??

TI__Mastermind 21775 points

Hi,

I will review the schematic and give feedback in 1 day.

Regards,
Arthur

0 ?? ?? over 3 years ago in reply to Arthur Brown

Prodigy 10 points

Hello.
How is the progress of checking the schematic?
Will it take a little longer?

0 Arthur Brown over 3 years ago in reply to ?? ??

TI__Mastermind 21775 points

Hi,

I apologize I will give feedback tomorrow

Regards,
Arthur

0 ?? ?? over 3 years ago in reply to Arthur Brown

Prodigy 10 points

Hello.

Since the investigation seems to be running into difficulty, please let me know immediately whether my understanding of the following two points is correct.

・During the period from PENIRQ transmission to X coordinate reading (red arrow), the voltage is applied along the path shown in Fig. 1, so the potential due to the contact resistance appears in the X waveform.

(Even if PENIRQ is sent, it does not switch to the route shown in Fig.2)

・When acquiring coordinates (after the red arrow), the route is switched to that shown in Fig.2, so the contact resistance does not affect the coordinates.

I'm very sorry to bother you at this time of year, but please confirm.

Fig.1

Fig.2

0 Brian Donoghue over 3 years ago in reply to ?? ??

TI__Intellectual 2620 points

Hi,

Sorry for the delay here, Arthur has been occupied by an urgent project. I can give some comments.

In your schematic, the series 49.9ohm resistors may not be required.

In fig 1, the device is looking for an initial touch on the screen which will trigger the PENIRQ output. In Fig 2 the device is measuring the X coordinate and PENIRQ function is disconnected.

Brian

0 ?? ?? over 3 years ago in reply to Brian Donoghue

Prodigy 10 points

Hello.

Thank you for your detailed comment.

49.9Ω resistor is inserted for burst protection.

Since it is much smaller than the 750Ω resistance of the touch panel, we believe that there will be no impact on this issue.

I would like to confirm the following points.

During the period from sending PENIRQ to reading the X coordinate (red arrow), through which route is the current flowing (Fig.1 or Fig.2)?

If it flows along the path shown in Fig.1, slow fall at weak touch is a natural phenomenon, and it is not a problem phenomenon even when using IC, right?

Does this phenomenon cause any problems in using the IC?

0 Brian Donoghue over 3 years ago in reply to ?? ??

TI__Intellectual 2620 points

Fig 1 shows the device looking for a PENIRQ. Fig 2 is when the device reads the X coordinates. Slow fall is OK and likely due to the properties of your touch screen, it will not cause any issue for the device.

Brian