ADS7843 - Problem

miguel ibarra

Other Parts Discussed in Thread: ADS7843

Hello:

I get the following problem with the tocuh controller ADS7843, when use capacitores for noise filter on X+,Y+,X-,Y- inputs. If the capacitores are present we can not move the cursor properly. Because mismatch exist between the pen and the cursor on the touch panel.

The funcion used for calibrate is tc_calibrate and the funcion used for test is ts_test my system is linux 2.6.27.5 and ts.lib 1.0. The circuit is the same that appears in the application note "Touch Screen Controller Tips" http://focus.ti.com/docs/prod/folders/print/ads7843.html

If i take the capacitores and the TVS all work fine, but i need protect that input.

best regards

over 14 years ago

Michael W over 14 years ago

TI__Expert 3260 points

Hello Miguel,

It sounds like it could be a few different possibilities. Would you mind providing the schematics around the ADC? Also, the capacitor values, if you don't mind. Many thanks and we look forward to assisting you with this.

Regards,

Michael

miguel ibarra over 14 years ago in reply to Michael W

Prodigy 20 points

0160.Display-Circuits.pdf

Hello Michael

Tanks for reply i attach the schematics, the capacitor value is .01uF and the TVS have 56pf .

best regards

Tom Hendrick over 14 years ago in reply to miguel ibarra

TI__Guru**** 180941 points

Hi Miguel,

Thanks for the schematic. Does the problem arise only when C162/V42 through C165/V45 are installed or is it all transorbs? Can you perhaps get some oscilloscope screen shots of the SCLK, SDI, SDO and /CS input as well?

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ADS7843 - Problem