Atmel QTouch Library User Guide

equired as shown in the case A of Figure 27. When the Resistive drive is option is not enabled,it is recommended to use 1kOhm resistors on X and Yk Lines external to the UC3L device. Thishardware arrangement is shown in case B.External Discharge modeWhen the External Discharge arrangement is used, a logic-level (DIS) pin is connected to anexternal resistor (Rdis) that can be used to control the discharge of the Capacitors. A typicalvalue for Rdis is 100 kOhm. This value of Rdis will give a discharge current of approximately1.1V/(100 kOhm) = 11 microAmp. The case C shows this arrangement. The Resistive driveoption on the X and Yk lines can be optionally enabled or disabled with this arrangement. Whenthe Resistive drive is option is not enabled, it is recommended to use 1kOhm resistors on X andYk Lines external to the UC3L device.SMP Discharge ModeWhen the SMP Discharge mode arrangement is used, a logic-level (SMP) pin is connected to thecapacitors through external high value resistors for the discharge of the capacitors. The case Dshows this arrangement. The Resistive drive option on the X and Yk lines can be optionallyenabled or disabled with this arrangement. When the Resistive drive is option is not enabled, it isrecommended to use 1kOhm resistors on X and Yk Lines external to the UC3L device.VDIVEN Voltage Divider Enable optionThe VDIV pin provides an option to make ACREFN a small positive voltage if required. The VDIVpin is driven when the analog comparators are in use, and this signal can be used along with avoltage divider arrangement to create a small positive offset on the ACREFN pin. The VDIVENoption can be used optionally with any of the QMatrix modes discussed in the previous sections.Typical values for Ra and Rb are Ra=8200 ohm and Rb = 50 ohm. Assuming a 3.3V I/O supply,this will shift the comparator threshold by 3.3V*(Rb/(Ra+Rb)) which is 20 mV. The VDIVEN pinoption usage in the Internal Discharge mode scenario is shown in case E.SYNC pin optionIn order to prevent interference from the 50 or 60 Hz mains line the CAT can optionally triggerQMatrix acquisition on the external SYNC input signal. The SYNC signal should be derived fromthe mains line and the acquisition will trigger on a falling edge of this signal. The SYNC pinoption can be used with any of the QMatrix modes discussed in the previous sections. TheSYNC pin usage in the Internal Discharge mode scenario is shown in case F.For QMatrix method SMP, DIS, VDIV and SYNC pin options discussed in this Section, Refer toSection 6.3.15.2.13.1208207K-AT42-09/11