ATQT4-XPRO Microchip

APPLICATION NOTE Atmel QT4 Xplained Pro User Guide ATAN0114 Preface Atmel QT4 Xplained Pro kit is an extension board that enables evaluation of self-capaci- tance mode proximity and touch using the peripheral touch controller (PTC) module. The kit shows how easy it is to design a capacitive touch board solution for the PTC without the need for any external components. Figure 1. QT4 Xplained Pro 9386A-AUTO-04/151. Introduction 1.1 Kit Contents 1 ATQT4-XPRO 1.2 Features QTouch Two buttons Two proximity sensors One unshielded sensor One driven shield sensor with external op amp driver LEDs One LED indicator for each self-capacitive button One LED indicator for each proximity sensor Op amp supply jumper Supply current monitoring of the driven shield op amp (1) Xplained Pro hardware identification system 1.3 Kit Overview Atmel QT4 Xplained Pro is an extension board designed specifically for Xplained Pro MCU boards featuring an MCU with a built-in peripheral touch controller. The extension board can be used to explore the touch functions on the PTC module in self-capacitance (SC) mode only and includes both touch and proximity functionality. Two of the extension board sensors provide proximity detection. The first sensor is unshielded. This sensor consists of a single electrode on the top layer of the PCB. All copper shielding has been removed beneath the sensor electrode. This sensor is response to touch/proximity from both sides of the PCB, top and bottom. The second proximity sensor employs an active or driven shield which consists of two electrodes a top-side sensor and a bottom-side shield. The shield is driven by the MCU (located on the Xplained Pro controller board) through an external op amp (Texas Instruments OPA357) on the extension board. The active shield provides two major benefits compared to the unshielded sensor. First, the active shield suppresses all touch and proximity detection from the bottom (shielded) side of the proximity sensor. Detection can only occur from the top side of the PCB (sensor side). Second, the active shield provides a modest increase in sensor detection range compared to the unshielded sensor of the same size. 2 ATAN0114 APPLICATION NOTE 9386AAUTO04/15