STMPE321QTR

STMPE321 3-channel capacitive touchkey controller Features ■ Up to 3 GPIOs ■ Up to 3 capacitive touchkey inputs ■ Operating voltage 1.65 - 1.95 V ■ Interrupt output pin ■ I2C interface (1.8 V operation, 3.3 V tolerant) ■ 8 kV HBM ESD protection ■ 40 fF resolution, 128-step capacitance measurement QFN12 (2.2 x 1.5 mm) ■ Advanced data filtering (AFS) ■ Environment tracking calibration (ETC) ■ Individually adjustable touch variance (TVR) settings for all channels ■ Adjustable environmental variance (EVR) for optimal calibration ■ Capacitive key sensing capability in 27 µA sleep mode Applications ■ Mobile phones and smartphones ■ Portable media players ■ Game consoles Table 1. Description The STMPE321 is a 3-channel capacitive touchkey controller. Capacitance measurement is implemented in fully optimized hardware. All 3 I/Os can be configured via an I2C bus to function as either capacitive touchkey, or as GPIOs (general purpose I/O). Device summary Order code Package Packing STMPE321QTR QFN12 (2.2 x 1.5 mm) Tape and reel August 2009 Doc ID 15791 Rev 3 1/40 www.st.com 40 Contents STMPE321 Contents 1 2 STMPE321 functional overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.1 STMPE321 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.2 Pin assignment and function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.3 STMPE321 typical application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 Capacitance compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1 2.2 Calibration algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.1 Noise filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.1.2 Data filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Power management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3 I2C interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 4 Register map and function description . . . . . . . . . . . . . . . . . . . . . . . . . 12 5 System and identification registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 14 6 Interrupt controller module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 7 GPIO controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 22 8 Capacitive touch module registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 24 9 Maximum rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 10 Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 10.1 Capacitive sensing characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 11 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 35 12 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 39 2/40 Doc ID 15791 Rev 3 STMPE321 1 STMPE321 functional overview STMPE321 functional overview The STMPE321 consists of the following blocks: 1.1 ● GPIO controller ● Impedance sensor ● Touchkey controller ● I2C interface STMPE321 block diagram Figure 1. Functional block diagram IO controller Touch 0-2 GPIO 0-2 Impedance sensor RST SCLK SDA Host interface Touchkey controller INT GND ARef VCC !-6 Doc ID 15791 Rev 3 3/40 STMPE321 functional overview 1.2 STMPE321 Pin assignment and function Figure 2. QFN12 pin assignment (top view)             !- Table 2. 4/40 Pin assignment and function Pin number Pin name Description 1 GPIO_2 / touch 2 GPIO 2 2 GPIO_1 / touch 1 GPIO 1 3 GPIO_0 / touch 0 GPIO 0 4 NC - 5 SDA I2C data 6 SCL I2C clock 7 GND GND 8 VCC Supply voltage 9 ARef Reference capacitor for touch sensor 10 NC - 11 INT INT output (open drain) 12 RST RESET (active low) This pin is internally pulled up to VCC Doc ID 15791 Rev 3 STMPE321 1.3 STMPE321 functional overview STMPE321 typical application The STMPE321 is capable of supporting capacitive sensors of up to 3 channels. Figure 3. Typical application diagram 34-0% 4OUCH 3#,+ 3$!4 4OUCH 4OUCH 3ENSORPADS "ASEBAND#05 234 ).4 !2EF  3ENSORPADSARETYPICALLY MM Doc ID 15791 Rev 3 5/40 Capacitance compensation 2 STMPE321 Capacitance compensation The STMPE321 is capable to measuring up to 5.1pF in capacitance difference between the reference point (Zref) and the individual channels. In the case where PCB connection between the sensor pads and the device is too long, the "REFERENCE DELAY" register is able to shift the reference by up to 5.1pF, allowing the TOUCH channels to measure added capacitance 5.1pF with offset of 5.1pF, as shown in following diagram. In the case where this is still not enough to compensate for the capacitance on sensor lines (due to very long sensor trace), an external capacitor of up to 30 pF could be connected at the A_Ref pin. This would further shift up the dynamic range of the capacitance measurement. Figure 4. Capacitance compensation P& P& 2EFERENCEDELAYREGISTER $YNAMICRANGE P& P& 2EFERENCEDELAYREGISTERP& $YNAMICRANGE P& P& P& P& 2EFERENCEDELAYP& !2EFP& $YNAMICRANGEP& P& )NCREASINGCAPACITANCE !-6 The sensed capacitance is accessible to the host through the IMPEDANCE registers. 6/40 Doc ID 15791 Rev 3 STMPE321 2.1 Capacitance compensation Calibration algorithm The STMPE321 maintains 2 parameters for each touch channel: TVR and CALIBRATED IMPEDANCE. CALIBRATED IMPEDANCE is an internal reference which, if the currently measured IMPEDANCE exceeds the CALIBRATED IMPEDANCE by a magnitude of TVR, is considered a “TOUCH”. If the IMPEDANCE is higher than the CALIBRATED IMPEDANCE, but the magnitude does not exceed CALIBRATED IMPEDANCE by TVR, it is not considered a TOUCH. In this case, 2 scenarios are possible: 1. Environmental changes have caused the IMPEDANCE to increase 2. Finger is near the sensing pad, but not near enough In case 1, the change in IMPEDANCE is expected to be small, as environmental changes are normally gradual. A value "EVR" is maintained to specify the maximum IMPEDANCE change that is still considered an environmental change. Table 3. Calibration action under different scenarios Scenario Touch sensing and calibration action IMP>CALIBRATED IMP + TVR TOUCH, no calibration IMPCALIBRATED IMP + EVR NO TOUCH, no calibration IMPCALIBRATED IMP CALIBRATED IMP + change in IMP IMP