STMPE821QTR

STMPE821 8-bit Xpander Logic™ with touchkey controller Preliminary Data Features ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ ■ Up to 8 GPIOs Up to 8 touchkey capacitive touch inputs Operating voltage 1.8 - 5.5 V Internal regulator Interrupt output pin I2C interface 8 kV HBM ESD protection 40 fF resolution, 128 steps capacitance measurement (5.0 pF dynamic range) Advanced data filtering (AFS) Environment tracking calibration (ETC) Individually adjustable touch variance (TVR) setting for all channels Adjustable environmental variance (EVR) for optimal calibration QFN16L (2.6 x 1.8 mm) Applications ■ ■ ■ Description The STMPE821 is a GPIO (general purpose input/output) port expander able to interface a main digital ASIC via the two-line bidirectional bus (I2C). A separate GPIO expander is often used in mobile multimedia platforms to solve the problems of the limited amount of GPIOs typically available on the digital engine. The STMPE821 offers great flexibility, as each I/O can be configured as input, output or specific functions. The device has been designed with very low quiescent current and includes a wakeup feature for each I/O, to optimize the power consumption of the device. Mobile and smart phones Portable media players Game consoles Table 1. Device summary Order code STMPE821QTR Package QFN16L (2.6 x 1.8 mm) Packing Tape and reel June 2008 Rev 2 1/55 www.st.com 55 This is preliminary information on a new product now in development or undergoing evaluation. Details are subject to change without notice. Contents STMPE821 Contents 1 STMPE821 functional overview . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 1.1 1.2 1.3 STMPE821 block diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4 Pin assignment and function . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5 STMPE821 typical application . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2 Capacitive compensation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1 Calibration algorithm . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 2.1.1 2.1.2 Noise filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 Data filtering . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2 Power management . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 3 4 5 6 7 8 9 10 Power schemes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 I2C interface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 Register map and function description . . . . . . . . . . . . . . . . . . . . . . . . . 13 System and identification registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15 Interrupt controller module . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18 GPIO controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 23 Capacitive touch module registers . . . . . . . . . . . . . . . . . . . . . . . . . . . . 25 Basic PWM controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 41 10.1 10.2 PWM function register map . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 43 Interrupt on basic PWM controller . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 11 12 13 Maximum rating . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 47 Electrical specifications . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 48 Package mechanical data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 49 2/55 STMPE821 Contents 14 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 53 3/55 STMPE821 functional overview STMPE821 1 STMPE821 functional overview The STMPE821 consists of the following blocks: ● ● ● ● ● GPIO controller PWM controller Impedance sensor Touchkey controller I2C interface 1.1 STMPE821 block diagram Figure 1. Functional block diagram GPIO controller GPIO 0 - 7 /Touch 0 - 7 PWM controller Impedance sensor INT RST SCLK SDAT 2 IC interface Touchkey controller ARef GND VCC VIO CS00046 4/55 STMPE821 STMPE821 functional overview 1.2 Pin assignment and function Figure 2. STMPE821 pin assignment (top view) 12 13 14 11 10 9 8 7 STMPE821 15 16 1 2 3 4 6 5 CS00045 Table 2. Pin assignments and function Pin name GPIO_2/Touch_2 GPIO_1/Touch_1 GPIO_0/Touch_0 ARef RST SDA SCL INT GND VCC VIO GPIO_7/Touch_7 GPIO_6/Touch_6 GPIO_5/Touch_5 GPIO_4/Touch_4 GPIO_3/Touch_3 GPIO 2 GPIO 1 GPIO 0 Reference capacitor for touch sensor RESET (active low) I2C data I2C clock INT output GND Supply voltage for I2C block Supply voltage for GPIO and internal regulator GPIO 7 GPIO 6 GPIO 5 GPIO 4 GPIO 3 Description Pin number 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 5/55 STMPE821 functional overview STMPE821 1.3 STMPE821 typical application The STMPE821 is able to support up to 8 channel capacitive sensors. Figure 3. Typical application diagram STMPE821 RST INT Baseband/CPU SCLK SDAT ARef CS00047 6/55 STMPE821 Capacitive compensation 2 Capacitive compensation The STMPE821 is capable to measuring up to 5.0 pF in capacitance difference between the reference point (Zref) and the individual channels. In the case where the 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 5.0 pF, allowing the TOUCH channels to measure added capacitance 5.0 pF with offset of 5.0 pF, as shown in following diagram. In case 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 can be connected at the A_Ref pin. This allows to further shift up the dynamic range of the capacitance measurement. Figure 4. 5.0 pF Capacitance compensation Reference delay register = 0 Dynamic range = 0 - 5.0 pF 5.0 pF 5.0 pF Reference delay register = 5.0 pF Dynamic range = 5.0 - 10.0 pF 5.0 pF 30.0pF 5.0 pF Reference delay = 5.0 pF ARef = 30 pF Dynamic range = 35.0 - 40.0 pF Increasing capacitance CS00052 The sensed capacitance is accessible to host through the "IMPEDANCE" registers. 2.1 Calibration algorithm The STMPE821 maintains 2 parameters for each TOUCH channel: TVR and CALIBRATED IMPEDANCE. CALIBRATED IMPEDANCE is an internal reference of which, if the currently measured IMPEDANCE exceeds the CALIBRATED IMPEDANCE by a magnitude of TVR, it is considered a TOUCH. If the IMPEDANCE is more 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 has 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. 7/55 Capacitive compensation Table 3. Calibration action under different scenarios Scenario IMP>CALIBRATED IMP + TVR No touch, no calibration IMPCALIBRATED IMP + EVR IMP