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Microchip rolls out 8-pin PIC MCU for touch sensing apps

28 Mar 2013  | Stephen Evanczuk

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Microchip Technology has recently launched its smallest and lowest-cost PIC MCU offering hardware I2C support. The PIC12LF1552 is an 8bit MCU offered in a 2x3mm UDFN package. It features a four channel 10bit ADC with hardware capacitive voltage divider (CVD) support for capacitive touch-sensing applications.

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Figure: The PIC12LF1552 features a hardware CVD module designed to simplify touch-sensing application development.

The PIC12LF1552 features an adjustable sample-and-hold capacitor array, allowing programmers to adjust the S&H capacitance as needed to achieve the optimum match between internal and external capacitance for better sensing performance with larger touchpads or proximity sensors. Because it is not connected during conversion, the additional capacitance does not affect analogue performance of the ADC. In addition, the new MCU provides automatic control of guard-ring drive, which minimises the effects of the parasitic capacitance on sensing electrodes or can be used as a mutual drive for

mutual capacitive sensing applications. It also features 3.5KB Flash program memory, 256B RAM, a 32MHz internal oscillator, low-voltage operation from 1.8V to 3.6V, and low power consumption for active and sleep currents of 50µA/MHz and 20 nA, respectively.

Designed to enable more efficient capacitive touch-sensing applications, the hardware CVD requires only an ADC and needs only minimal processing to implement automated sensing applications. In operation, the CVD method tracks changes in relative capacitance from the sensor created by touch or proximity. The process starts as an ADC channel discharges the ADC's internal sample-and-hold capacitor and charges the sensor channel to VDD. The sensor channel is then set to input and connected to the internal capacitor, forming a voltage divider, which the ADC samples after the capacitors settle. Consequently, a capacitive change in the touch sensor results in measured change in the ADC channel. Microchip's MLA (Library of Applications) provides an mTouch sensing Framework and Library designed to support CVD-based capacitive sensing applications.

Development support includes the MPLAB XC8 Compiler and Microchip MPLAB X IDE as well as the PICkit 3, MPLAB REAL ICE, and MPLAB ICD 3 programmers. The PIC12LF1552 MCU is available now in sampling and volume quantities in 8-pin PDIP, SOIC, MSOP and 2x3x0.5mm UDFN packages.

The PIC12LF1552's datasheet can be accessed here.

- Stephen Evanczuk

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