STMPE321 datasheet(6/40 Pages) STMICROELECTRONICS

No de pièce	STMPE321

Description	3-channel capacitive touchkey controller

PDF	40 Pages

Scroll/Zoom	100%

Fabricant	STMICROELECTRONICS [STMicroelectronics]

Site Internet	http://www.st.com

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6 / 40 page

Capacitance compensation

STMPE321

6/40

Doc ID 15791 Rev 3

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

The sensed capacitance is accessible to the host through the IMPEDANCE registers.

STMPE321 Fiches technique(PDF) 6 Page - STMicroelectronics