STMPE321 ST Microelectronics, STMPE321 Datasheet - Page 6

• Manufacturer Part Number: STMPE321
• Description: 3-channel capacitive touch key controller
• Manufacturer: ST Microelectronics

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Capacitance compensation
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Capacitance compensation
The STMPE321 is capable of measuring up to 5.0 pF in capacitance differences between
the reference point (Zref) and the individual channels. In cases 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 of 5.0 pF with an offset of 5.0 pF, as shown in the diagram in
If this is still not enough to compensate for the capacitance on the sensor lines (due to very
long sensor trace), an external capacitor of up to 20 pF can be connected at the A_Ref pin.
This furthers shifts up the dynamic range of the capacitance measurement.
Figure 4.
The sensed capacitance is accessible to the host through the IMPEDANCE registers.
Capacitance compensation
Doc ID 15791 Rev 1
Figure 4.
STMPE321