stmpe16m31 STMicroelectronics, stmpe16m31 Datasheet - Page 50

• Manufacturer Part Number: stmpe16m31
• Description: S-touch? 16/24-channel Touchkey Controller With Pwm And Ratio Engines
• Manufacturer: STMicroelectronics

Touch sensor controller
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The impedance reading is the output of an internal MAF (median averaging filter). As up to
16 samples are taken for each reading, the impedance reading is the sum of 16 of 9-bit
samples.
To allow maximum consistency, the 3 impedance readings are always 13-bit, whichever
MAF setting is used.
The touch variance (TVR) and enviromental variance (EVR) registers are specified in a 9-bit
format. For comparison with the impedances, the TVR and EVR would be INTERNALLY
shifted 4 bits up.
Auto-tuning
The capacitive sensor hardware in the STMPExxM31 devices has a sensitivity of 15 fF and
a range of 512 steps giving it a dynamic range of 7.5 pF. This means that at any time, the
device is able to sense a change in capacitance up to 7.5 pF. When the channel capacitance
moves out of the 7.5 pF window, the auto tuning feature kicks in to ensure proper sensing
operation.
Figure 15. Auto-tuning operation
Doc ID 16174 Rev 3
STMPE16M31, STMPE24M31