stmpe16m31 STMicroelectronics, stmpe16m31 Datasheet - Page 49

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

STMPE16M31, STMPE24M31
13.1
13.2
Figure 14. Touch sensing module flowchart
Sampling rate calculation
The capacitive sensor operates with a 2 MHz base clock, a single capacitive sensor scans
up to 24 active channels.
The SCLK_DIV divides the sensor clock by 64-1024, giving 2 kHz-32 kHz sensor clock.
For capacitive sensing, a PRBS sequence is utilized to remove the effect of surrounding
noise. This PRBS has an average value of 4.5.
The effective total sampling rate is thus 2 kHz-32 kHz divided by 4.5, giving 440 Hz – 7 kHz.
If all 24 channels of capacitive sensors are active, the channel conversion rate is thus
440 Hz/24 = 18.3 Hz (Min), 7 kHz/24 =296 Hz (Max)
Using the maximum MAF setting (18 remove 2), the maximum filtered channel output rate is
296 Hz/18 = 16 Hz.
Sensor resolution
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.
Doc ID 16174 Rev 3
Touch sensor controller
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