MPR121_10 FREESCALE [Freescale Semiconductor, Inc], MPR121_10 Datasheet - Page 22

• Manufacturer Part Number: MPR121_10
• Description: Proximity Capactive touch Senosr controller
• Manufacturer: FREESCALE [Freescale Semiconductor, Inc]

MPR121
22
AN3890: MPR121 Capacitance Sensing — Filtering and
Timing
INTRODUCTION
capabilities of a filtering system. The capacitance engine described in AN3889 act on a 1 μs - 32 μs per sample data rate. THis
application note will discuss the first and second level filters in the MPR121 and how they impact timing and power consumption.
AFE CONFIGURATION REGISTER
address of the AFE Configuration Register is 0x5C.
The capacitance sensing front end of the MPR121 produces data at extremely high rates, which significantly improves the
The first level filter is configured through the use of the First Filter Iterations (FFI) and the Charge Discharge Time (CDT).
The AFE Configuration Register is used to set both the CDC and the number of samples taken in the lowest level filter. The
Reset:
AFE AQUISITION
W
R
1 - 32 μs
DATA
RAW
7
0
FFI
= Unimplemented
6
0
Figure 19. AFE Configuration Register
Figure 18. Data Flow in the MPR121
1 - 128 μs
FILTER
1st
5
0
4
0
FILTER
2nd
4 - 2048 μs
3
0
STATUS REGISTER
CDC
TOUCH
IRQ
2
0
BASELINE
FILTER
1
0
Freescale Semiconductor
0
0
Sensors