MPR121_10 FREESCALE [Freescale Semiconductor, Inc], MPR121_10 Datasheet - Page 42

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

MPR121
42
7.0
These two registers set the numbers of samples for the 2 level filters and the sampling interval for the second level filter.
respectively. These two registers are powered up with default setting of 0x24 and 0x10 respectively. The default setting is already
workable for proximity sensing, but since ESI[2:0] is 100, the sampling interval is at 16 ms. If lower power consumption is desired,
the user can adjust it to the value to find a balance between the proximity detection response time current consumption. For a
detailed explanation on these registers, please refer to Freescale application note AN3890.
OTHER DESIGN CONSIDERATIONS
Refer to Freescale application note AN3863 for more detailed discussion on electrode and layout design considerations.
Table 42. Filter Configuration Registers 0x5D (Reset Default: 0x24)
Table 43. AFE Configuration Registers 0x5C (Reset Default: 0x10)
The last two registers relevant to proximity detection are the AFE Configuration Register and Filter Configuration Register.
The FFI[1:0], SFI[1:0] and ESI[2:0] bits in the registers are those related to the first filter, second filter and sample interval
0x5C
1. Remember the paralleled plate capacitor model when considering the proximity detection. Larger sensing area (the
2. The electric energy store in the capacitance (thus the strength of the sensing field) is proportional to the square of the
3. Since increasing the sensing pad area also has the problem of making it easier to receive the electric noise. It’s possible
0x5D
AFE and Filter Configuration Register
effective sensing area formed by the sensing pad and material under detection, e.g. the surface area of hand projected to
the sensing pad) gives longer proximity sensing distance.
voltage potential applied. Setting the auto-configure target level as high as possible will help extend the proximity sensing
range.
that the original solid sensing pad can be replaced by a series of circles or x hatch patterns.
Bit7
Bit7
FFI[1:0]
CDT[2:0]
Bit6
Bit6
Bit5
Bit5
Bit4
Bit4
SFI[1:0]
Bit3
Bit3
CDC[4:0]
Bit2
Bit2
Freescale Semiconductor
ESI[2:0]
Bit1
Bit1
Bit0
Bit0
Sensors