MPR121_10 FREESCALE [Freescale Semiconductor, Inc], MPR121_10 Datasheet - Page 14

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

MPR121
14
CONFIGURATION
ranging from 0.455 pF to 2874.39 pF. The two configurable components are the electrode charge current and the electrode
charge time. The electrode charge current can be configured to equal a range of values between 1 μA and 63 μA. This value is
set in the Charge Discharge Current (CDC) in the Analog Front End AFE Configuration register. The electrode charge time can
be configured to equal a range of values between 500 ns and 32 μS. This value is set in the Charge Discharge Time (CDT) in
the Filter Configuration Register.
AFE CONFIGURATION REGISTER
address of the AFE Configuration Register is 0x5C.
From the implementation above, there are two elements that can be configured to yield a wide range of capacitance readings
The AFE Configuration Register is used to set both the CDC and the number of samples taken in the lowest level filter. The
Table 9. AFE Configuration Register Field Descriptions
Reset:
Field
CDC
FFI
7:6
5:0
W
R
0.09
0.08
0.07
0.06
0.05
0.04
0.03
0.02
0.01
0.1
0
10
7
0
FFI
12
= Unimplemented
First Filter Iterations – The first filter iterations field selects the number of samples
taken as input to the first level of filtering.
00 Encoding 0 – Sets samples taken to 6
01 Encoding 1 – Sets samples taken to 10
10 Encoding 2 – Sets samples taken to 18
11 Encoding 3 – Sets samples taken to 34
Charge Discharge Current – The Charge Discharge Current field selects the supply
current to be used when charging and discharging an electrode.
000000 Encoding 0 – Disables Electrode Charging
000001 Encoding 1 – Sets the current to 1μA
~
111111 Encoding 63 – Sets the current to 63 μA
Sensitivity vs. Capacitance for V DD = 1.8 V and I =36 μA and T = .5 μS
6
0
14
Figure 8. AFE Configuration Register
16
5
0
Minimum
18
C/ADC
Figure 7.
Capacitance
4
0
20
Description
22
3
0
CDC
24
2
0
26
Maximum
28
1
0
Freescale Semiconductor
30
0
0
Sensors