Freescale Semiconductor Evaluation Board MPR031/2 for 2- or 3-pad touch sensor controllers DEMOMPR031 DEMOMPR031 データシート

Sensors
Freescale Semiconductor

19

From the implementation above, there are two elements that can be configured to yield a wide range of capacitance readings 
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 

A and 63 A. This value is set in the CDC 

in the AFE Configuration register (

).

The electrode charge time can be configured to equal a range of values between 500 ns and 32 

S. This value is set in the CDT 

in the Filter Configuration Register (

The AFE (Analog Front End) Configuration Register is used to set both the Charge/Discharge Current and the number of samples 
taken in the lowest level filter. The address of the AFE Configuration Register is 0x41.

7

6

5

4

3

2

1

0

R

FFI

CDC

W

Reset:

0

0

0

1

0

0

0

0

= Unimplemented

7:6

FFI

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

5:0

CDC

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 1uA
~
111111 Encoding 63 – Sets the current to 63uA