MPR03X

Sensors

Freescale Semiconductor

19

7.4

Configuration

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

μA and 63 μA. This value is set in the CDC

in the AFE Configuration register (Section 7.4.1).

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 CDT

in the Filter Configuration Register (Section 8.3.1).

7.4.1

AFE 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.

Figure 25. AFE Configuration Register

7

6

543210

R

FFI

CDC

W

Reset:

0

0

000000

= Unimplemented

Table 12. AFE Configuration Register Field Descriptions

Field

Description

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