CAP1208 datasheet(22/67 Pages) MICROCHIP

22 / 67 page

8-Channel Capacitive Touch Sensor

Datasheet

DS00001570B-page 22

 2014 Microchip Technology Inc.

If analog calibration fails for a sensor input, the corresponding bit is not cleared in the Calibration

Activate and Status Register, and the ACAL_FAIL bit is set in the General Status Register (Section 5.2,

"Status Registers"). An interrupt can be generated. Analog calibration will fail if a noise bit is set or if

the calibration value is at the maximum or minimum value. If digital calibration fails to generate base

counts for a sensor input in the operating range, which is +12.5% from the ideal base count (see

Table 4.1), indicating the base capacitance is out of range, the corresponding BC_OUTx bit is set in

the Base Count Out of Limit Register (Section 5.17, "Base Count Out of Limit Register"), and the

BC_OUT bit is set in the General Status Register (Section 5.2, "Status Registers"). An interrupt can

be generated. By default, when a base count is out of limit, analog calibration is repeated for the

sensor input; alternatively, the sensor input can be sampled using the out of limit base count (Section

5.6, "Configuration Registers").

During normal operation there are various options for recalibrating the capacitive touch sensor inputs.

Recalibration is a digital adjustment of the base counts so that the untouched delta count is zero. After

a recalibration, if a sensor input’s base count has shifted +12.5% from the ideal base count, a full

calibration will be performed on the sensor input.

4.4.1

Automatic Recalibration

Each sensor input is regularly recalibrated at a programmable rate (see CAL_CFG[2:0] in Section 5.18,

"Recalibration Configuration Register"). By default, the recalibration routine stores the average 64

previous measurements and periodically updates the base “not touched” setting for the capacitive

touch sensor input.

APPLICATION NOTE: Automatic recalibration only works when the delta count is below the active sensor input

threshold. It is disabled when a touch is detected.

4.4.2

Negative Delta Count Recalibration

It is possible that the device loses sensitivity to a touch. This may happen as a result of a noisy

environment, recalibration when the pad is touched but delta counts do not exceed the threshold, or

other environmental changes. When this occurs, the base untouched sensor input may generate

negative delta count values. The NEG_DELTA_CNT[1:0] bits (see Section 5.18, "Recalibration

Configuration Register") can be set to force a recalibration after a specified number of consecutive

negative delta readings. After a delayed recalibration (see Section 4.4.3, "Delayed Recalibration") the

negative delta count recalibration can correct after the touch is released.

APPLICATION NOTE: During this recalibration, the device will not respond to touches.

4.4.3

Delayed Recalibration

It is possible that a “stuck button” occurs when something is placed on a button which causes a touch

to be detected for a long period. By setting the MAX_DUR_EN bit (see Section 5.6, "Configuration

Registers"), a recalibration can be forced when a touch is held on a button for longer than the duration

specified in the MAX_DUR[3:0] bits (see Section 5.8, "Sensor Input Configuration Register").

Table 4.1 Ideal Base Counts

IDEAL BASE COUNT

SAMPLE TIME

3,200

320us

6,400

640us

12,800

1.28ms

25,600

2.56ms

CAP1208 датащи(PDF) 22 Page - Microchip Technology

CAP1208 датащи(HTML) 22 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67

датащи скачать

ссылки URL