AD7142 Analog Devices, AD7142 Datasheet - Page 20

• Manufacturer Part Number: AD7142
• Description: Programmable Controller for Capacitance Touch Sensors
• Manufacturer: Analog Devices

Specifications of AD7142

• Resolution (bits): 16bit
• # Chan: 14
• Sample Rate: 250kSPS
• Interface: I²C/Ser 2-Wire,Ser,SPI
• Analog Input Type: Diff-Uni
• Ain Range: ± 2 pF (Delta C)
• Adc Architecture: Sigma-Delta
• Pkg Type: CSP

AD7142
CDC CONVERSION SEQUENCE
FF_SKIP_CNT
The proximity detection fast FIFO is used by the on-chip logic to determine if proximity is detected. The fast FIFO expects to receive
samples from the converter at a set rate. FF_SKIP_CNT is used to normalize the frequency of the samples going into the FIFO, regardless
of how many conversion stages are in a sequence. In Register 0x02, Bits[3:0] are the fast filter skip control, FF_SKIP_CNT. This value
determines which CDC samples are not used (skipped) in the proximity detection fast FIFO.
Determining the FF_SKIP_CNT value is required only once during the initial setup of the capacitance sensor interface. Table 13 shows
how FF_SKIP_CNT controls the update rate to the fast FIFO. Recommended value for this setting when using all 12 conversion stages on
the AD7142 is FF_SKIP_CNT = 0000 = no samples skipped.
Table 13. FF_SKIP_CNT Settings
FF_SKIP_CNT
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
PROXIMITY DETECTION
Figure 31. Low Power Mode Proximity Detection with Forced Recalibration Example with LP_PROXIMITY_CNT = 4 and LP_PROXIMITY_RECAL = 40
RECALIBRATION
CALIBRATION
(INTERNAL)
(INTERNAL)
(INTERNAL)
(INTERNAL)
DECIMATION = 128
1.536 × (SEQUENCE_STAGE_NUM + 1) ms
3.072 × (SEQUENCE_STAGE_NUM + 1) ms
4.608 × (SEQUENCE_STAGE_NUM + 1) ms
6.144 × (SEQUENCE_STAGE_NUM + 1) ms
7.68 × (SEQUENCE_STAGE_NUM + 1) ms
9.216 × (SEQUENCE_STAGE_NUM + 1) ms
10.752 × (SEQUENCE_STAGE_NUM + 1) ms
12.288 × (SEQUENCE_STAGE_NUM + 1) ms
13.824 × (SEQUENCE_STAGE_NUM + 1) ms
15.36 × (SEQUENCE_STAGE_NUM + 1) ms
16.896 × (SEQUENCE_STAGE_NUM + 1) ms
18.432 × (SEQUENCE_STAGE_NUM + 1) ms
19.968 × (SEQUENCE_STAGE_NUM + 1) ms
21.504 × (SEQUENCE_STAGE_NUM + 1) ms
23.04 × (SEQUENCE_STAGE_NUM + 1) ms
24.576 × (SEQUENCE_STAGE_NUM + 1) ms
NOTES
1. SEQUENCE CONVERSION TIME
2.
3.
4.
t
t
t
CALDIS
RECAL_TIMEOUT
RECAL
USER APPROACHES
SENSOR HERE
= 2 ×
=
t
CONV_LP
t
CONV_LP
=
t
CONV_FP
USER LEAVES SENSOR
× LP_PROXIMITY_CNT × 4
CALIBRATION DISABLED
AREA HERE
× LP_PROXIMITY_RECAL
t
CONV_LP
16
t
CALDIS
=
t
CONV_FP
Rev. A | Page 20 of 72
+ LP_CONV_DELAY
FAST FIFO Update Rate
30
MEASURED CDC VALUE > STORED AMBIENT
RECALIBRATION TIME-OUT
BY PROXIMITY_RECAL _LVL
DECIMATION = 256
3.072 × (SEQUENCE_STAGE_NUM + 1) ms
6.144 × (SEQUENCE_STAGE_NUM + 1) ms
9.216 × (SEQUENCE_STAGE_NUM + 1) ms
12.288 × (SEQUENCE_STAGE_NUM + 1) ms
15.36 × (SEQUENCE_STAGE_NUM + 1) ms
18.432 × (SEQUENCE_STAGE_NUM + 1) ms
21.504 × (SEQUENCE_STAGE_NUM + 1) ms
24.576 × (SEQUENCE_STAGE_NUM + 1) ms
27.648 × (SEQUENCE_STAGE_NUM + 1) ms
30.72 × (SEQUENCE_STAGE_NUM + 1) ms
33.792 × (SEQUENCE_STAGE_NUM + 1) ms
36.864 × (SEQUENCE_STAGE_NUM + 1) ms
39.936 × (SEQUENCE_STAGE_NUM + 1) ms
43.008 × (SEQUENCE_STAGE_NUM + 1) ms
46.08 × (SEQUENCE_STAGE_NUM + 1) ms
49.152 × (SEQUENCE_STAGE_NUM + 1) ms
t
RECAL_TIMEOUT
t
RECAL
70
CALIBRATION ENABLED
t
CONV_LP