AD7142 Analog Devices, AD7142 Datasheet - Page 36

• 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
PCB DESIGN GUIDELINES
CAPACITIVE SENSOR BOARD MECHANICAL SPECIFICATIONS
Table 18.
Parameter
Distance from Edge of Any Sensor to Edge of Grounded Metal Object
Distance Between Sensor Edges
Distance Between Bottom of Sensor Board and Controller Board or Grounded
1
2
The 1.0 mm specification is meant to prevent direct sensor board contact with any conductive material. This specification does not guarantee no EMI coupling from
The distance is dependent on the application and the positioning of the switches relative to each other and with respect to the user’s finger positioning and handling.
Adjacent sensors, with 0 minimum space between them, are implemented differentially.
the controller board to the sensors. Address potential EMI coupling issues by placing a grounded metal shield between the capacitive sensor board and the main
controller board as shown in Figure 55.
Metal Casing
D
5
D
1
Figure 54. Capacitive Sensor Board Mechanicals Side View
Figure 53. Capacitive Sensor Board Mechanicals Top View
CONTROLLER PRINTED CIRCUIT BOARD OR METAL CASING
CAPACITIVE SENSOR
PRINTED CIRCUIT
SLIDER
2
CAPACITIVE SENSOR BOARD
METAL OBJECT
D
BUTTONS
2
1
SWITCH
8-WAY
D
D
4
3
Rev. A | Page 36 of 72
CHIP SCALE PACKAGES
The lands on the chip scale package (CP-32-3) are rectangular.
The printed circuit board pad for these should be 0.1 mm
longer than the package land length, and 0.05 mm wider than
the package land width. Center the land on the pad to maximize
the solder joint size.
The bottom of the chip scale package has a central thermal pad.
The thermal pad on the printed circuit board should be at least
as large as this exposed pad. To avoid shorting, provide a
clearance of at least 0.25 mm between the thermal pad and the
inner edges of the land pattern on the printed circuit board.
Thermal vias can be used on the printed circuit board thermal
pad to improve thermal performance of the package. If vias are
used, they should be incorporated in the thermal pad at a
1.2 mm pitch grid. The via diameter should be between 0.3 mm
and 0.33 mm, and the via barrel should be plated with 1 oz.
copper to plug the via.
Connect the printed circuit board thermal pad to GND.
D
5
Symbol
D
D
D
Figure 55. Capacitive Sensor Board with Grounded Shield
1
2
5
CONTROLLER PRINTED CIRCUIT BOARD OR METAL CASING
= D
3
= D
4
CAPACITIVE SENSOR BOARD
GROUNDED METAL SHIELD
Min
0.1
0
Typ
1.0
Max
Unit
mm
mm
mm