AD7148 Analog Devices, AD7148 Datasheet - Page 31

• Manufacturer Part Number: AD7148
• Manufacturer: Analog Devices

Specifications of AD7148

• Resolution (bits): 16bit
• # Chan: 8
• Sample Rate: 250kSPS
• Interface: I²C/Ser 2-Wire,Ser
• Analog Input Type: SE-Uni
• Ain Range: ± 8 pF (Delta C)
• Adc Architecture: Sigma-Delta
• Pkg Type: CSP

PCB DESIGN GUIDELINES
CAPACITIVE SENSOR BOARD MECHANICAL SPECIFICATIONS
Table 16.
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
Metal Casing
1
2
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 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 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 43.
D
5
D
1
Figure 42. Capacitive Sensor Board Mechanicals Side View
Figure 41. Capacitive Sensor Board Mechanicals Top View
CONTROLLER PRINTED CIRCUIT BOARD OR METAL CASING
2
CAPACITIVE SENSOR
PRINTED CIRCUIT
SLIDER
CAPACITIVE SENSOR BOARD
METAL OBJECT
D
BUTTONS
2
1
SWITCH
8-WAY
D
D
4
3
Rev. A | Page 31 of 56
CHIP SCALE PACKAGES
The lands on the chip scale package (CP-16-13) are rectangular.
The printed circuit board pad for this package 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
Figure 43. Capacitive Sensor Board with Grounded Shield
Symbol
D
D
D
1
2
5
CONTROLLER PRINTED CIRCUIT BOARD OR METAL CASING
= D
3
= D
4
GROUNDED METAL SHIELD
CAPACITIVE SENSOR BOARD
Min
0.1
0
Typ
1.0
Max
AD7148
Unit
mm
mm
mm