AD7147 datasheet(37/68 Pages) AD

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AD7147

Rev. 0 | Page 37 of 68

PCB DESIGN GUIDELINES

CAPACITIVE SENSOR BOARD MECHANICAL SPECIFICATIONS

Table 19.

Parameter

Symbol

Min

Typ

Max

Unit

Distance from Edge of Any Sensor to Edge of Grounded Metal Object

0.1

Distance Between Sensor Edges1

D2 = D3 = D4

Distance Between Bottom of Sensor Board and Controller Board or Grounded

Metal Casing2

1.0

1 The distance is dependent on the application and the position of the switches relative to each other and with respect to the user’s finger position and handling.

Adjacent sensors with no space between them are implemented differentially.

2 The 1.0 mm specification is intended to prevent direct sensor board contact with any conductive material. This specification, however, does not guarantee an absence

of EMI coupling from the controller board to the sensors. To avoid potential EMI-coupling issues place a grounded metal shield between the capacitive sensor board

and the main controller board, as shown in Figure 57.

SLIDER

BUTTONS

CAPACITIVE SENSOR

PRINTED CIRCUIT

8-WAY

SWITCH

METAL OBJECT

Figure 55. Capacitive Sensor Board, Top View

CAPACITIVE SENSOR BOARD

CONTROLLER PRINTED CIRCUIT BOARD OR METAL CASING

Figure 56. Capacitive Sensor Board, Side View

CAPACITIVE SENSOR BOARD

GROUNDED METAL SHIELD

CONTROLLER PRINTED CIRCUIT BOARD OR METAL CASING

Figure 57. Capacitive Sensor Board with Grounded Shield

CHIP SCALE PACKAGES

The lands on the chip scale package (CP-24-3) 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 the 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.

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