User guide

34 Document No. 001-64846 Rev. *A Getting Started with CapSense®
In Figure 3-6, two sensors are surrounded by a ground plane that is connected to CapSense controller ground, while
a third sensor is surrounded by ground which is connected to the other ground plane through the long traces of other
circuitry. This creates a large current loop. With this layout, the third sensor may be more susceptible to radiated
noise and have increased emissions. These two sections of ground are the same location on the schematic, so they
could potentially be one connected area with a better layout.
Figure 3-6. Improper Current Loop Layout
CapSense
Sensor
CapSense
µC
GROUND
FILL #1
GROUND
FILL #2
ISOLATED
OTHER
CIRCUITRY
PATH TO
SENSOR PAD
RETURN
PATH
PCB
Figure 3-7 illustrates the proper layout for the previous example. The loop area has been reduced by connecting the
two grounded areas.
Figure 3-7. Proper Current Loop Layout
CapSense
Sensor
CapSense
µC
GROUND
FILL
CONNECTED
PATH TO
SENSOR PAD
RETURN
PATH
PCB
OTHER
CIRCUITRY