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Getting Started with CapSense

Document No. 001-64846 Rev. *I 49

Figure 3-24. Recommended: Port Isolation for Communication, CapSense, and LEDs

The CapSense controller architecture imposes a restriction on current budget for even and odd port pin numbers. For

a CapSense controller, if the current budget of an odd port pin is 100 mA, the total current drawn though all odd port

pins should not exceed 100 mA. In addition to the total current budget limitation, there is also a maximum current

limitation for each port pin. See the datasheet of the CapSense controller used in the application to know the

specification of that particular CapSense controller.

All CapSense controllers provide high current sink and source capable port pins. When using high current sink or

source from port pins, select the ports that are closest to the device ground pin to minimize the noise.

The following three examples demonstrate common pin assignment mistakes. In Figure 3-25, CapSense and non-

CapSense traces are not isolated, and CapSense pins are far from ground. This is an example of a bad pin

assignment.

Figure 3-25. Not Recommended - CapSense and non-CapSense Pins in Proximity

CapSense Controller

VDDVDD

PWM or other

Non-CapSense traces

Communication

traces

X X

1 2 ... 44 45 46 47 48 49 50 51 52 53 54 ... 74 75

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