ESD and the Desktop NanoBoard NB2DSK01

The NB2DSK01 contains many digital devices that are highly sensitive to electrostatic discharge (ESD). To provide a level of protection against such discharge, the NB2DSK01 incorporates shielding for the following metallic-based components that are routinely handled:

• RS-232 port

• CAN port

• USB port

• PS/2 Keyboard and Mouse ports

• Power toggle switch

• SD Card reader.

Each of these components is connected to a common SHIELD point. When the NB2DSK01 is connected to a PC using the USB connection, the component SHIELD is essentially tied to the PC's chassis ground, and it is through this ground that any build-up of electrostatic charge will be dissipated (discharged). If the NB2DSK01 is not connected via USB, then the electrostatic charge is coupled via a 10M resistor and 4.7nf capacitor to logic ground (GND).

In addition, ESD, RFI/EMI and aggressive earth management requirements are achieved through protective shield nets – made available to the motherboard, daughter board and peripheral boards via the mechanical standoffs. This not only ensures the protection of the NB2DSK01 against damage arising from ESD events, but also prevents spurious resets due to 'ground bounce'.

A dedicated ESD pad is also provided on the motherboard – below the User LEDs. The ESD pad is also connected directly to the board's component SHIELD and should ideally be touched prior to touching another point on the board, and before removing/attaching a peripheral board or daughter board. As such, it is labeled 'TOUCH HERE FIRST'.

Figure 1. Dedicated ESD pad.