Section A.2 - Application Notes.Design Examples
Version 1.3 - 2009-12
45
Figure 23: No restore switch used but a green
LED in a 3.3V host system. The status of the
signal can also be used as input to a host
controller.
Figure 24: No restore switch used but a green
LED in a 5V host system. The status of the
signal can also be used as input to a host
controller.
A serial resistor to the restore switch must be used to prevent a short circuit when the
GREEN/Switch-1 pin is in output HIGH state and the switch is pressed (see Figure 25).
Sometimes, over time, switch contacts can get an oxide layer. This may cause the closed switch
resistance to become too high to sink the signal to logic LOW (the signal is internally pulled-up
to 20k
Ω
). A design that prevents this can be found in Figure 26.
The GREEN/Switch-1 pin can be left unconnected if none of its functionality is required.
Figure 25: A low resistance restore
switch used. Notice the 4.7k
Ω
Ω
Ω
Ω
serial
resistor.
Figure 26: If the resistance in the switch is not
guaranteed to be low enough, a safer design can
be used. Notice the 4.7k
Ω
Ω
Ω
Ω
serial resistor.
A.2.3.4 Switch-0
Signal
Switch-0 is not multiplexed with other functionality and a switch is easily implemented (see
Figure 27).
Sometimes, over time, switch contacts can get an oxide layer. This may cause the closed switch
resistance to become too high to sink the signal to logic LOW (the signal is internally pulled-up
to 20k
Ω
). A design that prevents this can be found in Figure 28.
The Switch-0 pin can be left unconnected if its functionality is not used.
