AN3271 datasheet(14/29 Pages) STMICROELECTRONICS

14 / 29 page

Various connections of push-buttons

AN3271

14/29

Doc ID 17933 Rev 2

6.3

Multiple button control

●

PB and SR inputs can be controlled by mechanical or electrical switches connected in

series or in parallel (see Figure 11 and Figure 12).

●

A reset circuitry with active low and open drain output is used as an example of an

electrical switch. This reset can monitor supply voltage other than VCC and trigger

power-down of an application if it drops below the voltage threshold.

Note:

Any output connected to PB or SR input must be open drain.

Figure 11.

Multiple button control

Figure 11 shows how two switches can be wired together to implement the AND function

requiring that both SR1 and SR2 be pressed to drive SR low.

In some applications, switches are packaged such that they share a common ground pin

and cannot be connected in that manner. Figure 12 shows how such switches can be used

to implement this active low AND function. In this case, a conventional OR gate is used.

When both its inputs are low, its output drives SR low.

Figure 12.

Adding external logic to implement more inputs

AN3271 Arkusz danych(PDF) 14 Page - STMicroelectronics