Hardware

AN3245

12/19

Doc ID 17747 Rev 1

1.5

Key column/row pins external capacitance

For enhancement of ESD performance, it is possible that external ESD protection diodes

are connected to the key column and row pins in the application. This, at the same time,

results in additional external capacitance loaded at the pins.

In order to ensure that the keypad controller scanning not be affected, the maximum

recommended external capacitance at the pins is shown below.

–

At VCC=1.8 V, recommended maximum external capacitance is 450 pF.

–

At VCC=3.6 V, recommended maximum external capacitance is 900 pF.

These values are based on the calculation of the internal active pull-up resistance and the

shortest KPC scanning time.