Keypad / Buttons

Circuit Protection of Keypad / Buttons

Design Notes:

Protection Application:
The keypads and various buttons found on a cell phone can be an entry way for ESD. These circuits are low-voltage DC switches, typically less than 5VDC.
Solution Description:
The examples shown at the left contain four lines for demonstration purposes. The actual number will vary by application. In the top example, discrete multilayer varistors are used to provide board layout flexibility. In the bottom example, a single Diode array is used to reduce part count.
Companion Solutions:
Other solutions within the Littelfuse portfolio exist in addition to these recommendations. For example, Diode arrays with different channel counts (2 "" 14 lines) can be used to match the actual conditions of the cell phone.
Regulatory Issues:
The IEC 61000-4-2 will be the most appropriate standard that applies for these circuits. It supplies a test method for verifying that the end product is not susceptible to ESD events.
Unique Features:
Does not apply.
Application Warnings:
Does not apply.