With multiple ESD ingress points, such as side function keys and individual keys in a keypad array, designers of smart phones need to pay particular attention to ESD design criteria. The robustness of the ESD protection, physical size and price are all important design considerations. Varistors, popular for their small size and low cost, also have high clamping voltages, slower response times than semiconductor based diode solutions and ESD performance which significantly degrades after each ESD event; as a result, they are not very effective.
When compared to other semiconductor based solutions, the CM1242-33CP offers performance and form factor advantages. With an extremely low dynamic resistance specification of 0.4 Ohm, the CM1242 features a lower clamping voltage and more robust ESD protection than competing solutions. An ESD protection device is only effective if it can shunt the majority of an ESD strike’s energy to ground. This ability is a function of the protection device’s dynamic resistance, which should be as low as possible. If the ESD protection device has a high dynamic resistance, energy that normally would be channeled through the ESD protection device will instead be allowed to reach the device under protection (DUP), resulting in a higher probability of damage.