Unwanted transients emanating from the power line back to the line-driver's output and back-EMF generated by the coupling circuit when the load is disconnected and connected, and vice versa, create undesirable overvoltage conditions. Back-EMF is also generated when the line driver outputs are toggled from high to low impedance state, if significant current was flowing at the disconnect time. The MAX44211 power line communications driver most often is placed facing the power line with an isolating stage between them. In case of such overstress conditions, external protection is required to protect the MAX44211 and downstream circuits.
The internal ESD clamping structure is present inside MAX44211 (see Figure) to protect the part from ESD or sub-microsecond events. When the application has hazards where these events can occur frequently and for comparatively longer time, it is recommended to have external protection circuitry. Failure to accommodate an output protection can result in over-stressing the outputs (OUT+/ OUT-) and eventually damage the part.
This application note provides insights and information on how to add external protection circuitry at the outputs of the MAX44211. A circuit using VAVDD = 15V is used in this application note.
The shows the internal ESD clamping protection structure.