External components are required to protect the MAX22088 Home Bus pins (HP, HN, AIO, BIO, and TERM) from high-voltage transient events. The Typical Application Circuits show a recommended protection scheme.
HP and HN Surge Protection
HP and HN must be protected with external components from surge transients. Connect a TVS diode between the HP and HN lines. Ensure that the maximum standoff voltage of the TVS diode does not exceed 24V (max). Connect a 1Ω current limiting resistor between the TVS diode and HP to force the current sharing between an internal Active Clamp and the external TVS diode (Figure 7).
Figure 7. HP and HN Surge Protection
AIO, BIO, and TERM Surge Protection
AIO, BIO, and TERM must be protected with external components from surge transients. Connect TVS diodes with a 5.8V (max) standoff voltage from AIO and BIO to GND. Connect a 4.7Ω serial resistor between each TVS diode and AIO/BIO to limit the current flows into AIO/BIO during the surge transients. Depending on the surge transients polarities, the residual current after the 4.7Ω resistor flows from AIO/BIO through the internal ESD clamping diodes to VCC or GND. Connect a 1μF (min) ceramic capacitor as close to VCC as possible, and a 10μF (min) bulk capacitor on the VCC bus to absorb this current and limit the voltage overshoot on VCC during surge transients.
Layout Recommendations
Although impedance matching is not required on H+ and H- lines, route them together as much as possible. To reduce the parasitic capacitance on signal lines, do not route H+ and H- lines, or their connected components, over the ground planes.
To ensure proper protection, connect the ground return of the protection diodes directly to the ground plane. Use a star configuration to connect all grounds together as close to the GND (pin 9) as possible. Place the external protection TVS diodes and the diode bridge as close to the Home Bus connector as possible.
Application Notes
Refer to AN7224, Introduction to Home Bus, for Home Bus System (HBS) standard and communication protocols.
Refer to AN7226, How to Transmit UART Packets Using Home Bus System (HBS) Compatible Transceiver, for data packet processing examples in microcontroller in the Home Bus System.
