ZHCSL09C April 2020 – December 2020 LM7480-Q1
PRODUCTION DATA
Load dump transients occurs on loads connected to the alternator when a discharged battery is disconnected from alternator while it is still generating charging current. Load dump amplitude and duration depends on alternator speed and field current into the rotor. The pulse shape and parameter are specified in ISO 7637-2 5A where a 200-V pulse lasts maximum 350 ms on 24-V battery system. Circuit topology and MOSFET ratings are important when designing a 200-V unsuppressed load dump protection circuit using LM74800-Q1. Dual gate drive enables LM74800-Q1 to be configured in common source topology in Figure 10-25 where MOSFET Q1 is used to turn off or clamp output voltage to acceptable safe level and protect the MOSFET Q2 and LM74800-Q1 from 200 V. Note that only the VS pin is exposed to 200 V through a 10-kΩ resistor. A 60-V rated zener diode is used to clamp and protect the VS pin. Rest of the circuit is not exposed to higher voltage as the MOSFET Q1 can either be turned off completely or output voltage clamped to safe level. MOSFET Q1 selection, input TVS selection and MOSFET Q2 selection for ISO 7637-2 and ISO 16750-2 compliance are discussed in this section.