6 Summary

This application report has presented different load connections found in OLD diagnostics, such as the half-bridge load connected to supply, the half-bridge load connected to ground and the H-bridge load, along with five types of OLD diagnostics: passive, active, low-current active, and negative-current active OLDs.

The passive OLD diagnostic is suited for the applications which require to check the connectivity of the driver to the load before powering the driver. In such applications, there can be hazard of the open wire connecting to other low-voltage circuitry, which can cause potential damage to this circuitry, or to power lines, which can cause an overcurrent event. Passive OLD in low-side integrated drivers only requires low-side OLD current sources to detect a passive OLD event. BLDC gate drivers require the load phase pin to ground capacitances to discharge before the passive OLD is enabled.

The active, low-current active, and negative-current active OLD diagnostics are suited for applications where the driver current is to be monitored while the load is running. The active OLD can operate in both continuous and in PWM operation. The DRV8873, DRV8873-Q1 and the DRV824x-Q1 devices can only detect an active OLD during high-side asynchronous rectification. BLDC gate drivers require the active load to be connected in an H-bridge configuration. The low-current active OLD sets a 10x current OLD threshold to give a larger flexibility to detect loads with smaller load nominal currents than the I_OLD. The negative-current active OLD changes the I_OLD to I_{OLD_NEG} to account for the negative high-side or low-side FET current re-circulation in synchronous rectification and prevent a false active OLD flag.