Simple Circuit Modification Adds Open-Load Fault Detection to the DRV103 Power Driver

Engineers working with solenoid and power driver applications often rely on versatile integrated circuits to handle heavy loads efficiently. Among these, the DRV103—as outlined in its official manufacturer datasheet provided by Texas Instruments—stands out as a robust, mostly complete, and efficient solution designed explicitly for driving solenoids and other demanding power applications. It arrives straight from the factory equipped with a formidable suite of built-in protective features, including comprehensive over-current and over-temperature detection mechanisms. Under these standard fault conditions, the device’s logic-level OK-status flag output automatically transitions to zero whenever an energize command is issued while such an error is actively occurring. Consequently, these particular varieties of operational mishaps and system hazards are already adequately covered by the manufacturer’s native architecture, requiring no additional external rework from design teams.

However, despite its extensive capabilities suite, the standard DRV103 lacks a crucial trick in its operational sleeve: the native ability to detect and report open-load faults. An open-load condition occurs when the driven load has drifted away, lost its physical connection to the primary power source, or when an internal coil winding has suffered an open circuit or otherwise lost electrical continuity. Out of the box, if the driver attempts to energize the load while these essential connections are broken, nothing useful or functional will happen in the physical circuit. More importantly, in an unmodified DRV103, neither before nor after this failed activation attempt will any diagnostic error indication be transmitted back to the primary system controller.

Without this feedback, the controller will happily but erroneously assume that its preceding operational commands are continuing to be successfully obeyed by the hardware. In many modern electronic environments, this silent failure mode can prove problematic, particularly if the application in question is mission-critical or safety-sensitive. Engineers frequently emphasize that in modern electronics engineering, virtually all applications carry a degree of criticality that makes blind operational assumptions undesirable. To bridge this gap, veteran designer Stephen Woodward has proposed a reasonably simple circuit modification that effectively addresses this specific hardware shortcoming by adding a relevant status-reporting bit to the device’s existing capabilities.

To understand the necessity of this fix, one must examine how the standard integrated circuit behaves during normal operational sequences versus failure states. The native over-current and over-temperature protections are triggered dynamically when the device is actively driving current and encounters a thermal overload or a short circuit. The internal logic handles these events by pulling the status flag low, alerting the microcontroller immediately. An open load, conversely, represents the exact opposite scenario: an absence of current flow due to a physical break in the circuit path. Because the DRV103 does not inherently monitor the downstream continuity of the load when the activation cycle is initiated or held in an inactive state, it fails to recognize that the circuit is incomplete.

The proposed modification introduces an elegant workaround utilizing a minimal number of discrete external components to provide a "wired-or" Status OK bit. This newly added reporting bit is pulled low by an external transistor configuration whenever an open-load error condition is present, signaling the issue to the system controller through a general-purpose input pin that should be configured for a passive pullup.

The mechanics of this supplementary circuit rely on the interplay between the controller’s general-purpose output pin, the primary input of the driver, and a small network of external transistors designated in the design schematics. When the system controller pulls the primary input low—typically utilizing a microcontroller’s general-purpose output bit—it turns off an associated transistor, which in turn releases the collector of another transistor in the network. Because this low state on the input also forces the internal transistors of the driver to turn off, the driver’s primary output pin is left to float either high or low. Whether it floats high or low entirely depends on whether an intact, continuous electrical connection to the positive supply voltage has been successfully established through a properly connected and unbroken load.

If a healthy, unbroken connection to the positive supply voltage exists through the load, the state of the output pin will drive the next stage of the external circuit into a conducting state, which subsequently releases the final status flag. This action allows the connected general-purpose input bit on the controller to go true, successfully sharing the good news of a healthy circuit with the main processor. Conversely, if the load connection is broken or missing altogether, the expected voltage level fails to manifest at the output pin, causing the external transistor network to hold the status line low. This sustained low signal acts as an explicit error indicator, notifying the controller that an open-load fault has occurred and preventing the system from operating under false assumptions.

This contribution builds upon a long and storied history of practical engineering solutions shared with the wider technical community. Stephen Woodward’s professional relationship with the publication’s Design Ideas column spans many decades, dating back to his very first contribution in 1974. Over the course of a prolific career in hardware design, he has had more than 200 submissions accepted and published, earning accolades such as the best Design Idea of the year awards in both 1974 and 2001. His enduring engagement with circuit optimization demonstrates how classic, mature semiconductor components can be adapted and enhanced to meet modern reliability standards through clever, cost-effective analog and digital external additions.

By implementing this straightforward modification, design engineers working with power drivers and solenoids can significantly improve system observability without undertaking a complete redesign or migrating to a more expensive, specialized integrated circuit. The addition of the open-load reporting bit ensures that controllers remain fully informed of physical disconnections before silent operational failures can cascade into larger system errors. As embedded systems continue to demand higher levels of diagnostic feedback and fault tolerance, such targeted hardware adaptations remain an essential tool for engineers striving to squeeze maximum reliability out of standard silicon solutions.