MyTechDailyNews Hardware Guide: Adding Open-Load Status to the DRV103 PWM Driver Through a wired-or Indicator
For solenoid and power-load control designs based on the DRV103, one missing diagnostic channel can be addressed with a compact add-on. The change does not rewrite the chip’s protection behavior. Instead, it supplies a status-reporting bit for an open-load event, using the wired-or Status OK arrangement shown in the source Figure 1.
The source explanation begins with the part itself: the DRV103 is presented as a mostly complete, robust, versatile, and efficient driver approach for solenoids and power loads. It already includes built-in over-current detection and protection, plus over-temperature detection and protection. When an energize command is issued and one of those covered faults occurs, the logic-level Status OK flag output is driven to 0. That existing coverage means the add-on is not needed for those mishaps.
The uncovered situation is different. If the commanded load is not connected—because the external circuit has become detached, because the path to V+ is lost, because a coil winding is open, or because continuity has otherwise disappeared—the unmodified 103 gives no useful error indication to the controller before or after the failed energize attempt. The controller may continue to assume the command succeeded. That may be undesirable in critical applications.
Hardware-oriented view of the change
From a Hardware evaluation angle, the modification is best understood as a focused diagnostic supplement. It reports whether an attempted energize could find the required V+ connection through the load. The added path can pull the wired-or Status OK bit low when Input = 0 and V+ is absent at OUT. The expected interface is a GPI pin configured for passive pullup.
Figure 1 reference In the described circuit, a low Input lets Q2 pull the wired-or Status OK line low if OUT lacks V+; the GPI connection expects passive pullup.
How the indicator logic behaves
Operation starts with the controller driving Input low. The signal is described as a µC general-purpose output bit. In that state, Q3 turns off, and Q1's collector is released.
The same low Input condition also turns the DRV104 internal transistors off. Once the driver output stops actively forcing a level, the OUT pin can float depending on whether an intact path to V+ exists through the properly connected load. That resulting condition controls whether Q1 turns on or off, and Q2's base follows that decision.
When the required connection is present, Q1 turns on. Q2 then turns off, and the Status OK signal is released. The connected GP input bit can then read true, informing the controller that the load connection condition was valid.
When that condition is not met, the indicator takes the opposite path: the wired-or Status OK bit is pulled low, creating the open-load fault report.
Feature-by-feature comparison
| Evaluation point | Unmodified 103 behavior | Modified behavior | Decision note |
|---|---|---|---|
| Open-load fault reporting | Not provided when energize fails due to a missing connection | Provided when Input = 0 and V+ is absent at OUT | Use when load-continuity loss must become visible to the controller |
| Over-current handling | Built-in detection and protection | The existing built-in path remains the relevant coverage | The add-on is not a reason to rework over-current behavior |
| Over-temperature handling | Built-in detection and protection | The existing built-in path remains the relevant coverage | Thermal fault reporting stays on the native Status OK logic |
| Status output style | Status OK reports 0 for covered error states | Status OK participates in a wired-or indication | Firmware must interpret the passive-pullup GPI state |
| Design complexity | Native suite only | Compact supplement for one absent report | Suitable for narrow scope: add a relevant status bit, not replace the driver |
Build checklist
- Confirm the target part is the DRV103 and the gap to solve is open-load reporting, not over-current or over-temperature protection.
- Verify the circuit topology uses the wired-or Status OK line to create the open-load indication.
- Plan the controller side so the GPI connection is configured for passive pullup, as described for Figure 1.
- Check the Input signal path: a µC general-purpose output can provide the low Input state required by the indicator.
- Review how V+ at OUT is established through a properly connected load, because that path determines the Q1 and Q2 states.
Common misconceptions
- The add-on does not remove or duplicate the DRV103’s built-in over-current detection. That fault class already has a status path.
- The add-on does not turn the part into a fully new supervisory system. It adds a focused open-load status-reporting capability.
- A good V+ connection is still required for the “good news” branch. If the connection through the load is absent, the indicator pulls the status line low.
- The unmodified 103 may not send a useful diagnostic error indication for an open-load failure; the modification addresses that specific blind spot.
Action recommendations
- Evaluate the add-on when your application treats detached coils, lost supply connections, or broken continuity as faults that the controller must know about.
- Keep the native over-current and over-temperature diagnostics as the primary handling route for those events.
- Before integration, trace Input, OUT, V+, Q1, Q2, Q3, Status OK, and the passive-pullup GPI relationship against Figure 1.
- Assign firmware behavior only after confirming the meaning of each wired-or Status OK state.
Data citation
The technical facts in this Hardware guide are drawn from the source article’s description of the DRV103 datasheet (PDF) and from Figure 1. The article states that the driver approach is mostly complete, robust, versatile, and efficient for solenoids and other power loads, that built-in protection covers over-current and over-temperature conditions, that Status OK goes to 0 for those reported errors, and that the open-load add-on uses a wired-or status arrangement with a passive-pullup GPI input.
For Hardware readers, the takeaway is narrow but useful: the DRV103 remains a capable driver, and the compact change is worth considering only when the controller needs visibility into an open-load condition that the native design does not report.