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DRV8860: Output 30uA Open-Load check current flows unconditionally?

Rick Hille
Intellectual 410 points
Part Number: DRV8860

I have an application that drives a bank of valves and has a few spare outputs.   I needed a couple auxiliary LEDs under software control and rather than adding a separate I2C/SPI IO driver, tried using the spare outputs of the DRV8860.  Unfortunately, the LEDs are so efficient they still produce visible light, albeit dim, with the 30uA Open-Load check current when the outputs turn OFF.  The chip enable doesn't seem to cut off the current sinks either.  The datasheet states the ENABLE input controls the output stage drivers and makes them high-Z when disabled; clearly it has no effect on the OL current sinks from my testing, however, the section describing the OL detection does not inform that the sinks are always ON.  Can you confirm this?

I'm tempted to go to the DRV8860A that does not feature OL detection (and presumably does not contain the sinks but I haven't checked), however, I need the OL detection for the valve circuits so looks like I can't use the driver outputs for this otherwise very simple application.

  • 0
    TI__Guru** 114905 points
    Hi Rick,

    We will investigate and confirm this.

    You are correct; the DRV8860A does not have the OL detection.

    Also, can you provide a schematic of the LED connections? Perhaps we can suggest a method to turn the LED off.
  • 0 in reply to Rick Duncan
    Intellectual 410 points
    It's a simple LED-resistor series circuit; DRV chip is sourced from 24V so the resistor is K-ohms for 10mA range. I have thought about placing a 330K resistor across the output as a ballast, but it would have to be included in the LED assembly rather than on the board to ensure the Open Load detect works for spare outputs that may be assigned to solenoid loads in the future.
  • 0 in reply to Rick Hille
    TI__Guru** 114905 points
    Hi Rick,

    The OL detection circuit remains active independent of the ENABLE pin. Although not explicit, the functional block diagram attempts to show that the OL circuit is not controlled by ENABLE. This clarification will be added to a future datasheet update.
  • 0 in reply to Rick Duncan
    TI__Guru** 114905 points
    Hi Rick,

    Could you possibly add a resistor/jumper combination on the board that is in parallel with the LED? This would allow you to pull the jumper when the output is re-assigned to a solenoid.
  • 0 in reply to Rick Duncan
    Intellectual 410 points
    Does the thermal shutdown only act on the output drivers or does it also shut off the current sinks? If it actively asserts the nFAULT pin, I guess the internal logic remains alive so it can't be a global chip power cut-off.

    I've added resistors temporarily; had to go down to 20K to completely quench the 525nm green (3V Vf rated) as it was still clearly visible with 100K. I've thought about a jumper option but this is for early exploratory work. If we actually do need the LEDs, there is likely a cleaner option for integrating a drive point for them in the beta design so I wouldn't need to bother with the solenoid drivers. It was just a bit of a shame that I couldn't use up what will likely remain spare outputs.