SLVAE49C April   2019  – April 2022 DRV8847 , DRV8873-Q1 , DRV8904-Q1 , DRV8906-Q1 , DRV8908-Q1 , DRV8910-Q1 , DRV8912-Q1

 

  1. 1Open Load Detection in Motor Drivers
    1.     Trademarks
  2. 1Introduction
    1. 1.1 Load Connected to Supply
    2. 1.2 Load Connected to Ground (GND)
    3. 1.3 Load Connected to H-Bridge
  3. 2Passive Open Load Detection
    1. 2.1 Circuit Operation and Detection
      1. 2.1.1 H-Bridge Open
      2. 2.1.2 H-Bridge Short
      3. 2.1.3 Load Connected in H-Bridge
    2. 2.2 Circuit Operation and Detection in DRV824x
  4. 3Active Open Load Detection
    1. 3.1 Circuit Operation and Detection
  5. 4Low-Current Active Open Load Detection
  6. 5Negative-Current Active Open Load Detection
  7. 6Summary
  8. 7References
  9. 8Revision History

4 Low-Current Active Open Load Detection

Low-current active OLD, found in the DRV89xx-Q1 devices, is designed for loads with a smaller motor nominal current than the IOLD of active OLD. Figure 4-1 shows that the low-current active OLD threshold (IOLD_LOW) replaces the IOLD from the active OLD. In low-current active OLD, IOLD_LOW is around 10 times less than the active OLD's current OLD threshold. With IOLD_LOW being 10 times less than IOLD permits for more flexibility in OLD when utilizing a load that requires a small nominal current to trigger an OLD event. If a low-side FET is turned ON and the current flowing in that low-side FET is less than the IOLD_LOW for at least the OLD deglitch time (tOLD), then an OLD event has occurred.

GUID-52A437EE-EA3F-4FC2-BF95-F929CB2B1C80-low.gif Figure 4-1 Low-Current Active OLD Operation

The low-current active OLD has trade offs that must be considered:

  • In the DRV89xx-Q1 devices, this OLD is only applicable for the current flowing in the low-side FETs, meaning it cannot be detected using the high-side FETs.
  • If low-current active OLD is used, the overcurrent protection threshold for the low-side FET is also reduced by 11 times.
  • The RDS(ON) of the low-side FET will increase by 11 times, hence the thermal performance has to be monitored. However, given the current across the low-side FET is expected to be low, the thermal dissipation of the low-side FET is expected to be limited.