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

2.1.3 Load Connected in H-Bridge

The OLD monitoring when there is a load to the H-bridge will depend on the load resistance (RL). The load's current (IL) for a load connected between OUT1 and OUT2 is calculated as,

Equation 7. GUID-848F35E1-A703-4534-8B11-CD2D7A911ADD-low.gif

This OLD example will trigger an OLD event. The voltages at the positive terminal of OL1_HS (VOL_HS(+)) and the negative terminal of OL2_LS (VOL_HS) will be as follows:

High-side comparator of OUT1's half-bridge (OL1_HS)

If VOL_HS(+) is greater than VOL_HS (2.3 V), the output of OL1_HS is set to "1". The voltage comparison between VOL_HS(+) and VOL_HS required for the output of OL1_HS to be set to "1" is determined as:

Equation 8. GUID-204B1994-ABC3-4012-A42C-F670499BB7FD-low.gif

Putting Equation 7 into Equation 8,

Equation 9. GUID-ECE5237E-BFE8-4933-AD31-E6EF259DB02F-low.gif

Solving Equation 9 for the load resistance (RL), RL is expressed as,

Equation 10. GUID-231E69D2-7CF7-47DC-B0BB-678A03F9DB4D-low.gif

By using the values of VAVDD and VOL_HS in Equation 10, the load resistance (RL) is calculated as (-)473.7 Ω. Since the value of the resistance is negative, VOL_HS(+) is greater than VOL_HS (2.3 V) and the output of OL1_HS is is set to "1".

Low side comparator of OUT2's half-bridge (OL2_LS)

If the voltage at negative terminal of OL2_LS (VOL_LS(-)) is less than VOL_LS (1.2 V), then the output of OL2_LS is set to "1". Hence, the voltage comparison between VOL_LS(-) and VOL_LS required for the output of OL2_LS to be set to "1" is calculated as:

Equation 11. GUID-963E7992-9423-40CB-84A6-E9115642B5F2-low.gif

Putting Equation 7 to Equation 11,

Equation 12. GUID-6D9D2370-0548-4E5E-95C3-91B1A8753AA8-low.png

Solving Equation 12 for RL, RL is expressed as,

Equation 13. GUID-165841C9-9EB5-409B-9E1F-B5DD7044A672-low.gif

Using the values of VAVDD and VOL_LS in Equation 13, RL has to be greater than 25.5 kΩ for OL2_LS to be set to "1". Since the output of OL1_HS is always set to "1", the OLD status is solely dependent on the output of OL2_LS. If the RL is less than 25.5 kΩ, then an OLD flag will not occur.