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

2.2 Circuit Operation and Detection in DRV824x

This section presents the circuit implementation of the passive OLD diagnostic of the DRV824x-Q1 device. DRV824x has the dedicated comparator for passive OLD which is called OLP_CMP.

The user can determine the impedance on the OUTx node using off-state diagnostics in the STANDBY state when the power FETs are off. With these diagnostics, it is possible to detect the following fault conditions passively:

  • Output short to VM or GND < 100 Ω
  • Open load > 1K Ω for full-bridge load or low-side load
  • Open load > 10K Ω for high-side load, VM = 13.5 V

The OLP combinations and truth table for a no fault scenario vs. fault scenario for a full-bridge load in PH/EN or PWM modes is shown in Table 2-1.

Figure 2-5 OLP Combinations
Table 2-1 DRV824x-Q1 Off-State Diagnostics Table PH/EN or PWM Mode
User Inputs OLP Set-Up OLP CMP Output
nSleep DRVOFF EN/IN1 PH/IN2 OUT1 OUT2 CMP REF Output Selected Normal Open GND Short VM Short
1 1 1 0 ROLP_PU ROLP_PD VOLP_REFH OUT1 L H L H
1 1 0 1 ROLP_PU ROLP_PD VOLP_REFL OUT2 H L L H
1 1 1 1 ROLP_PD ROLP_PU VOLP_REFL OUT2 H H L H

Example for test procedure is following. First execute test with first row. nSLEEP=1, DRVOFF=1, EN/IN1=1 and PH/IN2=0. If OLP CMP output is Low, output condition is expected as Normal or GND short. Then try next row as nSLEEP=1, DRVOFF=1, EN/IN1=0 and PH/IN2=1. If OLP CMP output is High, output is expected as normal. If OLP CMP output is Low, output is expected as GND short.