8.3.3.5.2 Low-current OLD

Low-current open-load detection is another type of active open-load detection in the DRV89XX-Q1 devices. In low-current open-load detection, the current detection threshold is around 10x lower than the active open-load detection scheme. This feature gives the user flexibility to detect a valid open-load condition when driving loads that require low current.

As shown in Figure 58, if the low-side MOSFET is in operating condition (switched-ON) and the current flowing in the particular MOSFET is lower than the low-current active open-load current threshold (I_{OLD_LOW}) for at least open-load detection deglitch time (t_OLD), then an open-load condition is detected. The OLD bit in the IC status (IC_STAT) register is set, the HBX_LS_OLD bit in the open-load status register (OLD_STAT_X) is set and nFAULT pin is driven low during an open-load detect. Normal operation resumes (driver operation and the nFAULT pin is released) when the open-load condition is removed and CLR_FLT command is issued. The OLD bit remains set until cleared through the CLR_FLT bit.

Figure 58. Low-Current OLD

Figure 59 shows the flowchart for implementing the low-current active OLD in continuous mode of operation. Following are the steps to configure and detect the low-current active OLD in the DRV89XX-Q1 device.

1. Enable OLD by setting the OLD_OP bit in OLD_CTRL_2 register. This setting will ensure that the OUTX outputs continue to operate when and OLD fault occurs.
2. Enable the full-bridge operation by setting the individual HBX_HS_EN/HBX_LS_EN bits in operation control (OP_CTRL_1, OP_CTRL_2 and OP_CTRL_3) registers.
3. Check for the nFAULT pin status and the OLD fault in the IC_STAT register.
4. If the nFAULT pin is low and the OLD fault is high, then check for the individual HBX_HS_OLD/HBX_LS_OLD bits in OLD status (OLD_STAT_1, OLD_STAT_2 and OLD_STAT_3) registers.
5. Disable OLD using the HBX_OLD_DIS bits for the OUTX pins acting as high-side drivers.
6. Enable the low-current OLD mode for the half-bridge which low-side is operating by using the HBX_LOLD_EN bit in OLD control (OLD_CTRL_3 and OLD_CTRL_4) registers. This will also disable the high-side OLD for the particular half-bridge.
7. Wait for the open-load deglitch time (t_OLD).
8. Issue the clear fault command (CLR_FLT) to release the nFAULT pin and clear the OLD bits if low-current OLD is not detected.
9. If the OLD bit is high and the nFAULT pin is not released (low), then low-current OLD fault is detected.

Figure 59. Flowchart for Enabling Low-Current OLD (Continuous Mode)